Small restore job on my Holbrook H20

[fizzy]

When I first had it there was loads of slop in the cross slide. Managed to adjust most of it out. Wasn't happy still. Then 2 weeks of freezing weather I left it alone. Just had a quick play and found this wrong with the taper turner
How can a ball race disintegrate like that?

 

[minimutly]

Sorry @fizzy , the pics don’t convey anything other than the whole lot has been unscrewed?

 

[fizzy]

Sorry @fizzy , the pics don’t convey anything other than the whole lot has been unscrewed?

Before I got it apart I thought it had some sort of wear pads - 2 each side - but one was missing. When I took it apart I realised they were ball races not wear pads - and one has completely disintegrated! No real force on it so no idea how it happened.
Smallish bearings so I thought I may as well replace all 4 - until I discovered they are about £35 EACH

 

[minimutly]

Before I got it apart I thought it had some sort of wear pads - 2 each side - but one was missing. When I took it apart I realised they were ball races not wear pads - and one has completely disintegrated! No real force on it so no idea how it happened.
Smallish bearings so I thought I may as well replace all 4 - until I discovered they are about £35 EACH

Pennies Vince, pennies...

 

[500e]

That's the cost of quality

 

[eLuSiVeMiTe]

Before I got it apart I thought it had some sort of wear pads - 2 each side - but one was missing. When I took it apart I realised they were ball races not wear pads - and one has completely disintegrated! No real force on it so no idea how it happened.
Smallish bearings so I thought I may as well replace all 4 - until I discovered they are about £35 EACH

Did you miss a zero and they are £350.
If not get em bought.

 

[Agroshield]

When you replace them, think about how they are lubricated. If there is no access other than by dismantling, then maybe grease is the word. I think they only actually move when you use the taper attachment, so maybe once every two years.

Consider also if they could have been showered in coolant for many years leading to an early demise.

 

[daleyd]

You can’t run a Rolls Royce lathe on Lada prices

 

[fizzy]

Found the same bearings for £9.95 each
There is a chap I know who is a Holbrook fanatic and has all the factory blueprints etc. He is very interested in my lathe as they are so rare. He has checked and say they aren't original and should be hardened solid steel rollers. I thought is was a strange application for needle rollers and they barely move and there is little force on them. Why anyone would go to so much trouble is beyond me. A phos bronze bush would be more than adequate. Also the bearings are a perfect metric size - as the lathe was built in 1960ish that is again strange. Maybe it was a prototype or something.

 

[fizzy]

When you replace them, think about how they are lubricated. If there is no access other than by dismantling, then maybe grease is the word. I think they only actually move when you use the taper attachment, so maybe once every two years.

Consider also if they could have been showered in coolant for many years leading to an early demise.

I think so as well. Well protected but no means of getting lube into them. I see the bearings are rated to 19,000rpm
I would be surprised if they get up to 3

 

[fizzy]

My next problem - and the one causing my backlash - is the threaded bit at the end of the cross slide screw. It is not just machined into the end of the rod but seems to be a loose bit pressed or screwed into the end of the shaft for some reason. It wobbles around quite a bit but perhaps it should? Can't get the bearings over the thread either. And what on earth are those little dots for? Maybe been pressed in to hold the threaded bit?

 

[Agroshield]

The little dots are inside the outline of a pin. It is very clear in the photos. They would have been used to peen/swell it out so it stays put in its hole.

Add one in the centre, then drill it out and that might release the threaded bit. There is a very slim possiblity that it is not a plain pin but is threaded - in that case try a left hand drill.

The machine was made pre-loctite.

Bearing manufacture is quite specialised and the mass-producers were European from the beginning (e.g. SKF) so metric bearings likely would have been more economic than imperial, especially for roller bearings. Clearly for niche stuff like spindle bearings, you have Gamet, and they are imperial but they are not commodity level.

 

[fizzy]

OB183530 Plain Oilite Bush

Inside Diameter: 18mmOutside Diameter: 35mmLength: 30mmMaterial: Oil Impregnated Sintered Bronze

www.bearingshopuk.co.uk

I am thinking of possibly replacing the needle rollers with phos bronze bushes - needle rollers just don't seem right for something that hardly ever moves! Be easy enough to bore this out to 22mm and shorten it to 20mm.
Any thoughts clever people?

 

[Pete.]

My next problem - and the one causing my backlash - is the threaded bit at the end of the cross slide screw. It is not just machined into the end of the rod but seems to be a loose bit pressed or screwed into the end of the shaft for some reason. It wobbles around quite a bit but perhaps it should? Can't get the bearings over the thread either. And what on earth are those little dots for? Maybe been pressed in to hold the threaded bit?

