1. What is 3D True Position?

True Position is a geometric dimensioning and tolerancing (GD&T) location control used to specify how much a feature's location may deviate from its "true" position. The 3D version accounts for deviations in all three axes (X, Y, and Z).

2. How Does the Calculator Work?

The calculator uses the 3D True Position formula:

Where:

• \( dx \) — Deviation in X-axis (inches)
• \( dy \) — Deviation in Y-axis (inches)
• \( dz \) — Deviation in Z-axis (inches)

Explanation: The formula calculates the diameter of a sphere within which the actual position must lie, centered on the theoretically exact position.

3. Importance of True Position Calculation

Details: True Position is critical in manufacturing for ensuring proper fit and function of assembled parts, especially in precision engineering and aerospace applications.

4. Using the Calculator

Tips: Enter deviations in all three axes in inches. The calculator will compute the total position tolerance zone diameter.

5. Frequently Asked Questions (FAQ)

Q1: Why multiply by 2 in the formula?
A: The multiplication by 2 converts the radial position error into a diameter value, which is the standard way to report true position tolerance.

Q2: How is this different from 2D true position?
A: 2D true position only considers deviations in two axes (typically X and Y), while 3D true position adds the Z-axis component.

Q3: What units should be used?
A: The calculator uses inches, but the same formula works with any consistent unit system (mm, cm, etc.).

Q4: When is 3D true position needed?
A: When the feature's position must be controlled in all three dimensions, such as holes for fasteners or mounting points for complex assemblies.

Q5: How does this relate to GD&T standards?
A: This calculation follows ASME Y14.5 and ISO 1101 standards for geometric dimensioning and tolerancing.