question on GDT Parallel per inch

tay2daizzo8 · Aug 22, 2019

i have a 5" dia disk .500 thick that calls a general tolerance of parallel .002/in

does this mean i have .002 for every inch on the dia or .002 for every inch on the thickness

Booze Daily · Aug 22, 2019

General tolerance, not in a feature control frame? I would say both.

tay2daizzo8 · Aug 22, 2019

there is a feature control frame around the call out but the call out is in the general tolerances box.

cant be both, it would equal .001 over the thickness and would be .01 over the dia.

also calls out flatness of .003 on one side

BoxcarPete · Aug 22, 2019

Well my interpretation would be pretty clearly .010 over the whole diameter. Parallelism .002 per inch is stated as a rise over run, which only makes sense if applied to something that can slope, e.g. parallel planes. Making the plate thicker doesn't make the faces any more or less parallel, that seems a little wonky to me.

If you are still not sure, call your customer. No sense in asking people with no particular reason to care and little to lose making guesses from partial information. Odd that there's a feature control frame that just points you to the titleblock, I don't think I've seen that before.

Mike1974 · Aug 22, 2019

BoxcarPete said:
Well my interpretation would be pretty clearly .010 over the whole diameter. Parallelism .002 per inch is stated as a rise over run, which only makes sense if applied to something that can slope, e.g. parallel planes. Making the plate thicker doesn't make the faces any more or less parallel, that seems a little wonky to me.

If you are still not sure, call your customer. No sense in asking people with no particular reason to care and little to lose making guesses from partial information. Odd that there's a feature control frame that just points you to the titleblock, I don't think I've seen that before.

This discussion has been done here before. Sometimes it's a no-no to ask the customer anything. Easier to ask here and maybe someone (or a few people) might come to the same conclusion as OP as to what it means, or might mean.

BoxcarPete · Aug 22, 2019

Mike1974 said:
This discussion has been done here before. Sometimes it's a no-no to ask the customer anything. Easier to ask here and maybe someone (or a few people) might come to the same conclusion as OP as to what it means, or might mean.

Fair enough. I've never had a situation where I felt like contacting the customer for clarification was a problem, but much of what I do is engineering related, so open communication is expected and encouraged. I've gotten a few flat looks as responses to questions I've asked, but I still consider that worth having done. It's better than the least little bit of doubt in my opinion.

tay2daizzo8 · Aug 22, 2019

BoxcarPete said:
Well my interpretation would be pretty clearly .010 over the whole diameter. Parallelism .002 per inch is stated as a rise over run, which only makes sense if applied to something that can slope, e.g. parallel planes. Making the plate thicker doesn't make the faces any more or less parallel, that seems a little wonky to me.

If you are still not sure, call your customer. No sense in asking people with no particular reason to care and little to lose making guesses from partial information. Odd that there's a feature control frame that just points you to the titleblock, I don't think I've seen that before.

this was my interpretation as well, .002 for every inch of surface it has to travel over...makes sense the bigger the dia the more tolerance allowed would be.

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