Saddle "stiction"

sru_tx

sru_tx

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I'm pretty much a newbie with my PM-1228. I'm the 3rd owner of this tool but it's in very good condition. My issue is with the jerky manual movement of my saddle. I see videos of people using various lathes and see them traversing their saddle easily and smoothly, oftimes one-handed. I also see people turning a diameter manually (not powerfeed) very smooth and with control. I can't seem to do that on my machine. When I move the saddle to the tailstock to get it out of the way it can be moved quickly with a bit of resistance on the handwheel using two hands; however, if I would want to turn down a cylinder diameter manually, the carriage has enough sticky friction (stiction) that it hops its way along.

I've lubricated the saddle via the oilers and brushed on the tops and bottoms of the ways. It helps a bit but it still doesn't move smoothly and easily enough that I could get an even and consistent feed rate. I'm using Mobil Synthetic lubricant, 75W-90 as my way oil.

I've checked all of the gibs and have even tried it with the gibs way too loose. Still not smooth and easy.

Are my expectations too high? The only way to turn a smooth even-fed cylinder is via the powerfeed OR the compound.
Is there an adjustment I'm missing?
Is the Mobil 75W-90 not a good choice for way lube?

thanks.

steve
 
When I have seen stiction like that it was because the gibs were too tight. If you are seeing it with loose gibs, you probably have a rough surface or surfaces in the ways. I would pull the cross slide off and closely examine the mating surfaces. I would also check the lead screw and nut. Overtightening the backlash compensation can increase the friction enough to cause stiction, especially if you have a dry lead screw.
 
The lubricant that you are using is absolutely inappropriate, it is basically a gear lubricant and much too heavy; you should be using a way lubricant, such as the Mobil Vactra series. https://www.mobil.com/en-us/industrial/pds/gl-xx-mobil-vactra-oil-numbered-series
It would seem that Vactra #2 would be the appropriate choice.
I agree that the saddle should be removed for inspection, something is not right. First I would look into the adjustment of the gib at the rear of the saddle, it need not be adjusted tight or even snug.
 
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might also try removing the way wipers and see if there is crude packed behind them before removing the saddle. Mike
 
Agreed with @benmychree , that oil is way too heavy. Actual way oil is surprisingly light and gives little gumption, so you're struggling with cold, heavy gear oil.
 
Also check the underside surfaces of the ways where the front and rear carriage gibs ride for factory paint remnants and built up crud. Those surfaces should be clean and lightly oiled.

Tom
 
Here's another possibility ... the rack and pinion. When you turn the handwheel, it rotates a pinion on the back of the saddle. The pinion engages a rack mounted below the front ways. Check both the rack and pinion for contamination and make sure they're lubricated. Also check the pinion for missing or malformed teeth.

If both look OK, you'll probably have to pull off the apron, then check the bearings in which the pinion shaft rides, check if the pinion shaft is bent, etc. If the handwheel is hard to turn when the apron is off, there's something bad going on inside the apron.

If the handwheel and pinion turn freely when the apron is off, check that the rack isn't mounted too low (and binding on the pinion). -or- is the pinion sticking too far out the back of the apron, and dragging on the ways???

Final thought - check that the longitudinal shaft(s) (leadscrew, power feed, etc.) are lubricated. They might be binding where they enter and exit the apron.
 
Mobil Vacuoline 1409 is superior to Vactra imo.
 
It's much more tacky. I've used both and much prefer the Vaculine.
 
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