Thread: Bronze Spindle Bearing Shells

I have acquired a Hercus headstock and spindle, both of which have seen better days.

I would like to bore out the headstock, grind down the spindle, and fit bronze bearing shells.
Information on this subject on the South Bend Forum indicates that others have achieved this objective, at least on a South Bend.

Can anyone comment on the amounts permissable to remove for the boring and grinding ?
What would be the minimum shell thickness that would work ?
Should the shell be split ?
How can I hold the shell in position to align the lubrication channels ?

I have access to a horizontal borer and cylindrical grinder.
Installing accurate centres in the ends of the spindle is something not resolved, but I have some good ideas.

If successful, the procedure will be repeated on my Sheraton A.

John.

Is this for practice or to be used.

Pipeclay,
The Hercus headstock is really only an exercise, to see what the traps are.

I don't have the rest of the parts to make a Hercus lathe.
My Sheraton is complete, but with failed spindle bearings.

If you inspected the Hercus parts, I do not think it likely anyone else would like to tackle the refurbisment.

I will be attempting to set-up the headstock on the horizontal borer tomorrow, but very unlikely to attempt a cutting pass, just get familiar with the machine, controls and set-up.
Setting the headstock parallel to the Z-axis will be the challenge, something like a straight bar to sit the headstock inverted "V" on, then DTI the bar.

If the Hercus assembly comes good, I can fit it to the Sheraton bed for a test run.

John.

Just some things for thought.

Do you intend to grind both ends of the spindle?

The outboard end does not allow a great deal to be ground before you get bellow the thread depth,if this end is badly scored you may be better off getting it metal sprayed ( theres only about .006" to play with).

With the inboard end there is plenty of meat for grinding.

Holding the spindle for grinding as you say will only take a little thought.

Not sure how involved the set up for the headstock should be,depending on the external condition it shouldnt be to hard,I wouldnt think any particular jigs should be required.

I think some of these types of rework are done on a similar lathe using the lathe bed itself as the mounting.

You should also be able to use the backgear bore for setting up,a bar passed through the bores should allow you to set parallel to the borer.

The reverse tumbler mounting face should allow you to set square to the borer.

The external faces of the spindle bore should also allow you to set square to the borer.

Are you going to machine this in one opperation or are you going to rotate the table.

The headstock has enough meat for you to be able to bore but you may only be able to get a bush with less than .125" wall thickness.

Were you considering splitting the bushes or using them solid?

If you were going to use them solid put your shims in and clamp tight.

Cant remember with the hercus if the top and bottom oil holes are in line,if they are you would probably just drill through after boring or the could be drilled before boring your bushes.

If you were going to use split bushes you may need to consider how you are going to retain the bushes during assembly.

Pipeclay,
thanks for the thoughtful response, you raise many valid issues.

I note you suggestion of 0.125 inch, (3 mm) bearing shell thickness.
If, say, 0.5 mm off the spindle, than the inboard housing bore will need a radial cut of 2.75 mm.
I will check to "see" (visual assessment without calculations) if the casting can accept this much metal removed.

The Hercus spindle is pretty chopped up at the outboard end with a good(ish) inboard end.
The Sheraton spindle has good outboard, terrible inboard.
I will grind the Hercus outboard to the suggested 0.006 inch limit, and live with the finish (perhaps cheat a few more thou and grind the gear teeth down to suit !).

It seems to me better to machine both bores on the one set-up, no table rotation.
A boring bar diameter nearly that of the inboard bore should reach the outboard without any problems.
There is a tailstock, but the use of that is part of the learning curve.

I will check the backgear bore alignment, I hadn't thought of that.

One way to achieve both location and lubrication channels is to split the bearing shell and glue it into place.

The Hercus headstock is interesting, it has both a bottom oil facility with reservoir and sprung felt and a top oiling point.

The Sheraton has only the top oiling point, is this a design weakness that should be rectified as part of the re-furbishment ?

John.

I think the Sheraton has a lubrication groove or grooves cut into the headstock.

Not having a bottom oil port should not be a problem.

The .125" was only a thought,they maybe the chance that you could live with bigger or it may need to be smaller,wouldnt like to go less than .0625" though.

Have you allready got a bar that will go through your headstock and into the support arm.

What length is there from the borer spindle to support arm,if its overly long that may give you some problem with surface finish and diameter.

The Sheraton maybe different on the outboard end,you maybe able to take more off grinding before you get down to the threads.

I think this is a very interesting subject, as there must be many plain bearing lathes with the same problem. Just some thoughts from the comfort of my armchair -
To get best accuracy when boring, I believe it's good to have a rotating bar with a single cutter fitted between centres, and having the thing you want to bore sliding along to be cut. That ensures no taper if the bed is straight. Of course every effort should be made to get the centres in line and in the correct position too, to prevent oval or badly placed hole. An identical lathe could be a good tool for the job.
If the spindle needs machining down beyond the tops of the threads, could the bush be halved to allow the threads to be untouched yet still the bush can fit well?

Jordan

Pipeclay,
The Sheraton does have coarse helical oiling grooves, should I try to duplicate this in the bronze ?

