GD&T Advanced Jan2013

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Aditi Consultancy Services #2, ANANDA, 19th Cross, 24th Main

J P Nagar 5th Phase, Bangalore-560078 Phone/Fax: 080-26580711; Mobile: 9449612671

Web Site: http://www.aditiconsultancy.com

2

Aditi Consultancy Services, Bangalore

Type of Tolerance Characteristic Symbol

Datum Required Yes / No

Applicable to Axis Yes / No

Form

Profile

Orientation

Location

Runout

Exercise Complete the following table:

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Type of Tolerance Characteristic Symbol

Datum Required Yes / No

Applicable to Axis Yes / No

Form

Straightness No Yes Flatness No No Circularity No No Cylindricity No No

Profile Profile of a Line Yes / No No Profile of a surface Yes / No No

Orientation Angularity Yes Yes Parallelism Yes Yes Perpendicularity Yes Yes

Location Position Yes Yes Concentricity Yes Yes Symmetry Yes Yes

Runout Circular Runout Yes No Total Runout Yes No

Exercise Complete the following table:

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Mistakes in the drawing Aditi Consultancy Services, Bangalore http://www.aditiconsultancy.com

Correct drawing Aditi Consultancy Services, Bangalore http://www.aditiconsultancy.com

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I

Dimensioning of a Shaft


RULE 1 (Limits of Size Rule): Where only a size dimension is given

a) The size dimensions at any cross section must be within the size tolerance.

b) The surface(s) shall not extend beyond the perfect form defined by the MMC Size.

c) The form may vary within an envelope between the MMC and LMC.

Geometric Tolerance Rule

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Straightness of Surface


Form variation

Form variation

15.89 16.00

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Limits of Size Rule


Limits of Size Rule

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Straightness of Surface


Difference between axis and surface straightness

The axis is straight, surface elements bent (barrel shaped)

The axis is straight, surface elements bent (hourglass shaped)

Both axis and surface elements are bent(bowed)


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Geometric Tolerance Rule

RULE 2

Geometric tolerances for a feature of size are understood to be applied regardless of feature size (RFS).

If MMC or LMC is required, it must be placed in the feature control frame.

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Straightness of Axis at RFS


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20.008 20.003

Precision Cylindrical Fit

(Minimum diameter of hole) (Maximum diameter of pin)


Should be less than 20.008

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RFS V/s MMC Modifier

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Straightness of Axis at RFS


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Straightness of Axis at MMC




H

S

B

Minimum Hole Size = Shaft Size + Bend in Axis of the Shaft

i.e. H = S + B 19



H

S

B

Since minimum size of the hole remains the same, if the shaft size is smaller it can bend more and still assemble 20

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H

S

B

Maximum Shaft Size = Hole Size - Bend in Axis of the Hole i.e. S = H - B

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H

S

B

Since maximum size of the shaft remains the same, if the hole size is bigger it can bend more and still assemble

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MMC Virtual Condition


Virtual condition is the collective effect of size and geometric tolerances that must be considered in determining the fit or clearance between mating parts or features.

To calculate virtual condition: External features: MMC size + Geometrical Tolerance Internal features: MMC size Geometrical Tolerance A virtual condition will exist only for tolerances that control size features.

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Straightness of Median Plane on RFS Basis


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Straightness of Median Plane on MMC Basis

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Straightness per unit length with specified total straightness


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Straightness per unit length with specified total straightness



LMC Principle


Actual Minimum Material Envelope


LMC Virtual Condition LMC Virtual condition is the collective effect of LMC size limit and geometric tolerances. It assures a protected core of part material within a pin, boss or tab or a protected case of part material around a hole or slot.

To calculate virtual condition: External features: LMC size limit Geometrical Tolerance Internal features: LMC size limit + Geometrical Tolerance

FLATNESS


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FLATNESS


Tolerance zone is limited by two parallel planes a distance t apart


FLATNESS OF SHEET METAL

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FLATNESS

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FLATNESS AT MMC

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FLATNESS AT MMC Functional Gauge

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UNIT FLATNESS AT MMC Functional Gauge

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Indicator reading is the flatness error of the surface

Flatness Measurement

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COORDINATE V/s ROUND TOLERANCE ZONE

20.40 20.28

20.40 20.28

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Round Tolerance Zone



Position Tolerance of a Hole at MMC

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Functional Gauge for Inspection

Part must slide over 13.88 gauge pin. Must lie flat on base of gage (Datum A). Touch Datum B along its length and simultaneously touch Datum C


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Exercise


Complete the drawings of the following 2 parts for interchangeable assembly.

