Cromwell Smallpeice Lathe restoration, advice required

[lucerneParticipant @lucerne]

Following for the very useful tips offered in my intro thread, I now have some more specific queries as to how to get this old boy up and running, 

1. There doesn’t appear to be any way of tensioning a new drive belt. The old leather belt is frayed and the motors are all missing so I’m hoping to install a motor/inverter using the (very heavy!) pulley arm. So, how to tension a belt, which will just sit on one pulley (they’re slightly crowned), what sort of belt is best, assuming it’ll need joining, what recommendations for best inverter / motor kit, and what size of motor would be appropriate?

 

2.0 Whilst I’m leaving the main internals, as they seem to be moving fine, just in need of a clean out and degrease, I was hoping to get into the back end, which involves removing a couple of covers, which looks straighforward other than theres this cog in the way, which I assume is removable, but how to go about it? The other cogs have come off no problem but this seems tight, and I think screwed on? Would this have a normal thread and just needs more force, and if so what tool do I need?

 

[Adrian R2Participant @adrianr2]

On 2. I would *guess* the gear is keyed and the plain round section unscrews by hand. Scroll down this page and there is a picture showing a threaded end of a spindle to back up my hunch.

https://www.lathes.co.uk/cromwell/index.html

On 1a (belts) I don’t know – a long enough plain belt of approximately the right length, material and wrap will sort of tension itself so maybe just make one up and see if it works?

Motor I leave to others – I bought a likely looking one of approx the right size and then a SEW VFD s/hand for my ancient flat belt lathe and got it running but probably only by good fortune.

[Clive FosterParticipant @clivefoster55965]

I’ve found spring loaded jockey pulleys effective for flat belt tensioning on drive systems that either lack appropriate adjustably or where re-engineering to fit in less space has necessitated removal of the factory system.

That cast pulley arm looks to be well up to the job of supporting a jockey pulley system. If you engineer the pulley, bearings and spring on a self contained carrier that can be attached to the pulley arm by a couple or four bolts in tapped holes loss of originality will be minimal.

If your useful bits box doesn’t have anything that could be used consider a car auxiliary drive belt tensioner as a source for most parts. On many vehicles the service schedule calls for the tensioner unit to be removed when the auxiliary drive belt is changes so there are plenty about.

The primary issue with VFD boxes when used for machine tool speed variation is loss of torque at low speeds. As such it’s generally advisable to retain the standard mechanical multi-speed drive system. If funds permit a 6 or 8 pole motor is abetter fit than a standard 4 pole one due to the lower running speeds giving a better match of torque to job requirements. Alternatively use a smaller drive pulley on the motor if thats possible. On my last time round that particular loop a second countershaft not only fitted nicely into the proposed layout but could also be done from stuff to hand in the useful bits box(es).

Clive

[HopperParticipant @hopper]

Looks like a solid old machine. On my similar vintage Drummond M-Type I use a modern poly-V belt run on the old flat-belt pulleys. I run it with the V side against the pulleys as it grips better than the flat side. Downside is you have to pull the spindle out to change the endless belt. But it will last forever and grips better than the old leather belts. No need to machine V grooves as it seems to grip very well as is.

Seems odd there is no adjustment for belt tension. Usually in that era the whole countershaft frame pivoted at the bottom for this purpose. Is there no pivot, or no slotted bolt holes for adjustment? Perhaps shims under the base were used? Some more pics showing details of what you have would be helpful.

Otherwise, as suggested already, some sort of small jockey wheel rigged off of the heavy cast countershaft support would be good. Such a wheel from a car engine used to tension the fan belt would work.

Removing that gear off the spindle most likely involves a small grub screw and then unscrew that round collar. They loved a good tiny grub screw in that era. Clean the whole area up with a wire brush and look for a screw either on the OD of the round collar or at then point where the round collar meets the spindle, with the screw going in axially along the join in a hole that was drilled and tapped after assembly.

Keep us posted on the restoration. Looks an interesting old machine.

[Nigel Graham 2Participant @nigelgraham2]

Flat belt drives seem often not to have a tensioner, but it may depend on the length. Two forms exist.

In one, the older type, the belt is cut to length then joined, if necessary in place, typically by a pair of steel staple lacings that look like strips of rather vicious teeth. They mesh like gear teeth and held together by a rod with little flats on it. This avoids having to dismantle anything to fit it.

