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Tolerance Stack Up of Critical Features

Assuming that the measured dimensions of a production part fall within a bell curve and assuming

the standard deviation to the maximum allowable tolerance = 3, the Root Square Sum theorem canbe used to estimate the standards deviation of the total assembly and then therefore the 3rddeviation value (Ttotal)

Assume that maxium tolerance for a part = 3

Using the Root Squared Sum Method

For components that are in parallel with other features that determine the placement of the same

mating

parts, the tolerance needs to be adjusted using the average tolerance using the equation below

T_ave=T/(n)

T_total=3((T/3)^2 +(T/3)^2+(T/3)^2+...))

T_total=Total tolerance

T=individual tolerance of part

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Prepared By: Cameron Staunch

Stack Description: To determine the tolerance between the flange hard stop and sensor surface for the Cmount Cover.Starting Point: Flange Hard Stop

Ending Point: Sensor Surface

From To

Upper

Tolerance

Lower

Tolerance

Upper

Limit

Lower

Limit

1 Flange Hard Stop Sensor Mount Front + 16.150 0.050 -0.050 16.200 16.100 16.200

2 Sensor Mount Front Sensor Mount Rear + 2.000 0.050 -0.050 2.050 1.950 2.050

3 Sensor Mount Rear Shim Rear + 0.127 0.000 0.000 0.127 0.127 0.127

4 Shim Rear Sensor Surface - 0.750 0.060 -0.060 0.810 0.690 -0.690

A positive or negative Max or Min total indicates only the DIRECTIONfrom the STARTING point to the END point of the stack. Totals: 17.687

0.093

Mean + Statistical Tolerance = 17.620

Mean - Statistical Tolerance = 17.434

Total Target Dimension= -17.527

Statistical tolerance [sqrt(sum of sqrd tol)*3] =

STACK-UP SPREADSHEET

Bi/Unilateral DimensionDescriptionTarget

Dimension

Limit Dimension+ Max

- MinStack Direction +/-

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Date: 20-Dec-13

16.100 0.100

1.950 0.100

0.127 0.000

-0.810 0.120

17.367

+ Min

- MaxTolerance