measurement design

7/28/2019 Measurement Design

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Geometric Tolerancing - Definitions

Maximum Material Condition (MMC) The conditionin which a feature of size contains the maximumamount of material with the stated limits of size, -fore example, minimum hole diameter and maximumshaft diameter

Least Material Condition (LMC) Opposite of MMC,the feature contains the least material. For example,maximum hole diameter and minimum shaft diameter

Virtual Condition The envelope or boundary thatdescribes the collective effects of all tolerancerequirements on a feature (See Figure 7-25 TG)


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Virtual Condition Envelope

All Required Tolerances

20.06 Maximum

Envelope

20.00

Maximum

Allowable

Diameter

0.06Maximum

Allowable

Curvature


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Feature Control Frame

This feature must be parallel to Datum B within .007 at MMC

(largest cylinder) as measured on the diameter

.007 M B

Geometric

CharacteristicSymbol

Tolerance

Material condition

Datum

Reference

B

.007


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Tolerance of Form - Straightness

19.89

19.76

0.03

0.03 Tolerance Zone

This cylinder must be straightwithin 0.03 mm.

What it means -


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Concentricity Tolerance Note

XX

A

YY

.007 A

This cylinder (the right cylinder) must be concentric

within .007 with the Datum A (the left cylinder)as measured on the diameter

.007 Tolerance

Zone

What It Means


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DIMENSIONING

Requirements

1. Unambiguous

2. Completeness

3. No redundancy0.83 ' 0.95 ' 1.22 '

3.03 '

Redundant dimensioning

0.83 ' 1.22 '

3.03 '

1.72 '

0.86 '

Adequate dimensioning

Incompletedimensioning


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TOLERANCE

unilateral

bilateral

1.00 0.05+-

nominal dimension

tolerance

0.95+ 0.10- 0.00 1.05

+ 0.00- 0.10

1.00 0.05+-

0.95 - 1.05means a range


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"TOLERANCE IS ALWAYS ADDITIVE"

What is the expected dimension and tolerances?

d = 0.80 +1.00 + 1.20 = 3.00

t = (0.01 + 0.01 + 0.01) = 0.03

0.80 ' 0.01 1.20 ' 0.01

1.00 ' 0.01

?


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Maximum x length = 3.01 - 0.79 - 1.19 = 1.03Minimum x length = 2.99 - 0.81 - 1.21 = 0.97

Therefore x = 1.00 0.03

0.80 ' 0.01 1.20 ' 0.01

3.00 ' 0.01

?x


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SURFACE FINISH

waviness width

roughness width

waviness

roughness


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STRAIGHTNESS

Value must be smallerthan the size tolerance.

1.000 ' 0.002

0.001

Measured error 0.001

1.000 ' 0.002

0.001

0.001

Design Meaning

Tolerance zone between two straightness lines.


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FLATNESS

1.000 ' 0.002

0.001

0.001

parallel

planes

Tolerance zone defined by two parallel planes.


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CIRCULARITY (ROUNDNESS)

1.00 ' 0.05

0.01

At any section along the cylinder

Tolerance zone bounded by two concentric circles.


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CYLINDRICITY

1.00 ' 0.05

0.01

0.01

Rotate in a V

Rotate between points

Tolerance zone bounded by two concentric cylinders

within which the cylinder must lie.


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PERPENDICULARITY

A surface, median plane, or axis at a right angle to the datum plane

or axis.

0.500 ' 0.005

1.000 ' 0.005

. 0 0 2 A

2.000 ' 0.005

A

. 0 0 2 T A


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ANGULARITY

A surface or axis at a specified angle (orther than 90) from a datum

plane or axis. Can have more than one datum.

3.500 ' 0.005

1.5000.005

40

0.005 A

A


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PARALLELISM

1.000 " 0.005

2.000 " 0.005

.001 A

A

The condition of a surface equidistant at all points from a datum plane,

or an axis equidistant along its length to a datum axis.

0.001


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PROFILE

A uniform boundary along the true profile within whcih

the elements of the surface must lie.

A

B

0.005 A B

0.001


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RUNOUT

0.361 " 0.002

1.500 " 0.005A

0.005 A

A composite tolerance used to control the functional relationshipof one or more features of a part to a datum axis. Circular runout

controls the circular elements of a surface. As the part rotates360 about the datum axis, the error must be within the tolerancelimit.

Datum

axis

Deviation on each

circular check ring

is less than the

tolerance.


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TOTAL RUNOUT

Datum

axis

Deviation on the

total swept when

the part is rotating

is less than the

tolerance.

0.361 " 0.002

1.500 " 0.005A

0.005 A


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TRUE POSITION

1.20 0.01

1.00 0.01

1.20

1.00

Tolerance zone

0.01dia

O0.01MA B

O.800.02

Dimensionaltolerance

True positiontolerance

Hole center tolerance zone

A

B


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TOLERANCE VALUE MODIFICATION

Produced True Pos tol

hole size0.97 out of diametric tolerance

0.98 0.01 0.05 0.01

0.99 0.02 0.04 0.01

1.00 0.03 0.03 0.01

1.01 0.04 0.02 0.01

1.02 0.05 0.01 0.01

1.03 out of diametric tolerance

1.20

1.00

O 0.0 1 M A B

O 1.00 0.02

M L S

The default modifier fortrue position is MMC.

MMC

LMC

For M the allowable tolerance = specified tolerance + (produced holesize - MMC hole size)

A

B


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MMC HOLE

Given the same peg (MMC peg), when the produced hole sizeis greater than the MMC hole, the hole axis true positiontolerance zone can be enlarged by the amount of differencebetween the produced hole size and the MMC hole size.

hole axis tolerance zone

MMC holeLMC hole

MMC peg will f it in t he hole

axis must be in the tolerance zone,

measurement design

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