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Lead screw bushing? Heavy 10

Doan

Plastic
Joined
Aug 10, 2021
The lead screw is 3/4" diameter where it enters the gearbox, but the gearbox bore is 7/8" id. This is between the inner 7203 angular contact bearing and the outer thrust bearing. There is an oil feed hole that would drip into the 1/16" gap between the gearbox casting and the lead screw. It seems like the there should be a bushing supporting this end of the lead screw, but the parts diagrams don't show one. Neither is a bushing mentioned in the 2 rebuild guides I have.

Is there supposed to be a large clearance around the lead screw?

Or, is my lead screw too small for the gearbox casting?

The first picture shows the gap. The second shows a bushing I could install.

Thanks for your help.
20210908_213320.jpg20210908_213907.jpg
 
I don't know a heavy 10 particularly well. Also I'm not sure what you mean by angular contact bearing. With camera shots from one side, I can't see the other side.

But I would have a couple of questions. First are all these pieces original, or in how you took the lathe apart ?

My next question would be, let's assume you assemble it all without the bushing. What does the leadscrew due in the bore ? does it bang around unsupported ? Or does what you describe as angular contact bearing hold it true to the bore ?

In the 2nd pic I see a roller bearing, is that part of this assembly ?

My guess is, if angular contact bearing means like a tapered roller bearing, and that bearing pulls tight when thrust collar of lead screw is up to the qcgb housing. . . No banging around of lead screw? Then the gap is probably supposed to be there. Allowing oil to drop on shaft and run in the void between thrust and taper bearing, lubing both sides. But that's truly a guess, until I could see all the pieces.
 
Are you saying the ball bearing goes inboard and locates the shaft/screw?

I'm not familiar with heavy 10's either, but that does not seem at all like SB original.
If it was a well done upgrade, then the hole you describe is probably clearance and fine, as Texas mentions.
If there is no other bearing, then the hole should have a purpose made bronze sleeve cross-drilled for oiling. (Not oilite)

If the shaft wore the hole, most likely it (shaft) will require a clean up pass to make it round and true again.
So the new bronze bearing should be made to that size, and the OD fit to whatever size single point bored hole cleans up.

I believe those holes were merely bored on-size for the shafts, in the casting, and the shafts run on CI. That is true for the smaller lathes.

My light 10 gearbox shafts all had 1/16" and more slop in oval holes, to the extent when gears at one end were used it would jam. I set up and located/single point bored them on the mill and installed bronze sleeves. The one at the thrust end has a hat brim section for thrust but if the CI face is good that is not necessary.

Again, if someone already did the work for you to accurately install a ball bearing, then just run it as is.

smt
 
Thanks for the help guys. This is how the lathe came apart and the angular contact bearing centers the lead screw in the bore so it works OK (no flopping around). But someone has been into it before so don't know for sure if gap between the lead screw and the gearbox casting is how it was designed. This was originally a turret lathe and there is evidence that it has parts from 2 or more lathes.

This links to a thread indicating that both the inner angular contact and outer thrust bearings are correct. (see post #9) https://www.practicalmachinist.com/vb/south-bend-lathes/gear-box-bearings-350122

This this links to the angular contact bearing design: https://www.mscdirect.com/product/details/05820915

It seems that a bushing would carry some of the weight of the lead screw and prevent oil running out of the gearbox, potentially directing more oil to the inner bearing.

Apologies for the loose bearing in the second picture - that is an imperial sized bearing for an old English motorbike.
 
Here's a picture of the inner angular contact bearing.
20210909_153158.jpg

Stephen, re-reading your post encourages me to install the bronze bushing. The bore in the cast iron is round and the outer face is in very good shape - little or no wear in either place. Perhaps some lead screws had a step with one diameter for the inner bearing and a larger diameter to run in the gearbox bore?

Also, why not use oilite bronze?
 
You don’t need the bushing in the middle. The angular contact bearing on the inside of the gearbox will support 1000+ pounds and the leadscrew maybe weighs 25. The thrust bearing on the outside allows for a preload on the angular contact bearing inside and also takes the thrust if you are threading away from the headstock.
As far as keeping oil in the gearbox, you won’t. The entire bottom is open and oil will find a way to run out, just add more before running it the first time for the day. The leadscrew typically doesn’t turn very fast so the little oil that clings to it is plenty.

Hope this helps.
 
Thank you BD. It's probably overkill, but based on what Stephen said about the holes in the casting bored to fit the shafts I've pressed in the bushing.

The gearbox was very difficult to shift, the center bearing was locked and all the felts were like clay so I'm looking forward to trying out the rebuilt version!
 








 
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