ML7R/Bearing 'Rumble'

Hi,

I have a Myford ML7R, had it for a few years in order to teach myself machining. I enjoyed it at school and now have the peculiar passion for gas turbines and wanted a ‘precision lathe’ to build my engines with. The previous owner used it to make steam engines.

When I first set the lathe up I did so as per instructions laid out in the handbook and all was good and I found I could turn quite accurately, (for a beginner).

Recently I noticed that the chuck seemed to be running out of true. I whipped it off and made a measurement with the DTI on the mandrel nose, in the photographs. Due to work commitments I’d not run the lathe for a year or so and during that time I’d changed the motor as the original stopped working. The motor was changed and nothing other than an oil and dust has been done. The lathe is located in my workshop/basement and is not subject to any great changes in temp’ or humidity.

The lathe runs very sweetly with no load but when cutting with hard steels or larger diameter soft material there is a nasty rumble that comes from the headstock. That is cuts bigger than a few thou’ on non-hardened stainless steel. This is is only heard when taking right-hand cuts and parting-off. There is no unusual sound when drilling from the tailstock. There is no obvious play in the headstock mandrel, in fact it all seems very smooth.

The lathe itself has had some use but is lightly used by me and regularly oiled and much loved, though I cannot tell if the headstock-bearing is receiving any oil via the wick system. It looks to me that oil may not be reaching the headstock-bearing as the cup remains topped-up whereas in the past I’m pretty sure it drained quickly under use. i should point out that heavy right-hand cuts previously produced a loud rumble from the headstock bearings even when there was no run-out on the mandrel. I should say the ‘rumble’ is loud and I back-off when I hear it.

I’m keen to adjust the headstock mandrel to see if that will sort the problem out, but as a complete novice I fear doing more harm than good. I understand how the mandrel is supported (in theory) and I’ve read how to adjust for wear and have the equipment for doing so. It’s my lack of experience and as I said fear of making things worse that is holding me back.

As for the photographs, these two images show the run-out of the mandrel nose. I have disengaged the cone-pulley to bull-wheel so the headstock mandrel can run free on it’s bearings. It has a smooth rotation and has no discernible play. The movement of the needle is approx. 5.5 thou’ and I’m presuming this is out of tolerances?

Any help in the way of knowledgable advice would be very gratefully received.

Cheers, Jonathan

Re your point about oil not getting to the headstock bearing. If you have not run the lathe for some time the wick may have dried out. Take the oil cup off and use a pump oil can to force oil into the resulting hole until it seeps out of the bearing. This will re-establish the "wicking" action.

Thanks for the input advice Robbo, I'll give it a go. Cheers, jonathan

If it is a rumbling noise it could be the rear thrust bearings. Maybe they have dried out. I thought they ran in grease but could be wrong on that.

I would suggest getting more of what ever it should into the rear lubrication nipple over them and running the lathe for say 1/2 hr without any load and then see if things have improved.

Plus the other suggestion.

The way the bearing set up works means that the rear thrust bearings locate the spindle. That is used to set the clearance on the front cone bearing. Lots of people have problems setting this up so do try the other option before dismantling etc.

John

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I cannot see how a spindle running in a plain bronze bearing can run this amount of true,unless the bearing is slack and while rotating the spindle there is an uneven "pull "'on the spindle,I would check the thrust bearings at he other end of the spindle it may be these that are rumbling and if they are very worn or damaged ,that end of the spindle may be running well out of true and causing the spindle to run out of true by a lot smaller amount in the front bearing.

Hi, I checked the oil cup by removing it. Plenty of oil dribbled out of the chamber and collected in a pool on the swarf-tray. Along with it also came swarf? which I presume is from the bearing?? Not sure what to make of it really!!! Is this normal?

I also checked the run-out on the rear of the mandrel and it's showing lest than two thou' of run-out unloaded.

Having recently replaced the two rear thrust bearings on my old Myford Super 7 I went through this experience. On mine anno domini had left its toll and the tracks were visibly worn and rumbling.

The two rear bearings are lubricated by oil, not grease. Because they are adjustable they cannot be sealed types and the end loading is very critical to get the correct amount of end float on the shaft. If the end float is too great then the front tapered bearing can get forced into too great a contact with the spindle when drilling from the tailstock. The typical end float is only about a thou when correctly set up.

You will need the special C spanner to unlock the two ring nuts that hold the two bearings in compression. The Myford manual is a bit vague in the description! Having unscrewed the front bearing ring by, say, 2 turns you then tighten the back bearing ring so it pulls the two cages back into full compression. Sometimes you need to give the back end of the spindle a smack with a rubber hammer to jolt the spindle forwards.

