PM-1228 Compound "Stickiness"

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Aurelius

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Hi everybody, hope you can help me out on this one.
I've had my 1228 for a little over a year now. I started knowing very little and have been building my skills.
Recently, I tried using the compound to cut a taper. Prior to this, I had literally never moved the compound for anything I did. When I attempted the cut, I immediately noticed that the compound was a lot tighter than the cross slide (which is buttery smooth) and there was a noticeable banding on the cut. This directly correlated to a tightness that happens at one point in the rotation of the handwheel. I'm not sure if I am describing this correctly but, as I turn the wheel, it starts tightening up at about zero on the scale ring, get tightest at 30 and then loosens up to it's loosest around 70. I know those number are arbitrary but that just happens to be where I have the scale ring.
Any ideas what could be causing this and, more importantly, what I can do to fix it?
Thanks!
 
Besides a bent screw there are a couple other things it could be but you'll need to disassemble it to pinpoint the problem
 
Ok, so to take the compound off I just need to:
  • take off the handwheel nut
  • pull off the handwheel and scale ring
  • remove the two screws holding the bracket and remove the bracket and thrust bearing
  • unscrew the lead screw
Did I miss anything?
Also, do I need to take the compound off the crosslide or is it ok to leave it on?
Thanks
 
So I took the compound apart last night.
There were a couple of metal shavings in the threads but nothing major. The thread itself seems to be straight and, while Ihad it out, I took off a bit of a burr on the leading edge of the screw and also around the edge of the scale ring. When I put it back together, I checked the tightness of the wheel as I went and dialed it in as I tightened the nut. I didn't torque it down as much as the factory apparently did and it is now actually pretty good. The only issue I am still having is at the end of the travel when the compound is mostly extended, I am getting a scraping noise that sounds like the scale ring rubbing against something. I will keep an eye out but do not think that requires any attention right now.
Thank you everyone for the help on this.
 
At the moment, I have an LMS 8.5”X20.
It does the same thing you describe & it SUCKS!!!
My compound lead screw is most definitely not concentric. I had LMS send me a new lead screw for the compound. The new lead screw they sent, exact same problem!
When I roll either of the lead screws across my surface plate, you really can’t see what’s happening. When I reinstall it into the compound & turn it, you can see what’s wrong very clearly. I set up my indicator to measure the deviation & both lead screws (original & its replacement) run out .0025!
When I put the compound all back together & reinstall it on the lathe you can watch the entire compound slide rise & fall when turning the hand wheel. Sort of like a rocking motion. This transfers to any part I would try to turn a taper on as a rippled or ribbed appearance & you can most definitely see & feel it.
I don’t even try anymore.
If I had the steady & follow rests for the LMS lathe, I would just make a new lead screw for its compound. However, I am not buying more tooling for that lathe as I have a 1340GT on order that should be here soon. When it shows up & I get it running, I’ll make a new compound lead screw for the LMS lathe & make sure it works properly before selling it. I feel it’s the right thing to do.
Seriously, I would call & talk to someone at PM about this. They might be able to send you a replacement lead screw for your compound & you may get actually get one that doesn’t run out (unlike the replacement I received from LMS).
I hope you get this worked out, because that’s a horrible problem to have with a lathe. It takes so much away from it. It’s not just the problem of it making the rippled appearance/feel on parts, it also affects your tool height depending on where the compound’s hand wheel is. To avoid tool height problems, I made my backlash nut tighter than normal (within reason of course) & I never touch it.

Best of luck

Randall

Edit:
I see that you’ve got your compound working better (sorry, I just now continued my post that I started at 4:45am). So your problem was much simpler that my compound on the LMS. Good to hear & I’m glad you got it sorted out.
 
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I have PM1340GT that has a similar problem with the compound (tight at about 60% extension). I have disassembled, cleaned, lubricated, adjusted the gibs with no effect. These PM lathes are not that good. I suspect mine was not ground and scraped properly.
 
@RandallsRaceShop Sorry to hear you had such trouble. I had been looking at the LMS lathe but had been advised against it. Sorry to hear you had such trouble. Honestly, with the 1340 on the way, I'm not sure what you'd use it for once the bigger one arrives so (hopefully) it's just a matter of making due until then.

@bretthl I knew what I was getting into with the PM machine. Is it the best thign ever made? By no means. I had space and power considerations so the 1228 was actually in a sweet spot as far as compromises and having actual customer service to help me out when I do inevitably run into problems certainly makes up for some of the shortcomings. Also, I'm working almost exclusively in plastics and softer metals so any shortfalls in rigidity do not have as big an impact for me.
 
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