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Chapter 14: A. Geometric Dimensioning and Tolerancing (GD&T) 141REVISIONSDO NOT SCALE SYM DESCRIPTION DATE APPQ.A H12 WAS 1/2 WHIT. 14-12-07 A.W.B.UNLESS OTHERWISESTATED ALL DIMENSIONSIN MILLIMETRES.TOLERANCESLINEAR:ANGULAR:DRAFTING STANDARDAS 1100MATERIALCAST STEELFINISHAS MACHINEDDRN 1 : 1 : 07CKD 2 : 1 : 07APPD 5 : 1 : 07ISSUED 4 : 2 : 074321TEHA7325DRG orPART No.Figure 14.3 Example of title and notes blocks on an engineering drawing.VALVE BODYDESCRIPTIONJKL[NAME OF FIRM]MJMAWB[TITLE OF DWG.]PFPSIZEDRG A24681A3No.SCALE 1 : 2 SHEET 1 of 11QTYPart III.A.11314 15 16Rev No Revision note Date Signature CheckedA SECTION ON A–A DELETED 29/12/03 R.B. All otherFigure 14.4 Example of a revision block.that can be accepted for a variation over the exact or nominal value expressed bythe designer (Cañas and Novak 2006). Figure 14.5 shows an example of a technicalengineering drawing with indication of geometric tolerances.Tolerance deals with the uncertainty of a real manufactured object comparedto the ideal design. By default, parts have to deviate from the ideal design, whichcreates the need for tolerancing practices. In the drawing world, tolerances arenoted on the drawing per notation standards such as ANSI Y14.5 or ISO 1101.There are two main classes of tolerances, dimensional and geometric.Geometric tolerances are the more complex of these two types. Geometric tolerancesprovide more flexible means for controlling shape than do dimensional tolerances.They achieve this by enabling tolerances to be defined independently ofexplicit dimensions. This enables tolerances to be specified that are more closely
142 Part III: Inspection and Test3× R. 135.003 A B MSimultaneous requirement.671.125 ± .001.001 M AB.130 ± .002.000 M A B MSimultaneous requirement.200.040.001.400.127 ± .002.000 M A B MSimultaneous requirementAFigure 14.5 Example of technical engineering drawing with indication of geometric tolerances.Part III.A.10.1 M A B CFigure 14.6 Visual representation of the control frame of a hole.related to the functional requirements of the design, such as strength and fit, byspecifying item features and characteristics (Griffith 1993).From the previous discussion we can understand that a geometric tolerancedescribes a constraint on the acceptable deviation of a manufactured object fromthe ideal design. Tolerances are applied to the geometric features of a part, suchas faces and holes.There are several subtypes of geometric tolerances, which are not mutuallyexclusive. For example, tolerances that reference datums are of type geometric tolerancewith datum reference. Tolerances that include a modifier such as maximummaterial condition are of type modified geometric tolerance. Many typical engineeringtolerances combine these (Briggs and Hendrix 2003).Consider an example of a location tolerance on a hole whose visual representationas a control frame is shown in Figure 14.6. Reading the control frame left toright, the location tolerance is a position tolerance, locating a cylindrical feature,with a tolerance value of 0.1, with a modifier condition of maximum material condition,referencing datums A, B, and C in that order (Briggs and Hendrix 2003).Common features that can be specified by geometric tolerancing are illustratedin Figure 14.7. Figure 14.8 provides a simple 2-D example wherein a positiontolerance (Symbol in Figure 14.8a) is imposed on hole H. The exact (true)position of H is defined in Figure 14.8a by two basic (boxed, signifying exact)dimensions that are anchored to part features A and B; the labels on these features
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142 Part III: Inspection and Test
3× R. 135
.003 A B M
Simultaneous requirement
.671
.125 ± .001
.001 M A
B
.130 ± .002
.000 M A B M
Simultaneous requirement
.200
.040
.001
.400
.127 ± .002
.000 M A B M
Simultaneous requirement
A
Figure 14.5 Example of technical engineering drawing with indication of geometric tolerances.
Part III.A.1
0.1 M A B C
Figure 14.6 Visual representation of the control frame of a hole.
related to the functional requirements of the design, such as strength and fit, by
specifying item features and characteristics (Griffith 1993).
From the previous discussion we can understand that a geometric tolerance
describes a constraint on the acceptable deviation of a manufactured object from
the ideal design. Tolerances are applied to the geometric features of a part, such
as faces and holes.
There are several subtypes of geometric tolerances, which are not mutually
exclusive. For example, tolerances that reference datums are of type geometric tolerance
with datum reference. Tolerances that include a modifier such as maximum
material condition are of type modified geometric tolerance. Many typical engineering
tolerances combine these (Briggs and Hendrix 2003).
Consider an example of a location tolerance on a hole whose visual representation
as a control frame is shown in Figure 14.6. Reading the control frame left to
right, the location tolerance is a position tolerance, locating a cylindrical feature,
with a tolerance value of 0.1, with a modifier condition of maximum material condition,
referencing datums A, B, and C in that order (Briggs and Hendrix 2003).
Common features that can be specified by geometric tolerancing are illustrated
in Figure 14.7. Figure 14.8 provides a simple 2-D example wherein a position
tolerance (Symbol in Figure 14.8a) is imposed on hole H. The exact (true)
position of H is defined in Figure 14.8a by two basic (boxed, signifying exact)
dimensions that are anchored to part features A and B; the labels on these features