MMC Virtual Condition


Virtual condition is the collective effect of size and geometric tolerances that must be considered in determining the fit or clearance between mating parts or features.

To calculate virtual condition: External features: MMC size + Geometrical Tolerance Internal features: MMC size Geometrical Tolerance A virtual condition will exist only for tolerances that control size features.

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Exercise Using positional tolerance improve the design of the following part

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Datum Reference Frame

Free Movement Restricted Movement


51 51 Aditi Consultancy Services, Bangalore

Datum Referencing


Datum Referencing

Position Tolerance of a Hole Defines a zone in which the center axis or center plane is permitted to vary from true (theoretically exact) position.


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Hole axes in relation to Positional Tolerancing


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Design a rectangular part that sits on surface A and three matching holes in it engage with the projecting cylindrical pins

A

X


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Dimensions (Without Datums)

150.1 30

a=150.1 b=150.1 c=150.1

30


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Dimensions (With Datums)

15 30


O 0.2 A 3X


Exercise Number of similar parts shown below are stacked one above the other and fastened using bolts passing through 4 holes. Central hole is used for locating and slot is used for aligning them. Complete the engineering drawing by adding the necessary datum and geometrical tolerances.


Position Tolerance


Two Datum Planes Through a Hole

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Restrained Features



Inclined Datum Feature


LMC Virtual Condition LMC Virtual condition is the collective effect of LMC size limit and geometric tolerances. It assures a protected core of part material within a pin, boss or tab or a protected case of part material around a hole or slot.

To calculate virtual condition: External features: LMC size limit Geometrical Tolerance Internal features: LMC size limit + Geometrical Tolerance

Boss and Hole at LMC


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Surface Plate, Granite Square, Straight Edge, etc.

Measuring Accessories


Measuring Accessories

Plunger Type Dial Gauges


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Lever Type Dial Gauges


Dial Stands


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Slip Gauges

Slip blocks are used as standards for precision length measurement in the Engineering Industry.

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Slip Blocks Four Grades of Accuracy

Workshop Grade Grade 2

Inspection Grade Grade 1

Calibration Grade Grade 0

Reference Grade Grade 00 or K

Care of Block Gauges

When not used, Slips should be kept in their Case.

Avoid Excessive Handling - Dont touch lapped faces.

Wipe slips clean before and after they are used.

Use soft linen or cambric cloth to clean slips.

Least Expensive

Most Expensive

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Wringing of Slip Gauges

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Plug Gauges

A Plug Gauge is an precision-sized gauge which is used for size control of internal diameters/holes.

Go No-Go gauges are double ended. If the Go end is sized to 20mm, the No-Go end is slightly bigger, i.e. 20.020mm. If the Go end fits in the machined hole and the No-Go end doesnt then the hole is the an acceptable size.

The tolerance on the gauges can vary and each gauge is usually specific to a particular job. 76


Ring Gauges

A Ring Gauge is a precision-sized gauge used for size control of external diameters/bars.

It can be fitted over a bar end and moved along the length to test for roundness and accuracy of diameter.

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Thread Plug and Ring Gauges


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Screw Pitch Gauges

A screw pitch gauge has a set of teeth which are of a known thread form. The gauge is used to determine the pitch of a thread on a bolt or screw of any diameter.


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Feeler

Gauges

Feeler Gauges

Feeler Gauges are manufactured from accurately rolled shims and are used to measure gap sizes from 0.05mm up to about 1.25mm (0.002 to

0.050 inches). The numbers are marked on the gauge to give the

thickness and thus the gap width.


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Radius

Gauges

Radius Gauges

Radius gauges are usually made of tool steel and cut with an inside and outside radius of a stated size. The gauges are grouped with other sizes to make a set.

An accurately machined component can be easily compared with the profile of a radius gauge.


