Chapter 6 Sawing Machines

8/14/2019 Chapter 6 Sawing Machines

1/18

TC 9-52

PURPOSE

The sawing machine is a machine

Chapter 6

SAWING MACHINES

GENERAL

TYPES

tool designed to cut The power hacksaw and the bandsaw are two common typematerial to a d esired length or contour. It functions by of sawing machines used to cut m etal in the machine shopdrawing a blade containing cutting teeth through the The pow er hacksaw u ses a reciprocating (back and forthworkpiece. The sawing machine is faster and easier than hand cutting action similar to the one u sed in a hand hacksaw. Thsawing and is used principally to produ ce an accurate square pow er hacksaw is used for squ are or angle cutting of stock

or mitered cut on the workpiece. The band saw u ses a continuous band blade. A drive wheeand an idler w heel supp ort and d rive the blade.

POWER HACKSAW MACHINES

DESCRIPTION

All power hacksaw machines are basically similar in design.Figure 6-1 shows a typical power hacksaw and identifies itsmain parts, which are discussed below.

Base

The base of the saw usu ally contains a coolant reservoir an da pump for conveying the coolant to the work. The reservoircontains baffles which cause the chips to settle to the bottomof the tank. A table which supp orts the vise and the m etalbeing sawed is located on top of the base and is usuallyreferred to as part of the base.

Vise

The vise is adjustable so that various sizes and shapes of

metal may be held. On some machines the vise may beswiveled so that stock may be sawed at an angle. The size of apower hacksaw is determined by the largest piece of metalthat can be held in the vise and sawed.

Frame

The frame of the saw supports and carries the hacksawblade. The machine is designed so that the saw blade contactthe w ork only on th e cutting stroke. This. action prev entsunnecessary wear on the saw blade. The cutting stroke is on

the draw or back stroke.

6-1


2/18

TC 9-524

Some machines feed by gravity, the saw frame havingweights that can be shifted to give greater or less pressure onhe blade. Other machines are power fed with the feed being

adjustable. On these machines, the feed is usually stopped oreduced au tomatically wh en a hard spot is encountered in th e

material, thus allowing the blade to cut through th e hard sp otwithout breaking.

SPEED-CHAN GE MECHANISM

The shift lever allows the number of strokes per minute toe changed so that a variety of metals may be sawed at the

proper speeds. Some saws have a diagram showing theumber of strokes per minute when the shift lever is in

BANDSAW MACHINES

Metal-cutting bandsaw machines fall into two basicategories: vertical machines (Figure 6-2) and horizontal

machines (Figure 6-3). Band saws use a continuous saw blade.Chip removal is rapid, because each tooth is a precisionutting tool and accuracy can be held to close tolerancesliminating or minimizing many secondary m achiningperations.

VERTICAL BAND SAWING M ACHIN E

The metal-cutting vertical band saw ing machine, also calledcontour machine, is made in a variety of sizes and models by

everal manufacturers. The size of a contour machine isetermined by the throat depth, which is the distance from theaw band to the column. Figure 6-2 shows a typical contour

machine and identifies its main parts, which are discussedelow.

The head is the large unit at the top of the contourmachine that contains the saw band idler wheel, the drivemotor switch, the tension adjustment handwheel andmechanism , a flexible air line (directs a jet of air at t hework to keep layout lines free from chips), and th eadjustable post which supp orts the upp er saw guide. The

job selector dial is also located on th e head .

The column contains the speed indicator dial, which isdriven by a cable from the transmission and indicates thespeed in feet per m inute (FPM). The butt w elder is alsomounted on the column.

different positions; others are merely marked F, M, and S(fast, medium, and slow).

ADJUSTABLE FEED CLUTCH

The adjustable feed clutch is a ratchet-and-pawl mechanismthat is coupled to the feed screw. The feed clutch may be setto a desired amount of feed in thousandths of an inch. Becauseof the ratchet-and -paw l action, the feed tak es place at thebeginning of the cutting stroke. The clutch acts as a safetydevice and permits slippage if too much feed pressure is puton the saw blade. It may also slip because of a dull blade or iftoo large a cut is attempted. This slippage h elps preventexcessive blade breakage.

-2


3/18

TC 9-5

The base contains the saw band drive wheel, the motor,and the transmission. The transmission has tw o speedranges. The low range gives speeds from 50 FPM to 375FPM. The high range gives speeds from 260 FPM to1,500 FPM. A shift lever on the ba ck of the base can be

placed in the high, low, or neu tral position. Low isrecommended for all speeds under 275 FPM. The basealso supports the table and contains the lower saw bandguide, which is mounted immediately under the table slot.The power feed mechanism is located w ithin the base,and the feed adjustment handle and foot pedal are locatedon the front of the base.

