Calculator Inputs
Formula Used
Coordinate error: dx = Actual X - Basic X, dy = Actual Y - Basic Y
True position: TP = 2 × √(dx² + dy²)
Projected addition: PA = 2 × Projected Height × tan(Angular Error)
Effective true position: ETP = TP + PA
Internal feature bonus: Bonus = Actual Size - MMC Size
External feature bonus: Bonus = MMC Size - Actual Size
Total allowed position: Allowed = Position Tolerance + Bonus + Datum Shift
Internal virtual condition: VC = MMC Size - Position Tolerance
External virtual condition: VC = MMC Size + Position Tolerance
Pass rule: The feature passes when size is within limits, ETP is within allowed tolerance, and functional clearance is not negative.
How to Use This Calculator
- Select internal feature for a hole or external feature for a pin.
- Enter the basic X and Y coordinates from the drawing.
- Enter the measured X and Y coordinates from inspection.
- Enter MMC size, LMC size, and actual feature size.
- Enter the stated position tolerance at MMC.
- Add datum shift, projected height, angular error, and gage allowances when needed.
- Press Calculate to see true position, bonus tolerance, virtual condition, and gage size.
- Use CSV or PDF export to save the result.
Example Data Table
| Feature | MMC Size | LMC Size | Actual Size | Position Tol. | Actual X | Actual Y | Expected Status |
|---|---|---|---|---|---|---|---|
| Hole | 10.000 | 10.200 | 10.080 | 0.200 | 0.080 | -0.050 | Pass likely |
| Pin | 12.000 | 11.800 | 11.930 | 0.150 | 0.040 | 0.060 | Pass likely |
| Hole | 8.000 | 8.150 | 8.010 | 0.100 | 0.090 | 0.070 | Review needed |
Understanding MMC Functional Gage Checks
A maximum material condition check is useful when a part must assemble with a mating part. It links feature size with allowable position error. A hole at its smallest limit has no bonus tolerance. A pin at its largest limit also has no bonus tolerance. As the feature moves away from maximum material, extra position tolerance becomes available.
Why Virtual Condition Matters
Virtual condition represents the worst assembly boundary. For an internal feature, it equals the smallest hole size minus the stated position tolerance. For an external feature, it equals the largest pin size plus the stated position tolerance. A functional gage is built around this boundary. It proves whether the feature can fit its mating envelope.
Using the Calculator
This calculator accepts basic coordinates, actual coordinates, feature size, size limits, and position tolerance. It also includes datum shift and projected height inputs. The result shows measured true position, bonus tolerance, total allowed tolerance, virtual condition, suggested gage build size, and pass status. It also estimates functional clearance.
Reading the Output
A positive margin means the feature is inside the calculated tolerance. A negative margin means the feature fails the mathematical condition. Functional clearance is another useful view. For holes, it compares actual hole size, position error, and gage pin size. For pins, it compares receiver size, actual pin size, and position error. Small positive values deserve review, because measurement uncertainty may change the decision. Record the units used and keep all inputs consistent. This prevents mixed unit errors during audits and costly rework.
Practical Shop Value
The tool helps inspectors make fast checks before formal reports. It can compare coordinate measurement data with drawing limits. It can also support gage planning. Use the CSV and PDF buttons to save results for inspection notes, routing sheets, or quality reviews. Always confirm drawing callouts, datum references, and company gage policy.
Important Limits
This calculator is a guide, not a replacement for a certified inspection plan. Functional gage design can require extra details. These may include datum simulators, material condition modifiers on datums, gage tolerance direction, wear allowance, thermal effects, and projected tolerance zones. Review the design with a qualified quality engineer when acceptance decisions affect production.
FAQs
What is MMC?
MMC means maximum material condition. For a hole, it is the smallest allowed size. For a pin, it is the largest allowed size.
What is true position?
True position is a diametric location error. It is calculated from X and Y coordinate differences between basic and actual locations.
What is bonus tolerance?
Bonus tolerance is extra position tolerance gained when the feature departs from MMC. It increases the usable positional tolerance.
What is virtual condition?
Virtual condition is the worst assembly boundary. It combines MMC size and position tolerance into one functional limit.
How is a hole gage size calculated?
For an internal feature, the virtual condition equals MMC size minus position tolerance. This calculator adjusts it for gage allowances.
How is a pin receiver size calculated?
For an external feature, the virtual condition equals MMC size plus position tolerance. The receiver may include maker and wear allowances.
Does datum shift affect virtual condition?
Datum shift affects the allowed position comparison. It usually does not change the basic virtual condition of the controlled feature.
Can this replace inspection software?
No. Use it as a checking aid. Confirm final decisions with approved drawings, standards, inspection plans, and quality procedures.