H7 h6 fit

[grunt58]

I'm at a mind blank here and wondering if some one can help.

I have two square mating parts is it aceptable to use H7 and h6 type fits or are those just for shafts and holes.

Thanks

 

[KENAT]

Those are usually for shafts & holes and if selected correctly will match standard drill/shaft sizes, so I'm told.

I have used the numbers derived from the fit table when dimensioning a square boss into a square hole but I actually detailed the values on the drawing, I didnt' just ref H7/h6.

If in doubt, exlpicity put the tolerance on the drawing rather than referencing a separate spec is my rule of thumb.

Not very definitive, sorry.

KENAT, probably the least qualified checker you'll ever meet...

 

[CheckerRon]

I would concur with what KENAT has said. You can use fit tolerances of say H7/h6 but I would dimension the sizes of both parts and not try to equate the bore fits to non-circular features.

 

[grunt58]

Thank! Wasn't sure if they could cross over into non cylindrical parts or not. It went ahead and used a +- tolerance.

Thanks again.

Grant
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[drawoh]

GB58,

There is a chart in the Machinery's Handbook showing the tolerances classes in relation to various fabrication processes. Search ahead from your Limits and Fits tables. In the 26th edition, it is on page 630. Not all the fabrication processes generate round features.

Otherwise, I agree with the notes above recommending explicit tolerances.

Note that the ANSI fits are based on the ISO tolerances, and that they do not mix the same letters and classes. For example, an RC3 fit is an f6 shaft in an H7 hole.

JHG

 

[gearguru]

GB58,
be aware that the H7/h6 fit can theoretically create the zero clearance - "line on line" situation if both parts are made at the MMC.