I mounted the Hercus headstock on the borer today.
The machine has a long boring bar mounted between centres.
It was agreed that I should attempt to cut both bores at the same time, if not, then in turn without changing the set-up.
The suggestion was to clamp the casing to the table directly, so not easy to dial off the inverted V.
The layshaft bores seem like the best option to get alignment.

I am assuming (?) at this stage that suitable bronze hollow cylinders can be purchased from Blackwoods.
Any alternative suggestions greatfully received.

Jordan,
I am reluctant to go with a split bearing (just a gut feeling).
We discussed bearing retention and the suggestion was that retention is not necessary.
I am not convinced, I would like something concrete, perhaps a grub-screw longitudinally at the bronze/cast iron interface.

Inspection today indicates at least some of the galling on the Hercus outboard spindle bearing surface could be pick-up from the cast iron, there is a possibility I do not need to take off too much.

I have now to produce two 1/4 inch square tools to go in the boring bar, and to source a straight accurate bar to provide the datum in the layshaft bores.

John

Blackwoods may have something,if not you would have to purchase some hollow bronze bar,for what you need it should be less than $40.00.

Is your intention to have these bushings fixed ( not removable ) if so are you going to shrink them in.

In regards to the grooves for lube you can do these in your boring set up,you could grind a round nose tool and set a coarse feed rate or just do a centre groove at the oil inlet and at each end of the bushing and then a longitudinal groove running from the end grooves top and bottom.This should supply plenty of area for oil to pool to supply lube.

If you shrink the bearings in there would be no need for secondary retention.

Pipeclay,
My intentions are flexible depending on advice.

Shrinking the bearings in sounds a bit too drastic.

I have seen information stating that a close-fitting thin solid shell will collapse with the housing as the clamp bolts are tightened, no need to split it all.
I think a modern approach would use a single shell bearing with a split opposite the housing shims with Loctite applied in the bottom area only.
Clamping then is not constrained in any way.

Machining the bearing shells is an unknown area (don't we love the challenge).
One way would be to prepare the bearing by getting the OD accurate to size,
- chuck a cylinder in the lathe and bore to fit the bearing OD,
- low strength Loctite into the cylinder,
- bore the bearing to size,
- remove assembly from chuck, heat up, remove bearing and clean.

The alternative is to make a split chuck to grip the bearing OD.

The lathe allows helical grooves as you suggested.
Racking the saddle could provide the trough.
The vetical mill can add the oiling entry hole (perhaps in the blank before any machining).

John

So your plan is not to bore the bushings on the borer?

Pipeclay,
You have made me stop in my tracks, I was assuming the shell would be machined totally away from the headstock, then inserted as a part during the assembly.

Are you hinting to install the bearings into the headstock, then return to the borer to get the bore correct.
Sounds like a good methodology - just never thought of it.

Perhaps the sequence is:
- get the spindle into good shape,
- decide on the shell thickness,
- machine shells to design OD with ID undersize,
- mount headstock on borer and size the bores to fit the shells,
- install the shells into the headstock while mounted on the borer,
- machine shell ID to fit spindle,
- then remove assembly from borer.

John.

Most jobs can be attacked in different ways,as long as the final result is achieved.

Apart from asking questions here is there anyone else guideing you through this rework,if so it maybe better to follow there advice.

Are you teaching yourself to use the Horizontal or are you following instructions.

For what its worth I will try and give an outline on my thought of attack.

1 measure headstock to make sure what you intend is achievable.

2 repair the spindle.

3 source suitable material for bearings.

4 setup and bore headstock.

5 machine OD of bearing/s allowing for shrink fitting and rough machine bore, also allow for facing both ends.

6 using dry ice or liquid nitrogen shrink bearings into headstock.

7 finish machine bore of bearing allowing for clearance for spindle.

8 cut oil grooves

9 face inner and outer ends of bearings (step 8&9 could be reversed)

10 drill oil port for lube.

Of course all sharp edges and burs would be removed.

Maybe you should ask the question in the general forum to see what suggestions you get there.

Pipeclay,
I have assistance from a trade instructor on the use of the borer, but very much a try-it exercise.

My original approach was based on duplicating what I have seen for bearing shells used on South Bend lathes.
These appear to be replaceable split bearings that can be purchased as spare parts.
I suspect the bearing has some details ( pressed-out ear etc) that ensure the bearing cannot rotate within the housing.

With the heat-shrunk fit suggested by you, I would be concerned that the bearing adjustment facility of the housing gap/clamp would be compromised.

The trade instructor was the person that suggested that (a) anti-rotation was not necessary, and (b) if required, a brub screw could be added, radially or longitudinally.

I think that so far, you have confirmed that my general approach is sound, and that there are many specific variations in detailed technique that will achieve the desired result.

I will keep you posted on developments.
My first task is to get centres into the ends of the spindle.
John.

There was no heat involved just freezing.
For the amount of use these machines get and the age of them running in a cast housing they take a long time to wear.
If you were to make a solid bearing I dont think the bearing would need replacing untill it got to the same amount of use as the present.