View attachment 377546View attachment 377547View attachment 377548

I think that when you fit the nut it should pull the bearings up to the end of the cross slide screw and that will take all the slack out of it. Is the thread significantly bigger than the bearing ID or is it just fouling the crests?

 

[fizzy]

I think that when you fit the nut it should pull the bearings up to the end of the cross slide screw and that will take all the slack out of it. Is the thread significantly bigger than the bearing ID or is it just fouling the crests?

The problem is the nut isn't doing that - it has been cross drilled and pinned. There is a spacer there - perhaps use a thicker one?
Hard to tell might just be fouling on the crests - perhaps I will try a needle file to clean it up a tad. Bearings actually feel fine.
Do you think that threaded section is meant to float around a bit and stabilise when tightened up?

 

[Agroshield]

With a bush, it usually has a shaft inside it and a housing outside it. The bush stays stationary. I think what you are proposing is to have the OD of the bush running on the lathe casting in the same way that the OD of the current bearing does. It also means the ID will rotate on its shaft.

It would be worth trying to find the tolerances on the ID of an Oilite bush: I have a suspicion that they are made slightly oversize so they are correct when squashed into their housing. You would not have an enveloping squash on the outside, just a line contact.

I have no rational reason for this, but it seems to me that a bronze bush inside a hardened steel outer shell or race might be the best - sort of like the needle bearing but with the rollers and inner race replaced with porous bronze.

One of these: https://www.bearingboys.co.uk/?catid=3665&display=&orderby=&att1=&att2=35mm&att3=20mm&att4=&att5=

 

[Pete.]

The problem is the nut isn't doing that - it has been cross drilled and pinned. There is a spacer there - perhaps use a thicker one?
Hard to tell might just be fouling on the crests - perhaps I will try a needle file to clean it up a tad. Bearings actually feel fine.
Do you think that threaded section is meant to float around a bit and stabilise when tightened up?

I can't see that ever coming from the factory especially the way the end of the screw is bashed up. If I had to guess I'd say that someone has either re-made the cross slide screw or perhaps taken a non-taper-attachment one (if such a thing even exists) and modified the end to fit the rear end bearing block of the taper turning model.

My approach would be to knock out that pin, remove the stub and bearings, face the end of the screw off so that the bearings sit true and re-make the retaining stub. I'd also make it so that the bearings can be removed from the screw.

 

[fizzy]

With a bush, it usually has a shaft inside it and a housing outside it. The bush stays stationary. I think what you are proposing is to have the OD of the bush running on the lathe casting in the same way that the OD of the current bearing does. It also means the ID will rotate on its shaft.

It would be worth trying to find the tolerances on the ID of an Oilite bush: I have a suspicion that they are made slightly oversize so they are correct when squashed into their housing. You would not have an enveloping squash on the outside, just a line contact.

I have no rational reason for this, but it seems to me that a bronze bush inside a hardened steel outer shell or race might be the best - sort of like the needle bearing but with the rollers and inner race replaced with porous bronze.

One of these: https://www.bearingboys.co.uk/?catid=3665&display=&orderby=&att1=&att2=35mm&att3=20mm&att4=&att5=

Good thinking.
TBH though I think even a nylon bush would work for this - I doubt there could be much force on it.
I think I will just go for the easy option and replace like for like. Pack them with waterproof boat trailer grease. Easy enough to change in the unlikely event I ever need to again.
Sorting that damn threaded bit is the bigger problem now.

 

[fizzy]

I can't see that ever coming from the factory especially the way the end of the screw is bashed up. If I had to guess I'd say that someone has either re-made the cross slide screw or perhaps taken a non-taper-attachment one (if such a thing even exists) and modified the end to fit the rear end bearing block of the taper turning model.

My approach would be to knock out that pin, remove the stub and bearings, face the end of the screw off so that the bearings sit true and re-make the retaining stub. I'd also make it so that the bearings can be removed from the screw.

Yes perhaps that was the case!
Best way to remove that pin?

 

[Pete.]

If the bearings are good and you're happy with evrything else, just make a spacer washer the right thickness to take up the lash.

Put the nut on with a washer under it. make sure the hole is lined up. Fit the cross-slide up and use a dial gauge to measure the lash in the assembly by pushing and pulling on the cross slide. Measure the washer you used, add that thickness to the amount of lash you measured and then part off a new washer to that dimension. You should be able to now fit the nut on and tighten it up nicely so the locking pit will fit.