METROLOGY-chapter2-

8/2/2019 METROLOGY-chapter2-

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CHAPTER 2

MAXIMUM MATERIAL CONDITION

(MMC) TOLERANCE

MET 3012

METROLOGY


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1.POSITION

Consider the following example:

50

0.15 M

2 holes

10 0.1


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Condition 1 Both holes at MMC (smallest size)

Center distance at minimum

49.852 holes

9.9

59.75


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Condition 2 Both holes at MMC (smallest size)

Center distance at maximum

40.252 holes

9.9

50.15


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Condition 3 Both holes are large as possible Center distance = x Maximum holes deviation same as condition 1

x2 holes

10.1

59.75

X = 59.75 holes= 59.75 10.1= 49.65


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Condition 4 Both holes are large as possible

Minimum holes deviation same as condition 2

40.25 2 holes

10.1

x

X = 40.25 + holes= 40.25 + 10.1= 50.35


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SummarySummary of the 4 condition can be explained in a tabular form as follow

Hole MMC Bonustolerance

Geometrictolerance

Totaltolerance

9.9

10.0

10.1

9.9

9.9

9.9

-

0.1

0.2

0.15

0.15

0.15

0.15

0.25

0.35


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2. STRAIGHTNESS

MMC diameter for the pin is 10

.2 (the largest size)

0.1 M

10 0.2


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Summary

Virtual condition of shaft

= MMC dia. + allow geometric tol.

= 10.2 + 0.1

= 10.3

Possible holediameter

MMCdiameter

Bonustolerance

Geometricaltolerance

Totaltolerance

Virtualcondition

10.2 10.2 - 0.1 0.1 10.3

10.1 10.2 0.1 0.1 0.2 10.3

10.0 10.2 0.2 0.1 0.3 10.3

9.9 10.2 0.3 0.1 0.4 10.3

9.8 10.2 0.4 0.1 0.5 10.3


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SummaryAs the diameter of the pinreduces from its maximum sizethe amount it differs can be

added to the straightnesstolerance

10

.3


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3. PARALLELISM

The axis of upper hole must be parallelto the axis of the lower hole to withina cylindrical tolerance zone of 0.1mm

MMC is being applied to the parallelismof the upper axis so as the diameter ofthe upper hole deviation from its MMCdiameter

0.1 M A

A

12.025 12.000


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Summary

Possible holediameter

MMCdiameter

Bonustolerance


Totaltolerance

12.000 12.000 - 0.1 0.100

12.005 12.000 0.005 0.1 0.105

12.010 12.000 0.010 0.1 0.110

12.015 12.000 0.015 0.1 0.115

12.020 12.000 0.020 0.1 0.120

12.025 12.000 0.025 0.1 0.125


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SummaryThe diagram holes how thetolerance zone grow as the holediameter increase.

The axis of the hole must lieanywhere within the hatchedareas.

The amount of bonus tolerance

depends upon the actual hole size.

0.125 0.1

Bonus tol.

Geo. Tolerance


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4. CO-AXIALITY

MMC is applied to both thecontrolled and the datumfeatures. This results moreflexibility is given in tolerance

ie.Concentricity + Datumtolerance

0.2 M A M

15 0.2 7 0.2

A


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Summary

Controlledfeaturediameter

MMCdiameter

Bonustolerance


Totaltolerance

15.2 15.2 - 0.2 0.2

15.1 15.2 0.1 0.2 0.3

15

.0

15

.2 0

.2 0

.2 0

.4

14.9 15.2 0.3 0.2 0.5

14.8 15.2 0.4 0.2 0.6

MMC is applied to both the controlled feature and thedatum feature. The effect of size on the controlled featureis shown the table below

Will be added to thebonus tolerancegained from datumfeature


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Summary

Datumfeaturediameter

DatumMMCdiameter

Bonustolerance(difference)

Totaltolerancefrom above

New

totaltolerance

7.10 7.10 - 0.2 0.2

7.05 7.10 0.05 0.3 0.35

7.00 7.10 0.10 0.4 0.506.95 7.10 0.15 0.5 0.65

6.90 7.10 0.20 0.6 0.80

The following table shown the effects when the size of thedatum feature differs from MMC

Only added when datumfeature was MMC symbol


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5. HOLEPOSITION

TOLERANCEa) Standard size hole tolerance with square tolerance zone

25 0.05 (x position)

10 0.05 (y position)

8 0.1


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Result of inspection of 3-components

Holes diameter X- Position Y - Position

A 8.01 24.96 10.04

B 7.93 25.06 9.99

C 8.08 24.88 9.91

The following table shown the effects when the size of thedatum feature differs from MMC

Question:Can all holes A,B and C be accepted?


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Exercise

Find the MMCtolerance of theshaft in Fig.

0.05 M A M

25 0.1 10 0.1

A

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METROLOGY-chapter2-