The other is a continuous belt that normally has to be made to order, and that appears to be the type your lathe has. Hopper’s poly-vee belt is a variation on that. It will need a tensioner, if only by the lengths of belt available. The tension should not be excessive, to protect the bearings.

Without more information I am guessing the countershaft arm pivots at the bottom to adjust the belt, and indeed to move the belt from step to step.

….

The big shiny red arrow points almost to a pimple on the gear boss. Is that pimple a grub-screw as Hopper suggests likely on that component?

There is a hint of perhaps a shallow flat on the spindle a little below the putative grub-screw. If so the grub-screw should bear on that. It is there to prevent the spindle’s outer diameter or thread being damaged by the screw.

(Cogs? Cogs? They be gears! Cogs are the inserted wooden teeth in mill gearing! 🙂  )

”””

That trio of shafts, if the lowest bar is a shaft not part of a travel-stop, and the tail-end gearing intrigues me.The top one is obviously the lead-screw, the middle one presumably the feed-shaft, and I guess the machine had powered cross- as well as long-feed.

However they seem geared together at the end.

I can only think they are analogous to the arrangement on the Harrison L5 I own, where the change-wheels drive both shafts linked in a three-speed gear-box on the front of the bed. A dog-clutch disengages the lead-screw when not needed, and the feed works though the key-wayed shaft. Only one direction can be engaged at once.

Otherwise does your lathe have a taper-generating arrangement that engages both feeds together? If so it is rare indeed but I have seen one in action, in a video made in Russia. There the machinist was making big “wood-screws” for log-splitters.

Looking more closely, I think the lowest “shaft” operates a clutch to stop the feed or screw-cutting at the required point.

 

[Adrian R2Participant @adrianr2]

I have the “alligator” type belt joiners – easy to mount/dismount and make a nice rhythmic noise when running. Belt material was originally leather but now some modern webbing stuff from ebay. Also acts as a handy slip clutch if you get a jam up!

 

 

[Nigel Graham 2]

On Nigel Graham 2 Said:

…

That trio of shafts, if the lowest bar is a shaft not part of a travel-stop, and the tail-end gearing intrigues me…

 

…Looking more closely, I think the lowest “shaft” operates a clutch to stop the feed or screw-cutting at the required point.

 

According to the (quite convoluted) description on lathes.co.uk, the bottom shaft powers the cross feed. The middle shaft powers the sliding feed and the top shaft is the leadscrew, used for screw cutting and for fine feed via the gearing on the tailstock end. A remarkably complex system.

No wonder each lathe took 900 hours of work to produce, the factory struggling but unable to get it down to an economical 700 hours. The Cromwell 3.5″ lathe cost 448 Pounds new, when the recently released Myford ML7 cost a measly 46 Pounds. Puts the Myford into a bit of perspective.

An interesting write up on an interesting old machine.

[lucerneParticipant @lucerne]

Thanks for the very useful replies, which I’m going to read through carefully. For clarification, the first image above is not my machine, mines the same model, just in dirtier condtion, but seems pretty useable and intact. Mine has a joined leather belt, with the staples and push through rod. I’m going to research the jockey pulley system option mentioned above, and possibly look at joining a Betalon flat belt. Would anyone have an image of a typical jockey pulley set up?

Apologies for any incorrect terminology used, I’m a complete novice where lathes are concerned, but I’m here to learn.

These are earlier pics taken when I first received it last month, looks rough but its been kept well lubed and so far has been remarkably easy to strip down and clean up:

 

 

[lucerne]

On lucerne Said:

Thanks for the very useful replies, …

 

 

Oh dear, that looks rather poorly, doesn’t it. Good thing the rest of the lathe is not in the same shape!

There may well be some facility for adjusting belt tension where that stepped pulley’s spindle mounts to that massive cast iron housing. Either mounting bolts in slotted holes that allow adjustment, or possibly some kind of eccentric arrangement where the bearing housing is rotated and the off-centre spindle provides belt adjustment.

Some pics of the spindle mounting both inside and outside the housing would maybe help.

It seems unusual that such a finely made toolroom lathe would have no facility for belt adjustment, even in those days.

[bernard towersParticipant @bernardtowers37738]

Dont forget that Lathes.co.uk do a flat belt making service!

[bernard towers]

On bernard towers Said:

Dont forget that Lathes.co.uk do a flat belt making service!

Thanks, yes I’m going to call them.

