Basic Workholding Techniques

BasicWorkholdingTechniques

Hardinge Inc.One Hardinge Drive

Elmira, New York 14902Phone: 800-843-8801

Fax: 607-734-3886www.hardingetooling.com

Introduction

The "Basic Workholding Techniques" brochure is meant to be a resource for yourtool box, your desk or your reference library. It contains basic material that willassist the new machinist or production engineer as well as the veteran looking fora source on practical workholding techniques.

We hope that you find some new ideas to help you improve your productivity andmake your job easier. If you find that we have omitted some material or if youhave a better explanation of a particular process or idea, please let us know.

A companion publication "Precision Length Control" (2285) will help you withlength control techniques related to draw-in collets and step chucks. We hopeyou enjoy "Basic Workholding Techniques".

NOTE: Information in this document is subject to change without notice.In no event will Hardinge Inc. be responsible for indirect or consequentialdamage resulting from the use or application of any of the information containedin this document.

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CHAPTER 1Basic Collet Configurations ......................................................... 8Basic Collet Introduction ............................................................. 9Head Angles................................................................................ 9

Lathe ColletStationary ColletTool Holder Collet

Back Bearing ......................................................................... 9, 10Stationary Screw Machine Collet .............................................. 10Slot Design .......................................................................... 11, 12

StraightRelief HoleTear Drop ReliefDouble SlotAngularZig-ZagReverse Tear Drop (Over-The-Shoulder Collet)

CHAPTER 2Draw-In Collets .......................................................................... 14Push-Out Collets ....................................................................... 15Push Sleeve (Stationary) Collets .............................................. 16Toolholder Collets ..................................................................... 16Actuating the System ................................................................ 17Air-Operated Mechanical Closers ....................................... 17, 18Pneumatic Closers .............................................................. 18, 19Hydraulic Closers ...................................................................... 19Machines Using Various Systems............................................. 20

CHAPTER 3Types of Collets ........................................................................ 22

CHAPTER 4Spindle Concentricity ................................................................ 25TIR Spindle ............................................................................... 25TIR Back Bearing ...................................................................... 25Thread Run-Out & TIR .............................................................. 25What is Spread.......................................................................... 26Grind Outs ................................................................................. 26Cam Grind ................................................................................. 27Flat Grind .................................................................................. 27Extra Spread—Over the Shoulder Collets ................................ 28Formula—Maximum Opening for Over Shoulder ...................... 28

CHAPTER 5Advantages of Hardened Collets .............................................. 30Problems Caused by Improper Hardness ................................. 30What Causes Collets To Wear Out ....................................30 - 33Wear: Illustrations of Causes .............................................. 31, 32Wear: Multi-Spindle Automatics .......................................... 31, 32Other Causes for Wear ............................................................. 33

BasicColletIntroduction

Colletand CloserSystems

Types ofCollets

Concentricityand Spread

ColletHardnessand Wear

Table ofContents

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CHAPTER 6Charts ..............................................................................36 - 38

CHAPTER 7Chucking Diameter Chart .......................................................... 40Collet Capacities ....................................................................... 40Collet: Correct Size ................................................................... 40

Oversize ............................................................................. 41Undersize ........................................................................... 41

Extra-Extra Spread Collet ......................................................... 42Four Split-Long Bearing ............................................................ 42Angular Slotted.......................................................................... 43Zig-Zag Collet ............................................................................ 43

CHAPTER 8Reasons for Serrations ............................................................. 46Flat Serration............................................................................. 46Tap Serration ............................................................................ 46Circular Serration ...................................................................... 46Saw/Buttress Tooth Serration ................................................... 47Diamond Serration .................................................................... 47Last Serration ............................................................................ 47Hex & Square Serrated Collets ................................................. 47Disadvantages .......................................................................... 47

CHAPTER 9Order Hole (Collet Bore) ........................................................... 50Smooth Bore ............................................................................. 50Serrated Bore ............................................................................ 50Diameter of the Order Hole ....................................................... 51

Bar Work ............................................................................. 51Maximum Grip .............................................................. 51Ground Rod & Tubing .................................................. 51Best Concentricity ........................................................ 51

2nd Operation Work ........................................................... 52Best Concentricity ........................................................ 52Results of a Large Order Hole ..................................... 52Results of Undersize Collet .......................................... 52

Length of Bearing ...................................................................... 53Short Bearing ............................................................................ 53Split Bearing .............................................................................. 53Extended Nose Collet ............................................................... 53Number of Slots .................................................................. 54, 55Micro-Finish of Order Hole ........................................................ 56Cloverleaf Grind ........................................................................ 56

Table of Contents

MaterialsHeld by Collets

ColletCapacity

Serrations

Concentricityand GrippingForce

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CHAPTER 10Expanding Collets ..................................................................... 58Preparing the Blank................................................................... 58Reasons for Out-of-Round Blanks ...................................... 59, 60Styles

Spindle-Mounted ................................................................ 61Basic Parts ............................................................. 62, 63Work Locating Stops .................................................... 63Advantages .................................................................. 64Special Considerations ................................................ 64

Master Expansion Collets ................................................... 65Parts ....................................................................... 65, 66Collet Pads ................................................................... 67Advantages .................................................................. 68Special Comments ................................................. 68, 69Small Diameter Work ................................................... 69

Other Styles ........................................................................ 69

CHAPTER 11Major Classifications ................................................................. 72

Master Collets ..................................................................... 72Advantages/Disadvantages of Master Collets/Pads ................. 72

Style S Collet ...............................................................72 - 74Style S Pads ................................................................. 74, 75Martin Collets ...................................................................... 76Martin Pads ........................................................................ 77CT Collets & Pads .............................................................. 78CB Collets & Pads .............................................................. 79New Britain Collets & Pads ................................................. 80Standard Master Collets & Pads ........................................ 81Manufacturing of Hex and Square Pads ............................. 82

Master Feed FingersStyle "B" .................................................................. 84, 85, 86BX/DX Adjustable ............................................................... 87AF Adjustable ............................................................... 88, 89Style "A" .............................................................................. 90

Adjustable Feed FingersDial-Adjustable ............................................................. 92, 93Squirrel Cage ................................................................ 94, 95Stock Saver ........................................................................ 95

Solid Feed FingersStandard Solid Feed Finger ................................................ 96Brazed On .......................................................................... 97Milled Through .................................................................... 98Bar Stock Puller .................................................................. 99

Basic Workholding

Techniques

ExpandingCollets

MasterCollets andFeed Fingers

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CHAPTER 12Reasons For Selecting

Chucks .............................................................................. 102Collets ............................................................................... 103

Reasons for Switching to Collets ............................................ 103Chucks

Mechanical—Manual ........................................................ 104Pneumatic ......................................................................... 105Hydraulic ........................................................................... 105Electro-Magnetic ............................................................... 106Vacuum ............................................................................ 106

CHAPTER 13Bar Pullers ............................................................................... 108

CHAPTER 14Rotating Parts Loader ..................................................... 110, 111

Table of Contents

Chucksvs.Collets

Bar StockPullers

PartsLoadingandUnloading

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CHAPTERONE

BASICCOLLET

INTRODUCTION

8 CHAPTER 1Basic Collet Introduction

3 BASIC COLLET CONFIGURATIONS

THREADRELIEF

BACK BEARING

BEARING LENGTH

ORDER HOLE

FACE

HEAD ANGLEKEYWAY

THREAD

STOP THREAD

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SLOT HEAD ANGLE

BACK BEARING

SLOTRELIEF

CAPACITYHOLE BACK DRILL

PILOT DIAMETER

LENGTH

SPANNER WRENCHHOLE

SLOT SEAL HOLE

SHOULDERFOR CAP

OVERALL LENGTH

DRAW-INCOLLET

STATIONARYCOLLET

PUSH-OUTCOLLET

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Basic Collet Introduction

The collet is a workholding device that grips the workpiece or tool in a machine tool spindle. Themore common machines that use collets are lathes, milling machines and cylindrical grindingmachines.

The basic collet is illustrated on the previous page. The common names of the various parts ofthe collet are shown.

The collet is pulled or pushed into a mating taper in the machine’s spindle or tool holder. As thecollet is moved linearly, it closes down on the workpiece or tool. The collet continues to close untilit can no longer move. The amount of force is determined by the closing mechanism such as anair closer, hydraulic closer, or mechanical closer.

THE HEAD ANGLE

Lathe ColletLathe collets generally have a head angle of approximately 10 degrees.When the head angle of the collet is less than 7 degrees it will have atendency to stick (not open when the closing force is removed).

Stationary ColletHigh production machines use stationary collets. Their head angle is muchsteeper than lathe collets, usually up to 15 degrees. This helps eliminatesticking and aids in opening the collet.

Toolholder ColletToolholder collets are made with less taper (7 degrees and lower) whichgives them greater holding power. Sticking is not as much of a concernbecause the collet is not opened and closed during the production cycle.

BACK BEARING

Probably one of the least (but most) critical factors inclose tolerance machining is the allowance betweenthe back bearing of the collet and the spindle.

When the clearance is too great, the collet will pivot orshift when tool pressure is applied to the part, causingexcessive runout.

Excessive runout can be caused by a worn spindleback bearing or a worn collet back bearing. For moreinformation see chapter 4, page 25.

10°

15°

7°

BACK BEARINGSPINDLE ANGLE

HEAD ANGLE


Items such as the headstock center have their backbearings held extremely close (.0002"), whichminimizes the clearance, assuring the best concen-tricity.

