Geometric Dimensioning and Tolerancing for Mechanical Design Part 7 ppt

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Position, General 107

w .010 M AB

A

w 2.500

w 4.000-4.020

B

Adjustable Jaws

4X w .510-.540

4X w .500

Figure 7-4 Inspecting the hole pattern controlled to a datum

feature of size at RFS.

datum feature, such as a chuck, vise, or adjustable mandrel, is used to position

the part. In Fig. 7-4, the outside diameter, datum B, is specified at RFS. The

pattern of features is inspected by placing the outside diameter in a chucking

device and the hole pattern over a set of virtual condition pins. If the part can

be set inside this gage and all the feature sizes are within size tolerance, the

pattern is acceptable.

Maximum Material Condition

The only difference between the tolerances in Fig.7-3 and Fig.7-5 is the MMC

modifier specified after the numerical tolerance in the feature control frame.

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Position, General

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MHBD031-07 MHBD031-Cogorno-v5.cls April 18, 2006 15:58

108 Chapter Seven

B

w 2.000-2.020

w .010 M A B C

w .010

C

2.00

A

True Position

Actual Location of Hole Axis

Total Tolerance

Size Dimension & Tolerance

Location Tolerance

Tolerance Zone

4.00

.008

.006

2.000

3.000

6.00

w .022

Figure 7-5 Location of a size feature with a position tolerance at MMC.

When the MMC symbol, circle M, is specified to modify the tolerance of a size

feature in a feature control frame, the following two requirements apply:

1. The specified tolerance applies at the MMC of the feature. The MMC of a

size feature is the largest shaft and the smallest hole. The MMC modifier,

circle M, is not to be confused with the MMC of a size feature.

2. As the size of the feature departs from MMC toward LMC, a bonus tolerance

is achieved in the exact amount of such departure. Bonus tolerance equals

the difference between the actual feature size and the MMC of the feature.

The bonus tolerance is added to the geometric tolerance specified in the

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Copyright © 2006 The McGraw-Hill Companies. All rights reserved.

Any use is subject to the Terms of Use as given at the website.

Position, General