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View Full Version : Wonky spot in the steel? (grooves not consistent)



madwilliamflint
03-15-2011, 10:19 AM
Well THIS is odd. I have a round piece of 1018 that's about 0.3" in diameter and 3" long. I've chucked it up and, with a carbide insert tool, cut grooves every quarter inch or so, about 0.015 deep. For purely aesthetic reasons.

It was all going swimmingly until about 3/4 of the way down the piece (successive cuts being going from left to right, away from the chuck.)

Then, suddenly, the groove would only cut about 1/3 of the depth that the others had. I was certainly dialing in the right size, clearing away anything that might make the tool rub rather than cut against the piece and generally doing all the things I knew how to do. And I did have a live center in the tailstock.

My first thought was that I'd chipped away the bit in some way I couldn't quite see. So I first twisted it 60 degrees to get to a new surface... nothing. Then I changed the insert to a fresh one altogether... nothing.

I turned the piece around in the chuck, so the problematic groove was scarcely more than 1/2 of the tool width out, thinking maybe, despite the presence of the live center, I had a workpiece rigidity problem of some kind.

Nothing.

I'm flummoxed. The last 3 grooves cut are simply not as deep as they ought to be. I can feel the pressure as I dial in the tool. But it's "just not going". I WAS able to make a similar cut on the second piece, so I've eliminated "something suddenly going wrong with the setup."

Lathe speed is constant and very slow (don't have a tach. But it's not more than a couple hundred rpm.)

Any ideas?

Walter
03-15-2011, 10:34 AM
Mad,

Sounds as if you've covered the bases pretty well. About the only thing that comes to mind would be trying some kind of lubricant on the cut. That said, I'd agree with the wonky steel assessment. I've cut a good deal of pretty hard stuff with carbide, so I can't think of another good reason.

madwilliamflint
03-15-2011, 10:37 AM
Mad,

Sounds as if you've covered the bases pretty well. About the only thing that comes to mind would be trying some kind of lubricant on the cut. That said, I'd agree with the wonky steel assessment. I've cut a good deal of pretty hard stuff with carbide, so I can't think of another good reason.

Yeah. I'm about to write it off as "a design feature" because frankly, this is the aesthetic garnish after about 5 hours of work I don't have time to reproduce before gift time this Friday.

Weird the way it was just pushing back against the tool post.

DICKEYBIRD
03-15-2011, 11:10 AM
Did you try speeding up? Sounds like it's too slow to me. I had a similar problem although not grooving, just turning. I doubled the spindle speed and the insert was "happy" again.

madwilliamflint
03-15-2011, 11:21 AM
Did you try speeding up? Sounds like it's too slow to me. I had a similar problem although not grooving, just turning. I doubled the spindle speed and the insert was "happy" again.

Hmm. I didn't. I was a bit caught up in the fact that it was an inconsistent behavior at constant (well...equal) rpms, so I didn't think to speed it up. Plus I was trying to keep the sound down. But I'll give that a shot tonight. Does mean I'm going to have to sit there with 3 different grades of sandpaper for an hour again. But hey, what am I gonna do. I lack the kung-fu (and equipment) to get rid of chuck tool marks any other way.

Thanks o/

rmuell01
03-15-2011, 11:28 AM
sounds like the work piece was hardened at that point.

lakeside53
03-15-2011, 11:30 AM
Chuck marks? Wrap some brass shim around the part... for other softer material. I've even used small pieces of aluminum plate (with care!) between each jaw and the work.

Cutting? Not sure why it's inconstant, but check your tool height..

madwilliamflint
03-15-2011, 11:46 AM
sounds like the work piece was hardened at that point.

It does, doesn't it? Given my meager experience at a lathe it sure feels precisely like that. Though it's all out of the same bar of...

crap.

*hangs head in shame*

I'm a moron.

I'll bet I know what happened.

So this piece isn't "A" piece. It's two pieces, threaded together, upon which I was doing finishing work. I'd started several of these projects and had a number of unfinished bases and caps.

It's possible that I've encountered a cap I made out of that piece A36 structural that I bought 6 months ago, not knowing what I was doing.

That piece that behaved suspiciously like it had been pre-hardened.

Black_Moons
03-15-2011, 12:40 PM
0.3" x 3" long? Sounds like the part was just bending away from the cutting forces. Next time try using a tailstock, follow rest, and cut from right to left so you don't make it any more unstable where you have to be cutting.

madwilliamflint
03-15-2011, 12:42 PM
0.3" x 3" long? Sounds like the part was just bending away from the cutting forces. Next time try using a tailstock, follow rest, and cut from right to left so you don't make it any more unstable where you have to be cutting.

I had a live center in the tail stock and did try reversing the piece.

My money is on mismatching steel right now. Rookie mistake. But then... I'm a rookie.