Tips for adjusting spindle bearing preload on a lathe

[nc5a]

Don't think you would be adjusting a spindle preload by moving an 1/8" at a time......
More likely it should read 1/8 of a turn at a time.....


Cheers Ross

I can tell you from much messing around trying to get the spindle bearing preload correct that 1/8" turn (movement) on the adjusting nut is exactly what they mean. eKretz is correct that the 1/8" turn is of course measured on the perimeter of the nut.

 

[J_R_Thiele]

I have a Maximat V-13, and I believe I know what occured, based on what happened to mine.

I am guessing that it was fine for years, then started to occur, but varied. It would go from being OK, to there a little bit, then back to OK, then a definite problem, then OK- but always more noticable when parting.

That allen head cap screw pinches shut a slot in the threaded preload nut. In mine the slot was not deep enough. When as tight as you could get the SHCS the nut could slip. As the spindle would accelerate the nut would slowly work its way tight or loose, depending on direction and the speed you were using. If you are doing work in a collet there is not much mass, no chuck, the work is small and the speed high- so it would shift more. I was often using boring bars, both L and R handed, and was often running in reverse. I realized what was occuring when working between centers making a 5C test bar. I could tell things were shifting as I put the part between the centers and carefully adjusting the tailstock. I found the runout that should not have been there at all- and it would be gone with the "right" pressure from the center.

There is a bit more to the story, but I now have a lathe that needs new bearings.

Addendum

MCritchley-- I believe it was you who checked the runout of that 5C test bar at the first scraping class at Borne ad Koch.

 

[MCritchley]

I have a Maximat V-13, and I believe I know what occured, based on what happened to mine.

I am guessing that it was fine for years, then started to occur, but varied. It would go from being OK, to there a little bit, then back to OK, then a definite problem, then OK- but always more noticable when parting.

That allen head cap screw pinches shut a slot in the threaded preload nut. In mine the slot was not deep enough. When as tight as you could get the SHCS the nut could slip. As the spindle would accelerate the nut would slowly work its way tight or loose, depending on direction and the speed you were using. If you are doing work in a collet there is not much mass, no chuck, the work is small and the speed high- so it would shift more. I was often using boring bars, both L and R handed, and was often running in reverse. I realized what was occuring when working between centers making a 5C test bar. I could tell things were shifting as I put the part between the centers and carefully adjusting the tailstock. I found the runout that should not have been there at all- and it would be gone with the "right" pressure from the center.

There is a bit more to the story, but I now have a lathe that needs new bearings.

Addendum

MCritchley-- I believe it was you who checked the runout of that 5C test bar at the first scraping class at Borne ad Koch.

Yep, that was me. Ironically enough i bought a 5-C test arbor from another class mate Daryl at a later date. I am still working on scraping my TM-UM

 

[adammil1]

I have a Maximat V-13, and I believe I know what occured, based on what happened to mine.

I am guessing that it was fine for years, then started to occur, but varied. It would go from being OK, to there a little bit, then back to OK, then a definite problem, then OK- but always more noticable when parting.

That allen head cap screw pinches shut a slot in the threaded preload nut. In mine the slot was not deep enough. When as tight as you could get the SHCS the nut could slip. As the spindle would accelerate the nut would slowly work its way tight or loose, depending on direction and the speed you were using. If you are doing work in a collet there is not much mass, no chuck, the work is small and the speed high- so it would shift more. I was often using boring bars, both L and R handed, and was often running in reverse. I realized what was occuring when working between centers making a 5C test bar. I could tell things were shifting as I put the part between the centers and carefully adjusting the tailstock. I found the runout that should not have been there at all- and it would be gone with the "right" pressure from the center.

There is a bit more to the story, but I now have a lathe that needs new bearings.

Addendum

MCritchley-- I believe it was you who checked the runout of that 5C test bar at the first scraping class at Borne ad Koch.

JR did you ever resolve the issue? On my end the problem has always been difficulty running a parting tool.

Thanks for all the help to those who provided it here. I followed everyone's advice and finally got it to be able to part a lot better. It took 2 tries the first time I got it a bit too high after running the 15min high speed spin test. I was quite interesting to see how stiff things got at speed and temperature. I loosened it up a little from there and that seemed to yield better results, and now can handle plunge cutting a lot better. If nothing else now I have a custom made wrench if needed again in the future. I was surprised by how much force it actually took to adjust preload to where it actually started to add resistance to turning the spindle by hand.

Sent from my SM-J737V using Tapatalk

 

[J_R_Thiele]

I cut the slot deeper, and it now holds its settings. The lathe is usable, noisier than it was, and now has runout it did not before. Prior to this the runout was well under .0001 TIR measured on the taper in the spindle. Far better than there was any reason to anticipate.

I would strongly suggest you put some opposing indexing marks in the spindle and nut and keep an eye on it.

Its one of those things that I would not have thought possible had I not seen it happen, then had the "opportunity" to confirm that I was actually seeing what I thought I saw.

I was recently doing some reading about 3 phase motor starting inrush current and learned that on starting the torque a motor can generate can be several times its rated maximum, if the alignment of the poles is in the "right" place.

 

[Milland]

I cut the slot deeper, and it now holds its settings. The lathe is usable, noisier than it was, and now has runout it did not before. Prior to this the runout was well under .0001 TIR measured on the taper in the spindle. Far better than there was any reason to anticipate.

The bearing may be shifted enough (even tilted) to create the new runout. If it's stable and you have acceptable temperature rise, at some point try setting up a die grinder in the tool holder and dust the relevant faces of the spindle to bring it back in. A die grinder isn't perfect for this, of course, but should be acceptable with some care and bluing/checking.

One thing to confirm before doing any grinding is that the new error is one cycle per revolution, if it's some other ratio you'll be chasing it rather than fixing the TIR. At that point it may be wiser to replace the bearings if you need the accuracy.

 

[J_R_Thiele]

Part of "the rest of the story" is that one of the gear shift levers was poorly adjusted from the factory and did not fully engage the gears when shifted to high speed ranges. When the spindle nut shifted one time it was enough that the gears came out of mesh, shaved off metal and this circulated through all the bearings. You can see visible damage to the bearings.

I know I need new bearings. Standard for the lathe was P5- but there apparently was an option for higher tolerance tolerance bearings. I assume P4. I am hoping to find those, but most bearings I find in the size needed are P3.

 

[enoyobatta]

Spindle bearing pre-load .. tapered rollers

One approach is to place both the spindle and the feed gear box in neutral. You then turn the spindle by hand and note the increase in torque as the spindle bearings are tightened. It will transition from very easy to turn to a slight resistance to turning. The preload is about right once the resistance is noticed. This needs to be done after the lathe head stock has warmed up. The preload will change with operating temperature. This is the easiest procedure for spindles supported by tapered roller bearings.

For the Clausing Craftsman Commercial (tapered roller bearings) the procedure is .. reduce end play while cold, then run spindle for an hour to warm it up, and then remove drive belts from spindle, and give the bull gear a sharp crank by hand. The spindle should rotate about a half turn, to give recommended pre-load.

I bought this machine new in 1976, and had to look it up, after replacing the main drive belts. It's a 12 x 36, and I have the original price list published by Clausing. Perhaps both Clausing and Atlas made different models for Sears.

I also have a Monarch EE 3hp DC here which has the back-to-back type spindle bearings at the chuck/headstock end, but fortunately I've never had to mess with them. As I recall, the ass end is actually allowed to "float" as the spindle grows as it warms up, through 2 or 3 bearings.