Position Tolerance at RSF On a Slot 1

[lameparime]

Hello,

I’m inspecting a call out identical to figure 8-38 on the attached image. The issue is that my mobile CMM is only capable of checking position of a 2D slot feature. There is not a single mention online of inspecting the position of a slot along the whole length of a hole. For circular holes you can inspect the hole as a cylinder and check it with cylindrical position tolerance.

I’m considering either:

1. Checking position of a 2D slot at the top and bottom of a through hole separately

2. Taking points at various depths so that the 2D slot is average of the whole length

3. Taking two planes on opposite side walls of the hole (since I’m checking position in one direction anyway) and somehow checking if their mid plane is within position tolerance

4. Taking slot at each end, making a line from their midpoints and checking if that line is within the tolerance

The concern is to find out if the hole is in tolerance at all depths

 

[Burunduk]

What CMM software are you using?

 

[lameparime]

Creaform handyprobe and c-track. But it’s more of a Polyworks issue of not having 3D non circular shape options. Since there is no cube either maybe I’m missing some sort of inspection strategy that’s common knowledge

 

[MaxSka9]

If your callout is exactly as the provided picture then I would say that your third strategy is the way to go. Create two planes, one on each side of the slot, from those planes you create a median plane. Then you compare the location of that median plane to the location of plane A. In ISO thats how I would do it in your case. I’m unsure if rule 1 in ASME somehow makes this strategy not viable though (regarding what algorithm to use to create the first two planes).

 

[Burunduk]

3. Taking two planes on opposite side walls of the hole (since I’m checking position in one direction anyway) and somehow checking if their mid plane is within position tolerance

Can you define these two planes to be parallel to each other + some kind of fit like a modified least squares to the measured slot walls? The "actual mating envelope" as mentioned in your figure is from ASME Y14.5, and technically, to follow the standard the planes should coincide with the highest points on the side walls while at maximum separation from each other. But CMM measurement programs often substitute the tangency at high points with some semi-best fit to avoid repeatability issues.