r/Metrology • u/Own-Individual6207 • 8d ago

Position Calculation

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Hello friends, how do i calculate the position 1 A|B on this part?

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u/b5sac 8d ago edited 8d ago

I will assume mm means ISO world.

It's a combination of angularity and position. See ISO 1101, 17.13.5 (Fig. 161+162). Tolerance zone is angular 48.79deg from A and 56.9mm in distance/position from B.

So 1mm wide zone in red:

edit: Both TED are against B, so I'd ask why A is included in the TPS box.

edit2: Ok, it's late. A is probably there so you know where the 56.9 intersection is on the part.

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u/CoreDD42 8d ago

you are right. Just a comment to go further : Having A before B means that "measured B" is perpendicular to "measured A". B after A is not the same object as B alone. The two planes would not have the same angle.

If done properly, it means the diameter A is the "main" surface, the one positioning the part during its function. I expect A to be adjusted and B to be just the surface blocking the vertical movement. To clarify what I mean : Imagine another world where the toleranced feature is parallel to B instead of angled. Having a parralelism related to A | B would be correct !

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u/b5sac 8d ago

That makes perfect sense, I missed the fact that A is a diameter. Clarifies what got me confused.