Forgot to mention the bearing pre-loading is performed by the screwed collar on the far end of the spindle that the primary gear is attached to.  This sets the rear bearing loading and because they are angular contact bearings it is fairly high.  Slacken off the grub screw and slacken off the adjusting collar half a turn or so.  The rear bearing work the same way as taper roller bearings and the two bearings are back to back so as you tighten the collar the two bearings get squeezed tighter together.  A split ring washer sits between the two outer parts of the bearings so the inner "cones" can be squeezed without moving the outer races.  The bearing C spanner nuts contact only the outer rings holding them in correct alignment with the rear housing bore.

Having freed the front bearing pour copious oil into the gap to flood the front bearing and also force more oil from the oil cup until it is seen to exit the front bearing gap. Then pull the spindle back into the tapered bush by reversing the screwing of the bearing rings, until the spindle just nips in the front housing. Then back off about 1/4-turn and lock the bearing rings again. This should give a preliminary setting to try for end float. A final tweak is often needed, it can take half a day trying minute adjustment to get everything 100%, so take your time. When you think it about right, spin the lathe up at max rpm and leave running for 10-minutes and keep checking the front bearing housing for temperature. They do run a little warm at high rpm but not excessively so. 

Minor adjustment to the rear bearing pre-loading is done by the screwed collar to eliminate the last little bit of end float.

Edited By John Fielding on 04/03/2016 08:38:36

Edited By John Fielding on 04/03/2016 08:40:42

Edited By John Fielding on 04/03/2016 08:43:23

Lots about adjusting spindle bearings here ; **LINK**

That swarf does look like bronze, but how can it get up into the oil cup if there is a wick in the way.  Maybe check that there is a wick.   If the bearing was run dry then a bit of trapped turning swarf could scrape the bearing.

Edited By Robbo on 04/03/2016 09:00:49

Hello Jonathan,

I have never seen the oiling cup end of the front bearing open before but I would expect to find the end of the oiling wick at that point. It is spring loaded to help keep it up in contact with the bronze bearing and if the spindle has been taken out in its time before the lathe came to you, it might have been removed entirely. Myford sell the replacements.

I am though sure it should not be possible to get bronze swarf out of the oiler, the wick alone fills the oiling passage, so I fear damage has occurred and is on-going. You also have far more free play than you should.

There is an old trick with a long screwdriver to use as a stethoscope to listen to running bearings, put the blade into good contact with the journal and press your ear up against the handle end. Try each end of your spindle under varying loads to listen to them, it will tell you plenty

It would pay dividends to buy the handbook from Myford, they give full instructions on setting the bearing clearance, how to retain the wick with the spindle removed and other useful information

Kind regards

Brian

Jonathan,

I have sent you a PM Please check your inbox, located on the top green band,that should be flashing

Eric

The problem with adjusting these bearing is down to realising which nut does what. Myford don't explain it very well. Adjustment has to be a bit iterative and mentioning ant clockwise on some etc just adds confusion. All of the nuts use right hand threads. Some one on the yahoo myford group asked me to put a run down on adjusting them in their files section. It's still there and more verbose. Key points.

Starting from the left end of the spindle call the nuts A, B and C. A sets the preload on the ang contact bearings which is crucial. B and C holed the out races together against a spacer so need to be tight when the preload is set. The relative position of B and C when tight set the front bearing cone clearance.

Get the preload correct first. As myford point out don't slacken the clamp screw off too much, just enough to allow it to be turned by hand but not easily. At this stage the front cone bearing mustn't be tight. Myfords aim seems to be to set zero clearance in the rear bearings and not some degree of preload. The front of the spindle can be supported and rotated by hand as the preload nut is adjusted ideally looking for slight increase in stiffness. This is likely to increase further when the nuts clamp screw is tightened. I suppose people could put a dti on the spindle nose and waddle that end about to detect when the rear bearings are fully home but I think they will find they need to be tighter than that might indicate.

Next comes nuts B and C to set the front cone clearance. These move the whole spindle back and forth without changing the rear preload. That is a balancing act. More drag can help with finish but will also reduce the max size of a hole that can be drilled in one go. I have heard figures like 1/2" for that on well set up machine. An ordinary ML7 will manage more.

Bearings generate heat when they are run for a while so excessive preload on the rears can be checked by running the machine at say 1000 rpm for 20 min. A finger in the spindle under the bearings can give a fair idea of what's going on. Even loose bearings will generate some heat. I usually reckon on very very warm rather than hot.

