What is the purpose of a true position tolerance for multiple holes on a bolt circle?

What is the purpose of a true position tolerance for multiple holes on a bolt circle?

• A. To ensure the holes are perfectly circular.
• B. To ensure all hole axes lie within the specified cylindrical tolerance relative to the DRF and bolt circle.
• C. To limit the depth of holes.
• D. To control the surface finish around holes.

Answer: (B)

The key idea is that true position controls where the hole axes must be located relative to a defined reference frame, especially when holes are arranged on a bolt circle. For multiple holes, the true position tolerance creates a cylindrical zone around each hole’s theoretical axis, anchored to the datum reference frame (DRF) and the bolt-circle geometry. This means every hole axis must lie within that tolerance zone, preserving both the radial placement (distance from the circle center) and the angular spacing around the circle so the pattern will align with the mating part. This doesn’t directly govern how round each hole is (that would be a circularity or true roundness control), nor does it set hole depth or surface finish.

The key idea is that true position controls where the hole axes must be located relative to a defined reference frame, especially when holes are arranged on a bolt circle. For multiple holes, the true position tolerance creates a cylindrical zone around each hole’s theoretical axis, anchored to the datum reference frame (DRF) and the bolt-circle geometry. This means every hole axis must lie within that tolerance zone, preserving both the radial placement (distance from the circle center) and the angular spacing around the circle so the pattern will align with the mating part.

This doesn’t directly govern how round each hole is (that would be a circularity or true roundness control), nor does it set hole depth or surface finish.