VARIABLE SPEED UNIT

The variable speed unit is located within the base of themachine. This unit consists of two V-type pulleys which aremounted on a common bearing tube. A belt on one pulley is

driven by the transmission, while the belt on the other p ulleydrives the saw band drive wheel. The two outside cones of thepulleys are fixed, but the m iddle cone is shifted w hen thespeed chang e wheel is turned . A shift in the mid dle conecauses the diameter of one pulley to increase and the diameterof the other pulley to decrease. This slowly changes the ratiobetween the tw o pulleys and p ermits a gradu al increase ordecrease in the speed of the machine.

HO RIZONTAL BAND SAW MACHIN E

The horizontal band sawing m achine does the same job asthe power hacksaw but does it more efficiently. The blade ofthe band saw is actually a continuous band wh ich revolvesaround a drive wheel and idler wheel in the band supportframe. Two band guides use rollers to twist the band so thatthe teeth are in th e prop er cutting position. The guides areadjustable and should be adjusted so that they are just slightlyfurther apart than the width of the material to be cut. This willgive maximum support to the saw band and help assure astraight cut.

The vise on the horizontal bandsaw is much like the one the power hacksaw. However, the horizontal bandsaw hasmu ch greater capacity for large stock than does the p owhacksaw. The stationary jaw can be set at several angles. Tmovable jaw adjusts automatically to whatever position t

stationary jaw is in when the vise handwheel is tightened.The horizontal bandsaw is operated h ydrau lically

controls on a control box, which is located on the front sidethe machine. A motor and p um p assembly supp lies hydraufluid from a reservoir in th e base to a cylinder, which raisand lowers the support arm and also controls the feed pressuand band tension. A speed and feed chart is sometimprovided on the machine, but when it is not, consult thoperators manual for the proper settings for sawing.

A coolant pump is located in one of the legs of the baswhich serves as a coolant reservoir. The coolant cools the saband and also washes away chips from the cut before they caclog the band.

SAFETY PRECAUTIONS

Sawing machines have some special safety precautions Use a miter guide attachment, work-holding jaw devic

that m ust be observed. These are in addition to those safety or a wood en block for pushing m etal workpieces into tprecautions d escribed in Chapter 1. Here are som e safety blade of the bandsaw wherever possible. Keep fingeprecautions that must be followed: well clear of the blade at all times.

Keep hands away from the saw blade of the hacksawing When removing and installing band saw blades, handmachine or bandsawing m achine w hen in operation. the blades carefully. A large springy blade can b

dangerous if the operator does not exercise caution.Ensure the power su pply is disconnected prior to removalor installation of saw blades.

6
http://ch1.pdf/http://ch1.pdf/http://ch1.pdf/


4/18

C 9-524

TOO LS AND EQUIPMENT

POWER HA CKSAW BLADES

The following arePower hacksaw blades d iffer from han d hacksaw blades in hacksaw blades.

at they are generally heavier, made in longer sizes, and haveewer teeth per inch. Hacksaw blades are discarded when theyecome dull; sharpening is not practical.

Materials commonly used in manufacturing power hacksawlades are high-speed tungsten steel and high-speed

molybdenu m steel. On some blades only the teeth areardened, leaving the body of the blade flexible. Other bladesre hardened throughout.

The set is the amount of bend given the teeth. The set makespossible for a saw to cut a kerf or slot wider than the

hickness of the band back (gage), thus providing side

earance.

This is the pattern in which the teeth are set. There are threeet patterns: raker, wave, and straight, as shown in Figure 6-4.

The pitch of hacksaw blade teeth (Figure 6-5) is expresseds the nu mber of teeth per linear inch of blade. For example, a

guidelines for the selection of power

Select power hacksaw blades for material to be cut.

Soft materials require a coarser blade to provide adequatespaces between the teeth for removal of chips. Hardmaterial requires a finer blade to distribute the cuttingpressure to a greater nu mber of teeth, thereby redu cingwear to the blade.

At least three teeth must be in contact with the workpieceat all times or the blade w ill snag on the w orkp iece andbreak teeth from the blade. Therefore, a blade must beselected with sufficient pitch so that three or more teeth

will be in contact with the workpiece, no matter what typeof material is being cut.

