PM1236 Surface finish issues

L

linuxbatm

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Hello,
I recently took delivery of a 1236 lathe, and have been trying to get it set up over the last few weeks. So far I have leveled the bed to the ground, and mounted it on the feet provided by Matt. The issue is no matter what I turn, I end up with a very rough surface finish. I have tried many feed rates and RPMs on the spindle, but it seems to make little or no difference. Occasionally it will look slightly better, but never really smooth. The only previous lathe experience I have is from a 7x12 from harbor freight, so I am looking for some help here troubleshooting. After searching a bit I saw that some in the past have had motor issues, so I did pull the drive belts and run it under no load. It does seem to be getting rather hot with short amounts of runtime, plus it may be a bit noisy. I have attached a few pictures of cuts I have done, as well as a short video of the motor running.


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Hard to say. It might be the cutter or the material. Have you tried switching them? Give us an idea of speeds, feeds, cutter, stickout,
and workpiece material.
 
all your pieces look like aluminum stock not steel except the one on the left upper looks like steel , don't look bad to me
 
The picture shown of the steel is 2 fold, the narrower part is what it looks like when the machine makes a decent pass, however using the same settings without even turning the spindle off I brought it out to the larger part and you see how choppy the cut is. Doesnt seem to be any rhyme or reason to it. As far as spindle speeds I have tried anything from 500rpm to 1800rpm. Feeds I have tried .002/rev to .007/rev, as well as fast and also manually advancing the cutter at a variety of speeds. The stick out is no more than 2-3 inches. I have tried straight and slightly raked indexable cutters, both in HSS and carbide. The steel and the aluminum are just round stock from lowes I had laying around, not sure on what material they are exactly, but both turned pretty well on my mini-lathe.
 
Are you absolutely positive that your cutter is on center and not a tad high? Any steel you get at a hardware store is usually gummy garbage. When chasing down problems you want to rule out the variables, get some good steel to practice with, 12L14 would be my recommendation, turns like butter leaves a great finish.
 
linuxbatm said:
The picture shown of the steel is 2 fold, the narrower part is what it looks like when the machine makes a decent pass, however using the same settings without even turning the spindle off I brought it out to the larger part and you see how choppy the cut is.
Click to expand...

Based on this statement, the only thing that has changed is the SFPM when you move to the larger diameter. If you calculate what your SFPM is on the small diameter and make adjustment to your spindle RPM to accomplish the same SFPM on the larger diameter, theoretically, you should get the same finish. Give that a try if you haven't already.

Also, just based on what I hear in your video, I would say that your motor is indeed noisier than it should be. The noise doesn't sound mechanical (eg; bad bearings, etc.) to me. It sounds like an electrical issue. I can hear the centrifugal switch operate as the motor slows down after the power is shut off to it, so it would seem that mechanically that switch is operating properly. Check your supply voltage to the motor with a good VOM. It should be within about +/- 5% of the required nameplate voltage. Also, if you have an Amprobe (or ammeter) available, check the running current of the motor. It should be well under the FLA on the motor nameplate while running with no load.

Ted
 
Linux........
I have a PM1236, & have converted it to VFD & 3-phase. I also have had some surface finish issues; however, somewhat different than yours. But that is not the crux of this reply.
I listened to your video several times, & wondered about your motor. I re-purposed mine into a 2x72 belt grinder. So, I just went out to the shop & removed the belt and fired it up. The only difference is that I now have a 7 inch by 2.25 inch aluminum drive wheel attached. Based on what I can hear in your video, mine & yours sound very similar. So, unless both are bad, I would suspect that the motor is not the root of your problems.

Would it be possible for you to take some closer pics of the metal you have turned? It is really difficult for me to see what you are describing--finishwise.
I normally use position B5I with the 52 tooth gear for most fine (finish) turning. B5II for roughing.

I have tried different Carbide inserts, and several different styles of (homeground) HSS cutters. I have tried turning dry & with a few different types of fluids.
I just never get a finish as good as I did (on any material) when I owned a 9x20. This is not a complaint, just a fact.

BTW, the VFD & 3 phase motor was a significant (although expensive) improvement.

I totally agree with the poster who stated that the Big Box store steel is junk--makes great tent pegs, though.
Try locating some 12L14 steel. You will not regret it. Sources might include local machine shops (not automotive repair shops), or the online sellers.
Here is a link to a supplier that I have used successfully:

http://www.onlinemetals.com/merchant.cfm?pid=9561&step=4&showunits=inches&id=265&top_cat=197

One more thing. You stated that you used 2-3 inches of stickout. Based on the pics, that might be a bit excessive for the diameter of stock you used.
I doubt that the stickout caused all of your issues; however, it certainly did not help it.

Here is a link to the thread about my surface finish issues and the VFD install:

http://www.hobby-machinist.com/thre...6-long-post-kb-electronics-vfd-install.49178/

Keep us posted and best to you,
Jerry in Delaware
 
I don't have any experience with using lathes, but I recently purchased a PM-1236 in January and Im getting the same quality finish on my cold hammer forged barrels. I thought it was normal?
 
I replaced the standard V-belts with the green link belts. With the originals I could put a hand on the headstock and feel a slight vibration as mid range speeds. It went away with the link belts though I had to fiddle with tightness.
 
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