Thread: Adjusting or replacing babbit bearings in a Mars Great Scot lathe (brisbane)

Chris
I thought someone else would have responded by now. From what I can see in the pics it looks like your machine might have some sort of adjustment on the headstock bearings. The bit on the chuck side of the front bearing that has the small holes drilled into the outside edge. To me that looks like some sort of adjusting nut that you would use a pin spanner on. I can't see whats on the other end of the spindle.
As to how it works I can't comment on from the pictures. I'm only quessing here, but its probably a fine taper in the housing and a split bush of some kind with a matching taper on the outside and a thread on the end that the nut screws onto. Tightening the nut pulls the bush further into the taper in the housing, which in turn reduces the id of the bush. It might only be a case of tightening the nut up to reduce the play. Not sure what sort of locking method would be used though.
There doesn't appear to be any bolts on either side of the bearing which you would expect if it was a split bronze or whitemetal bearing.
Hopefully someone else with a bit more knowledge of these will chime in.

hope this helps
bollie7

Hi bollie
I would have answered but I am not familiar with those type of lathes.

What you describe above sounds like the bearing set up on the arbour support on my old horizontal mill that I picked up with the shaper. It needs a C type spanner on the inside and has a big nut on the out side to adjust the bearing smaller to suit the arbour spacer. A very good idea, and far better than the HM52 bush which has no adjustment.

Dave

UB,

I have a friend who recently purchased a Mars lathe. I'm impressed, it's really well made.

Next time I visit him, I'll take a closer look at the headstock bearing arrangement. Couple of dayz.

Ken

Originally Posted by Dave J

Hi bollie
but I am not familiar with those type of lathes.
Dave

Me neither Dave. It just seemed logical from what I could see in the pics. My old Purcell lathe that I got rid of a few years had split bronze bearings. The only adjustment was by scrapping the bearing and filing a bit off the underside of the caps.

bollie7

Originally Posted by bollie7

Chris
From what I can see in the pics it looks like your machine might have some sort of adjustment on the headstock bearings. The bit on the chuck side of the front bearing that has the small holes drilled into the outside edge. To me that looks like some sort of adjusting nut that you would use a pin spanner on. I can't see whats on the other end of the spindle.
...

hope this helps
bollie7

Thanks to all who have responded.

I think the pin-spanner arrangement on the bearings allows alignment to be adjusted due to eccentric sleeves. The bearings and mounts don't appear to be have the common split-and-shim tightening.

The problem I (hope to) have isn't one of alignment, but the spindle having slight play due to wear. The owner says this tiny amount of play causes the lathe to grab during parting or heavy cuts. I'm hoping there's some kind of way to tighten the bearings, as I understand this is designed for with white-metal era machines. I'm familiar with how myfords use removable shims for this.

The lathe is still in the back corner of my FiL's shed where its hard to get a good look at the bearings. We'll have to dig a tunnel through his collection of car parts to get it out!

Also, any recommendations for engineering shops in brisbane that have know-how in reconditioning old lathes would be greatly appreciated. Aparrently the cross-slide halfnuts were rebuilt once already, and the bed re-ground, but my FiL cannot recall the name of the place that did it for him.

Chris

Here's a link with some info on your lathe (edit - Doh - just seen you've already linked to another page on the site):

Page Title

I too think that the threaded ring acts on the bush to push it into its tapered housing, so deforming it to take up slack. I'd just have a gentle go, checking for tightness in the bearings frequently. Is the wear only apparent vertically, or in all radial directions? If the latter then the adjustment should be straightforward.

Cheers

Si

Originally Posted by unixbigot

I think the pin-spanner arrangement on the bearings allows alignment to be adjusted due to eccentric sleeves. The bearings and mounts don't appear to be have the common split-and-shim tightening.

Thats interesting, do you mean the spindle alignment in relation to the bed? I'd assumed the pin spanner nut was for tightening the bearings because there doesn't appear to be a removable cap as you would have on a tradional split bearing design.

[/QUOTE]The problem I (hope to) have isn't one of alignment, but the spindle having slight play due to wear. The owner says this tiny amount of play causes the lathe to grab during parting or heavy cuts. I'm hoping there's some kind of way to tighten the bearings, as I understand this is designed for with white-metal era machines. I'm familiar with how myfords use removable shims for this..[/QUOTE]
Play in the spindle bearings could also cause the job to try and climb up over the tool under a heavy cut as well

[/QUOTE]The lathe is still in the back corner of my FiL's shed where its hard to get a good look at the bearings. We'll have to dig a tunnel through his collection of car parts to get it out!.[/QUOTE]
Would be interest in seeing some more and better pics once you are able to get to it.
[/QUOTE]Also, any recommendations for engineering shops in brisbane that have know-how in reconditioning old lathes would be greatly appreciated. Aparrently the cross-slide halfnuts were rebuilt once already, and the bed re-ground, but my FiL cannot recall the name of the place that did it for him.[/QUOTE]
If the bed has been reground there is a good chance it will still be ok. re your cross slide nut, you could strip the machine down, measure it all up and then machine a new nut yourself. FIL's new lathe would be handy for that. The cross slide spindle is more than likely an acme thread (or possible a square)
Cross slide spindle thread will probable be left hand as well.
If acme, you can set it up and track it out just taking a skim off the flanks of the thread unti it cleans up over the full length. This would mean that the thread form wouldn't be a std acme any more but it wouldn't be far out. You then would have machine a new nut to fit. A bit of Phosphor bronze would be suitable for this. I did this on my old Purcell years ago. worked fine. Ground up a HSS bit slightly narrower than std profile, welded that to the end of a 6 mm Hi Ten bolt and used that as a boring bar. Had to take a lot of passes to get the spring out of the bar. Once it was to the correct depth, just kept shaving a bit off the flank of the thread until the spindle screwed in ok. OD was 5/8" x about 1&1/4" long so the bar was pretty long and springy. All work fine though. Went from almost a full turn of back lash in the cross slide spindle to almost none. The old lathe is still powering along I believe.

