// Question

[Underspec]

My print is calling out minimum of 3 control points for //. Print is dimensioned using ANSI Y14.5M-1982. I do not have a reference to this standard. Do I take 3 points, average it, then dimension to the datum plane? Or do I take the highest or lowest points?

[kmcmm]

Someone correct me if I am wrong, but I think that means you need to contact that surface in a minimum of three place before checking the // callout. I would take at five points then construct a plane and dimension it to the datum plane.

[Underspec]

I'm using an indicator is why I asked

[Paul Sarrach]

Then just tram the surface, add up the high and low and give that reading, or take 3 reading only and do the same. but then you have the flatness issue, why not use the cmm?

[bob mappes]

without seeing the actual drawing and callouts......

sounds like the 3 points are your "reference plane"...you will need to level to these 3 points, then sweep the feature plane with the // callout. total indicator movement is the actual result to report....high and low doesn't matter ( it does, but for simplicity we won't look at that right now), it's the difference between the high and low

so if you indicator shows a high of .002 and a low of .001 your total // is .003

good luck

[Paul Sarrach]

Bob is correct, I should of stated that on a certified flat granite plate, you should put the part on say for example three .100 gage blocks If you have certified balls that would be great, certified pins will do. Zero out you indicator on top of the part and then take you high and low.