Once that has been done chances are that things will have loosened off as oil levels have settled down so more adjustment is likely to be needed - hopefully just the cone bearing clearance.

One thing to realise about lathe bearings. Generally they tighten as they warm up. The headstock offers a better conduction path for the outers than the spindle does for the inners. I was told a long time ago that actual inner bearing temperatures are usually some what over 100C on ones with rolling elements. It's interesting that Pultra state hot for the plain ones in their lathes.

John

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I should add a bit to that post. All is fine when the cone and it's bearing are round. Getting perfection once they have any significant ovality in them is likely to be impossible. That can mean having to accept a compromise on the front cone clearance in the bearing. The drag from it increases because one side of the cone is running clear and the other is rubbing / too thin a film of oil which puts and uneven load on the rear bearings as well.

John

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Hi Ajohnw,

I concur with your comments, the Myford manual and the Myford book seem to do more to confuse the reader and only once you have successfully adjusted this lot do you really understand what makes it tick!

When I pulled the spindle out of my Super 7 a few months back to replace the rear angular contact bearings I was pleasantly surprised to find I could see the original scraper marks on the front tapered bronze bush. The shaft was also like new, no scoring at all. Since my S7 was made in 1971 I thought that must be a good advert for the quality of the original machining and choice of material.

I can only assume the wick feed in the questioners ML7R has been removed, there is no way bronze could find its way from the bearing into the oil cup normally. One oddity I notice with my S7 is when I lift the sprung loaded top of the oil cup I can see the oil level suddenly start to fall. I can only assume that the spindle generates a vacuum when the top is in place and top cap must seal really well?

John,

"One oddity I notice with my S7 is when I lift the sprung loaded top of the oil cup I can see the oil level suddenly start to fall".

Exactly the same thing happens on my S7. I am sure that John is correct , the rotation of the shaft creates a small change in pressure down the hole containing the wick and spring. I take this as a sign the lubrication system is working correctly as designed and the spindle adjustment at the front cone bearing is correct.

Since buying an oil gun capable of actually forcing oil trough Myford oil nipples I have found that over lubrication of the rear bearings makes then noisy (even brand new ones) at about 1000 rpm until the excess oil has drained away. I have changed the relevant oil nipple for a flip top gravity feed type and apply just a few drops of oil a few times each turning session.

Eric

And for those interested, my oil cup acts in the same way, always after running. I fill it up, watch it drink that and repeat the fill. Left idle the oil level remains largely unchanged.

Regards

Brian

Mine would empty the oil out all on it's own if just left standing - down to the wick doing what it should.

I have a Pulta that uses the same system and have noticed that the rear bearing wicks out it's oil but the front one doesn't suggesting that there isn't a wick in it. Some one may have removed it and then over filled a bit to oil the front bearing each time it's used. Probably done to avoid being splashed now and again.

John

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Hi all, been away with my boys to see 'Flying Scotsman' in York. Nice. Really I wanted to say thank you for all who offered advice and instruction.

I think the best course to take right now is to have an expert take a look rather than 'tinkering' myself. The problems I have are mainly due to lack of hands-on experience and it would be helpful to watch someone else adjust the headstock spindle or tell me the bearing need replacing. Once I've seen it done I'll be more able to have a go myself in the future.

Looking at some past threads on another forum topic I've found someone who may be able to help though I'm yet to make contact despite trying? If anyone knows anyone who is qualified to repair/adjust my lathe please do let me know, I would be most grateful. Obviously this would be treated as a professional service i would be willing to pay for. I'm based in North London not far from Liverpool Street Station.

Thanks again for all your help, best Jonathan

Unless you find a local model engineer willing to help as a favour I don't think you will have much luck Jonathon.

I'm basing that on the Midlands, A supplier here has often had requests and suggested I did exactly what you want. I had other reasons but one problem is that on lathes one thing often leads to finding another and so on.

John

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Sure thing John. Though I'm not looking for favour, I'm willing to pay, inc travel. I'd even consider delivering the lathe myself only it's heavy and awkward and I'd rather not. Still, cheaper than buying a brand new Super 7!

Right now I'm stuck and can't progress so I've got no choice. Not a great place to be!

Cheers, Jonathan

There were a couple of guys doing Myford work a few years ago, I think they travelled to jobs and were ex Myford.

I never needed their services but they got good reviews at the time.

I do not know if they are still active, and am only able to locate the following email address on my system now, for Darren Boden (I think).

[email protected]

Edited By V8Eng on 10/03/2016 12:00:35