Thread: Thrust on plain bearing lathes

I will be looking on with interest as I have an old old German lathe with a similar set up. There are 2 oiling wells that have to be topped up. A couple of times I have been so engroced in the turning that I let the oiling go too long and had a seize up. No damage just annoying.

Hi Ewan,

Is it possible to fit AC bearings?

Regards
Ray

Hi Ray,
Ac bearings?.....oh just clicked, angular contact. Hmmm I'll look to see if they might fit.

Hi Rod,
Mine has oilers too, didn't draw them in the pic. Mine has never seized through lack of oil.

Hi Ewan,
If you were to place shims between the split faces on the bearings you could tighten the nuts up and the bearings wouldn't move any further. Any adjustment would require the removal of a shim or replacement with a thinner shim. All my bronze bearings are done this way.

Phil

Is there some mis-adjustment?
If end thrust causes the spindle to wedge into the conical bush, it sounds like the thrust race isn't doing anything to prevent it.

Jordan

Originally Posted by Ueee

Hi All,
I know a lot of the lathes members have will have roller bearings. But i'd like to know how a plain bearing lathe deals with thrust. My Mars has a very poor system that relies on a thrust race that pushes on the rear bearing, which, if you put too much pressure on the TS or your work heats up and expands, drives the rear bearing into its taper and clamps it to the spindle. Yes, i have seized it a few times. Normally you can catch it and bail before it's too late......
I really need to do something about it, but i can't really see a neat and practical solution. There is not enough bronze around the spindle to thrust against at the nose end, but there is at the rear. I'm wondering if a new pair of bearing adjustment nuts with a thrust race in each would work, that way i can get some pre-load on the spindle, something which is lacking now.

The horrifying thought of line boring the casting and pressing tapered bearings in has crossed my mind......but i'd really rather not go there....even for a moment.

Attached is a pic to hopefully help describe whats going on.

There's a couple long threads on the PM antique & machinery history sub-forum on how to adjust Hendey thrust bearings IIRC. You'd be well advised to dig through and read those postings because the system sounds very similar and it is possible to adjust them not to bind.

WRT line boring & fitting tapered bearings, my advice is, don't. I've done that myself when I had the use of a Kearns horizontal boring machine. It was a PITA and I doubt I improved the machine in any way. I was changing to a different size of roller bearing for reasons that now escape me - something to do with making a new spindle with a bigger bore & upsized chuck mounting threads from hardened 4140 I think.

PDW

Just to make it clear-Unless i shim the slit in the rear bearing there is NO way of adjusting them so they "don't bind" The thrust race pushes on the bearing, forcing it into the taper, its that simple, and the only thing stopping thrust left to right is the fiber washer. The Hendey's system is a bit different, as is the Leblonds. It has no tapers, just 2 halves to the bearings which are shimmed for fit. The Babbit in the rear bearing takes the thrust in both directions.

Maybe i should re-phrase, What are opinion on the beast method of fixing said problem?

I was hoping one of the other Mars owners might come forward and show what their lathes have. As i have said before mine is not the same as any other Mars i have seen, maybe the bearings have been messed with along with everything else.

Originally Posted by nadroj

Is there some mis-adjustment?
If end thrust causes the spindle to wedge into the conical bush, it sounds like the thrust race isn't doing anything to prevent it.

Jordan

Hi Jordon,
The problem is the thrust race pushes on the conical bearing. The bore of the bearing is cylindrical, the outside is conical.

Originally Posted by Ueee

Hi Jordon,
The problem is the thrust race pushes on the conical bearing. The bore of the bearing is cylindrical, the outside is conical.

If the conical bush stands proud of the headstock casting, you could machine a groove in it and fit a large circlip to take the end thrust and prevent it from being forced into the taper.

Rob

Hi Ewan,
I must be missing something here. If the bush is shimmed to clear the shaft, then it can't possibly bind. When the bush is pushed or pulled into the conical section it will clamp the two halves together the same as the top cap being bolted down on parallel bushes.

Phil

Hi Phil,
The bush is not currently shimmed. Nothing stops it from being forced into the taper by the thrust race.

Hi Rob,
I like the idea, but i dont have the overhang and it will remove the option of re-adjustment in the future.

I'm beginning to thing the thrust race was not original and the thrust was taken on the nose of the front bearing and the rear of the register for the spindle nose. This would also move the spindle back a touch and close up some side play in the pulleys.

Originally Posted by Ueee

I'm beginning to thing the thrust race was not original and the thrust was taken on the nose of the front bearing and the rear of the register for the spindle nose.

You could be right about that. Thrust at the front bearing just behind the register wouldn't tend to close up the split conical bush, whereas your current arrangement looks ideal for causing binding problems. Maybe a better upgrade would have been to install a thrust race at the front. Can you change to a front thrust face?
A fibre washer for left to right turning is what's done on Hercus and South Bend lathes too. I guess, as it's much less done than right to left, that the system works and lasts OK, with low cost. Some people replace the fibre disc with thrust races nevertheless.

Jordan

Originally Posted by Ueee

Hi Phil,
The bush is not currently shimmed. Nothing stops it from being forced into the taper by the thrust race.
.

HI Ewan,
If you put some shimming in the bush it wont bind. This is standard practice when fitting a bush to a journal.
As the bush wears, shims are removed.
I'm sorry but I really must be missing something here.

Phil

Originally Posted by Steamwhisperer

HI Ewan,
If you put some shimming in the bush it wont bind. This is standard practice when fitting a bush to a journal.
As the bush wears, shims are removed.
I'm sorry but I really must be missing something here.

Phil

Do you mean the shims should be in the split, to prevent it closing up?

Jordan