rings in work piece

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

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Re: rings in work piece

Post by BadDog » Wed Mar 14, 2018 8:13 pm

I got the same lecture ;) from Harold when I joined right after getting my first lathe, a Griz 9x19 G4000 (aka "the noodle"). I went straight for the carbide for the same reason, something along the lines of "one less thing I have to worry about". But with Harrolds ham fisted, er, I mean "gentle persuasion", I got myself a proper wheel on my bench grinder and learned to sharpen my own. Probably the single best skill I learned since starting down this dark path. That skill served me very well through my progression of machines right up to my old Rockwell 11x37. Along about then I started using carbide as needed, particularly for hard and/or abrasive steels and irons. But it's top speed was only 1500 rpm, and it was really too slow for some of the small stuff I was doing, so HSS stayed at the forefront in my shop. My current lathe lives and breathes for carbide, and having accumulated a good stock at auctions and such, I most often do use carbide now. But there are still MANY cases where HSS serves best even now, not the least of which is that I would go broke trying to acquire enough insert holders to cover all needs. So I would guess close to half of my 20 odd CXA tool blocks have HSS mounted in them right now.
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Re: rings in work piece

Post by RMinMN » Thu Mar 15, 2018 6:14 am

I've gone somewhat the other way as I found that the carbide inserts are a compromise with commercial use in mind where speed of cutting is the main driving point and longevity is a close second. With those constraints, the carbide is chosen as it wears well but it isn't usually as sharp as a lower powered, slower speed lathe would like. A honing with a diamond stone can bring the edge of the carbides much sharper and they cut better but then one has to contend with the possibility of breaking the edge since carbide is more brittle. That requires a lower relief angle as the edge needs more support but since it is used in a lower powered machine, one isn't planning on such a high feed rate that the relief angle needs to be so large.

Inserts used in industry work well too because it only takes a few seconds to remove one to turn to a new edge or replace it as necessary and the new one will cut just as well (or poorly) as the one it replaced had when new. Sharpening takes more time and time equates to money in industry. As a hobbyist, time isn't the driving force it is in industry. Several hobbyist have found that the edge of a carbide insert can be fairly quickly restored for cost saving or to keep going on a project while waiting tor replacement inserts to arrive.

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Re: rings in work piece

Post by senorgilamonster » Thu Mar 15, 2018 11:16 am

Oh, I went back and checked my gear setting and it is in low, so I have been turning at something like 700 - 900 rpm.

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Re: rings in work piece

Post by stephenc » Thu Mar 15, 2018 12:13 pm

When I got my lathe I knew absolutely nothing about machine tools .
I didn't know a thing about cutting tools and I had zero budget left after buying the lathe .
So I bought a box of the harbor frieght brazed carbide tools and a box of assorted hss blanks .
In short order I had chipped broke or otherwise ruined the brazed carbide so I set my sights on the hss blanks and very quickly learned something .

Hss is very forgiving, if you grind something that looks like it might cut chances are that it will cut .
I didn't know a darn thing about angles and still don't give them much consideration,
What I did understand was clearance, having a tool cut means it can't rub the part
The very first tool I ground cut ..and it did a pretty decent job .

After that things kind of fell into place once I started playing around to see what worked and what didn't .

Short version ... fire up the grinder and start making a tool . It's not all that hard and it doesn't have to be perfect to work

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Re: rings in work piece

Post by BadDog » Thu Mar 15, 2018 6:10 pm

Regarding "looks like it will cut", the first thing to keep in mind is sufficient clearance in the direction of feed (and/or not rubbing on the exit side). That and a sharp edge will get you cutting. Then you can sort out the back rake and side rake to ease the cut, particularly on light DOC, and varies by material. Now you can start thinking about lead angle, and maybe thinking about radius points and rear clearance angles. Finally, when you get everything working nicely and are tired of the rats nest of long stringy chips (worse for some materials/bits than others), you can add in chip breakers, and work out how that fits with various rake angles and point radius. Boring bits and ID threading should probably wait till you get OD turning bits sorted as they add in a whole lot more things to think about, and less margin of error for success.
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Re: rings in work piece

Post by SteveM » Fri Mar 16, 2018 12:50 pm

One tip I learned about tool rubbing:
Mark your tool with sharpie on the faces that might be rubbing - if the sharpie wears off, you are rubbing.


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Re: rings in work piece

Post by Glenn Brooks » Thu Apr 19, 2018 10:31 pm

Did you ever resolve this rings in the work problem with your lathe?

Probably Has nothing to do with HSS or carbide, etc. Pretty clearly it seems your compound screw and nut are worn. Causing all the variation in your cut. I had the same issue with a nicely maintained Southbend Fourteen. Replaced the screw and nut and all the problems went away.

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Re: rings in work piece

Post by Ray Wangler » Wed Jan 02, 2019 4:38 pm

Senior, did you ever figure out the rings? I noticed "lead screw upgrade" in the original post. I once had a 14" Rockwell lathe. Not a bad machine. The carriage casting was open around the lead screw, so I (in my infinite wisdom) made bushings that were a few thou bigger ID than the lead screw OD. No problem right? Had rings......poor surface. Found later, after much gnashing of teeth, that the small amount of nearly unnoticeable wear near the headstock was lowering the carriage just enough to push the lead screw down and cause it to move ever so slightly and worse near the headstock. Knocked the bushings back out like the original designers had it, and all was well. So! In your case, I'd look for something bumping the carriage in the drive. Of course after changing material and cutting tools as those are more likely to be the problem..

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Re: rings in work piece

Post by tornitore45 » Thu Jan 03, 2019 10:28 am

2) frequent stops to let the material cool down.
Something is definitively wrong if your machining is getting the part so hot that needs cooling down.
Industrial metal removal rate calls for coolant. When one puts 5HP between part and tool heat is a problem.
Hobby metal removal rates on a small machine like yours (7x10) should hardly generate enough heat to hurt.

Rubbing and or "plowing" metal generate substantially more heat than cutting/shearing.
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Re: rings in work piece

Post by pete » Fri Jan 04, 2019 4:07 pm

He mentioned on page one he found a loose cross slide gib and that fixed the problem.

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Re: rings in work piece

Post by liveaboard » Sat Jan 05, 2019 9:37 am

I had the same problem when I first started using my ancient lathe, and the same solution too; tightened the gib slide screws a touch, and all was ok.
It was the compound slide, and the movement of the slide was due to exerted pressure on its little crank.

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