Adjusting Myford spindle bearings

[Ron ValeParticipant @ronvale24328]

I know exactly what mick means, as i have the same problem.

When drilling from tailstock,mostly in the larger (1/2in up)sizes too much pressure on drill bit causes the spindle to stop rotating/jam/lock solid, whilst the motor and drive belt to the spindle are still moving. i.i the belt s slipping on the cones

As there is no measurable play on the spindle in both axis, i just give the gear end of the spindle a small tap with a rubber hammer when it jams. Temp solution but will get around to spending several days on solving it when i need to use the mill more that the lathe

[mickParticipant @mick65121]

Right I'll have one last stab at trying to get to the bottom of this problem. I'm no expert at machine maintenance, but having been a machinist for most of my working life I have a pretty shrewd idea of how to adjust various parts of most conventional machine tools.

I've gone back to the Myford operators hand book.

First unlock the RH ring towards you. Then the LH ring same direction until the outer races are again locked. Undo the back adjusting ring and advance by hand till met with resistance, this now has the inner races adjusted. Slacken off the LH collar one turn + a bit. Tighten the RH collar until the spindle cone and front bearing close to give zero clearance. Slacken RH ring by 0.250'' or 15 degrees rotation to obtain correct clearance between spindle cone and front bearing, tap spindle end with copper mallet to ensure the clearance is applied and check for free rotation. Tighten LH collar to secure adjustment. Pump oil into the front bearing using an oil gun placed in the front filler cap. Pump oil into rear bearings. Using the tail stock revolving center apply pressure to the spindle as if drilling, here the spindle will stop as will all the drive pulleys. When the pressure is released the spindle starts to rotate again, which would suggest that the spindle is being forced back against the bearing cone, so the rear bearings are not holding the spindle adjustment and allowing the small degree of movement to stop rotation. Any ides would be gratefully appreciated.

Thanks.

Mick

[KWILParticipant @kwil]

Mick,

Where are you located?

Someone nearby may well be able to assist if we only knew where you are!

[Michael GilliganParticipant @michaelgilligan61133]

Mick,

At the risk of stating the obvious …

I can see only two ways in which the spindle can move sufficiently to lock-up the cone bearing:

1. The pair of angular contact bearings is not acting as a single preloaded unit [so, either the outer races and spacer are not firmly clamped together, or the inner races are not correctly preloaded]
2. The pair is not sufficiently free to slide in the bore, and moves with a 'slip/stick' action … I have no idea what fit is required, but I suspect that this may be critical.

Sorry; no advice as such, but it may help to focus your mind.

MichaelG.

[CotswoldsPhilParticipant @cotswoldsphil]

Mick,

You state in your original post that the machine was OK before you took the spindle out. So it is safe to assume that the bearings are correctly orientated, ie they were not removed, and that everything else, spacer and 2 * woodruf keys are installed as per the drawing…So it must be down to adjustment, which from my experience, is very fine….

I replaced the bearings on my S7 late last year and found that after following the standard (book) adjustment procedure, the spindle locked-up when turning, just as you describe. It all resolved itself by following the revised instructions (to the letter) which requires a final tightening tweak (tap) to the L/H bearing nut by using a hammer on the end of the c-spanner – (Quote: which moves the spindle a couple of tenths to the right). All I can think is that the clearance is so critical that oil used in assembly, alters the feel / fit, and the final tap with the hammer helps disperse the oil.

Since that one lock-up event, I have had no further trouble. I can use a 1 inch drill in the tail-stock with no problem. One thing that I did notice, that has been reported elsewhere, is randomly noisy bearings until the excess oil drains away – sounds like a coin being drawn along the teeth of a metal hair comb.

One other thing that might make a difference is that when you move the spindle out of the cone to set the pre-load (L/H nut towards you) that you lock the outers together by tightening the R/H nut temporarily. I found I needed an allenkey in the grub-screw to get any form of puchase on the pre-load adjusting collar. The instructions also warn about loosening the collar too much which will affect the fit of the thread.

Just my personal experience which I hope you may use as a sanity check.

Regards

Phil H

[mickParticipant @mick65121]

Thanks for the moral support Phil, I do lock the outer races before setting the pre-load, but seeing as there's rain forecast for tomorrow I'll give it another go, as by the law of averages I must get lucky one day. Thanks to one and all for your input, if there are any ex-Myford service engineers within easy driving distance of Hastings, East Sussex, I be interested!!

[Maurice Cox 1Participant @mauricecox1]

I have just read through this thread again. I know this sounds a bit obvious, but, since the spindle has been dismantled, when put back together, was the spacer between the bearing outers refitted? If this was accidentaly left out, the preloading would not work and the spindle would be able to float endwise. Just a thought.

Regards Maurice

[mickParticipant @mick65121]

I didn't remove the bearings, so the spacer is still in place. I got lucky with adjusting the bearings yesterday and was able to do a days machining, unfortunately the adjustment has settled down today is and producing some chatter, but on readjusting I was unable to repeat yesterday's success, so its back to the drawing board tomorrow, mind you I am machining a six and a half inch Aluminum billet which is bound to highlight and problem with the bearings

[Author]

Posts