bollie7

Originally Posted by SiJ

Chris

Here's a link with some info on your lathe (edit - Doh - just seen you've already linked to another page on the site):

I too think that the threaded ring acts on the bush to push it into its tapered housing, so deforming it to take up slack. I'd just have a gentle go, checking for tightness in the bearings frequently. Is the wear only apparent vertically, or in all radial directions? If the latter then the adjustment should be straightforward.

Yes, the Mars page on lathes.co.uk was where I first read about the bearing adjustment. The play is in all directions, but either slightly worse or just more noticeable vertically.

Originally Posted by bollie7

Thats interesting, do you mean the spindle alignment in relation to the bed? I'd assumed the pin spanner nut was for tightening the bearings because there doesn't appear to be a removable cap as you would have on a tradional split bearing design.

Well, I was told that's what that adjustment was for, but I think perhaps the source for that factoid may have been mistaken.

I plan to return tonight or tomorrow with an proper camera (i.e. not my phone) to take a closer look and some more pictures.

Thanks for the advice on the cross-slide, also. My FiL is keen to help me get this lathe back in running order, and I'm sure his new lathe will be looking for some tasks when he gets it set up.

OK, as is traditional on these "newbie gets a lathe" threads, I've discovered I have told you what might be charitably called a collection of confused misremembrances, or less charitably bull#@$@.

The mechanism with the C-spanner slots *is* for tightening the bearings, nothing to do with alignment. The bearings themselves are one piece sleeves with a single split, and turning the rings (which are nuts, and not part of the bearing proper) does tighten them. For a while. I'm told they work loose again quickly.

Apparently this lathe was restored by its previous owner, then when it came to the current owner, about 20 yrs ago, he had the bed reground, the bearings replaced, and the cross-slide half nuts replaced. Of the three, the bed is still in good condition. As you will see from the pictures linked below, cleaning and lubrication haven't entirely been by the book

Back to the headstock bearings, I wonder if there's a locking mechanism that's been lost or something (or whether a sacriligeous dob of loctite will achieve anything)?

Still impossible to get a view of the geartrain, but I have uploaded some more pictures to this flickr set: Great Scot Lathe - a set on Flickr

My father-in-law still seems intent on finding a local engineering shop that could replace the worn parts, as part of his gift of the lathe to me. Any suggestions here?

Thank you all for aiding me on this journey to discover the limits of my own ignorance.

I think you would be better off wiating untill you can get clear access to the lathe from all sides,then do your checks,for clearances on the spindle.

You reffer to half nuts on the cross slide,do you know if there is actually half nuts there or are they a full nut with the cross slide screw passing through it.

If it is a full nut depending on the shape of the nut or physical size you maybe able to modify the nut to take up the majority of backlash present.

Probably have got to mention this but the Headstock needs a good clean before it is rotated either under power or manually.

The configuration of the headstock looks similar to the Hercus,Sheraton and Southbend,you may be able to adapt there gear guards to your lathe or even fabricate your own,at least then you will be able to keep the majority of swarf off the Gears.

Originally Posted by pipeclay

You reffer to half nuts on the cross slide,do you know if there is actually half nuts there or are they a full nut with the cross slide screw passing through it.

(snip)

Probably have got to mention this but the Headstock needs a good clean before it is rotated either under power or manually.

(snip)

Thanks, I am of course excited to be getting this lathe into my own shed and out of its current cramped and abrasive quarters. Taking much longer than I'd hoped to achieve this.

The lathe has a powered crossfeed arrangement using bronze half-nuts, according to the owner.

A thorough cleaning and construction of a headstock cover are naturally
first order of business. Its pretty clear how the delicate mechanisms *got* so worn. You should have seen the swarfbergs before the owner "cleaned" it!

Not doubting what you have been told,I find it unusual to have half nuts that engage the Cross slide.
I havent had the privilidge to see a Lathe with double half nuts before.

If you dont mind when you get around to working on the Cross Slide half nuts would you mind puting some detailed photos up.

What I am interested in is the way the Feed is transfered to the Cross slide through the Cross slide half nuts.

By looking at your pictures it appears that the second screw running the length of the lathe has a keyway in its length,this normally is what I would reffer to as being the Feed Screw shaft.

The feed screw shaft would in most cases run the Longitudinal and Cross Feed through a worm and worm wheel.

The lever to the left of your carriage appears to be for the Leadscrew,this normally has the Half nuts.

Originally Posted by unixbigot

Thanks, I am of course excited to be getting this lathe into my own shed and out of its current cramped and abrasive quarters. Taking much longer than I'd hoped to achieve this.

The lathe has a powered crossfeed arrangement using bronze half-nuts, according to the owner.

A thorough cleaning and construction of a headstock cover are naturally
first order of business. Its pretty clear how the delicate mechanisms *got* so worn. You should have seen the swarfbergs before the owner "cleaned" it!

Sounds like FIL is confusing his terms and says cross slide when he means carriage. Half-nuts are used to engage the lead-screw which drives the carriage for thread cutting. I can't think of a reason you would want half-nuts on a cross slide. I think the sooner you can get it out of his well-meaning clutches the better.