# PM1236 Surface finish issues



## linuxbatm (Mar 30, 2017)

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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## Bob Korves (Mar 30, 2017)

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.


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## Kernbigo (Mar 30, 2017)

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


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## linuxbatm (Mar 30, 2017)

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.


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## Doubleeboy (Mar 30, 2017)

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.


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## talvare (Mar 30, 2017)

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.



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


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## Kernbigo (Mar 31, 2017)

try your spindle speed around 250 and see what happens


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## Muskt (Mar 31, 2017)

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


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## CalRon (Mar 31, 2017)

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?


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## Steve M (Mar 31, 2017)

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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## cmantunes (Mar 31, 2017)

linuxbatm said:


> Hello,
> I recently took delivery of a 1236 lathe [...] I end up with a very rough surface finish.



Hmm, spindle preload (or lack thereof)? "Something" appears to be vibrating. Are you locking the compound?


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## Glenn Brooks (Mar 31, 2017)

As others have said, Hardware steel is definitely gummy and will give you a poor finish - as will most 1018 bought from a steel yard - although you can work with the latter if you have a really sharp and honed cutting edge.

You show one photo with wavey marks in the finish.  I have had similar results when thin diameter work protrudes out to far from the chuck.   I think the rule of thumb is support all work extending over 3 diameters from the chuck.  So 3/4" OD round stock - hold the end  with a Live center in the tailstock for any length over 2 1/4" .  Makes the work much more rigid and produces better finish.  

The other thing to try is sharpen your HSS tool bits periodically, including touching up the top(chip breaker area). And manually run the cutting edge over an oil stone.  Also round off the pointy end with a small radius - (1/32 to 1/16" r) to insure the cutting tip doesn't individually score the work, leaving randomly deeper cuts.  I took a close look at a couple of brazed carbide bits recently and learned they all have a tiny flat edge at the pointy end, causing a smooth finish with a flat overlapping cut, versus a series of tiny deep v cuts - that look and feel rough to the touch.  So look geometry also.

LAST thing that might help.  Put a dial indicator on your tool holder and watch the dial as you take a cut.  The tool itself should be rock steady. If not, if the tool moves even .001" in and out during the cut, you have something wrong with the cross feed screw and the bit will produce deeper then shallower cuts - resulting in a rough finish.  Maybe tighten up your cross feed thrust bearings. You have a new lathe, so wear likely not an issue, but it's very interesting to watch the dial indicator a couple of times to see what is happening with the tip of the tool.

Good luck. I am sure this  will sort itself out with a little experimentation.

Glenn


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## CalRon (Apr 1, 2017)

How do you lock the cross slide on a lathe with DRO?  The scale covers the set screw.  Im not sure if there is another way to lock it in place?


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## Glenn Brooks (Apr 1, 2017)

Cal Ron,  I have no experience at all with this machine, so may be all wet.  In your photo, are you sure the cross slide lock you point to, is actually intended to lock the cross slide.?  Usually this set screw is a gib tensioning screw, designed to position the gib to reduce side to side movement.  You could of course lock down the cross slide by over tightening, but normally just adjust the gib for finger free movement of the compound. On my machines the  cross slide screw and thrust bearings take the load and do not move of their accord.

The only time I lock down my cross slide is when taking a facing cut, across the work. Then I tighten a nut that bears through the apron against the ways.

Maybe PM machines are designed differently??

Glenn


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## CalRon (Apr 1, 2017)

I could be wrong, but that picture was taken straight from the owners manual that came with the lathe.  I will contact PM to see what they recommend.


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## darkzero (Apr 1, 2017)

I have a PM1236 also, yes that is the cross slide lock. I never use it anymore cause my DRO scale covers it now. I never have an issue with finishes like mentioned & having it unlocked. I do keep the compound slide locked though when not using it.


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## cmantunes (Apr 1, 2017)

darkzero said:


> I do keep the compound slide locked though when not using it.



The compound is more often than not the weakest link in terms of rigidity when it comes to hobby lathes. I replaced mine with a slab of steel and the results are nothing short of impressive.

In the picture below, you can see a piece of mystery (and very gummy) steel being turned to a nice shiny finish. This was my first cut after replacing the compound with a block of steel. Closer to the spindle, you can see my previous attempt with the compound installed.

View media item 96125


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## qualitymachinetools (Apr 1, 2017)

From what I can see, none of them look too bad other than that one piece of steel with the chatter in it?  Lots of good advice as always here.   As far as the cross slide lock, yes its covered by the DRO, but that wont matter with surface finish.     One thing to check, make sure the tool post is tight to the compound. Just had a few recently where the mounting nut was a little too high, and it wasnt clamping the tool post down tight. Anyone else who has a new 1236 too, we found it on a few of them in the last shipment. Think we got them all but might not have.


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