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Chapter 14: A. Geometric Dimensioning and Tolerancing (GD&T) 141
REVISIONS
DO NOT SCALE SYM DESCRIPTION DATE APPQ.
A H12 WAS 1/2 WHIT. 14-12-07 A.W.B.
UNLESS OTHERWISE
STATED ALL DIMENSIONS
IN MILLIMETRES.
TOLERANCES
LINEAR:
ANGULAR:
DRAFTING STANDARD
AS 1100
MATERIAL
CAST STEEL
FINISH
AS MACHINED
DRN 1 : 1 : 07
CKD 2 : 1 : 07
APPD 5 : 1 : 07
ISSUED 4 : 2 : 07
4
3
2
1
TEH
A7325
DRG or
PART No.
Figure 14.3 Example of title and notes blocks on an engineering drawing.
VALVE BODY
DESCRIPTION
JKL
[NAME OF FIRM]
MJM
AWB
[TITLE OF DWG.]
PFP
SIZE
DRG A24681
A3
No.
SCALE 1 : 2 SHEET 1 of 1
1
QTY
Part III.A.1
13
14 15 16
Rev No Revision note Date Signature Checked
A SECTION ON A–A DELETED 29/12/03 R.B. All other
Figure 14.4 Example of a revision block.
that can be accepted for a variation over the exact or nominal value expressed by
the designer (Cañas and Novak 2006). Figure 14.5 shows an example of a technical
engineering drawing with indication of geometric tolerances.
Tolerance deals with the uncertainty of a real manufactured object compared
to the ideal design. By default, parts have to deviate from the ideal design, which
creates the need for tolerancing practices. In the drawing world, tolerances are
noted 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 tolerances
provide more flexible means for controlling shape than do dimensional tolerances.
They achieve this by enabling tolerances to be defined independently of
explicit dimensions. This enables tolerances to be specified that are more closely