Stationary Screw Machine Collet

With the stationary screw machine collet, concentricity is more difficult to obtain because there isa sleeve clearance as well as a back bearing clearance.

With this style collet, it is important that the face of the cap is perpendicular to the spindle andthat the face of the collet is perpendicular to the back bearing and the head angle.

When a collet requires an extreme amount of spread, as do most screw machine collets, the backbearing often develops a 3- or 4-point out-of-round condition due to the distortion caused byspreading. Because this condition can cause sticking of the collet, additional clearance is allowedon the back bearing of the screw machine collets.

Face of Spindle & Cap

Sleeve Back Bearing

SleeveLabyrinth Seal

Collet Back Bearing

Nose Cap

Draw Bar

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Slot Designs

Lets take a look at the slots in a collet. There are slot variations. Some of the more common onesare shown below. The Straight, Slot with Relief Hole and Tear-Drop Slot are used to make thecollet more flexible.

Straight-SlotThe straight slot is the least flexible and is usedfor collets that have very little spread, such aslathe collets. "Spread" is the amount a colletopens beyond the size of the collet. A .500"collet may spread to .510" when the bore ismeasured. This measurement is taken with thecollet outside of the machine.

Slot with Relief HoleThe relief hole is designed for flexibility in acollet requiring more spread than the straight-slot shown above.

Tear-Drop Slot(Screw Machine Collet)Screw machine collets, which require consider-able spread, use the tear-drop slot for maximumflexibility.

Double-SlotThe double slot is used for small order holecollets where a standard slot would be biggerthan the order hole. The secondary slot can beas narrow as .005" wide.

Angular-SlotThe angular-slotted collet is used when holdingregular shaped polygons (hex, octagon, square,and triangles) on their corners, or outsidediameter, instead of on the flats. The angularslot prevents the corners of the stock from fallinginto the slots.

Zig-Zag SlotThe zig-zag slotted collet solves the sameproblem as the angular slotted collet but is usedfor stock under 1/4". The corners of small stockmay fall into the slots of the angular slottedcollet, making it impractical. Because of the highcost of the zig zag slot, always consider theangular slotted collet first.

StraightSlot

Relief Hole

Angular-Slot

Zig-ZagSlot

Double-Slot

Tear-Drop Slot


Over-The-Shoulder Collets

When more flexibility is needed, such as when using the over-the-shoulder collet, not only is thetear-drop relief slot used but the wall thickness is also reduced. This practice will reduce the life ofthe collet but is necessary to be able to grip the part over a shoulder. Part of the requirement forgreater flexibility needed for the over-the-shoulder collet can be achieved by increasing thenumber of slots.CAUTION: The amount the collet will open is controlled by the stroke of the collet closer.

Other Slot DesignsOther slot designs, such as those shown below, are used for special applications.

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CHAPTERTWO

COLLETAND

CLOSER SYSTEMS

14 CHAPTER 2Collet and Closure Systems

Collet SystemsThere are three different types of collet systems—

the Draw-In, the Push-Out, and the Stationary.

Draw-In Collet

The Draw-In collet is the most common and also the most accurate for holding concentricity. Toclose the collet, it is drawn into the spindle angle. The only moving part (other than the collet) isthe draw tube.

Concentricity depends on the accuracy of the spindle and the collet. The order hole of the colletmust run concentric with its head angle and back bearing which also must be concentric witheach other. There are no other factors involved.

Head Angle

Nose Cap

Spindle

Draw Tube

Collet

Collet Back Bearing

Coolant Shield

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Push-Out Collet

The Push-Out collet is becoming obsolete. In the past, it was used in many manual turret lathes.

To close the collet, it is pushed against a cap which is threaded or bolted to the spindle. The caphas an internal angle which mates with the front angle of the collet. The collet is closed by aforward force from the push tube.

There are several items that affect concentricity: the collet, the spindle and the cap, along with itslocating shoulder. All of these items require a tolerance when being manufactured. It is the buildup of these tolerances which effects the total concentricity and accuracy of this system. Otheritems that affect concentricity are worn caps and caps that are not square with the face of thespindle.

Push Bar

Back Bearing

Spindle

Nose Cap

Labyrinth Seal


Push Sleeve—Stationary ColletThe Push Sleeve system is the only system that allows length control of the workpiece. This ispossible because the face of the collet is located against the back face of the hardened spindlecap. The collet is closed with a sleeve which pushes against the angle on the collet causing thecollet to close, but not move longitudinally. Note: There are collets designed for part lengthcontrol that are available for other collet systems.

There are even more parts in this system to affect concentricity: the collet; the cap and how italigns with its locating shoulder and thread; the sleeve with its allowance; as well as the clear-ance between the spindle back bearing and the collet’s back bearing. This system is the leastaccurate when trying to hold concentricity because of the large number of parts involved.

ToolholderColletAssembly

The collet is closed bytightening a threadedcap on the tool holdersleeve.

Draw Tube

Collet Back Bearing

Spindle

Face of Spindleand Cap

NoseCap

ColletSleeveLabyrinth Seal

Collet

Drill Stop

Cap

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Mechanical Collet Closer

Mechanical closers are used on manual machines. Because they require human intervention tooperate them, they are seldom used on automatic machines. The exception is the cam-operatedmachines which still use a mechanical closer, but it is closed with a cam instead.

Air-Operated Mechanical Closers are manual closers that have been fitted with an air cylinder toactuate them. These were common on the first Hardinge Automatic machines. They were eventu-ally phased out for the totally air-operated closers.

Actuating the SystemEach one of these collet systems require some means for opening or

closing the collet. The following closing systems are used.


Pneumatic or Hydraulic Closers

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Pneumatic and Hydraulic Closers

Pneumatic - Air

The Pneumatic closer allows the light chucking pressures necessary when gripping thin-walledparts or tubing. When doing precision work, this system is most versatile. When doing extremelyheavy stock removal work, the gripping pressures may not be adequate.

Disadvantages:Air is compressible, therefore any tool pressure that pulls on the workpiece could actually loosenthe collet if its force is greater than the force created by the air pressure against the piston.

Hydraulic

The Hydraulic and the Pneumatic closer systems look almost identical. The major difference isthe pressure medium (hydraulic oil /air) and the higher pressures that are used. Hydraulic oil isnot compressible, therefore any pressures opposite the piston force should not allow the collet toopen. The pneumatic closer uses shop air pressure, usually 90 - 100 PSI, whereas the Hydrauliccloser pressures can be as high as 1000 PSI. The same size piston used on a pneumatic closerwill now deliver 10 times the force.

Disadvantages:Disadvantages include the added expense required for the hydraulic pump and sump. Thehydraulic collet systems cannot be used for delicate or thin-walled parts. The pressures cannot beturned down low enough to eliminate crushing the workpiece.


Machines that use the various collet systems

DRAW-IN COLLET:

• Acme Gridley• Cone• Davenport• Euroturn• Gildemeister• Greenlee• Grinder Collets• Hardinge• Lathe Collets• Mill Collets• National Acme• New Britain• Schutte• Tornos• Warner Swasey• Wickman

PUSH-OUT COLLET:Turret Lathes

• Warner & Swasey• Jones & Lamson• Gisholt

PUSH SLEEVE - STATIONARY COLLET:

• Brown & Sharpe• B. S. A.• Index

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TYPESOF

COLLETS

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CHAPTER THREE

22 CHAPTER 3Types of Collets

Types of Collets

There are many types of collets available to the machine tool industry.Listed below are the styles available for 5C spindles. These same styles

can be made for other types of collets.

1. Fractional sizes

2. Decimal sizes

3. Number

4. Letter

5. Metric sizes

6. Special Accuracy (.0002" TIR for

5C collets only)

7. 4-Split Long Bearing (Drill Collet)

8. Angular Slotted

9. Zig-Zag Slotted

10. Angular Hole

11. Flat Face

12. Taper Hole

13. Short Bearing

14. Long Bearing (5C ST & others)

15. Bearing Relief

16. Light Force

17. Heavy Duty

18. Stop Collets (SC)

19. Blanks

20. Serrated

21. Hex

22. Square

23. Rectangular

24. Special Shape & Extruded

25. Octagon

26. Eccentric

27. Stepped

28. Plug Chucks

29. Extended-Nose

30. Extended-Taper Nose

31. Emergency

32. Contact Lens

a. Extended Nose Step Collet

b. Solid Extended Taper

c. Shank

33. Solid Collet

34. Brass Collet

35. Nylon Collet

36. Morse Taper Collet - Female

37. Threaded - Solid - Order Hole

38. Threaded - Split - Order Hole

39. Dead-Length® Collet

40. Dead-Length - Thru Hole

41. Mill Arbor

42. Expansion Collet- Spindle

mounted

43. Master Expansion - Collet type

44. Step Chucks

a. Hardened & Ground

b. Emergency

c. Extra-Depth

d. Closers for all Step Chucks

e. Dead-Length Step Chucks

45. Pin Step Chucks (Dead Length)

46. Male Headstock Centers

47 Female Centers

48. Driver Center

49. SURE-GRIP® Expansion Collets

50. Dead-Length Step Chuck-Spider

Stop

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CHAPTERFOUR

CONCENTRICITYAND

SPREAD

24 CHAPTER 4Concentricity and Spread

100.

0

1"

Concentricity

Concentricity is measured by putting a gauge pin or ground plug in the collet order hole andmeasuring the Total Indicator Reading (TIR) of the pin’s runout with a .0001" dial indicator at aspecific distance from the face of the collet.

