Is this normal turning on a lathe?

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

Moderators: Harold_V, GlennW

User avatar
Vern2
Posts: 283
Joined: Wed Jan 13, 2010 11:31 am
Location: Arizona
Contact:

Is this normal turning on a lathe?

Post by Vern2 » Wed Jun 16, 2010 5:54 pm

When turning a lead screw down with a Sieg 9x20.

I'd set the crossslide for a .003 cut, which would realy be .006. I'd take a cut, then back off tool, reset tool to right. Now reset the cross slide to the exact same setting. The next cut with same setting would take a .003 cut. I would measure it. Now, do it again, with moving back to the same setting it would take more metal off. What I'm saying I would take more cuts without advancing the cutting tool on each pass, with the same cross slide setting. I'd get down to 4th pass and it's still taking smaller and small cuts What's going on?

I'd just say to myself, I should have bought a bigger stronger lathe.

Edit: Yes, the one I broke. Also I'm using carbide indexes.

Vern
Last edited by Vern2 on Wed Jun 16, 2010 10:26 pm, edited 2 times in total.

EdK
Posts: 688
Joined: Tue Apr 13, 2010 6:20 am
Location: Minnesota

Re: Is this normal turning on a lathe?

Post by EdK » Wed Jun 16, 2010 6:41 pm

Vern,

If I'm understanding you correctly, I think you're dealing with spring-back and slop in the cross slide. I also have a 9x20 lathe and I'm not very impressed with it at all. My mini-lathe is designed better than the 9x20. Luckily I have a nice 14x40 lathe just waiting for a stand to be welded up then I'll be a happy camper. The 9x20 will go to a local farmer that can't afford to buy a lathe so I'm donating it to him. :D

Ed
Vectrax 14x40 lathe, Enco RF-45 clone mill, MillerMatic 180 MIG.

User avatar
GlennW
Posts: 6811
Joined: Sun Apr 15, 2007 9:23 am
Location: Florida

Re: Is this normal turning on a lathe?

Post by GlennW » Wed Jun 16, 2010 8:04 pm

Are you using a sharp HSS tool bit that is set excatly on center?

Didn't you break the 9X20 and just buy a larger HF lathe?
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

kenh
Posts: 24
Joined: Sat Jan 28, 2006 9:27 pm
Location: bonners ferry,id

Re: Is this normal turning on a lathe?

Post by kenh » Wed Jun 16, 2010 9:27 pm

Gibbs in cross slide and compound tight?

Small diameter stock + large tool = plenty of spring!

I made an adapter so I can use a 1/8" tool if need be. Looks cute in a BXA holder on a 14X40!

User avatar
Vern2
Posts: 283
Joined: Wed Jan 13, 2010 11:31 am
Location: Arizona
Contact:

Re: Is this normal turning on a lathe?

Post by Vern2 » Wed Jun 16, 2010 10:22 pm

Gibbs in cross slide and compound tight very tight. Can't turn compound handle, don't use it. Cross slide handle hard to turn. I tried to get the slop out of of everything Even tightened down clamps on ways. I was 1 1/2 inch away from dead head in tail stock, with it tight and locked.

Hope the 12x37 coming friday with m3 at tail stock will be a little stronger. Have all the steel for table. Saturday, steel stand and leveling legs should be done. Then build 2 ... 3 inch "t" nut for AXA QCTP, Drill and tap with 9/16, and bolt it on.

JackF
Posts: 1564
Joined: Mon Jan 26, 2009 3:56 pm
Location: Caldwell, Idaho

Re: Is this normal turning on a lathe?

Post by JackF » Wed Jun 16, 2010 11:04 pm

Ah yes, the old spring back. I am still a novice at this hobby but I learned right away about spring. I would take some heavy cuts (for me) to get close to final size, Get to about .005 or .006 then set the dial to maybe .004 to sneak up on it and ... what happened.... I'm 2-3 thou under. Took the .004 + the spring. I should have taken a spring cut or two at .010 before sneaking up on the final size. Even the Graziano Sag 20 I have run on occasion had spring. BTW, any cross slide dial I used read diameter so .003 on the dial meant a .0015 cut for a total .003 removed from the diameter, not .006.

Jack.

User avatar
mechanicalmagic
Posts: 1431
Joined: Sun Nov 04, 2007 12:11 am
Location: Pleasanton, CA Land of perfect weather

Re: Is this normal turning on a lathe?

Post by mechanicalmagic » Wed Jun 16, 2010 11:25 pm

I think your biggest problem is the CARBIDE.

Carbide IS NOT DESIGNED for cuts that small. They have a minute radius on the cutting tip, it's needed to prevent chipping when taking a reasonable cut. (Unless you have specially honed Carbide.)

Yes, spring is a common issue, but a SHARP HSS tool should resolve your problem.

Dave J.
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.