Figure 6-5 is provided to assist in the proper selectionoxf power hacksaw blades. Note that sheet metal andtubing are listed separately from solid stock. It is assumedthat solid stock will be sufficiently thick tha t three or

lade having 10 teeth per inch is said to be 10 pitch. more teeth will be in contact with the stock at all times.

Power hacksaw blades are coarser in pitch (fewer teeth pernch) than han d h acksaw blades. Common p itches for poweracksaw blades range from 4 to 14 teeth per inch.

-4


5/18

TC 9-52

BANDSAW BLADES

GeneralPitch

Bandsaw blades are manufactured in two forms. They areThe pitch of bandsaw blades is expressed as the n umber o

teeth per linear inch of the blade. Metal cutting blades rangsupplied in rolls of 50 to 500 feet for use on machines thathave butt welders for forming their own blade bands.

from 6 to 32 teeth per inch, the coarser tooth blades being

Bandsaw blades are also supplied in continuous welded bandsused for sawing large stock and soft metals.

for machines having no provisions for welding.

Materials

Bandsaw blades are made from special alloy steels. Theblades are made flexible by annealing the body of the bladeand hardening only the teeth.

Set

Metal cutting band saw blades have their teeth bent (Figure6-4). This bend p rodu ces a kerf slightly wider th an thethickness of the blade, which prevents the blade from beingpinched by the stock. There are three set patterns: raker, wave,and straight, as shown in Figure 6-4.

Selection of Bandsaw Blades

Select bandsaw blades according to the type of material tobe cut, the thickness of the material to be cut, and the sawingoperation to be performed. Always use the widest and thickessaw band possible. However, consider the curvature of the cutsince wide saw blades cannot cut sharp curves. Figure 6-6shows saw band selection for various radii.

For general sawing, use the raker set pattern. The wave sepattern is used where thin work sections are encounteredduring the cut, such as tubing, angles, and channels.

Three teeth of the bandsaw blade must be in contact with thework piece at all times to preven t chatter and sh earing ofteeth. Therefore, use fine tooth blades to cut sheet metal and

6-5


6/18

TC 9-524

tubing. If the sheet metal is too thin to meet this requirement The bandsaw blade cutswith the finest tooth blade available, place the metal between workpiece is fed by hand.plyw ood fiberboard , or thicker metal. Figur e 6-7 is a guide

slowly or not at all when the

for selecting the proper pitch band saw blade for differentmetals and metal thickness. With the machine stopped or the bandsaw blad e

removed, run a finger slowly over the teeth in the cutting

The finish depends largely upon the saw pitch. The faster direction. If sharp edges are not felt the blade is dull.

the saw speed and the finer the sawpitch, the finer the finish.Lubricating helps to improve the finish. A fine saw pitch,high velocity, and light feed produce the finest finish.

Band saw Blade Wear

Bandsaw blades naturally become dull from prolonged use,but some conditions promote greater than normal wear on theblades. Blades dull quickly if used at too high a speed for thematerial being cut. Also, if the material to be cut is too hardfor the pitch of the blade, abnormal wear will result. The most

common cause of prematu re blade du lling occurs from u singtoo fine a pitch blade and from feeding too heavily.

The following symptoms indicate a dull bandsaw blade.When these symp toms are noticed, the blade should bereplaced.

It becomes d ifficult to follow a line, the blad e beingforced to one side or the other.

The chips are granu lar (except for cast iron, wh ichproduces granular chips with both sharp and dull blades).

6-6


7/18

TC 9-5

FILE BANDS

The bandsawing m achine is adap ted for filing by u se of theband file attachment. A band file is fitted over the drive and

idler wheels and in place of the bandsaw blade. The band ismad e up of several parts or segments which are riveted at oneend (the leading end ) to a spring steel band. The trailing endof each segment is free to lift during th e time wh en the bandbends over the d rive and idler wheels of the band saw. Whenthe band straightens out, the segments lock together. Figure6-8 shows the constru ction of and terminology for file bandparts.

