Using note callouts for holes with positional tolerances

[Gilmiril]

Our company has always called out hole patterns for flanges using leader notes such as:

1.25 DIA THRU
8 HOLES ON 8.00 DIA BC
EQ SP AT 45 DEG APART

That was for directly toleranced dimensions, but now we're switching to positional tolerancing for these. It seems to me that the dimensions for the BCD and angular spacing would be best shown directly in the drawing view as basic, but our management still wants to use the same notations but with basic symbols added. This means the 8.00 DIA and 45 DEG would have boxes around them within the existing leader notes (and of course a positional tolerance control frame added).

Is this acceptable practice?

 

[KENAT]

I'd prefer to see directly dimensioned as you suggest but doesn't necessarily mean a note can't be made to work - however yours as is may not be ideal.

EQ SP should be EQLSP per ASME Y14.38a-2002 if you care.

BC means specifically Bolt Circle per ASME Y14.38a-2002 if you care - Pitch Diameter (PD) may arguable more correct for a hole pattern.

Saying Equally Spaced & 8X 45 is arguably dual dimensioning, and I've got a feeling the meaning of Equally Spaced isn't explicitly supported in the dimensioning spec but I can't recall for sure.

Maybe something like:

8X Ø 1.25 THRU
[Ø 8.00] PD
[8X 45°]

[] is meant to be the box as in basic dims.

I assume you have a FCF with appropriate datums or some such to indicate what the PD is centered on.

I think this or similar has been discussed before you may be able to find a previous thread.

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[drawoh]

Gilmiril,

Will the dimensions in your note be associative to the actual feature?

Practise in ASME Y14.5 is to apply dimensions directly to the pitch circle and to the angle. Not everyone knows what BC, BCD and PC mean. The directly applied dimensions are clear, unambiguous, associative, do not require good knowledge of English initialisms, and they can be boxed as per ASME 14.5.

--
JHG

 

[Gilmiril]

Thanks for the feedback (including the extra clarifications). And I completely agree that the most unambiguous way to dimension the pitch circle is to directly dimension it; as we farm out more machining overseas, our use of BC and EQ SP may not be as clearly understood as we think it is.

 

[CheckerHater]

BTW, there is school of thought out there saying that EQUALLY SPACED (regardless of how you shorten it) should be made BASIC as well:

 

[drawoh]

CheckerHater,

What is wrong with boxing 6X 60[°]?

--
JHG

 

[ctopher]

Also...
If:
1.25 DIA THRU
8 HOLES ON 8.00 DIA BC
EQ SP AT 45 DEG APART

You don't need "45 DEG APART" if they are EQ SP.
Should be one or the other.

Chris, CSWA
SolidWorks 13
ctopher's home
SolidWorks Legion

 

[Tunalover]

I don't think that the term "pitch diameter" can apply to a bolt circle group. It only has meaning with regard to screw threads.


Tunalover

 

[Gilmiril]

Only screw threads? What about gears?

As for circular patterns of holes, in North America, in my experience, this is typically called a bolt circle or a circle of centers. But on drawings originating in Europe, I commonly see pitch circle, and the abbreviation PCD (pitch circle diameter) in leader notes.

 

[KENAT]

Hmm, tuna you've got me second guessing myself over the PD and you're correct.

PD= Pitch Diameter - this would be on screw threads etc. as you say.

PC = Pitch Circle - this is what I meant to suggest.

both are in ASME Y14.38 I just looked up and posted the wrong one - sorry.

8X Ø 1.25 THRU
[Ø 8.00] PC
[8X 45°]

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[Tunalover]

Gilmiril: You are right. PD applies to gears as well. My oversight.

Tunalover