Slack Tolerance of Size of Feature in Pattern But Variation Must be Tighter

[JCReynolds79]

Basically, I am trying to think of a way to dimension a pattern of holes where the size of the hole isn't too important, BUT the variation of the size of the holes IS important.

e.g. array of holes: 8X dia10 +/-0.5 (quite a slack tolerance as the size is not too important)
but whatever size the holes end up they must be within +/-0.05 of each other. So if min. size hole is 9.6 then all other holes must be between 9.6 and 9.65.

Not sure how best to put this clearly on a drawing other than adding some sort of NOTE description like above.

Thanks.

Regards,

Jon Reynolds

 

[pmarc]

If this is ASME print, note is the only solution.

If this is ISO print, there is the SR (letters SR within an oval) modifier for what you want to accomplish. SR stands for Size Range - see ISO 14405-1.

 

[Belanger]

This might be a good example of the "dynamic profile" modifier that will probably be added to the GD&T system next year.
I guess that doesn't help you right now -- you might have to use a written note to communicate the idea.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[CheckerHater]

Am I allowed to ask - why?
I am genuinely curious - what kind of fit causing this requirement?

Also, it is highly unlikely that 8 holes made "at once" in the same fixturing will vary greatly in tolerance. And it could be fairly tight.

Just trying to educate myself

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[pylfrm]

e.g. array of holes: 8X dia10 +/-0.5 (quite a slack tolerance as the size is not too important)
but whatever size the holes end up they must be within +/-0.05 of each other. So if min. size hole is 9.6 then all other holes must be between 9.6 and 9.65.

Keep in mind that the actual size of any particular hole, which will inevitably have some form error, is not really a single value. If you end up writing a note, I'd recommend you consider something along the lines of the following:

8X diameter D +/- 0.025, where D is any single value between 9.525 and 10.475

pylfrm

 

[JCReynolds79]

Hi Folks,

Yes, sorry should have stated, it is ASME. So text note it is.

pylfrm, many thanks for the suggestion.

CheckerHater, the reasoning is because the holes are lightening holes in a circular pattern on a rotating part, so nothing fits in the holes (hence free size tolerance) but want them close in relative size to reduce balance issues.

Thanks all for your input.

Regards,

Jon Reynolds

 

[CheckerHater]

Thank you Jon.

I understood your concern. Drilling may consistently produce holes 10+/-0.2, so you may be safe size-wise.

Do you think specifying positional tolerance may be in order? having your hole pattern off-center may be as well throwing your part off-balance.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[JCReynolds79]

Hi CheckerHater,

Yes, holes are tied up pretty tight positional-wise.

Cheers.

Regards,

Jon Reynolds