Worm Gear and Bushings in Logan/Powermatic 11"

[DAHoyle]

For those who have had their apron apart, I was wondering what kind of wear you observed on the worm gear. I was trying to turn a taper with the top slide today, and it is so bad(long story) that I have just about given up on it. In light of that, and just for the sake of improving the overall capability of the lathe, I am leaning very hard towards doing away with it all together, and machining a new, more robust cross slide with a selection of t-slots and a riser for the QC tool holder. With that in mind, I started some disassembly to start working up a plan. I wanted to take a good look at the saddle to confirm some of the ideas I was tossing around, and since I had it off, I went ahead and slid the apron off the end of the screw to examine everything and clean the sludge out of the bottom(when I drained it, nothing came out until I poked a hole thru the sludge on the bottom.

Everything looked really good until I got to the worm gear and the so called bearings that contain it. The worm looks fine, as does the key in the bore, but the whole worm slid back and forth at least a quarter inch, and the bearing surfaces are tapered and scoured badly., and the bearings are just as bad. I don't want to disparage my my machine, or the manufacturer, but even a casual inspection reveals that they were not getting adequate lubrication, and call me a skeptic, but steel on steel with no lube is not a recipe for long term durability. The worm is fine, so I think I will button things back up without the worm, long enough to machine some new bearings, and clean/true up the worm gear bearing surfaces. Can't really leave it as it is, because when the worm shifts, it ends up riding offset to the wheel gear, and that can not be good for long term health of either. Have to come up with a plan that doesn't include dropping $500 on a new gear and bearings. Part of that plan will be an improved lubrication setup, because what was there was not working. I keep the apron overfilled, and keep the screw wet with oil, but none was getting to those bearings, and hadn't ever as near as I could tell.

So, for those who have been inside their aprons, I am curious what you encountered. I can not believe that mine is unique. It is probable that the damage was done long before I bought the machine. Maybe it had been run without lube, but I have no way of knowing. Everything else in there looked great.

 

[KyleG]

Assuming yours is similar to my Logan 825… I was also surprised when I saw how much axial play there is in the worm. I think it must have been intentional though. For a normal worm gear, the axial position doesn’t matter for alignment, so that’s no concern.

 

[DAHoyle]

Assuming yours is similar to my Logan 825… I was also surprised when I saw how much axial play there is in the worm. I think it must have been intentional though. For a normal worm gear, the axial position doesn’t matter for alignment, so that’s no concern.

Yeah, I don't have any way to know what is normal play for these, but this was very obvious wear. The bearing surface of the gear was worn to a taper. badly scoured, and you could see where the end of the gear was also worn away in an uneven pattern. Not much I could do with it at the moment, so I re-drilled the dog screw spots on the bearings so they could ride farther inboard, which removed most of the axial play. Because the bearings had worn to a taper, bringing the bearings inboard also significantly reduced the radial play. I slathered the surfaces with a good moly grease, and overfilled the apron, in the hopes of postponing the eventual replacement of the parts, but I know all of that is a temporary solution. I did everything I could think of to reduce the load on the gear, mostly just really paying attention to the way gib adjustments. The bed really has no apparent wear on the ways, so I can adjust the gib out on the tailstock end, without really having it loosen up towards the chuck. All things considered, I am happy with the way it turned out, for the moment. Trying to decide if I want to clean up the bearing surfaces, and turn new bearings from bronze, or just bite the bullet and replace everything.

 

[Razzle]

As luck would have it I am also in the process of tearing down my 820 apron to replace the bushings on the hand feed crank. I also noted the wear in the worm bearing cups and the excessive play. According to Scott Logan you are supposed to tighten the spacing as they wear by drilling a new dimple to lock them in place closer in. Mine are really wallowed out and one cup end almost worn through. So my solution is to put in a bronze thrust washer in the back of each cup, put it back together and turn new bronze cup bearings to replace the steel ones. My worm is fine. There is a drawing of the cup dimensions on the site. I verified that they are accurate for my 820. But YMMV.