Note that the gate segment (a segment at one end of theband that is specially designed to allow the two band ends tobe locked together) has a shoulder rivet and a dow el rivetprotruding from beneath it. The shoulder rivet locks into the

other file band end , and the d owel rivet aligns the tw o endsegments and prevents the shoulder rivet from sliding out ofthe locked position during tiling. The gate segment of a file Selection of Band Files

band is identified by yellow paint.Choose band files on the basis of workpiece thickness an

Cu t of File Teethtype of material to be filed. In general, the thicker thwork piece, the coarser the file should be. This is due tolarge; chip accumulation from the larger area of th

File bands are either coarse or bastard cut and normally workpiece, thus requiring additional space for the chiprange in pitch from 10 to 20 teeth per inch. The coarse 10- between the teeth. On thin sheet m etal, a fine pitch file pitch bands are used for filing softer metals such as aluminum,brass, copper, and cast iron. A bastard-cut 14-pitch band is a

requ ired to p revent cha tter. Use fine pitch files for filing tou gcarbon and alloy steels; use coarser pitch files for filing soft

good choice for general steel tiling, while 16 to 20 pitchbastards are recommended for filing tool steel.

metals. Figure 6-9 is provided to aid in selecting the prop

file for filing specific materials.

6-


8/18

TC 9-524

Care and Cleaning of Band Files

Clean the file often, using a stiff brush or a file card. Movethe brush in the direction of each cut of the file to dislodge allparticles hidden between the teeth.

The file band should not be coiled into m ore than threeloops. The best means of storing file band s is in a cabinetooped over a 16-inch radius support with the ends hanging

free.Band File Attachm ent

A band file attachment (Figure 6-10) is provided with mostbandsaw machines to permit the use of band files. A typicalband file attachment consists of a band file guide and upperand lower guide supports that attach to the frame and part ofthe band saw. A sp ecial filing filler plate is provided to adap tthe table slot to the extra width and depth required for the

band file and file band guide.

POLISHING BANDS

Polishing can be performed on the bandsaw using apolishing attachment and polishing band. The polishing

and is usually 1 inch wide and has a heavy fabric backing.

Types of Polishin g Band s

Polishing bands for bandsawing machines are usuallysupp lied in various grain sizes of aluminum -oxide or siliconecarbide abrasive: No 50 grain (coarse) for heavy stock

removal and soft material, No 80 (medium) for generalsurface finishing, and No 120 or No 150 grain (fine) for highpolishing and light stock removal.

Selection of Polishing Bands

Polishing band s should be selected a ccording to theparticular job to be performed, For removing tool marks an ddeburring edges, use the N o 50 grain p olishing band. Finergrain polishing bands should not be used on soft metals likealuminum or cast iron because the ban d will quickly fill withmetal particles, reducing the cutting action

Polishing Attachment

The polishing attachment (Figure 6-11), similar to the bandfile attachment, p rovides supp ort for the polishing band. Thepolishing ban d plate acts as a solid backing for the p olishingband to prevent stretching and distorting the band when theworkpiece is held against it. Use a polishing band filler plateto fill the table slot so the workpiece can be supported close tothe polishing band.

6-8


9/18

TC 9

DISC-CUTTING ATTACHM ENT

Use the disc-cutt ing attachmen t (Figure 6-12) to sawinternal or external circles and discs. The d iameter of thecircle that can be cut is limited to the length of the cylindrical

bar on the attachment or to th e throat dep th of the machine.The disc-cutting attachment consists of three main parts aclamp and cylindrical bar, which is fastened to the sawguidepost; an adjustable arm, which slides on the cylindricalbar; and a pivot or centering p in. The d isc mu st be laid outand center-drilled to a d epth of 1/ 8 inch to 3/ 16 inch toprovide a pivot point for the centering pin. The centerline ofthe centering p in mu st be in line with the front edge of thesawteeth and at the desired distance from the saw band.

ANG ULAR BLADE GUID E ATTACHM ENT

This attachment (Figure 6-13) twists the blade so that longworkpieces that would not normally clear the machine columncan be cut. The blade is twisted to a 30 degree angle on mostmachines.

MITER GUIDE ATTACHMENT

A typical miter guide attachment is illustrated in Figure 6-14. The workpiece is supported against the miter head whichattaches to the slide arm. The attachment can be set at an anglewith a protr actor, using the table slot as a reference line. Agage rod can be extended from the attachment and used as astop when identical lengths are sawed. When not in use, swingthe attachment on the slide rod so that it han gs below thetable.


10/18

C 9-524

LAYING OUT AND MOUNTING WORK

POWER HACKSAWING

Layout

Power h acksaw m achines are primarily intended forraight line cutting of stock to specific lengths. Laying ou te workpiece consists of measuring the length to be cut anddicating the position for the cut by scribing a line on theock.