Oh dear, that looks rather poorly, doesn’t it. Good thing the rest of the lathe is not in the same shape!

Agree, been sat in a bramble bush for years but surprising the pulleys came off very easily and first go at cleaning them up looks promising. The grub screws look like new and the grease nipple came off easily.

 

The arm bearing is also in good nick, as there was a wodge of grease protecting it;

 

Adjusting tension on the motor to encased V-pulley should be doable as the mountings are slotted. Still not figured out the flat belt though…

 

The steadies are cleaning up nicely:

 

 

 

 

 

 

 

 

 

 

[lucerne]

On lucerne Said:

…

.. been sat in a bramble bush for years but surprising the pulleys came off very easily and first go at cleaning them up looks promising. The grub screws look like new and the grease nipple came off easily.

…

My advice is to keep a close eye out for damage that will be too expensive to repair.   When new this was an expensive machine, but somehow it’s history ended in a bramble bush!

CAD/CAM/CNC caused large numbers of manual industrial and educational machines in excellent condition to be dumped cheap on the second-hand market.  We, therefore, are inclined to expect wonders.  But before CNC made manual machines unwanted, ageing machines were often used for ever rougher work until useless.

Worst case, a high-end lathe would start in the tool-room until it could no longer hold tool-room tolerances.   Then it would be demoted to ordinary work, until wear in that role got too troublesome.  Then maybe several years making simple low accuracy parts.   Next step, demotion to rough work like skimming rust, where severe wear isn’t a problem, nor are broken clutches, knackered lead-screws, and other major faults.  Final indignity was being moved outside as an anvil or saw bench!      Most industrial manual lathes were worked extremely hard, think semi-skilled machinists driving them piece-rate on a 3-shift system for years on end, until the lathe was scrap.   This is why very few hobbyists before about 1965 owned ex-industrial machines.   If in good order, they cost big money.  If worn out, they cost a fortune to fix.

Anything is possible:  maybe yours came from a firm who treated it well until they needed the space, didn’t think it worth selling, and dumped a decent machine in the hedge!

Normally I recommend cutting metal as the best way to start fault finding, but that assumes the machine is in basic running order.  On this one, beware spending a lot of time and money only to discover after a few months that it has unaffordable problems.   For example, if the bed is badly worn under the chuck, detected with a straight-edge, are you up for having the bed reground?   And if the bed is badly worn, then the leadscrew probably is as well…

Dave

 

 

[lucerne]

On lucerne Said:

On bernard towers Said:

Dont forget that Lathes.co.uk do a flat belt making service!

Thanks, yes I’m going to call them.

Oh dear, that looks rather poorly, doesn’t it. Good thing the rest of the lathe is not in the same shape!

Agree, been sat in a bramble bush for years but surprising the pulleys came off very easily and first go at cleaning them up looks promising. The grub screws look like new and the grease nipple came off easily.

 

The arm bearing is also in good nick, as there was a wodge of grease protecting it;

 

Adjusting tension on the motor to encased V-pulley should be doable as the mountings are slotted. Still not figured out the flat belt though…

 

If that  bronze bush in the massive belt guard casting is fixed, as it appears to be, then the only way to adjust belt tension may  be shimming the four mounting bolts at its base. U-shaped shims around the front two mounting bolts would pivot the belt cover back away from the lathe headstock spindle and tighten the belt.

Adjustment would be limited but once set could be left alone. You don’t need to slacken off flat belts to change them from one pulley step to another, so probably not worth mucking about with a jockey pulley. You just push the belt over to the next smaller pulley as you rotate the chuck by hand.

That grease nipple may well be an oil nipple for an oil gun, a la Myford etc, or not.

[duncan webster 1Participant @duncanwebster1]

I my youth we changed belt from one pulley to another under power with a piece of stick. It’s a wonder I’ve still got all my arms, hands and fingers

[duncan webster 1]

On duncan webster 1 Said:

I my youth we changed belt from one pulley to another under power with a piece of stick. It’s a wonder I’ve still got all my arms, hands and fingers

Hmm, I must try that next time I have the old Drummond flat-belter fired up. I will report back — if I can still type.

[Howard LewisParticipant @howardlewis46836]

The Motor to countershaft belt was tensioned by moving the motor within the slots, and then the belt from Countershaft to Spindle tensioned by the weight of the Motor and Countershaft assembly pivoting about its shaft?

Howard

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