Harold_V
Posts: 17938
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Is this normal turning on a lathe?

Post by Harold_V » Thu Jun 17, 2010 12:01 am

Vern2 wrote:Also I'm using carbide indexes.
Fatal mistake, especially if you are using negative rake tooling. It simply is not suited to that kind of work.

Learn to grind HSS and to apply it properly. Carbide is rarely the answer for light duty machining, and should NEVER be used as a dodge to avoid learning to grind tools properly. That is likely one of the biggest mistakes you can make if you intend to learn machining.

Give this some thought. Owning a Selmer Paris alto saxophone will not allow you to play like Paul Desmond. And so it is with carbide.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

User avatar
Dave_C
Posts: 960
Joined: Mon Apr 21, 2008 10:34 am
Location: Springfield. MO.

Re: Is this normal turning on a lathe?

Post by Dave_C » Thu Jun 17, 2010 8:51 am

Vern2,

I share your frustration with trying to take light cuts. I bought a new Grizzly G4003 Gunsmith lathe about two years ago and I also bought carbide inserts to start with.

After going through the same frustration with my final cuts I learned how to grind HSS and have been doing so ever since. I had to buy the correct grinding wheels to do it but it was worth it.

What I discovered was most of the inserts I was buying did not have a very sharp edge, not like what I could produce by grinding good HSS myself and honing with a diamond stone. I still use the carbide inserts for heavy cuts and turn chips so hot you don't want them to touch any part of your body but I'm doing most of my finish work with HSS.

Even though my lathe is a 12 X 36 it too has some spring back when using inserts. I wish the machine had less flex but I most likely can not afford the machine that has none!

I've learned to cut, measure, cut, measure and so forth. By taking the same depth of cut each time and seeing the repeat in material reduction I can approach the final cut well enough to hit a half thou for a press fit. Leaving .003 for a final cut just won't work on these machine as they are not solid enough. A good heavy machine, yeah, but mine, no way!

Dave C.
I learn something new every day! Problem is I forget two.

User avatar
Vern2
Posts: 283
Joined: Wed Jan 13, 2010 11:31 am
Location: Arizona
Contact:

Re: Is this normal turning on a lathe?

Post by Vern2 » Thu Jun 17, 2010 9:53 am

Thanks drdave,

That's what I was doing, cut measure, cut measure, cut measure. I was trying to get to the point I could control what was going on. Or teaching myself control over facing and how good or bad the 9x20 was. Speed has a lot to do with it, I guess, maybe I wasn't learning anything. I was running lathe as slow, as it would go. That helped when threading, which was almost a complete failure. So tomorrow I've got a "Will Call" with Consolided Fright to pickup my 12x37 Sieg at there dock. I hope it works out better then the 9x20.

Vern

User avatar
rudd
Posts: 677
Joined: Wed Dec 12, 2007 11:21 pm
Location: savannah ga.

Re: Is this normal turning on a lathe?

Post by rudd » Thu Jun 17, 2010 8:39 pm

Vern,

You can have the stoutest lathe in the world and the material in it will still spring. I think Harold and DaveO have most of your problem nailed, it's the inserts and spring in the material. Also, you said you were going as slow as the lathe would go - rpms or feed? If you are running low RPM's - i.e., low surface feet per minute compared to what the material wants, you're not going to get the best results.

On threading, I find the faster I go, the better the finish. I have to admit I did buy one of those lay-down insert threading tools - and I like it. Getting the correct geometry on the end of the HSS tool was taking alot of time, and did not work so well for fine threads.

I use inserts for heavy cutting, but as Harold has said, since I know how to grind HSS, I know what the problems are with insert geometry. I still use HSS when I need to take off a thou or two. I like the inserts for hogging and working with cast iron. If you are threading mild steel or the stuff you get at home stores that they call steel (Actually an alloy of bubble gum and anything else that didn't get out of the melting pot) you are going to hate threading, or turning in general. Grab some 12L14 from one of the online houses and give it a try for practicing.

User avatar
Vern2
Posts: 283
Joined: Wed Jan 13, 2010 11:31 am
Location: Arizona
Contact:

Re: Is this normal turning on a lathe?

Post by Vern2 » Thu Jun 17, 2010 11:16 pm

I may have the use of one arm, but I'm an artist when it comes to working with grinders and steel. I've just not tried to make my own hss tool bit yet. Most of the stuff I've sold, but I'd make side locks for percussion mussel loaders by hand. No mill, no lathe. Drill press, file and a lot of work.

I guess I'm pushing myself on the project I'm on too hard, to stand at the grinder and make cutting bits. Just screw on another index and try again. Today I recieved the wrong 12x37 lathe from HF. There sending another and taking back the wrong one. I'm on my 5th metal band saw (5). My second Mill and now going on my second lathe. Things have to start turning around soon! I keep hitting the wall, not giving up!

Vern

Post Reply