Mount ing

Before mounting the stock to be cut, the vise should behecked for squareness with the hacksaw blade. Place aachinists square against the blade and the stationary visew. Adjust the jaw, if necessary, at 90 to the blade. If theor kpiece is to be cut at an an gle other than 90, loosen these and swivel it to the desired angle, measuring the anglerefully with a protractor.

Stroke

Move the blade frame and hacksaw blade by hand th roughne draw stroke and one return stroke. Observe whether theroke is centered on the w ork and if the blade holders w illear the w orkp iece at the end of the stroke. Readjust theosition of the vise if the stroke is not centered on the

or kpiece. Shorten the stroke if the blade holders h it theorkpiece at the end of each stroke.

Stop gage

Use a stop gage to speed up mounting stock when severaleces of the same length are to be cut. Mount the first piece

n the vise and align with the h acksaw blade to cut at thecribed line, When the wor kpiece is correctly p ositioned ,ove the stop gage up to the end of the workpiece and lock it place. Cut subsequent pieces by moving the stock up to theop gage and clamp ing the wor kpiece in the vise at this

osition.

Vise

The vise must be securely tightened on the workp iece torevent loosening during cutting. Blade breakage might resultom shifting workpieces not clamped tightly in the vise.

HORIZONTAL BAND SAWING MACHINES

The stock should be measured and the position of the cutmachinists square or a protractor against the bandsaw bladeand the stationar y vise jaw. Position the stock in the v ise sothat th e saw blade a ligns with the scribed line on the stock. If.more than one piece is to be cut to the same size, move thestock stop arm ag ainst the end of the stock and lock it inplace. Additional pieces can then and moved up against thestop to produce pieces equal in length to the first piece

VERTICALBANDSAWING MACHINES

When laying out workpieces for vertical bandsawingoperations, consider the size of the stock in relation to theclearance of the bandsaw machine column. For straight-linesawing the clearance is easy to judge, but for contour sawingof large size stock, the d irections of cut m ust b e carefullyfigur ed to p revent th e stock from hitting the colum n. If asmall section is to be cut from a large sheet of metal, thesection shou ld be rou ghly cut oversize from the sheet andthen carefully cut to the prescribed outline.

CIRCULUAR SAWIN G

When a circle or disk is to be sawed using the disk cutting

attachment, lay ou t the circle on the stock as follows:

Using a compass or pair of dividers, scribe a circle in thedesired location and of the desired diameter on the stock.

Center-punch and drill a center hole in the disk to acceptthe center pin of the disk cutting attachment. Make thehole only as deep and as large as required for the centerpin; too large a hole will cause the center pin to fitloosely, which will result in an inaccurate cut .

CONTOUR SAWING

When an outline to be cut consists of more than twointersecting lines, the following procedure should befollowed.

Scribe the exact shape required on the stock. Takeadvantage of straight, clean edges on the uncut stock inlaying out the piece to save unnecessary cuts.

-10


11/18

Determine the bandsaw blade size necessarysmallest radius laid out on the workpiece

TC 9

to cut the If an internal section is to be removed from the stockthe edge mu st remain unbroken, layout and drill a stahole (Figure 6-15) using a drill larger in diameter

Select a twist d rill equal to or greater in d iameter than the the, width of the band saw blade. The bandsaw bladewidth of the bandsaw blade. Drill a hole in each comer of be inserted through this hole before being welded in

the pattern, making sure the holes fall within the section band and installed on a bandsawing machine.of material that will be removed. The comer sections arenotched out after the piece is cut.

GENERAL SAWING

Efficient sawing with sawing machines requires sharp sawblades in good condition. To prevent dulling and breakage ofsaw blades, proper speeds and feeds mu st be maintained. Thespeed of the saw blade for any specific operation d epend supon the nature of the material being cut.

POWER HACKSAWING

Power hacksawing machines cut by drawing the hacksawblade toward the motor end of the machine. At thecompletion of this mov ement called the draw stroke, thehacksaw blade is lifted slightly to clear the material being cutand moved an equal distance in the opposite direction.

Mou nting Workpieces

Workpieces for metalcutting machines are not mounted tothe machine, but are supported by the table of the machine andguided by one of the sawing machine attachments or by hand .

Power Hacksaw Speeds.

Since the cutting speed of hacksawing machines is measin strokes per minuet, the length of the stroke is an imporconsideration. A longer stroke at a given speed will cut fathan a shorter stroke at the same speed. Thus. to obtaproper cutting speed the length of the stroke mustspecified.

