Cutting an angle in a bore

Simple question. If you bored, say, a 1" diameter into a part mounted on your lathe, and then wanted to do an accurate chamfer, how would you go about measuring it. Say you want to chamfer out at 10° and the resulting slope is to extend 1/4" into the bore. I know how to set up the tooling, BUT, how do I precisely measure the 1/4" "daylight point". Alternatively, I could simply figure the increase in diameter at the working end. (tan 10°x0.25)x2. Okay, so now I know that the new diameter should be

1.088". How do I measure that. Seems like measuring this larger diameter would end up to be an 'eyeball' job. My eyes are old.

Ideas with how to proceed would be greatly appreciated.


Ivan Vegvary

Reply to
Ivan Vegvary
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Same way you measure the diameter of a countersink. Put a ball into the hole and measure the height of the ball above the face of the bore. Do a bit of trig and you can derive the diameter of the countersink.

Regards, Marv

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You can do it with a 1-1/16 diameter bearing ball and a little trig.

If I didn't have a ball handy, I think I'd turn a hat-shaped gage. The small diameter corresponds to the diameter of the chamfer at depth equal to the length of the small diameter over the brim. Use a feeler gage under the brim of the hat as you approach full size to figure the final cut.

In other words, if the cham is to size, the brim will contact the face of the part while the small diameter is touching the chamfer.

Reply to
Ned Simmons

=EF=BF=BDSeems like measuring this larger diameter

Ivan Vegvary

Start by setting the compound rest very accurately. Then cut the chamfer deeper than needed. Determine with the Z axis feed the distance you cut the chamfer. Trim the oversize from the face of the piece you are cutting. Then the chamfer that you cut was precisely done and you have the dimensions. Or mesaure the dimensions with a dial indicator and do some math.

I would probably do the latter.

Bob AZ

Reply to
Bob AZ


You could make a male plug with the 10=B0 chamfer on it, put it in the bored hole and measure the protrusion, then stop cutting your chamfer when the plug goes in 0.250" further.

Rough out the plug and part in to 0.9" or so on the left end before setting the compound to 10=B0 so you can taper the plug and chamfer the hole without moving the compound.


Reply to
Jim Wilkins

Simple answer.

Set the compound to 10 degrees. touch off on the bore. touch off on the face. put a dial indicator on the Z axis ,, (carriage) mave the carriage into the chuck the amount that your lathe can handle on a cut and feed in the compound. Keep cutting until you move a 1/4 inch on the dial indicator.

If you have a carriage stop, set it while touching off the face with a

1/4 inch shim (allen wrenches work fine) between it and the carriage. Then do the same as above until you hit the carriage stop.


Reply to

Set compound rest for 10 degree angle. Adjust carriage until cutting tool JUST barely touches sharp inside corner, at closest approach with compound slide. Take a few cuts, advancing toward work with carriage, using dial indicator, DRO, or whatever, until carriage has moved 1/4" toward headstock. The chamfer should reach exactly 1/4" deep in the bore. Make sure not to move cross-slide during this procedure.


Reply to
Jon Elson

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