Myford headstock bearing replacement

[Martin KyteParticipant @martinkyte99762]

The spindle should have a scribed line to the rear which when new should line up with the slit in the locking collar when new. Apparently with wear it can 'migrate between 5 and 10 degrees.

If it's way out it would indicate that something is amiss. It could of course be some integral number of whole turns out in which case you have not proved anything

Previously described in the diagram on this thread.

**LINK**

Maybe this will give you some additional indication.

regards Martin

[LambtonParticipant @lambton]

It is important to have the front bronze bush secure so I suggest that you remove it clean up the surfaces and use some suitable Loctite to secure it. You will need to hold the bush in the fully back position until the Loctite sets completely – Use a length of studding and some large washers for example to hold it in firmly. Then readjust the preload on the back to back ball races EXACTLY as per the Myford instructions. When the Loctite has set reinstall the spindle taking great care to get the minute clearance necessary between the spindle ant the front bush by adjusting the ball races as a "locked together pair". In my experience you should not see much, if any, oil emerging from the front bush during normal use IF the clearance is set correctly.

Eric

[AjohnwParticipant @ajohnw51620]

There shouldn't be any need to loctite the front bearing in. It's not something I would do even though it's unlikely to need taking out again.

The bearings aren't easy to set up and wear can make it even more tricky. More of that later.

It sounds me like you haven't got the rear bearings sufficiently pressed together to actually locate the spindle. It's been a long time and I could do with a drg of the headstock in front of me however think about it this way.

The rear most ring nut locates the spindle under cutting pressure. Unscrewing it move the cone further into the front bearing. Tightening it the opposite, it moves it out.

The next ring nut sets the pre load on the rear bearing pair. Tightening increases it etc. There must be some preload.

People seem to have a lot less trouble adjusting once they look at it this way rather than the usual description as many people are aware of which way to turn things to move screws in and out.

The front cone is not intended to take end loads only side loads so it needs to be sat to maintain a minimal space for an oil film. The end loads are taken by the rear bearings. If the front cone moves further in under load it's effectively forming a wedge so the oil film doesn't stand a chance of standing up to the load.

This gives some idea of how finely the rear bearings need to be adjusted. Fractions of a thou can make a difference. In fact for ultimate performance the lathe needs to be set up according to the temperature of the headstock and spindle and it needs to be run for some time to allow friction to warm it up. I wont bore you with how I know that but there is always some friction in bearings and on lathes when they are adjusted correctly they will warm up.

If the rear bearings are set up correctly the main problem with the front bearing may show up. Cutting and belt tension loads will tend to make it wear oval. This is why on just about all lathes belts shouldn't be any tighter than they need to be. Some people might over tighten to try and pull the front bearing into the oval. More common on ML7's with plain bearings.

Without a lot of practice people are likely to need a number of goes at setting it up over a period of time to get it right. From what I can gather a good compromise limits an S7 to a max single drill size of 1/2" in mild steel. That's from people who use them. A plain bearing ML7 can do a bit bigger. It suggests that they still have some movement in the rear bearing though and I never got as far as fully sorting this out on mine as my Boxford cropped up. The next owner didn't finish of the rest of the refurb work otherwise I would have had a go at setting them up for him.

The only way I have found of sorting preload out is to feel for heat under the bearings inside the spindle. After about 15mins running on a boxford they get very very warm but not what I would call hot. I also found that each time I drilled a larger hole they loosened off a bit, probably because they use grease which is hard to displace. It settled down after several adjustments. Trouble is I now know that the front bearing is slightly oval so it's going to get changed. The same cut takes a minuscule cut if it's run down the work again and it's not due to the bar bending.

John

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[Martin KyteParticipant @martinkyte99762]

I agree with most of the above but would question this statement.

"The next ring nut sets the pre-load on the rear bearing pair."

My understanding is that the locking ring on the end of the spindle sets the preload which is why it is adjusted first with the front cone free and the journals locked together with the castleated rings.

The rings move the entire pre-loaded assembly into or out of the headstock thereby adjusting the front bearing clearance.

regards Martin

[KWILParticipant @kwil]

Martin you are quite correct,

Simply set the bearing preload and leave it alone. The front cone adjustment is a separate activity and to be honest, it is a lot easier using two "c" spanners, the difference between touching and the normal clearance is around a 0.25" peripheral movement of the locking ring, so final tightening is carefully done.

[Martin KyteParticipant @martinkyte99762]

Nice being right sometimes.

It's easy to see why the old Myford way works. The clearance is gradually reduced until the front cone is just too tight and then the final rap with the (small) hammer on the C spanner of the second ring just eases it off that fraction to give the right clearance.

Took me ages to figure it out too.

regards Martin

[AjohnwParticipant @ajohnw51620]

Posted by Martin Kyte on 24/11/2016 12:31:14:

Nice being right sometimes.

It's easy to see why the old Myford way works. The clearance is gradually reduced until the front cone is just too tight and then the final rap with the (small) hammer on the C spanner of the second ring just eases it off that fraction to give the right clearance.

Took me ages to figure it out too.

regards Martin

Well I did say that it was a long time ago and I could do with the drg.

I was on the Myford Yahoo groups at the time. I wrote up some instructions that people seemed to have a lot less difficulty understanding. They may still be there. From memory it just uses the terms screw in screw out. The other ways just confuse people.

However once that is understood actually getting them dead right is not easy and is likely to take a number if adjustments even after the lathe has been used for a while.

Boxford set a torque on the spindle for setting preload. For most it just doesn't work and leaves them too loose. Maybe they do it before adding grease or there is a lot less grease or very slight bearing wear causes problems. Some of the bearings are way too tight to allow sensible adjustment as well.

John

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[KWILParticipant @kwil]

Simple way to test your A belt tensions, with your fingers, check that you can put a 1/4 turn twist on the belt between pulleys, no heavy weight acts, just a light touch.

[Nathan SharpeParticipant @nathansharpe19746]

I'm glad I bought a Harrison! 25 yrs in my ownership and none of this sort of faffing about. Nathan.

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