How to tolerance non-orthogonal holes

[SteveMartin]

Alright, I'm hitting a mental block. Can somebody suggest a good way to tolerance the location and orientation of the 1/2-20 holes in the attached print? The print is incomplete by design, trying to eliminate most of the clutter not related to the question (though I missed a couple).

Functional requirements: should be perpendicular to the 'top' compound angled surface (currently marked datum D), and should start the given distances from datums B & C.

 

[SteveMartin]

Forgot to mention: drawing should follow ASME Y14.5-1994.

 

[PeterStock]

I would give a profile tolerance for datum D to A B C and a true position tolerance for the 1/2-20 holes to D B C.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[ewh]

Make the angled surface a datum and use that datum instead of A.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[ewh]

OK, I see that you have already labeled it D. Just reference D instead of A

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[pmarc]

1. If function is to keep both 1/2-20 holes perpendicular to D, I would just put position tolerance callout like |pos|dia.xxx|D|B|C| or |pos|dia.xxx|D|C|B| (I do not know which face is secondary and which tertiary).

2. However if for some reasons you want to control angularity of the holes to A, I would add basic angular dimension from A to one of the holes axis in side view and apply position callout |pos|dia.xxx|A|B|C| or |pos|dia.xxx|A|B|C| respectively. This would works as typical position callout where holes are perpendicular to primary datum and basic 90deg dimension is not shown.

3. If there is a requirement that tolerance for pattern location is greater than angularity tolerance for the holes you could go with callout similar to the ones shown on figs. 6-6 or 6-8 of Y14.5-2009 std.

 

[dingy2]

With the information provided, the primary datum is D with secondary B and tertiary C.

Since these are holes, one should place a positional tolerance with a diametrical tolerance zone of some value beyond MMC (M with a circle around it). If you have a small run, delete the MMC. If your run is large and you have used MMC, place MINOR DIA below the feature control frame so that it can be checked on the shop floor with a fixture. Without the statement "MINOR DIA", it would default to its pitch diameter which is tough to measure.

Hope this helps.

Dave D.

http://www.qmsi.ca

 

[SteveMartin]

Thanks for the answers. With a new day (and a fresh cup of coffee) this makes sense now. For whatever reason I just couldn't wrap my head around it yesterday.

 

[SeasonLee]

POS|Ø.xxx|A|B|C
POS|Ø.xxx|D

Two single segmented control frames will meet your requirement, the first FCF starts the given distance from datum B and C, and the second FCF controls the perpendicularity with datum D.

Please ref to the Fig 5-28 from ASME Y14.5M-1994 or Fig 7-55 from ASME Y14.5-2009 for more detailed information.

SeasonLee