There are many factors to be considered when trying to achieve the best concentricity possible.

The Concentricity of the Spindle

1. TIR of the spindle angle

If the spindle angle does notrun concentric, it is impossiblefor the collet and workpieceto run concentric.

Head Angle

Spindle Angle

Back Bearing

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1"

1"

2. TIR and wear on the back bearing

a. The back bearing must also run concentric because it will affect the concentricityof the collet.

b. If the back bearing of the spindle is worn, it will allow the back bearing of the collet topivot, which will cause excessive runout.

3. Runout of the collet thread

a. The thread must run concentric and square with the head angle and the order hole ofthe collet.

b. If these conditions are not met, the pressures will be exerted on one leaf of the colletinstead of all three. The parts manufactured with this collet will not be concentric withthe chucking diameter. The uneven forces on the collet leaves may cause them tobreak.


What is Spread?

Spread is what puts the spring in the collet to help open it. This spring keeps the collet angleagainst the spindle angle, helping to eliminate chips which would cause runout. When the colletcloser on a screw machine is opened, it is the spread in the collet that opens the collet so that theworkpiece can be loaded or unloaded. Too much spread makes it harder to close the collet,reducing the gripping force on the workpiece. There is very little spread in a lathe collet, justenough to allow the workpiece to be loaded when the collet is opened. When a Brown andSharpe style collet is not in the machine, the workpiece will very easily slide into the collet withplenty of room to spare. With other types of collets, such as lathe collets, a .003" (minimum)oversize plug will slide through the order hole (bore).

Screw Machine Collet - Large Amount of Spread

Lathe Collet – Very Little Spread

Grind Outs

Grind-outs are collets that have been finished and are then re-ground to a new larger size. Thisprocess is used when a quick turnaround is needed. Maximum stock removal is 1/64" on casehardened collets. If more than a 1/64" is removed from the order hole, it will be softer than astandard collet because most of the case has been removed. There is no limit to grinding the IDwhen thru-hardening steel is used to manufacture the collet.

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CAM and Flat GrindScrew Machine Collets, 16C, 20C, 25C Collets(5C collets and standard lathe collets are not cam ground)

The cam grinding process helps reduce sticking problems. As the order hole of the collet wears,the collet is drawn further into the spindle seat. When this happens, the bearing area shifts from afull bearing to a bearing on the edges of the leaf (see above illustration). This edge bearing ismost undesirable because it reduces the bearing (surface contact) between the spindle and thecollet. To help alleviate this condition, collets are cam ground or flat ground (see illustration onnext page). These two processes remove material from the slot area of the collet. This allows thecollet order hole to wear and still maintain a bearing between the center of each leaf and thespindle angle.

NEW COLLET-NO CAM GRIND

WORN ORDER HOLE - NO CAM GRIND

FLAT

CAM

CAM GRIND FLAT GRIND


There are restrictions on its use:• The collet closer must have enough linear stroke to allow the collet to open up sufficiently

to clear the larger diameter.• The Davenport automatic, with the special burring attachment, uses pick-off collets which

can handle a shoulder that is .100" larger than its gripping diameter.• Collet closers with a 1/2" stroke and a 10-degree spindle head angle may use a special

collet which can handle a part with a shoulder approximately .150" larger than the bore.

To find the amount that a special collet can open in relationship to the stroke of the collet closer,multiply the tangent of the collet head angle by the maximum closer stroke, then multiply theanswer by 2. Don’t forget there will be some loss due to manufacturing tolerances.

EXAMPLE: 16C Collet = 2 (Tan 10 degrees x stroke)16C Collet = 2 (.17633 X 5)16C Collet = .1762" (maximum difference in diameters)

Over-The-Shoulder collets are special collets which are custom designed and manufactured foreach part or family of parts. They require special collet head angle designs, special slots and veryprecise heat treatment.

Extra-Spread

Extra-Spread (Over-The-Shoulder) collets are used when gripping on a diameter that is smallerthan the first area of the part which goes into the collet. These are commonly called Over-The-Shoulder Collets.

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CHAPTER FIVE

COLLETHARDNESSAND WEAR

30 CHAPTER 5Collet Hardness and Wear

Advantages of Hardened ColletsHardened collets have a longer life than collets not hardened

• The harder the surface, the longer the life - wear resistance.• Reduces the cost of running a job because fewer collets or pads have to

be purchased.• Reduces downtime because there are less collet changes.

PROBLEMS CAUSED BY IMPROPER HARDNESS

• Collets that are made too hard will be brittle and will break easily.• When collets are not tempered properly will lose their spring.• Collets that are too soft will wear out very quickly.

What Causes Collets and Padsto Wear Out?

Poor housekeeping• Not keeping the collets & draw tubes clean. Take them out and

clean them after each job.• Not using seals with screw machine collets.

Surface condition of the material being gripped• Hot-Rolled Stock—it is rough with surface scale. The out-of-

roundness causes irregular contact with surface of order hole.• Cast Bars—same as hot rolled stock.

Types of materials• Abrasive materials shorten life—Aluminum, Cast Iron, Carbon and Ceramics.

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Types of Machining Operationsthat may cause collets to break down:

Heavy stock removal andheavy drilling may cause push back.

Heavy forming-cross slide tends to open the collet.May cause stock to slip which would cause wear.

Forming and drilling at the same time.


Intermittent cuts can cause radial slippage.

Out of Balance parts. Uneven pressure on the leaves.

All of the illustrated applications are common machining practices. Slippage can be overcome byusing a properly designed workholding system which includes a collet that has the right headangle design, the proper serration and hardness, a collet actuating system with adequate drawbar force, a spindle drive system with adequate horsepower and torque, cutting tools that areproperly sharpened and centered, and proper feed rates and spindle speeds for the tooling andmaterial selected.

Types of Machining Operationsthat may cause collets to break down:

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Other Causes for Wear

Multi-Spindle Machines

(Causes also related to single spindle machines)

• The feed tube and the collet are not keyed together—this causes radialslippage when the collet opens and closes.

• Crooked or bent bars put stress on one leaf of the collet or feed finger whichcauses slippage and loss of tension in that leaf.

• Dirty bars create a very abrasive action between the bar and the feed fingerand/or collet.

• Bent feed tubes cause runout of bar and excessive wear on the leaves of thecollet and feed fingers. The tubes are bent due to running bent or crookedstock and with considerable use.

• Excessive tension on feed fingers. This is hard to check. You can push downon scale to check tension.


notes:

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CHAPTER SIX

MATERIALSHELD BYCOLLETS

36 CHAPTER 6Materials Held By Collets

MATERIAL SPECS. PROBLEMS RECOMMEND

CARBON STEEL Steel None StandardTOOL STEEL Thru- hardening None Standard

HOT-ROLLED Certain alloys can’t Stock is not round, Saw Tooth,be cold drawn—hot diameter varies Serrated,rolling is less expensive considerably and or 3-Jawthan cold drawing they have a very Power Chuck

rough surface finish

COLD-DRAWN Most common steel None Standardused for screw machinestock

EXTRUDED Special-shaped stock In most instances Special-shape(Made by drawing cannot be held in (Usuallythru a series of dies in a round collet—shape made usinga semi-molten state) usually does not EDM methods)

conform exactly to theprint, thereforeactual samples ofstock must be sentwith the order

COLD-HEADED Part is cold-formed to Chucking diameters Serratednear net shape—many are not always collet orare done from coil stock accurate, out-of-round, Power Chuck

etc.

SHEET METAL Punched from flat stock Size variation Standard &Serrated

SHEET METAL Extruded thru several Size variations Standard,EXTRUDED dies—such as a can shape & thin walled special-shaped

& tapped hole

STAINLESS There are many different Marks very easily Standard &kinds—magnetic, non- Serratedmagnetic, corrosionresistant, etc.—300 & 400Series—some are harden-able and some aren't

Materials Held by Collets

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IRON Made same as cold None Standard &COLD ROLLED Darwin steel—we use serrated

Nickel Alloy-Dura bar—can be hardened to42-45 Rockwell “C”

IRON Made same as hot- Scale, out-of-round SerratedCAST BARS rolled steel

IRON Produces very fine Variation of SerratedCONTINUOUS grain iron—can be chucking area and/orCAST BARS round or special-shaped special-shaped

IRON Permold and sand Large variations— 3-jaw powerCASTINGS castings draft angle, rough chuck,

surface finish serrated

BRASS & Cold-drawn bars Easy to work— Standard &BRONZE marks easily serrated—

nylon forhighly polishedstock

BRASS Near-net shape drawn Requires special Special-shapedEXTRUSIONS through dies shapes —need a

piece of stock 8"long to use asEDM electrode

BRASS Sand casting process— Large variation 3-jaw powerCASTINGS die-type castings on chucking chuck,

surface, draft special-shapedangles and rough & serratedsurface finish

ALUMINUM Cold-drawn Stock is abrasive— StandardBARS cutting tools

wear fast


38 CHAPTER 6Materials Held By Collets


ALUMINUM Near-net shape Requires special Special-shapedEXTRUSIONS drawn thru dies shapes—need a

piece of stock 8"long which isused to make theEDM electrode

ALUMINUM Sand casting process— Large variation 3-jaw powerCASTINGS die type castings on chucking surface, chuck,

draft angles and rough special-serratedsurface finish collets

ALUMINUM Much more precision Some variation on Special-shapedDIE CASTING than sand casting chucking surface, & sometimes

out-of-round, serratedgood finish

PLASTICS: Size variation, soft, StandardNylon® - Delrin® marks easily—

Teflon® - Bakelite® much of this material isAcrylic® - Glass- slippery—requires lightfilled - Synthene® chucking pressure

CARBON Comes in cast bars Very brittle, will break if StandardCARBIDE castings and molds chucked too tight—

GRAPHITE powdery and abrasive—CERAMICS causes collets and the

machine tool to wear outvery quickly


Basic Workholding

Techniques

39

CHAPTERSEVEN

COLLETCAPACITIES

40 CHAPTER 7Collet Capacity

Correct Collet Size

When the collet is the proper size for the workpiece, there is full bearing along the angle and thecircumference of each segment of the collet where they mate with the spindle angle (seat). Theresult will be good concentricity and excellent holding power.