The length of the stroke of most pow er hacksaws is betw4 and 10 inches depending upon the size of the machine.machines with an adjustable stroke, the wider the stock bcut, the shorter the stroke to prevent the blade holders fhitting the stock.

With most power hacksaws, the stroke length is adjustwithin 2 or 3 inches. and on some m achines more than speed can be selected. On single-speed hacksawing machithe speed must be regulated by changing the stroke.


12/18

C 9-524

If the stroke is doubled the machine will cut twice as fast,nd if the stroke is decreased by one-half, the machine will cutalf as fast. This proportion can be applied to any fraction tocrease or decrease the cutting speed of the machine.

The speed s given in the chart, Figure 6-16, bellow are forxample only. The correct speeds for cutting various metalsill depend on the type of machine you are using. In generale faster speeds are used for cutting soft materials and theower speeds are used for cutting harder materials. If acommended speed cannot be approximated either by

hanging the stroke or changing the speed, the feed can beecreased to p revent undu e wear to the hacksaw blade.

Power hacksaw machines having a mechanical feed canually be regulated to feed the saw downward from 0.001 to025 inch per stroke, depending u pon the type and size of the

aterial to be cut. On these machines, a device to stop theed when hard spots are encountered is usually incorporated

The feed of machines having gravity feed is regulated by theweight of the saw frame and any additional weights or springsthat m ight be connected or attached to th e frame to increase ordecrease the d own w ard force of the hacksaw blade.Maximu m an d m inimu m blade p ressures obtainable are

determined by the manufacturer of the hacksawing machine,and are specified as relatively light or heavy.

The following general ru les apply for selecting proper feedsfor hacksawing machines:

The feed should be very light when starting a cut and canbe increased after the cut is well started.

Hard materials require a lighter feed than soft materials;reduce the feed when welds or hard spots in materials areencountered.

Wide material requires a heavier feed than narrowmaterial because the pressure is distributed over a larger

to the design. surface.

Sharp hacksaw blades will cut well with lighter feeds.Heavier feeds are necessary for cutting with dull blades.

12


13/18

TC 9

BANDSAWING

The cutting speed of the bandsaw machine is the speed ofthe band s blade as it passes the table measured in feet perminute. The feed of the horizontal band saw m achines

downward pressure applied to the material being cut by thebands blade. The feed of vertical bandsawing machines is thepressure applied to the bands blade by the material being cut.

Band sawing Speeds

Proper bandsaw speeds are important in conserving bandsblades. Too great a speed for the material being cut w ill causeabnormally rapid blade w ear, while too slow a speed w illresult in inefficient production. The chart of recommendedspeeds (Figure 6-17) are guidelines only. It shows the speeds

for a given type of machine. The cutting speed alwaysdepend s on the type of machine you are using and themanufactures recommendations.

All bandsawing m achines have several cutting speeds.Since the diameter of the drive wh eel of the bandsaw machineestablishes a fixed ratio between the motor or transmissionspeed in RPM to the blade speed in FPM, it is not necessary toconvert RPM into FPM as with most other machine tools. Thespeeds are id entified in FPM on the saw ing machine speedselector controls. Some machines have a speed indicator so acareful check of sawing speeds may be made when themachine is operating w ith or without a load.

In general the following principles apply to speeds ofbandsaw blades:

The faster the speed, the finer the finish produced on tcut sur face. This principle applies to light feeds inconjunction with fast feeds.

Horizontal Bandsawin g M achine Feeds

Feed of horizontal bandsaw machines is controlleadjusting the p ressure applied by the saw blade againsmaterial being cut, as with hacksawing machines.

The horizontal saw has a spring counterbalance and a sliweight to ad just the p ressure of the blade. When the slidweight is moved toward the pivot point of the saw frameband saw blade p ressure is reduced. When the w eighmoved away from the pivot point, the pressure is increased

The following general principles apply when regulatingfeed of horizontal band saw machines.

The feed should be very light when starting a cut. Athe cut is started, increase the feed.

Wider material requires a heavier feed than narrmaterial.

Wide blades will stand greater pressure than narrblades and can therefore be used with heavier feeds.

A lighter feed is requ ired for hard mater ials; a heafeed can be used for soft materials.

Redu ce the feed wh en hard spots in the material

The harder the material, the slower th e speed; conversely, encountered such as chilled spots in cast iron and w

the softer the material, the faster the speed. in joined sections.

6


14/18

9-524

Vertical M achin e Feeds

With vertical machines, the feed is the pressure applied tosaw blade by the material being cut. The workpiece may

hand fed or power fed depending u pon the operation to berformed. Cutting curves or special contours requires thatworkpiece be guided and fed into the saw blade by hand.

