Callouts on partial radial bolt patterns

[SwinnyGG]

Hey there gents.

I've been a long time lurker on this forum, and it has often answered questions I've had on interesting problems regarding how to call out specific features on drawings.

I'm working on a part today with a feature for which I've never been able to come up with a highly robust callout/dimension.

This part is an adapter flange which mates two parts. It contains two circular bolts patterns nested inside of each other, with dowel holes for location. Each pattern is 12 holes, equally spaced. The holes at the 12 and 6 o-clock positions are reamed dowel holes, with the other 10 places of each pattern either threaded or counterbored for a flush-fitting cap screw.

I can't say I've ever had a bad part arrive because a supplier didn't understand what was actually needed, but I'm curious if there's a defined way to call this out. I've gotten away with not adding any specific instructions regarding the interrupted pattern, but that's not really a robust practice in my opinion.

Has anyone had to deal with a callout of this type before?

Thanks in advance.

Also, I've attached a screen cap of part of the drawing to try and make this clear.

 

[drawoh]

jgKRI,

You have called up the tapped holes twice, and the counterbored holes not at all.

Leave out the text "BCD". Lots of people have no idea what it means. Without it, it is obvious what your diameter is applied to.

You are implying that the the holes are equally spaced. If you were to apply an angle between a set of holes like 12X[ ]30[°], you would make the spacing explicit.

Don't specify tap drills unless you are confident you know more about it than your machinist. Call up M10X1.5, and buy a thread gauge.

You have not applied tolerances to anything. I assume your drawing is preliminary, and you have not gotten around to this yet.

A lot of my points, above are pedantic. I understand your drawing, so it is not seriously wrong.

--
JHG

 

[SwinnyGG]

Thanks for the feedback.

This drawing was a quick hack-job to demonstrate the problem, not an actual part.

Big 'oops' on my part for calling out the same pattern twice...

I have used the 12x 30 deg callout before. I'm always looking for simpler/lighter/better callouts, as the parts I design typically incorporate this feature into a much more complicated part with a lot of dimms on one sheet.

Anyways, thanks for taking a look.