ORDER ACCEPTABLE FOR BEST ORDER HOLECOLLET HOLE BAR SIZE CONCENTRICITY GROUND TO

5C Standard Fractional +.002 to -.001 .001 Under order .001 under thehole size order hole

5C Standard Decimal +.002 to -.001 Same as order Same as thehole size order hole

16C Standard Fractional +.002 to -.001 .001 Under order. .001 under thehole size order hole

16C Standard Decimal +.002 to -.001 Same as order Same as thehole size order hole

Screw Machine Fractional +.002 to -.001 .001 Under order .001 under thehole size order hole

Screw Machine Decimal +.002 to -.001 Same as order Same as thehole size order hole

Master Collets — Hole size Order hole —

There are many discussions as to how much variation in stock size a collet can handle. Hardingecollet engineering has developed a chart (above) of suggested stock sizes that an order hole canhandle. This refers to bar stock or chucking diameter.

Chucking Diameter

Basic Workholding

Techniques

41

Collet is Oversize

If the collet is oversize as shown above, the part may pivot at the line of contact. The turneddiameters may not be concentric with the bar or chucking diameters, and the machined diameterscan be out-of-round. There will be line contact at the center of the leaf.

Collet is Undersize

If the collet is undersize, the contact will be at the head of the head angle on the spindle angleand the order hole. This can help with bar push-back because the more tool pressure exerted onthe bar the tighter the collet becomes. The part may pivot around the point of contact whenexcessive chucking pressure is NOT applied. The turned diameters may not be concentric withthe bar or chucking diameters. The edges of the slots will bite into the workpiece and may causedamage or mark the bar.


HA

RD

EGNI

Four-Split, Long-Bearing Collets

Four - split collets are also called “5ST Collets” or “Drill Collets”. They come standard in varioussizes for the 5C style spindles. Those with under 1/16" order hole are two-split. The variousstyles are:

• Number sizes• Letter Sizes• Fractional from 1/64 to 1-1/16" (5C collets)• Decimal (special order)

Extra, Extra-Spread Collets

The shoulder normally cannot be larger than the chucking diameter by more than .100" on thediameter. As the length of the bearing in the order hole gets shorter, the collet can be made toclear larger diameter shoulders.

.050" Max.

Basic Workholding

Techniques

43

Angular-Slotted Collets

These are special-order collets that are used to grip triangular, hex, square and other eccentricstock with corners that would normally fall into the slots of the collet. The angular-slotted collethas the following characteristics:

• The slots are normally cut on a 7-degree angle instead of straight• The parts are gripped by the outside diameter of their corners• They are used for high production loading by eliminating the need for

orienting the part with the shaped hole in the collet• Greatest use is for carburetor needle valves

Zig-Zag Slotted Collets

These are special-order collets that are used to grip small diameter triangular, hex, square, andother eccentric stock with corners that would normally fall into the slots of the angular slottedcollet. The zig-zag slotted collet has the following characteristics:

• The slots are double-cut with the zig-zag EDMed (Electrical DischargedMachine) as the second slot

• The parts are gripped by the outside diameter of their corners• They are used for high-production loading by eliminating the need for

orienting the part with the shaped hole of the collet• The Zig-Zag overlaps even in the relaxed (open) position so that even the

corners of the smallest stock cannot get into the slot• Expensive


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Basic Workholding

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45

CHAPTEREIGHT

COLLETSERRATIONS

46 CHAPTER 8Serrations

Serrations

Why do we use serrations?

• Better gripping pressure by concentrating force in a smaller area

• Reduces push-back of stock under the load of cutting

• Reduces spinning or rotation of the stock

• Under a heavy cut they may help prevent stock from "walking out" of the collet

• Maximum contact area when gripping irregular surfaces such as

hot-rolled & cast bars

Standard Flat Serration

Increases gripping pressure butdoes not score the workpiece whenusing the correct closing pressure.This is the best all-around serration.

Tap Serration

Tap serrations are used on padswith small holes that areimpractical to groove and broach.

Circular Serration

Circular serration is used to in-crease the gripping pressure but notbite into the workpiece as much asother serrations would.

?

Basic Workholding

Techniques

47

Sawtooth/ButtressSerration

The grooves and broach have thesame shape as a buttress thread.This helps prevent both push-backand radial slipping of the workpiece.The sawtooth serration is the bestdesign when doing heavy formingand/or drilling. This serration isdesigned to bite into the stock orworkpiece.

Diamond Serration

The grooves and broach have a 90-degree “V” shape. This serration isdesigned to bite into the stock.

Hex and Square ColletSerrations

Circular serrations are used onHex, Square and Polygons.

Additional Information

If the last serration is less than onefull serration in length, the lastgroove will not be cut. This makesfor a stronger area and eliminateschipping out of the serrations whenloading bars.

Disadvantages of SerrationsSerrations may score the stock or workpiece, and generally cost more than smooth pads or collets.Additional information in the following chapter.

48 CHAPTER 8Serrations

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Basic Workholding

Techniques

49

CONCENTRICITYAND

GRIPPING FORCE

CHAPTERNINE

50 CHAPTER 9Concentricity and Gripping Force

Chucking Surfaces

The Order Hole

The bore, order hole, or ID of the collet comes in many different surface finishes, diameters andbearing lengths. Let's take a look at these aspects.

Smooth Bore

Most lathe collets are smooth bore. They achieve a full bearing on a finished part.They are typically less expensive than serrated collets and are used whenever the stock surfacecannot be marked.

Serrated Bore

Serrated Bore gives maximum gripping force when doing heavy machining operations. They areused for cast or hot-rolled stock which is usually out-of-round and has a rough surface finish. Theserrations will bite into the material and reduce slippage and push back.

Basic Workholding

Techniques

51

Diameter of the Order HoleFor Bar Work

Small Order Hole

The order hole shouldbe smaller than the barstock size for maximumgripping.

Exact Sizeor Slightly Under

The order hole should beexact size when runningground rod or tubing.Decimal-size order holesare made to the exactthree place decimal size.

Exact Decimal Size(3 decimal places)

The order hole shouldbe exactly the same sizeas the bar for bestconcentricity and leastpossibility for marking thestock. If you were running1/2" stock, and neededbest concentricity, butthe stock actually mea-sured .497, you shouldpurchase a .497 decimalcollet.


Holding Power When Doing Chucking Work

Exact Size

For best results without marking, the order holeshould be exactly the same size as the stock,resulting in:

• Full bearing on chucking diameter• The best concentricity possible

Oversize

When the order hole is larger than the chuckingdiameter, the following happens:

• Less gripping force due to line contactat center of leaves

• Diameter runout• Radial marks on the chucking diameter

Undersize

When the order hole is smaller than the partchucking diameter, the following happens:

• Distortion of the part• Diameter runout• Linear marks on chucking diameter

BUT, the holding power will be greater.

For Best ConcentricityWhen Holding Any Workpiece

The order hole should be exactly the same size asthe workpiece's chucked diameter.

Basic Workholding

Techniques

53

CAUTION: Extended-Nose Collets

Extended-nose collets are used to extend the part out farenough to clear tooling interferences. This collet is easilydamaged by applying moderate closing forces. Because thegriping area of the collet is substantially forward of the headangle, the collet will bellmouth. This creates what is called ascissors grip on the part which is very unstable. Concentricity isdifficult to hold using this style collet. Extended-nose colletsshould only be used for the lightest of cuts. If you need anextended-nose collet for normal machining, you're using thewrong machine tool.

Short Bearing

• The smaller the order hole, the shorter thebearing length, mainly due to the length of thegrinding wheel used during manufacturing.

• A short bearing would be used to clear threads ona part. The threads could be damaged with astandard collet.

• Special over-the-shoulder collets have very shortbearings to allow for maximum opening withminimum collet stroke.

Split-Bearing (Bearing Relief)

• Improves gripping pressure with the sameamount of force. Many Davenport and Brown &Sharpe collets come standard with split bearings.

Length of Bearing


Number of Slots

No Slots

• Plug chucks and blank collets• Used for arbors and fixtures• Taper-hole collets - Morse, B&S• Headstock centers• Stub arbors• Headstock mill drivers

Two Slots

Two-slotted collets are used for special applications.

TWO SPLIT ANGULAR2 Split Drill 5CST

ROUND SQUARE HEX

Three Slots

Three slots are most common. It is the most accurate design for centering a workpiece.They are usually used for Round, Hex and Square collets.

Basic Workholding

Techniques

55

Four Slots

Four slots are used on larger collets to reduce closing pressure and are very common for squareand rectangular collets.

More Than 4 Slots

More than four slots are used on larger collets to reduce closing pressure, for crimping collets,special collets and other special applications.

