positional tolerance
positional tolerance
(OP)
Good Evening,
I'm looking at a drawing of two parts. One is a component with a diameter flange with a series of holes in with a positional tolerance of 0.1 on them. Our plate which the component sits on has the same pattern of holes in and we locate with pins through the holes.
Now I've been given this job and I think I've confused myself. The guy has put a positional tolerance on our holes of 0.025. Now is it just me or does that have a potential to not fit? Should our holes not be the same as those in the component, I.E positional to 0.1. Then obviously the location pins down size to suit the component holes tolerance.
Thanks in advance
I'm looking at a drawing of two parts. One is a component with a diameter flange with a series of holes in with a positional tolerance of 0.1 on them. Our plate which the component sits on has the same pattern of holes in and we locate with pins through the holes.
Now I've been given this job and I think I've confused myself. The guy has put a positional tolerance on our holes of 0.025. Now is it just me or does that have a potential to not fit? Should our holes not be the same as those in the component, I.E positional to 0.1. Then obviously the location pins down size to suit the component holes tolerance.
Thanks in advance





RE: positional tolerance
RE: positional tolerance
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: positional tolerance
RE: positional tolerance
RE: positional tolerance
If the former the projected tolerance zone should be used.
RE: positional tolerance
RE: positional tolerance
I would agree with that,but still I my opinion the virtual boundaries (VC) should be the same for the upper plate to fit.
Am I right? Are the VC's the same?
RE: positional tolerance
I think I'm getting confused with previous work done, and examples I've looked at recently, especially that formula that basically states one must equal the other, so I've gone over previous tools and mine follow this formula. However this one isn't. I've just gone over it again and I'm getting errors.
RE: positional tolerance
Are you working in inches or millimeters? 0.025mm is a very accurate positional tolerance. Your call-out may be good. Your math may be good. If the shop cannot fabricate it, this all is a waste of time. This is why you specify diamond pins, or slots.
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JHG
RE: positional tolerance
However, have you considered a change in process? This is one of those times that it may be an exceptional circumstance that the standards just don't adequately cover. If you specify that the pin holes are to be match-drilled/reamed together, you eliminate a lot of hair pulling. Then you just have to chase the clearance hole with a slightly larger reamer to get it to size. Or make a spring cut with the interpolated end mill, or whatever suits the manufacturer's preference.
It's not uncommon practice in tooling and die work, but it obviously does not result in completely interchangeable components.
RE: positional tolerance