ML7 spindle and bearings

[Martin DowingParticipant @martindowing58466]

From time to time I play with different upgrades of my ML7.

About 17 years ago I got new spindle for it together with bearings made of phosphor bronze.

These bearings have never been scraped in so they are not perfect. Machine is turning well and parallel and some troubles are only when you are trying to part off lets say 1 inch BDMS or stainless (chatter, weird noises – real pain to proceed).

I have inspected bearings and it is obvious that they need scraping as extend of contact area is self evident.

There is no way that professional will do it for me as none are around where I live so I want to have a go at it.. There are few detailed youtube films treating the subject which I understand.

I understand that it is best to make "dummy spindle" for this job.

Is it correct that it should have relevant diameters 1 thou larger than original?

Also – such bearings can no longer be purchased so I need insurance – want to make a spare set of phosphor bronze bearings BEFORE any scrapping work.

Together with dummy spindle made to exact Myford specifications it could then be sold, assuming that my scraping job is successful.

I have a chunk of good tool steel, Toolox 44.

It has 44-45 HRc but still can be turned on my lathe with proper tools, gets nice polish easily and should be good for a mandrell.

Now I have question – how hard is original hardened Myford spindle meant to work with phosphor bronze bearings?

Will phosphor bronze bearings work well with 45 HRc spindle or you need to go for something in range of 60?

[Martin DowingParticipant @martindowing58466]

[HopperParticipant @hopper]

See issue 292 of Model Engineer's Workshop for a full guide with pics on how to scrape the bearings on an ML7.

You absolutely don't want a dummy spindle. It will almost certainly introduce extra errors into the process and is just a lot of totally unnecessary work. You scrape the bearings to fit the existing spindle then add half to one thou of extra shimming between the bearing halves to provide oil clearance. You can then scrape a tiny bit extra off the near-vertical surfaces adjacent to the join in the bearing halves to provide a tad of oil clearance there.

That's the way the professionals do it on machinery ranging from tiny hobby lathes to power station turbines bigger than your house. Beware of self-appointed gurus' wet dreams on YouTube. There is some good stuff there, but its buried amongst the world's largest repository of engineering misinformation.

Edited By Hopper on 15/10/2020 00:02:04

Edited By Hopper on 15/10/2020 00:05:07

[duncan webster 1Participant @duncanwebster1]

The original bearings are soft white metal, so I reckon you'd be OK with leaded bronze if you're making a new set. It's designed for bearings.

[Kiwi BlokeParticipant @kiwibloke62605]

With reference to Hopper's experience and knowledge, I would suggest that, for a Myford, shimming a well-scraped bearing 'to provide oil clearance' is wrong. Let's have a debate!

The ML7's spindle bearings will rarely if ever be working as true hydrodynamic bearings, so the added clearance is unnecessary and just leads to chatter – particularly under conditions of high radial load, at low spindle speed. Also, shimming changes the bearing's shape, rather negating the care taken when scraping.

[Martin DowingParticipant @martindowing58466]

Thank you for these comments.

@Hopper,

One oldtimer was telling me that dummy spindle is important but if for small lathe it is not a good idea then even better. Still will fabricate spare bearings up front, just in case.

Youtube guru which seem to know what he is doing is here:

https://www.youtube.com/watch?v=nxckVqdPVTA

 

There is also second part following this one.

 

Any comments on his work would be appreciated.

Will get thise MEW back issue online to learn more.

 

@Kiwi,

On number of occassions I have heard contradicting opinions about that. An argument is that you cannot just squeeze all oil out by perfect fit because galling of spindle or/and bearing wear leading to fast reconstitution of oil clearance will occur.

But I would appreciate any comments in this respect.

 

@duncan,

I have hardened spindle and phosphor bronze bearings.

 

Edited By Martin Dowing on 15/10/2020 08:06:00

Edited By Martin Dowing on 15/10/2020 08:06:34

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