HEX RECTANGULARSQUARE

8-SPLIT6-SPLIT Crimping9-SPLIT


Micro-Finish of the Order Hole (Bore)

Machined—lathe bored

Emergency style are usually bored by the operator. Special applications collets and brass colletsare usually bored for the customer.

Grind

Grinding is the most common method for finishing the order hole.

Lap—Hone—Polish

• Extremely small collets that are too smallto grind.

• Stripper collets used to pull the workpieceoff a die.

• Capsule collets that require a very finesurface finish.

• Workpieces that cannot be scratched.

• Collets used on extremely high-speedmachines where operating parts mustbe super-finished.

Stripper Collet

Extremely Small

Clover Leaf Grind—Special Process

The order hole is cleared at the slots using an endmill or grinding wheel. Chucking force is increased.Edges of the slots do not bite into oversized stockand they help eliminate marking on nominal stock.Used on hot-rolled stock.

Capsule Collet

Basic Workholding

Techniques

57

EXPANDINGCOLLETS

58 CHAPTER 10Expanding Collets

Expanding Collets

When doing secondary work, where extremely close length and concentricity tolerances arerequired, most of us hope that the part has a hole in it. It has long been known that using anexpanding collet is the most accurate way to hold a workpiece.

True, there are certain machining practices that have to be adhered to when doing the firstoperation on the workpiece. There are many different styles of expanding collets, each onehaving their strengths as well as weaknesses.

Preparation of the Blank

Many people feel that as long as the part has a hole, it can be held accurately using an expansioncollet. Unfortunately, this is not the case.

When machining the bore, the section to be machined should not be inside the collet or under thejaws of the chuck unless it is round. If it is not round, there may be considerable distortion of thebore when it is removed from the workholding device.

Basic Workholding

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59

If the outside diameter of a solid blank is out-of-round, and that diameter is chucked using a colletor step chuck, the bored hole will also be out of round after removal from the collet.

1. Out-of-Round Part(Collet shown open)

2. Rough Bore(Material flows into hole)

3. Finish Bore(Rounds out)

4. Collet released(OD returns to original shapeand ID follows)

A precision bore is required when gripping the part with an expansion collet. Prior to boring thepart, the outside chucking surface must be round within a tolerance that is less than the desiredbore tolerance.


H A R D EGNI

SI

ZE

M

OD

EL

SI

ZE

BORE

1. Tubing orDrilled Hole

When boring a part which will be held on an expansion collet, it should always be rough boredand then finish bored.

When only one boring operation is done, the resulting hole will generally have the same out-of-roundness the blank or drilled hole had.

2. ChuckedID forced round

1. BlankID out-of-round

4. Distortion after removal3. Turned

If the bore to be gripped by the expansion collet is out-of-round, it will be forced round by theclosing pressure. Any outside diameter turning work accomplished while being held by theexpansion collet will be round until it is removed from the expansion collet. The bore will thenreturn to its original out-of-round condition which in turn will make the outside diameters also goout-of-round.

2. 1st bore notround due to un-

even tool pressure

3. Finish boretruly round

Basic Workholding

Techniques

61

By now you have probably gotten the message, “If you want to do precision work, while holdingwith an expansion collet, the bore you are locating on must also be a precision bore.”Work done on the outside diameters will not be any better than the tolerances and condition ofthe inside diameter being located on.

StylesThere are many different styles of expanding collets. Let’s start out with a precision style, thespindle-mounted expansion collet assembly.

Spindle-Mounted Expansion ColletThis system can only be used on Hardinge-style thread or taper-nose 5C spindles.

CAUTION: Do not use on Hydraulic Collet Closers with 5C spindle adapters. The assembly willbe damaged and will be unsafe to use.


Basic Partsof the Spindle-mounted Expansion Collet

1. The Spindle Mount

The spindle mount bolts, threads or istaper-locked onto the spindle nose ofthe machine. It has a locating face thatis square with the spindle centerline.The collet is held in and adjusted tocenter with four adjusting screws. Thescrews are used to center the collet andforce it against the locating face of thespindle mount to square the collet up.

2. The Collet

The collet is usually four-split, hardenedand ground. The 5C-version can handlework with bores from 1/2" to 3". It hasan ID taper which accepts a draw plug.The draw plug expands the collet as thedraw collet is closed (pulled into thespindle). There is a locating face whichmust be perpendicular with the colletdiameter.

3. The Draw Plug Assembly

The draw plug assembly consists of the draw plug with an angle which mates with the collet’s IDangle. This plug mounts into a draw collet and is pulled pack by the collet closer. The draw colletdoes not have a head like a regular collet. Its only purpose is to center the draw plug in thespindle and to connect the collet to the collet closer. The clearance between the spindle backbearing and the draw collet’s back bearing is much less than a standard collet. This featureallows the assembly to hold part concentricities to within .0002" TIR.

Locating Face

Locating Face

Draw Collet

Draw Plug

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63

Work Locating Stops for different applications

4. Machineable Work Locating Stop (Backing Plate)

This part is bolted to the spindle collar and machined by the operator to conform to the locatingpoint of the part. It gives greater stability to the collet and helps eliminate any flexing of the colletby supporting the workpiece. Two common problems when NOT using a backing plate are chatterand taper on the turned diameters which, many times, are caused by deflection of the collet.


Advantages of the Spindle-MountedExpansion Collet

• One of the most accurate expansion collets available• Gives dead length control, even without a backing plate• Can hold .0002" concentricity between the bore and turned diameters

(the blank must be good to start with)• Can be used for large diameter work• Custom collets can be made with extra long bearings• Custom backing plates for complex datum surfaces• Longest life—hardened & ground• Soft blanks available for machine-in-place applications

Special Considerations

• Long set up time—10 to 30 minutes• Requires skilled personnel• Collet can be destroyed if collet is closed without a part on it• 1/2" collets and above are guaranteed to have runout• Special collets as low as 5/16" with a special draw plug and adapter

can be easily destroyed by a careless operator, therefore, there isno guarantee on collets smaller than 1/2"

• Collets are available to a 3/8" minimum diameter

Basic Workholding

Techniques

65

Parts of the Master Expanding Collet

1. The Body

The allowance between the body and the spindle back bearing is extremely close (much closerthan a collet). This assures very close tolerance capabilities. The master collet is part of the bodyand is very large, giving extremely good stability. The leaves of the collet have holes threaded inthem to accept interchangeable collet pads.

Master Expanding Collet5C & 16C collets—Collet-style

This expansion collet can be mounted in any machine or workholding device that uses 5C and16C collets. It does not require a spindle mount. It mounts directly into the spindle and usesinterchangeable pads which are machined by the operator to fit the part. These pads can beremoved and saved for use on the same part at a later time. There are two exceptions to doingthis:

• The pads must go back on the same master collet in their original position• The TIR tolerances cannot be critical


2. The Draw Plug

The plug is very large in diameter. This cuts down on the deflection normally associated withdraw plugs.

3. Keyed Special Thread

The draw plug is thread into this part. When the closer pulls back, this part goes back with it. Thethreaded part pulls away from the body which, in turn, pulls the draw plug against the collet angle,closing it.

4. Spring

The spring pushes against the back of the master collet body keeping the head angle in contactwith the spindle angle at all times. Without this spring, chips would get behind the master andcause runout of the master collet.

Basic Workholding

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67

Master Collet Pads

Pads are made from steel (2" capacity) and aluminum (3" capacity). The steel pads are thestandard pads. These pads are bolted to the master collet with six screws. A limit ring (the ringused for set up) is placed around them and the collet is very lightly closed, using just enoughpressure until the ring cannot be turned by hand. The pads are then machined to the exactbore size.

The 3" aluminum pads are for large diameter light work. They are bolted to the master colletleaves. Instead of a set ring going over the OD of the pads, there is a pilot on the front of thepads. A cap is placed over this pilot. The collet is very lightly closed and the pads are machinedto the size of the part within a few ten thousandths.

Hardened and Ground

For high production runs, hardened and ground collets should be used. When purchasing thesecollets, you must also purchase the master collet body. The pads will then be ground on thatbody, ensuring the best TIR possible.

LIMIT RING

PADS


Advantages of Master Expanding Collets

• Can be taken from the lathe to a milling fixture without the needfor special spindle fixturing

• For noncritical work, pads can be remounted without re-machining• Pads can be re-machined for a smaller diameter workpiece• Concentricity is excellent because pads are machined in place• Small hole chucking—.250" diameter to a depth of .250"• Part length control

.100" diameter chucking is possible

Hold the pads in the customer-bored step chuck and re-bore the back counterbore. This elimi-nates the space in the slots, allowing a smaller chucking diameter to be turned.

Special Comments—Scissor Gripping

This type of expansion collet is designed for light chucking only for small diameter work. Scissorgripping of part may occur, especially when using 3" aluminum pads.

POOR GRIPTurned undersize or without set-ring

GOOD GRIPTurned with set-ring to exact

size of bore

Pads have beenre-machined round

Pads held instep chuck forre-machining

Normal Slots inMaster Pads

Basic Workholding

Techniques

69

1

1

SMALL DIAMETERRatio 1 : 1

OVER TIGHTENINGof small diameter work

deforms pads

Special Comments—Small Diameter Work

When doing small diameter work, overtightening the collet can permanently deform the pads.Heavy tool pressure can deflect the collet. The backing plate used with the spindle mountedexpansion collet eliminates the problem.

