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How do you call out a square counterbore?

How do you call out a square counterbore?

(OP)
I have a cast part with a square counterbore on the the backside of a hole so the nut will seat against the face. I am working on getting my GD&T skills up to speed though wondering the best way to define this feature? Can you still use a diameter position tolerance just as you would with a circle counterbore or would it be better to use a profile tolerance?

RE: How do you call out a square counterbore?

apMechE,

Counterbores are round. If your feature is not round, it is not a counterbore. I recommend drawing it out.

--
JHG

RE: How do you call out a square counterbore?

(OP)
drawoh,

Attached is a screenshot. From your statement I am guessing we add a profile tolerance and relate it back to the primary datums along with a parallel tolerance to the opposing face or a perpendicular tolerance to the hole?

RE: How do you call out a square counterbore?

You treat a feature like this in exactly the same way you would treat any other pocket- this one just happens to have a hole through the floor of the pocket.

What's critical for you is which feature drives position- from your description it sounds like the position of the hole is most critical relative the part, and the position of the pocket is critical only in relation to the hole, not to the rest of the part.

That sets up your chain of references. Hole relative to part datums, pocket dims relative to hole.

RE: How do you call out a square counterbore?

apMechE,

You apply whatever tolerances make your pocket work.

--
JHG

RE: How do you call out a square counterbore?

apMechE,
Unless that pocket is produced just by casting , your machinist is going to hate you , This is going to require a long skinny end mill which will whip around. A bigger bottom radius may help.
B.E.

You are judged not by what you know, but by what you can do.

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