True position calculator, with bonus tolerance.
Enter the X and Y deviations from your CMM or height gauge. Get the position diameter, any MMC or LMC bonus, and a pass or fail with the math shown, so you can check the CMM report or explain it to QC.
Result
- Measured position Ø
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- Bonus tolerance
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- Allowed position Ø
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- Margin
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Work shown
Position is a diameter, not an offset.
The tolerance zone is a circle around the true location. A feature 0.005 off in X is already using 0.010 of its position tolerance.
Position Ø = 2 × √(ΔX² + ΔY²)
At MMC, the part gets bonus tolerance as the feature moves away from its maximum material size. For a hole, MMC is the smallest allowed hole, so bonus = actual − MMC. For a pin, MMC is the largest allowed pin, so bonus = MMC − actual.
At LMC it runs the other way. A hole's LMC is its largest size (bonus = LMC − actual). A pin's LMC is its smallest size (bonus = actual − LMC).
RFS (no modifier) means no bonus. The stated tolerance is all you get.
If the actual size is outside its own limits, the feature is already bad and no bonus applies.
Good to know
Why is position twice the offset?
The position tolerance is a diameter. A feature 0.004 from true location sits on a circle of radius 0.004, which is a diameter of 0.008. That's why the formula doubles the distance.
Where do ΔX and ΔY come from?
Measured location minus the basic (boxed) dimension, in each axis. Signs don't matter because they get squared. Your CMM report usually lists them as deviations.
Does this handle datum shift?
No. It covers bonus from the feature's own size only. Datum features referenced at MMC can add more movement, and that depends on the part. Check those with your QC or on the CMM.
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Upload a PDF drawing. Deburr numbers every dimension, GD&T frame and note, and gives you the ballooned PDF and a Form 3 spreadsheet. No account needed.