Other Styles of Expansion Collets

Double-angle expansion collets

Hydraulic expansion collets

Hydraulic expansion arbors

Push-style expansion collets


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CHAPTER

11

MASTER COLLETSAND

FEED FINGERS

72 CHAPTER 11Master Collets and Feed Fingers

Master Collets and Feed Fingers

Master ColletMajor Classifications

Name ManufacturerStandard Masters AllStyle "S" HardingeMartin Master Hardinge/Patented design

Somma-BalasCT (2 Holes in Pads) AllCB (1 Hole in Pad) AllNew Britain Master Obsolete

Master Collets

Master collets are available for automatic screw machines, turret lathes and most of the newerCNC lathes. They were developed to reduce set up time. The collet no longer has to be taken outof the spindle of the machine when changing to another size bar. Most can be replaced from thefront of the spindle, which only takes a few minutes. The standard master collet still requires thecollet to be removed when replacing the pads. This style is not very popular, due to this require-ment.

The two major players are the Style "S" originally patented by Hardinge Inc. and the MartinMaster originally patented by Balas. The following pages show illustrations of each style colletand pad along with the advantages and disadvantages of each.

Advantages of Master Collets over Solid Collets

• Purchase masters only once• Pads are 60% less expensive than solid collets, while masters are roughly

30% more expensive than solid collets• Pads are available in different materials as a "special"• Pads are available in hex, square, and special shapes• Pads require less shelf space than collets• Many different machine masters use the same size pads• Emergency pads are less expensive than emergency collets• Hex and square pads are more accurate than hex and square solid collets

Feed Finger Classifications

Name ManufacturerStyle "B" HardingeAdjustable Tension HardingeAF Adjustable HardingeDial Adjustable Somma/BalasStyle "A" AllStyle "PB" Somma/Balas (Obsolete)

Standard Feed FingerClassifications

Name ManufacturerSolid Feed Fingers AllSquirrel Cage AllSetters Spiral Slot Setters

Basic Workholding

Techniques

73

Independent clamp is aself-contained unit whichslides into the master. Thedovetail anchors pad in place.

There are no holes in the collet head angle,therefore no reduction of precision bearingsurface. Also there are no tapped holes in themaster collet.

Trouble-freedovetail anchorsection

Pad has full bearing on thestock. No threaded holesthrough pads to reducebearing surface.

Independent clamp slidesfreely in and out of mastercollet. There are no threadedholes to get damaged.

Mating dovetails anchor the padand clamp together independent ofthe collet. The clamp cannot beloosened by vibration.

Style "S" Master Collet and Pad Features

Dovetail

Clamp

Pad With Clamp


Rear Shoulder takesEndworking Thrust

Endworking tools exerta tremendous amount ofpressure. With the Style "S"

there is no strain on the clamp or clamp screw.The force is absorbed directly by the pad shouldersin the recess of the collet, thus affording positivepad location and accurate work.

The clamps stay with the collet when stored. Martin Masters require a set of clamps with each set of pads.

Additional Style "S" Advantages

• No holes or slots in the head angle of the collet. This gives the collet maximumbearing surface between the spindle and head angle.

• No uneven wear caused by holes and slots. High spots left after use of other masterswill reduce head angle bearing when using solid collets.

• No threaded holes in the collet to be stripped or damaged.• If clamp screw is stripped or damaged they can be removed without damaging

the collet or the pad.• The pads are interchangeable without removing the master collet from the spindle.

Disadvantages

• Clamps can come out of collet when being stored and are easy to lose.• Clamp screw threads and wrench sockets can be stripped due to overtightening.

The Shoulder Takes the Thrust

There can be no strain on the clamp orclamp screw due to impact of the barstriking the back of the pad. This isbecause the clamp is secured to the padonly. All of the end thrust is beingabsorbed by the pad shoulders in therecess of the collet.

Bar Stock

Collet

Pad

FrontShoulderRear Shoulder

Bar Stock

Collet

Pad

Basic Workholding

Techniques

75

Style "S" Pad Advantages

• Easily inserted and removed without taking the master collet out of the spindle.

• Pads gives maximum gripping surface no matter what size.

• Dovetail anchor securely holds pads in place when bar is loaded. They cannot bedislodged. No other front-loading pad can make this claim.

• No threaded holes in the pad that can be stripped or damaged.

• Pads are available in standard sizes up to the rated capacity of the machine.

• Available in round, hex, square and special-shapes to rated capacity of the machine.

• Available in serrated or smooth to the rated capacity of the machine.

• Available in English and metric sizes.

• Available in the following materials:

– Hardened Steel– Steel - Emergency Style– Bronze– Carbide Impregnated– Nylon

• 60% less expensive than purchasing solid collets.

• Hex and square and special-shaped pads run more concentric than solid collets.

• Clamps not fixed to pads, therefore less storage area is needed for style “S” incomparison to Martin Pads.

• Dovetail design pulls pads into the pad seat.

Disadvantages—none


Martin® Master Collets

Advantages

• The collet does not have to be removed to change pads.

Disadvantages

• Loss of bearing surface when mated to spindle due to slots for clamps.• Uneven wear caused to the machine tool spindle due to slots in collet.

This creates high spots on the spindle angle and causes solid collets to havevery poor bearing to the spindle angle.

• Clamping the pads into the collet may distort the head of the collet.• Clamps and pads loosen very easily.• Pads can be knocked loose when loading a new bar.• These collets not stocked in all sizes—may require a special order.

The Martin Master has a slotin the face of the collet,through the head angle. Thepad is held in the collet usinga square lug that is threadedinto the pad. Each lug has ataper-threaded locking-screw which clamps the padto the collet.

Clamping cross section

Tapered Screw

ClampPad

Collet

Basic Workholding

Techniques

77

Advantages

• Easily inserted and removed without taking master collet out of the spindle.• Clamps stay with the pads and cannot be lost.

Disadvantages

• Machine capacity sizes are not available as standard pads because the clampwould protrude into the bore. Depending upon the machine, between 1/16" to 1/8"is lost from its maximum capacity when using these pads.EXAMPLE: Maximum size standard pad for a 1" Acme is 15/16".

• More space is needed to store Martin pads because the clamp stays with the pad.• Due to the lack of popularity, the stock is not as complete as with the Style “S.”• When locked, they are not drawn back into the pad seat.

Martin® Master Pads


Tapered Screw

ClampPad

Collet

The Martin Master pad has a squarelug threaded into its side with a taperthreaded hole in the lug for tighteningit into the collet slot.


"CT" Style Master Collets

Each pad is locked into the collet using twoset screws (cone point) locating into detentes in theshoulder of the pad. The threaded holes are in theface of the collet. This collet was used as originalequipment on National Acme machines.

Advantages

• Pads can be removed without removing the collet from the machine.

Disadvantages

• Tapped holes for locking screws can be damaged by overtightening whichcan destroy the collet.

• Pads can be locked without the set screws being seated in the detentes onthe shoulder of the pad.

• When loading new bar stock, the screws take all the shock, causing the padsto loosen up. This allows chips to get behind the shoulder of the pad.

Pad

Cone PointSet ScrewCollet


Pad Advantages

• No clamps to lose.• Can be loaded without taking collet

out of the spindle.• Pads can be easily stored because

there are no clamping lugs.• Full bearing surface - no holes thru

pads on large capacity sizes.

Pad Disadvantages

• Flaring of set screw detentes due toover torquing of the set screws.

• Can be dislocated when loading anew bar.

• Expensive to manufacture dueto special needs of set screwlocation area.

• Subject to cracking and/or chippingif shoulder is not properly heat-treated.

Basic Workholding

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79

"CB" Style Master Collets

The collet has one locking screw (cup point)per pad. The back shoulder has a back taperwhich helps lock pad in place. This colletwas used as original equipment on NationalAcme Machines.

Advantages

• Front-loading collet does not have to be removed to replace pads.• Locking screws stay in the master collet—no clamps to lose.

Disadvantages

• There is no way to make certain the pads are lined up with the set screwbefore tightening.

• Tapped holes for locking screws can be damaged by overtightening,which can destroy the collet.

• The screws take all the shock when loading new bars, causing the pads to loosen,allowing chips to get behind the shoulders.

• Any misalignment of the screw or detente in the pad will cause it not to seat properly.

Pad Disadvantages

• Flaring of set screw detentesdue to over torquing of set screws.

• Can be easily dislocated whenloading a new bar.

• Expensive to manufacture due tospecial needs of set screw location.

• Subject to cracking and/or chippingif shoulder is not properly heat-treated.

Pad Advantages

• No clamps to lose.• Can be loaded without taking collet

out of the spindle.• Pads can be easily stored because

there are no clamping lugs.• Full bearing surface—no holes through

pads on large capacity sizes.

Pad

Cup-PointScrew

Collet




The collet does not contain the lock screws. Two locking screws are in each pad which locksagainst a detente in the collet back seat.

Advantages

• Front loading—collet does not have to be removed to replace pads.• No tapped holes in the collet.

Disadvantages

• If the set screws are over-torqued, the collet can be permanently damaged.• The cutting pressure and load is against the set screws.

New Britain Master Collet(O B S O L E T E)

Collet

Pad

Cone PointScrew

Pad Advantages

• Locking mechanism stays with padsand cannot be lost.

Pad Disadvantages

• Cutting thrust is against the set screwsrather than the full back shoulder.

• Some bearing loss due to holesfor seals.

Basic Workholding

Techniques

81

Standard Master Collet

A screw goes through the head angle of the collet and into the side of the pad’s shoulder.The collet must be removed from the machine spindle to change the pads. These collets areavailable for all style machines.

Advantages

• Once the collet is purchased, the pads are less expensive than solid collets.