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Sine Plate


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Sine Bar


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Sine Bar


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Angle Gauges


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Angle Gauges


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Angle Gauges


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Profile Projector

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Electronic Height Gauge


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Electronic Height Gauge


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Coordinate Measuring Machine (CMM)

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CMM PROBES

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CMM Scanning

Probe Head

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COORDINATE MEASURING MACHINE


Cantilever Type CMM Bridge Type CMM

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COORDINATE MEASURING MACHINE


High Precision and Multi Sensor CMM

Gantry Type CMM

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Portable CMM


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LASER scanner with an articulated arm


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Table Rotation

Precision Form Tester

COLUMN SPINDLE AND

GAUGE

Spindle Rotation Aditi Consultancy Services, Bangalore


SURFACE FINISH & FORM MEASURING MACHINE

101

3D Measurement


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103

Position all 5 the Holes relative to the two Centre Planes and the Bottom Surface of the part


Exercise

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Positional Tolerancing relative to Datum Feature Centre Planes


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Multiple Pattern of Features


106 Tolerance Zones for Patterns Aditi Consultancy Services, Bangalore


PLTZF & FRTZF

PLTZF

FRTZF


Composite Position Tolerancing



One possible relationship between the PLTZF and FRTZF

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Composite Position Tolerancing (Circular Pattern of Features)


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AME of 50

+0.25 0

Functional Gage with Datum at RFS

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Functional Gage with Datum at MMC


50.25


Functional Gauge with Datum at MMC

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Bi Directional Position Tolerancing

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Bi Directional Position Tolerancing


Projected Tolerance Zone

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Fastener and Hole


When the projected tolerance zone symbol is shown, it means that the stated tolerance zone is extended beyond the surface of the part, not within the part.


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Gauge for Projected Tolerance Zone

Profile of a Surface Profile of surface is a tolerance zone, three-dimensionally extending

along the length and width of the considered feature or features.


Tolerance zone for the part


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Profile of a Surface (In Between) Profile of surface is a tolerance zone, three-dimensionally extending along the length

and width of the considered feature or features.


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Profile of a Surface with Datums


Profile of a Surface with Datums


Profile of a Line


A geometric tolerance that limits the amount of error for line elements relative to their true profile

Profile tolerances are often used to control irregular shapes. e.g. contours.

Profile of a Line


Profile of a Line (In Between) Profile of a line between two points of the considered feature.


Profile of a Line (In Between)


Profile of a Line with Datums


Profile of a Line



Unilateral: all outward from the basic profile.

Unilateral: all inward from the basic profile.



Checking Profile using Template


Profile Tolerance Zone ASME

For profile of a surface or line, the tolerance value represents the distance between two boundaries equally or unequally disposed about the true profile or entirely disposed on one side of the profile

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Profile Unilaterally Disposed


144

Profile of a surface All around


145

Profile All-Around Application


146

Profile of a surface All Over


147

Profile of a surface All Over



Profile of a Surface

149




Profile of a Surface (All Around)


Composite Profile of a Surface

153

Profile - Multiple or Co-Planar Surfaces



Tangent Plane

A plane contacting the high points of the surface shall lie within two parallel planes 0.1 apart


Tangent Plane

0.01


Tangent Plane

157

Angularity


158

Angularity


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Concentricity The condition where the median points of all diametrically opposed elements of a cylinder (or a surface of revolution) are congruent with the axis of a datum feature.


Concentricity Circular tolerance zone of 0.1 mm diameter

Median points should fall with in the tolerance zone

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Concentricity


Concentricity Between Features

CIRCULAR RUNOUT A composite control that affects the form, orientation, and location of circular elements of a part feature relative to a datum axis.


Run-out

A

Rotating about datum axis A

Full Indicator Movement (FIM) should be less than .002


Datum axis A


Circular Runout

Circular Runout - Axial The tolerance zone is limited to any radial position by two circles with a distance t apart lying in a cylindrical section, the axis of which coincides with the datum.


TOTAL RADIAL RUNOUT


Total Runout - Axial The tolerance zone is limited by two parallel planes a distance t apart and perpendicular to the datum.



Checking Axial Runout


CIRCULAR RUNOUT

The tolerance zone is limited by two coaxial cylinders with a difference in radii of t, the axes of which coincide with the datum.

Control affecting the form, orientation, and location of all surface elements of a diameter (or surface) relative to a datum A composite axis.

Total Run-out Tolerance -- Radial



CIRCULAR RUNOUT

174


Coaxial Features


Co-axiality Control


Functional Gauge

177


Symmetrical Tolerancing

178

Symmetry



Position Tolerance for Symmetry


If you have any queries please contact:

A Raghunath

Aditi Consultancy Services

Email: [email protected]

Tel / Fax: 91 80 26580711; Mobile: 9449612671

http://www.aditiconsultancy.com

GD&T Advanced Jan2013

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