Page 1 of 1

OT lathe question

Posted: Fri Jan 25, 2019 7:31 pm
by Standing Elk
Hay guys, I have a early 1950 vintage Lablond 13 X 48 lathe. Lathe is in pretty good shape and is tight. The issue I am having is the top spindle speed is only 550 rpm. I am having problems making a really smooth finish when OD turning. I have played with my feed speeds and of course the slower I feed it the better the finish but it is never really nice and smooth like it should be. I am not a life long machinist but am not a newbie either. My tool height is correct, I have tried both high speed steel, sharpened to the correct angles and honed after sharpening and carbide inserts but still am unable to achieve a really smooth finish. I think some of it may be the junk steel that is available now days. I wonder about this because I chucked up an old model A rear axle that I had lying around and turned it down to use for another project and it turned really nice with a nice finish. So after rambling on here my question is, what would be the down side to changing the shiv on the motor and increasing the top speed to around 800 rpm? Any ideas would be welcome. Thanks

Re: OT lathe question

Posted: Fri Jan 25, 2019 8:08 pm
by Ruxstel24
Have you tried slowing the feed down ?

Re: OT lathe question

Posted: Fri Jan 25, 2019 8:29 pm
by George Andreasen
Don't fiddle with modifying spindle speeds until you find the actual problem.

On any gearbox style lathe, your feed speed (and hence, your finish) determines the result. Since the feed speed is determined by the finest thread setting, spindle speed doesn't affect it much. In fact, most of my ancient machinist books recommend the highest spindle speed and a slow feed speed with a tool sharpened with a whetstone. I would recommend that you visit the "Practical Machinist" website and go to the antique section. Ask for help there, and you'll get some excellent advice from many old timers who know the machines inside and out.

Think you've got problems? I spent the better part of six months rebuilding a Hendey cone head (flat belt) lathe back to truth, only to find out that my finest feed was 80 t.p.i. :shock: ! I went through the same routine as you, playing with tool angles, etc. and found the best results were with a healthy round radius on the tool and razor sharp edges. That reduced the "threading" effect of a narrower radius, but it's still not perfect. Suits my needs though. If I need a really "perfect" finish, out comes the tool post grinder with a fine stone! :D

Re: OT lathe question

Posted: Fri Jan 25, 2019 9:20 pm
by Dan McEachern
You will find it difficult to get a good finish on most any steel part with carbide unless you can get the surface speed up around 300-400 feet/min.

Consider changing the size of the motor pulley to increase your top speed. Those old leblonds are great machines just not made for carbide turning on smaller diameters. You don't say what your junk steel is, but you might well be correct if you are turning Chinese water pipe or some such material.

Re: OT lathe question

Posted: Fri Jan 25, 2019 10:06 pm
by Flathead
Using cutting oil will probably help

Re: OT lathe question

Posted: Fri Jan 25, 2019 10:28 pm
by Scott_Conger
I believe much of your problem is in the steel you're trying to cut. So long as you're not welding it, 12L14 if fabulous stuff to turn; 1018 if you're going to weld it, or case harden it; 1045 if you wish to harden it (but is not too great for lathe work...just thought I throw it in for info). Different steels are for different applications...just picking up a rusty rod off of grandpa's barn floor and expecting it to turn nicely would be like making a canoe out of pecky cypress and expecting a dry trip...some things just are not meant to be.

If you are in a city big enough to have a scrap yard, go there and look for a barrel of nicely turned identical parts that have been scrapped. This will have come from a screw machine shop and the stuff they use is perfect for home shop use...you can be nearly guaranteed that anything of any useful size that is pulled from that barrel will turn exceptionally well.

In the event that you are not able to frequent a scrap yard, a place like this will be your best bet: https://www.onlinemetals.com/merchant.c ... op_cat=197

Re: OT lathe question

Posted: Fri Jan 25, 2019 10:50 pm
by Tmodelt
Are you using a live or dead center in the tailstock? If not, you may be experiencing vibration of the piece being turned.

I also think like earlier answers and your thought that cheap steel may be "tearing" vs cutting.

In a past life I was a machinist. You might be surprised at what a file and / or Emory cloth would clean up.

Re: OT lathe question

Posted: Sat Jan 26, 2019 2:14 am
by Mark Gregush
You might be surprised at what a file and / or Emory cloth would clean up..I did the bushing area finishing on my shortened drive shaft that way. I have had the worst luck doing anything with drill rod. I wish I could remember which I used, but it might have been the 1018, nice to work with.

Re: OT lathe question

Posted: Sat Jan 26, 2019 9:50 am
by gridleak
not familiar with the lablond but a buddy could not slow his lathe down. he did not know his lathe had a back gear.

Re: OT lathe question

Posted: Sat Jan 26, 2019 1:07 pm
by Dave Sullivan
My experience is, you can't hardly machine A36 steel smooth, made in China, or not. By far the most common steel "lying around". Dave in Bellingham,WA

Re: OT lathe question

Posted: Sat Jan 26, 2019 1:21 pm
by BobD
Cold rolled steel (e.g.1018) tends to tear when turning. Surface finish can be improved as others have stated by application of emery cloth or tool post grinding.

Steels I have found that turn nicely include 4000 series alloy, 12L14 and A2 tool steel.

550 Rpm max spindle speed is quite slow. Good for turning large diameters. I don’t see any reason not to try increasing the spindle speed to 800 rpm for smaller diameter turning.

Re: OT lathe question

Posted: Sat Jan 26, 2019 5:03 pm
by Jerry VanOoteghem
Does your cutting tool have any kind of tip radius, or are you sharpening it to a point? Try using a .015 - .030 tip radius, along with a little bit of cutting oil. Also, check the ways on your compound to check for any slop. The gibs should be adjusted for just a slight drag.

Re: OT lathe question

Posted: Sat Jan 26, 2019 7:36 pm
by LVRR2095
I find that I can get an improved finish if I take a second pass without touching the settings. Basically you are cutting a fine thread. If you take a second final pass you will knock off the tops off of the “threads.”
And the posts that recommend 12L14 (Ledloy) are right on the money.

Keith