Disadvantages

• Must remove the collet to replace the pads.• The hole in the collet bearing angle causes uneven wear of the spindle. The resulting

high spots make other style collets perform poorly.• Screw can be sheared when loading new bar stock.

Pad

ColletLocking Bolt


Pad Advantages

• Considerable savings over the priceof solid collets.

• Firmly held into the master collet.

Pad Disadvantages

• Must remove collet to change pads.• Threaded holes remove bearing area

on larger capacity pads.• Screws can shear when pad is hit

when replacing bar stock.


Hex and Square PadsMasters are Better Than Solids

Hex and square pads run much more concentric than hex and square solidcollets. If you are considering precision work and are going to grip on the flats ofthe hex or square stock, always use Style "S" master collets and pads. Solidcollets will not run as true. Therefore, if the corners of your hex stock do notclean up all the way around the part, switch to a master collet with hex pads andthey will clean up correctly.

The alternative to gripping on the flats of any polygon is to grip on the OD (cor-ners) using either an angular-slotted collet or a zig-zag slotted collet (see chapter1). The corners will not fall into the slots, making it easier to load the part andhold them concentric.

Basic Workholding

Techniques

83

MASTER FEED

FINGERSChapter 11 Continued

Master feed fingers come in several styles from nonadjustable to fully-adjustable.The main reason for buying master feed fingers is to reduce expense as com-pared to the cost of solid feed fingers. The storage requirements for the pads areless than the area required for storing solid feed fingers.


PAD

PAD

BAR STOCK

HA

RD

ING

E

The Style "B" Master Feed Finger & Pads are the most practical feed finger forhigh production bar machining. The pads & feed finger design is the most stableon the market today. They were designed to take the abuse of your roughestoperator and still give you the precision your machine tool requires. Below is areview of the Style "B" in greater detail.

Style "B" Features:

No Screw or Pinsto Hold Pads in Place

Full Bearing on theBar Stock

Heat Treated for Tension OnlyPad diameter controls

different tensions

Three Pads Several Standard Shapes

Style "B" Master Feed Finger

Basic Workholding

Techniques

85

Additional Advantages

• Pads cannot come loose.

• Quick changeover using Hardinge-designed wrenches.

• Full bearing on the stock.

Disadvantages

• Centrifugal force at high speeds can cause feed fingers to loose gripping force.

• They are not adjustable.

Pad Advantages

• Heat treated for hardness only. Maximum hardness possible which gives maximumlife.

• Cheaper than solid feed fingers.

• Normally stocked in 1/64" sizes. Many decimal sizes are also stocked.

• Pads stocked in round, hex, square.

• Take up less storage space than solid feed fingers.

• Special feed fingers are made for rectangular, other polygon shapes andextruded stock.

• Pads come in many different materials.

Pad Disadvantages: None


Materials Used for Standard Stocked Pads

Hardened Steel

• Used for hot-rolled and cold-drawn steel bars.• Long wearing and reasonable abrasion.• Hard Pads—61-63 Rockwell “C” scale.

NickelCast Iron

• Used for brass, aluminum, polished and plated stock—help eliminate scoring.• Greater life than bronze because they are harder. (If nickel scores, switch to bronze

pads)

Bronze

• Used for ground drill rod, brass, aluminum, polished and plated stock. These willeliminate scoring.

• The best choice for stainless steel.• Only recommended when cast iron pads score the stock—bronze pads

have a shorter life.

Nylon

• Used on chrome-plated and highly-polished stock.

Basic Workholding

Techniques

87

"BX" and "DX" Adjustable-TensionMaster Feed Finger

Adjusting Sleeve PadBody

The Style BX & DX feed finger has a sleeve that is moved to increase or decrease the tension onthe pads. The sleeve locks against the feed tube. This feature eliminates the possibility of havingit loosen up. The collet takes standard style “B” pads.

ADVANTAGES

• Tension can be adjusted.• Adjustment is approximately 1/64" on diameter.• Takes standard “B” pads.• Positively locks against the feed tube.• Loss of tension due to centrifugal force is reduced.

DISADVANTAGES

• Only available for B&S 00, 0, DA2 and 9/16 Cone.


"AF" Style Master Feed Finger

13/1

6

13/1

6

Support Bushing Pads

Adjusting Cap

The "AF" Style Feed Finger uses inexpensive pads which are adjustable in 5 - 7 pound incre-ments. The feed finger has a support bushing in the back to eliminate bar whip within the feedfinger. No screws are used to hold the pads. They are adjustable for different tensions and stocksizes.

Advantages

• Can adjust for different size stock—a full 1/32" adjustment from the rated size down.– Eliminates the need for decimal or metric pads and pads in 1/64" increments.

• Feed bushings are used to control bar whip.– Eliminates feed hang ups.– Better finish on part because of less bar whip.

• Adjustable tension on the stock.– More tension can be achieved using this feed finger than with any other feed

finger produced, whether master or solid finger.– Extremely light tension for thin wall tubing and delicate stock.

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Pad Advantages

• Same master feed finger pads can be used for many different machines using thesame style feed finger, which results in reduced inventory.

• One tool cabinet drawer can hold hundreds of pad sets and still only weigh a fewpounds. The same quantity of pads of any other type would take two or three toolcabinets, not just one drawer.

• AF Pads are less expensive than style “B” pads, and much less expensive than solidfeed fingers.

Pad Disadvantages

• Cannot go under or over the rated capacity of the pad. For example, an AF6 pad for a1" Acme feed finger has a minimum capacity is 3/8". If you wanted to feed a 1/4" bar,another style feed finger would have to be used.

• Cannot go to the maximum capacity of the machine.• Pads will break when used without the support bushing.• Some people feel it is difficult to change pads.• The Model 3A AF pads cannot be used under 3/16".


MODEL "A" MASTER FEED FINGER

The pads are held in a groove with a shoulder locating the pad on both ends.One key holds one pad in place which eliminates rotation of the other pads.

Advantages

• No pins or screws used to hold pads into place.• Thrust supported by shoulders.• Pads less expensive than solid feed fingers.

Disadvantages

• When loading bar stock, the pads can be knocked loose.• Pads are tricky to install.

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Techniques

91

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234

8

20123456

78

9

10

Other Adjustable Feed Fingers

Dial-Adjustable Master Feed Finger By Balas

Rear Support Bushing

Inner Master

Outer Sleeve

Basic Workholding

Techniques

93

The dial adjustable master uses style “A” pads. It has a master body which ac-cepts the pads. The body also accepts a rear support bushing. The outer sleeveis turned counterclockwise to adjust for more tension on the inner master.A wrench is required to spread the master collet for pad insertion. The samewrench is used to adjust the outer sleeve. There are numbers on the masterbody that indicate whether the tension is being increased or decreased.

Advantages

• Tension is adjustable by hand. Wrenches are used to hold one member from turning.• Carbide pads available for maximum wear resistance.• Will not lose setting because feed tube locks against outer sleeve.• Minimally affected by centrifugal force.

Disadvantages

• Outer assembly must be removed to change pads in the master’s body.• Size restriction—maximum capacity of machine cannot be utilized.• The same problem as with all adjustable masters—too many pieces.

234

8


Cross Section and Adjustment Method

The squirrel cage-style feed finger has slots like a cage. They are swagged tosize against an undersize plug and then heat treated.

Squirrel-Cage Feed Finger(Adjustable, but not a Master)

Whack it herewith a hammer

ANVIL

Basic Workholding

Techniques

95

Stock-Saver Feed Finger

Advantages of Squirrel-Cage Feed Finger

• Inexpensive.• Adjustable.• Not affected by centrifugal force as much as masters with pads or solid feed fingers.• No moving parts.

Disadvantages of Squirrel-Cage Feed Finger

• Crude adjustment—“whack it” with a hammer.• Concentricity problems after adjustment.• Tension life is short.• No precise way of telling what the tension is on the finger or a way to make certain that

each leaf has the same tension.

Stock-Saver Feed Finger (squirrel cage -style)

Same as the squirrel-cage but it has two adjustable areas—one in front and onein the middle of the finger.

ANVIL

Whack it herewith a hammer

ANVIL


Types of Solid Feed Fingers

Standard Solid Feed Finger

Advantages

• No moving parts.• One costs less than a master.

Disadvantages

• Expensive if more than one is ever purchased.• Non-adjustable.• Tension controlled by heat treatment.• Require finger for each size stock.• Requires considerable storage space.• Entire feed finger must be replaced when worn.• Expensive because it requires additional feed tubes for each size stock.

Basic Workholding

Techniques

97

BRAZEFEED TUBEFEED FINGER

Brazed On / In Style Feed Finger

The brazed style feed finger is used when overcapacity stock is to be fed throughan oversize collet. Instead of threads, there is a machined diameter. The feedtube threads are removed to the machined diameter on the special feed finger.The two are then brazed together.

Advantages

• Allows feeding of oversize stock not possible with standard feed fingers.

Disadvantages

• Requires changing the "feed tube/finger" combination for each change in bar size.


"Milled-Through" Solid Feed Fingers

The "milled-thru" feed finger accepts rectangular, square and hex stock that has a thicknessequal to the milled slot. One feed finger can do the work of several.

Example:When there are four different flat stock jobs to run, a feed finger or pad would be needed foreach size. Suppose we have four pieces of flat stock: 1/4" square, 1/4" x 3/8", 1/4" x 9/16, and1/4" x .744. When using a “milled-thru” 1/4" feed finger, all of these pieces of stock can behandled by the same feed finger with a considerable dollar savings. A 1/4" hex could be fed, butbecause of the small amount of bearing surface, feeding problems may result.

