I'd suspect the heel, too. Try an hss bit (which would have more
relief) and see it anything is different.
I don't know what size insert you are using, but with a relief of
only 7° or so, the heel could easily be rubbing.
I have pretty much quit using carbides for boring for that reason.
Especially for small holes.

Pete Stanaitis
-----------------

Wes wrote:
I just had something weird happen.

I was boring a .475 deep .624 dia hole in some 11L14 on my lathe.

Work was held in a 4 jaw chuck, boring tool was a boring bar for my Bridgeport's offset
boring head, one of those brazed carbide bars.

I noticed I'd start taking a cut and after a certain distance in, I'd start hearing
chatter. I removed the tool, double checked it was set it on centerline, and even gave
the cutting edge a light honing to touch it up. Didn't help any. I also looked for tool
rub as in insufficent relief.

Anyway, as I worked away, it became apparent my finishing cuts where not tracking the
amount of infeed. I was using a telescoping gage and mic to measure.

Getting near where I thought I should be at the right diameter, I tried the hex bushing
that I planned to press into the hole and it went in about 1/8". Now that is weird. Why
only that far?

On each pass, I had stopped the lathe, and retracted the carriage w/o backing off the
cross feed. That little scratch that can result isn't an issue since I'm pressing
something in.

I decided to dismount the work and use the bushing to check the back side and that was at
least 0.006" oversize.

The ways do not have detectable wear. This isn't a whooped lathe.

So what the heck happened? 11L14 generally cuts like butter and I've used a lot of the
stuff.

I've turned a shorter piece from the same round w/o issues using the same setup and I made
the same piece I was making tonight earlier.

For those that remember my recent post about screwing up a barrel plate by tapping the
wrong sized holes, this was the replacement.

Wes