The power feed on band saw m achines is operated byustable weights in the machine pedestal. The weights are

nnected by cables to one of the work-holding attachmentsthe sawing m achine to p ull the w orkpiece against thend saw blade. To operate the pow er feed, the weights aresed by depressing a pedal and the cables are then fixed towork-holding attachment. When the pedal is released the

ights pull the piece into the blade.

The following general rules apply to feeding workpieces onndsawing machines:

The feed shou ld be light w hen starting a cut. Thepressure can be increased after the cut is established.

Hard materials require lighter feeds than softer materials.

Wider band saw blades will stand greater pressure thannarrow blades and can therefore be used with heavierfeeds.

When hard spots in the material being cut areencountered, reduce the feed until the spots are cutthrough.

Use a light feed when cutting curves;straight-line cutting.

COOLANTS

Most sawing machines used in military

a heavier feed for

operations are d rytting machines; that is, they are not intended for use withuid coolants. However, some power hacksaws andrizontal bandsaws are equipped with a coolant attachment.

oluble oil prod ucts, when mixed with water to formmulsions, are used for these machines. This type of coolant

s p roven very satisfactory for sawing w here cooling is anportant factor. Most manufacturers of water oil emulsionolants add a rust inhibitor to the solution to prevent rustingused by the water in the coolant.

STRAIGHT-LINE SAWING

Straight-line sawing is the most common machine sawingoperation. It may be performed using the power hacksaw,

horizontal, or vertical band saw.

Power Hacksawing

The power h acksaw machine is designed p rimarily forstraight-line sawing. A typical sawing operation is outlinedbelow:

Select a h acksaw blade of the p roper length for themachine and proper pitch for the material to be cut. Installthe hacksaw blade with the teeth pointing downward andtoward the motor end of the hacksawing machine.

Check the alignmen t of the vise and hacksaw blade andmount the workpiece in the vise. Make sure the vise holdsthe workpiece securely.

Check the stroke of the hacksawing machine and adjust ifnecessary. After adjusting the stroke, move the hacksawblade and sawing machine frame through one cycle (drawstroke and return stroke) by hand to check the bladeclearance at each end of the workpiece. Readjust theposition of the vise if necessary.

Position the hacksaw blade abou t 1/ 4 inch above the

workpiece and set the feed control to its lightest feedsetting.

Set the desired speed of the hacksawing machine.

Start the machine and let the blade feed lightly into theworkp iece for about 1/ 4 inch. Readjust th e feed towhatever the material will stand for normal cutting.

Permit the hacksaw blade to cut completely throu ghworkpiece. The blade frame will trip a switch onsawing machine bed to stop the sawing machine.

Horizontal Bandsawing

thethe

Like hacksawing machines, the horizontal bandsaw machineis used primarily for straight-line sawing. The typicalsequence of operation for this machine is outlined on nextpage.

14


15/18

TC 9-

Select and install a bandsaw blade of the proper pitch forthe type and size of material to be cut.

Set the vise to the d esired an gle and check the an gle bymeasuring it from the line of the band saw blade.

Mount th e workp iece in the vise. Make sure the w orkpiece is secured and will not loosen during cutting.

Check the alignment of the blade guides for verticalpositioning and adjust if necessary.

Position the saw frame so that the bandsaw blade is 1/ 4inch above the workpiece. The power feed weight shouldbe placed at its lightest feed setting.

Set the desired speed on the horizontal band saw ingmachine.

Start the machine and let the bandsaw blade cut into theworkp iece about 1/ 4 inch. After the cut has beenestablished, readjust the feed weight to exert the desiredamount of pressure on the workpiece.

The machine w ill stop itself w hen it cuts comp letelythrough the workp iece.

Vertical Band Saw Operation

Straight-line sawing is performed on the vertical band saw

m achine by using one or a combination of severalmechanisms or attachments: the miter guide attachment, withor without p ower feed, with or w ithout the work-holding jawdevice-. and the work-holding jaw device with power feed andangular blade guide attachment.

The miter guide attachment on some m achines can beconnected to the pow er feed mechanism and on othersmust be fed by h and. The workpiece is clamped or hand-held against the miter guide attachment and the workpieceand attachment are moved on a track parallel to the blade,thereby assuring a straight-line cut.

The work-holding jaw device on some m achines can beconnected to the power feed to produce straight-line cuts(Figure 6-18).

