Can I relate a hole pattern to be parallel and/or perpendicular only?

[buchner]

Hi, I have a part where I only care if the reamed hole pattern is aligned with the datums. That is, the rows and columns of the pattern are parallel and perpendicular to 2 datums (A and C). I want these to be within +/- 0.05 mm range to allow for a small angle in relating the parts. The tolerance between holes needs to also be in +/- 0.05 mm.

I don't care where the holes are located in distance to the datums (maybe a tolerance of +/- 1 mm.)

I have a laser pointing down at a surface. I don't care where it is - I just need it pointing directly down.

If I make a true position 0.1 | B | A | C | then they will be parallel but I am wasting money because they are over-tight dimensions to the datums.

true position 0.1 | B | does not control the angle at all but does control the pattern.

Any ideas?

 

[KENAT]

A composite tolerance may be appropriate.

That way you can roughly locate the pattern of holes on the part, but more closely tie the holes together.

Posting guidelines faq731-376

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(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[buchner]

Dear Kenat, thanks for replying.

I think that the composite will only tighten within the pattern but will not locate the pattern any better for the angle.

Maybe if I only composite
true position 2.0 | B | A | C |
true position 0.1 | B | A |
?

Then I am making one side tight - that corrects the angle but I am still tighter than I need.

buchner

 

[KENAT]

What drawing standards do you work to, ASME Y14.5M-1994?

Fully fleshed out I think if you just put datums A & C in the lower part of a composite it may do what you want.

Make sure and use a composite, not 2 FCF's.

There are folks on here a little better than me at the implications of composite tols, hopefully one of them will chime in.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Belanger]

Why not just use the symbol for parallelism and reference datums A and C? That symbol can certainly be applied to holes to control orientation to surfaces.

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

 

[pmarc]

I agree with what Kenat and John-Paul suggested. You could either specify:
- composite positional tolerance (common position symbol for both segments) with |dia. 2.0 |A|C|B| in upper segment and |dia. 0.1 |A|C| in lower segment;
or
- two separate FCF's with |pos|dia. 2.0 |A|C|B| in first FCF and |paral|dia. 0.1 |A|C| in second FCF.

The meaning of both would be pretty the same - upper segments would define less important requirement for location (+/- 1mm) of holes within the pattern, while lower segments would control parallelism of holes axes in more restrictive way (+/-0.05 mm).

Notice that I added diameter symbol in front of each tolerance values since cylindrical tolerance zones are more functional than cubicoidal in case of round holes / round pins assembly.