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Flexispeed main bearing replacement

Any ideas

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Julian Tolley19/04/2022 15:56:16
10 forum posts
9 photos

Has anyone replaced the main bearings on a Flexispeed or simat lathe please. The nose main bearing on mine is pretty worn judging by the rate of oil flow. From what I can find out its just a plain bronze bearing. Has anyone done the deed - always want to learn from others experience

Roderick Jenkins19/04/2022 17:01:39
2184 forum posts
608 photos

In all the Flexispeed and Simat lathes I have seen there is no separate bearing. The spindle is un-hardened and bears directly in the cast iron of the head stock. It is usual for the spindle to have much more wear than the headstock.



Nick Clarke 320/04/2022 10:07:28
1425 forum posts
63 photos
Posted by Roderick Jenkins on 19/04/2022 17:01:39:

In all the Flexispeed and Simat lathes I have seen there is no separate bearing. The spindle is un-hardened and bears directly in the cast iron of the head stock. It is usual for the spindle to have much more wear than the headstock.



While not for one moment disputing your experience in the case of these particular lathes - at University 50 years ago we were told that a soft material running in a harder one will pick up particles of the hard one which become embedded turning the spindle into a lap, so the harder one can wear more.

Andrew Tinsley20/04/2022 12:33:04
1630 forum posts

I am told that RR Merlin engines have the steel camshaft running directly in the aluminium block. The cams wore far more than the block for the reason Nick gives. It was said that the block could wear out half a dozen camshafts before the block became too worn for further service.


Hopper20/04/2022 12:48:27
6393 forum posts
334 photos

And yet certain Honda motorbikes of the 1970s commonly chewed out the aluminium head where the steel camshafts ran. Fitting a bronze bush in the ally head was a common fix. Camshafts survived unscathed.

The unhardened steel spindle on my Drummond M-Type is terribly worn where the cast iron step pulley rotates on it when in back gear. Seems like pieces of the harder steel get stuck in the softer cast iron and turn it into a lap that destroys the steel spindle. Cast iron makes a good lap. It's what we use for lapping Harley con rod bearing races etc.

It probably depends too on what grade and hardness of both iron and steel are used. Some cast iron can be quite soft as can some steel. But you would think lathe spindles might be made from something stouter than mild steel, even if they are not hardened. Probably something like 4140 or whatever the equivalent was back in the day the old lathe was made. I know old ME articles recommended " a suitable piece of truck axle" for making replacement or larger spindles for old lathes. That would be some stout stuff.

Roderick Jenkins20/04/2022 13:17:45
2184 forum posts
608 photos

It's a complex problem. Nominally "soft" bearing materials like white metal (Babbitt) work because there are harder crystals in a soft matrix. I imagine that Aluminium ALLOYS can offer a similar microstructure since the more advanced alloys are age hardened which means that by either time and/or heat treatment harder components are allowed to precipitate out into the aluminium matrix.

Here's the spindle of a Flexispeed lathe that I refurbished.

old spindle.jpg

Galling and wear can be seen at the headstock end. With the aid of some blue and 1/2" silver steel I could not find any indication of wear in the headstock. One of the problems with buying these small lathes second hand is that they have often been used without a countershaft (as mine was). This means that they have spent much of their life running at considerably more than the recommended maximum speed of 1000rpm.


Bazyle20/04/2022 17:08:56
6324 forum posts
222 photos

Cast iron and mild steel are a bit of a special case. Cast iron is steel with so much spare carbon that it makes flakes of free carbon or graphite as we all know. So you have steel rubbing on steel except that carbon gets in there and provides emergency lubrication when the user doesn't provide any.

Nigel McBurney 120/04/2022 18:09:02
1000 forum posts
3 photos

A steel shaft running in a cast iron bearing will last for a very long time provided it has plenty of lubrication,run short of oil and the steel shaft will pick up and score.I had a Volvo 240 ,the camshaft ran direct in the aluminium head,no wear after 110 k miles, a lot depends on using correct oil,new filters and change oil at the correct mileage.

Hopper20/04/2022 22:20:03
6393 forum posts
334 photos
Posted by Julian Tolley on 19/04/2022 15:56:16:

Has anyone replaced the main bearings on a Flexispeed or simat lathe please. The nose main bearing on mine is pretty worn judging by the rate of oil flow. ...

I'm not sure that oil flow is much of an indicator of wear. On Myfords they seem to throw oil everywhere out of the bearings even when good, all depending on the rate you put the oil in. There are no seals so nothing to stop the oil coming out of the bearing.

Better to put a length of bar in the chuck and yank it up and down while putting a dial indicator on the spindle between the chuck and headstock and actually measure how much spindle movement you have. Anything over a thou would be considered excessive. But half or even quarter of a thou would be ideal.

Neil A20/04/2022 22:55:06
107 forum posts

As originally built, the Flexispeed spindle runs directly in the cast iron of the headstock. That is unless someone has already done a modification and fitted separate bushes, always a possibility.

I don't think that the rate of oil flow through the bearings is a very good indicator of the degree of wear in the bearings. The bearings on the headstock of the Flexispeed are not a complete circle, being split for adjustment at the front. This discontinuity tends to wipe the oil film off and so increase the oil flow.

I would be more interested in how much measurable movement I could detect in the spindle. Tightening the adjusting screws can reduce the free movement, but it does alter the shape of the bore a little. Should not be a problem unless it really is badly worn.

The maintenance instructions state that given proper lubrication and run below 1000 rpm the bearings should have a long life. Having said that, The speeds on my machine with the pulleys supplied by Flexispeed, North Walsham, are approximately 1420, 815, 460, 355, 203, 115. Not quite in line with their own recommendations.

The instructions for adjusting the bearings are to tighten until a resistance is felt, then back off 1/8 of a turn. Then repeat for the other bearing.

I'm sorry that this does not really answer your original question, but I have added it just for information.

A photo of the headstock bearings might be interesting.


Julian Tolley15/05/2022 18:21:48
10 forum posts
9 photos

Thank you to all for the great replies. Of course it became apparent when I went to replace the belts with some 8mm Optibelt VB which run very well and go around the tightest radius pulley well. Going to post another question .....this time I'm really going to show how much of an amateur on this lathe I am..

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