The angular blade guide attachment is used for straight-line sawing when the workpiece cannot be cut in the usualma nn er because it is too large or too long to clear thecolumn of the bar, sawing machine frame.

A typical example of straight-line sawing is outlined belo

Select a band saw blade of the desired p itch for the natuof material to be cut. The blade shou ld be as wid epossible for straight-line sawing.

Set the desired speed on the bandsawing machine.

Position the workpiece at the desired angle in one of machine attachments and connect the cable to the powfeed mechanism if power feed is to be used.

Start the bandsaw ing machine and feed the w orkpilightly into the blade to start the cut. Once the cutstarted, the feed can be increased. If feeding is by hathe pressure applied to the workpiece by the operator be varied to find the best cutting conditions.

RADIUS SAWING

Radius sawing is performed on the bandsaw by eithguiding the w orkpiece by hand or by using the d isk-cuttattachment.

Blade Selection

Care must be taken to select a bandsaw blade of the prowidth for the radius or circle to be cut. If the blade is too wfor the radius, the heel of the blade will press against the ouedge of the kerf(Figure 6-19). When the heel contacts tedge, any further twisting of the workpiece in an attemptcut a sharper radius will twist the bandsaw blade and mresult in the blade breaking.

6


16/18

TC 9-524

Cutting Pressure

When cutting a radius, app ly a slight side pressure at theinner cutting edge of the bandsaw blade (Figure 6-19). Thispressure will give the blade a tendency to provide additional

clearance.

CONTOUR SAWING

Contour sawing is the process of cutting shap es in whichthe direction of the cut must be changed at intervals. Holeslarger in diameter than the width of the saw blade must bedrilled at each corner where a change of direction of thebandsaw blade will occur. Figure 6-20 illustrates themethods of changing direction of a cut at a hole.

16


17/18

TC 9-5

Sawing Aw ay From the HoleSawing Toward the H ole

To saw away from the hole on a line tangent to the hole,the saw blade mu st cut away from the center of the hole, orthe blade will bow and cause a belly in the cut. The cut

should be started as in A, Figure 6-20, in wh ich a curve iscut outward from the hole to meet the layout line, leavingapiece of excess metal which can be removed later byfiling. An alternate method is shown at B, Figure 6-20, inwhich a section of metal is notched ou t with a saw blade byseveral short cuts to give the blade clearance for starting thecut along the layout line.

The diagrams at C and D, Figure 6-20, show the propmethod of sawing up to a hole in two cuts. The excess me

can be removed later by tiling. After the shape is cut and thslug or waste m aterial is removed, the comers should bfinished by filing or notching. The bandsaw blade should nbe used for these operations because the blade will bow ancut unevenly.

SPECIAL OPERATIONS O N SAWING MACH INES

INTERNAL SAWING

Internal sawing is performed in the same manner ascontour sawing except that the bandsaw blade cannot startcutting from the edge of the workpiece but must start cuttingfrom a d rilled h ole in the workp iece (Figure 6-20). With thepattern laid out on th e workp iece and th e starting holedrilled, insert an unwelded bandsaw blade of the properlength through the starting hole. Bring the two ends of theblade together at the butt welder of the bandsawing machineand weld the blade into a continuous band as described inthe pertinent operation manual for the machine. Install thebandsaw blade on the sawing machine and make thenecessary adjustments to the m achine. With the cut startingfrom the hole as shown in A or B, Figure 6-20. When the

sawing is completed, cut the band saw blade so that it can beremoved from the workpiece.

BAND FILING

Filing is performed on the vertical band saw machineusing a band tile and the band file attachment. As with

sawing, the quality of filing and the economical wear of thband file depend up on p roper selection of files and filinspeeds for different materials and conditions.

Band Filing Sp eed

Band files should be run at relatively slow speeds compared to speeds u sed for band sawing. Figure 6-21 lisrecommend ed sp eeds for band filing. Note that, in generthe slower speeds are used for filing harder metals and fastspeeds are used for filing softer metals.

Band Filing Feeds

Work pressure on the band file should not be excessive. med ium am ount of pressure applied against the band fimoving at the prop er speed w ill produ ce curled chips wh iwill not clog the file. Heavy pressure will cause clogginand can cause the file to break or the machine to stall. light pressures should be used for finish filing, with a slosideways motion that will not leave vertical file marks on tworkpiece.

6-


18/18

Chapter 6 Sawing Machines

Documents

Transcript of Chapter 6 Sawing Machines