Basic Workholding

Techniques

99

The feed finger style bar puller is used for pulling bar stock and also loading and unloadingworkpieces. Every size bar or workpiece requires a separate feed finger. See section on partsloading–chapter 14.

Bar / Stock Puller—Feed Finger Style

Feed FingerRound Shank

Threaded Adapter


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CHAPTER

12

JAW CHUCKSVS.

COLLETS

102 CHAPTER 12Chucks vs. Collets

Chucks vs. Collets

The collet and jaw chuck are the two major methods for holding workpieces ortools on a machine tool or fixture. Throughout the years, machinists have de-bated which was the best device for holding a workpiece or tool. Let's take a lookat many of the different applications for each method of workholding. We will thenfinish out the chapter by describing each style of jaw chuck.

Reasons for Selecting a Jaw Chuck

• Variation of chucking diameter greater than the collet's limits.

• Parts too large for the collet capacity of the machine.

• Eliminate large inventory of collets.

• Machine does not have collet or step chuck capabilities.

• Cost of a collet for a short run job.

• Delivery time for a new collet for a short run job.

• Rough chucking surfaces such as castings.

• Non-symmetrical work requiring a 2- or 4-jaw chuck.

• Customer has the facilities to machine chuck jaws for complex shapes but does nothave them for machining collets.

Basic Workholding

Techniques

103

Reasons for Selecting a Collet

• Maximum gripping force—most critical on long overhang.

• Life of a hardened and ground collet is much greater than machined chuck jaws.

• Inexpensive precision workholding device—less expensive when using pads.

• Special-accuracy collets are available in hardened and ground styles forsuper-precision chucking.

• Collets are available in .001" increments (5C's).

• Best TIR because there is no overhang. Most chucks extend from the face of thespindle between 4 to 6 inches, not counting the length of the jaws.

• Centrifugal force does not cause problems with collets or step chucks that use closers.The working portion of the collet is completely enclosed and cannot expand at highspindle speeds.

• Part tolerance or a long-run job dictate a collet to reduce downtime and the necessity tore-bore the chuck jaws.

• Less chance of expensive wrecks.

One Shop's Reason For Switching to Collets

One shop with two machines started out with jaw chucks on their CNCslant bed lathes. Within one year they had to replace the turret assembly twice,replace the spindle once, replace the jaw chuck twice, rebuild the jaw chuckthree times, plus expend many man hours repairing the machines due to jawchuck interference related wrecks.

They then changed to collets and step chucks, which increased the grip-ping forces, decreased the overhang by 6 inches, increased their ability to holdclose tolerances, and reduced spindle tooling interference problems, whicheliminated major wrecks. Their down time was substantially reduced.


Types of Spindle Chucks

• Mechanical (manual-operated)

• Pneumatic (air-operated)

• Hydraulic

• Electro-Magnetic

• Vacuum

3-Jaw Universal

• Comes in many versions—the most common are shown above.• Inexpensive.• Uses a key wrench to tighten and loosen workpiece.

2-Jaw Universal 4-Jaw Universal

4-Jaw Independent Pie Jaw

Mechanical (manual-operated)

Basic Workholding

Techniques

105

• Allows for lighter gripping pressures than hydraulic chucks.• Smaller sizes can have accuracy very close to precision collets.• Air cylinder is usually mounted at the rear of the spindle with a draw tube running

through the spindle.• The air cylinder can also be part of the chuck. This style chuck is usually longer in

length than the rear-mounted cylinder chuck which increases the TIR problems.This style is usually heavier, which puts more weight on the front of the spindle.

• Some air chucks actually use the draw bar of the collet closer. These chucks usuallyhave a thru-hole capacity equivalent to the collet capacity of the machine tool.

• The internal construction of the chuck can restrict the maximum RPM it can be run.• Precision air chucks usually cannot be run faster than 3,000 RPM. The exception is the

small 3" air chucks which can run at 5,000 RPM or higher.

Pneumatic (air-operated)

Hydraulic Chucks

• Much greater gripping pressures than air chucks.• The hydraulic cylinder may be either at the rear of the spindle or built into the actual

chuck.• Thin-wall tubing and delicate parts cannot usually be run with hydraulic chucks be-

cause the chucking pressure cannot be reduced enough.• Weighs more than air chucks creating additional spindle loads.


Electro-Magnetic Chucks

• Normally used for flat magnetic steel and iron parts—if surface is flat, there will be nochucking distortion.

• Expensive.• Cannot be used for nonmagnetic materials.• Requires special electrical rotating connection.• Requires a large power supply. This type of chuck uses an electric-powered magnet

which consumes large amounts of DC (direct current) power. A power supply is re-quired to change the normal AC (alternating current) to DC. Because of the amount ofcurrent that is required, a rather larger power supply is required.

Vacuum Chucks

• Will hold all types of material with even chucking pressures.• No distortion caused by chucking if the chucking surface is not distorted to begin with.• Requires a separate vacuum pump.• Expensive.• Materials to be chucked cannot be porous.• There are universal rotary vacuum chucks that have vacuum ports that can be turned

off or on to conform to the chucking surface area.• There are special techniques for holding bandsawed blanks for the first operation.

Basic Workholding

Techniques

107

BAR STOCKPULLERS

CHAPTER

14

CHAPTER

13

108 CHAPTER 13Bar Stock Pullers

There are several different style bar pullers on the market. The two mostcommon are the feed finger style and the two-finger style.

Feed Finger StyleThe feed finger style consists of an adapterthat fits in the machine's turret. The specialfeed finger threads into the adapter. Thesefeed fingers can be acquired for all nominalsizes, usually from stock. The bar pullerfunctions the same way that a feed fingerworks in an automatic lathe. When usinga bar puller, the part has to be cut offapproximately 1/2" from the face of thecollet. The bar puller feeds onto the bar,forcing the fingers to spread apart. Theremust be enough tension on the fingers to beable to pull the bar out, after the collet isopen, without slipping. A large diameter and/or a long length of bar will require consider-able tension.

Two-Finger StyleThe two-finger style is universal. Onepuller will handle stock from 1/8" to1-5/8" and larger. This makes it lesscostly to use than the feed finger style.The unit can also be mounted parallelto the centerline of the spindle as wellas perpendicular to it, and can be heldin either a round shank or square shankholder.

Both Styles Feature

• Up to 1-5/8" stock. (Hardinge-brand bar puller)• Can pull up to 12 foot bars when using a "non-pusher" type bar support.• Inexpensive.• Can pull short or long bars.• Uses spindle liners for precision parts with no whip.

CAUTION: Stock should never extend beyond the end of the machine tool spindleunless supported with a “Non-pusher” style bar feed tube, or similar device.

Bar Pullers

Basic Workholding

Techniques

109

PARTS LOADINGAND

UNLOADING

CHAPTER 14

110 CHAPTER 14Part Loading and Unloading

Parts Loading and Unloading Aids

Let's consider that we have a good operator but we want to assist him to in-crease his productivity by reducing potential scrap due to human errors.

These devices can be loaded by hand, but only if the machine functions havebeen completely stopped, per OSHA (Occupational Safety & Health Administra-tion) regulations.

Feed Finger Style Parts Loader

Solid Tube Parts Loader

Holds part with friction from the “O” ring. This device should be spring-loaded to hold the partagainst the shoulder in the collet as it is closing.

Basic Workholding

Techniques

111

Rotating Parts Loader

• Can load parts that are not round.• Can load round parts without scratching.• Requires special collet for each part.• To load parts that are not round or parts that cannot be scratched, a special step chuck

or driver plate is needed.

Parts Unloading Aid

Spring Ejector Stop

A spring ejector collet is used to eject the part into a parts catcher. The parts catcher can be anair-operated parts chute.

A wire basket held by the turret or cross slide. Many times these are arranged to automaticallydump their contents at the return of the slide or index of the turret.

Hardinge Workholding®

Products

Sure-Grip® ExpandingCollet Systems:Brochure #2270

Sure-Grip® 3-JawPower Chucks for

All Brands of Lathes:Brochure #2357

All specifications subject to change without notice. All marks indicated by ® or ™ are trademarks of Hardinge Inc.

Brochure 2316BPart No. HA B-0009500-2316October 2002

Litho in USA© Hardinge Inc. 2002

Spindle Tooling forManual and CNC

Lathes:Brochure #2348

Precision ToolHolding Systems& Mill Tooling:

Brochure #2350

Toolholder Collets,Bushings & Round

Shank Holders:Brochure #2351

Swiss-Type Collets &Guide Bushings:Brochure #2283

The HardingeAdvantage:

Brochure #2327

HQC® Quick-ChangeCollet Systems:Brochure #2339

Sure-Grip® ChuckJaws for All

Brands of Chucks:Brochure #2358

Collets forAutomatics:

Brochure #2287

To order in USA: 800-843-8801To order in Canada: 800-468-5946All other calls: 607-734-2281Fax: 607-734-3886Internet: www.hardinge.com

www.hardingeworkholding.com

Hardinge Inc.One Hardinge DriveP.O. Box 1507Elmira, New York 14902-1507 USA

HCAC™ ColletAdaptation Chucks:

Brochure #2352

Worldwide Manufacturer ofMachine Tools andWorkholding/Industrial Products

www.hardingetooling.comyour online purchasing source for workholding

Machine ToolProducts Overview:

Brochure #1190

http://hardingetooling.com

Basic Workholding Techniques

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