Myford ML7 judder

[ace]

Hi all

I have been parting off some 1" round stock on the lathe with a rear mounted tool post (Myford type) and always get a judder / vibration. I have all tooling sharp and well bolted down including the saddle and turn at a lower speed but it makes no difference. I am wondering if the problem lies in the main bearings. There appears to be no movement in the shaft and it turns freely but I am not sure how to check the bearings for play. they are of the split white metal type. My last attempt to part off ended in tragedy for the tool holder as the parting off knife jammed and snapped the locking cam. The use of cutting fluid does not remove the chatter either. Any ideas on how to check the main bearings are
1/ free of play
2/ bearing caps are tight enough.

Thanks

[S.D.L.]

My best lesson on this was on a colchester master trying to part some 316 stainless steel M24 Bolts off at work when I hadnt ordered the right length bolts. Tried to do it as taught at school (many years ago) and as discussed in most model engineering books. Ie slow speed slow hand feed. Wouldnt cut.

Mick the machinest came over and said no chance that slow. and Put the RPM up and did it on power feed, cut like butter then.

So try more RPM and if no power feed feen in staedy so that it cuts not rubs.

Try doing a facing cut on a poiece of scrap at your parting settings then try at your nornal facing settings. Parting shouldnt be that different from facing.

The upside down tool at the rear is designed to compensate for bearing lift so that the tool goes free instead of digging in.

Steve Larner

[houstonceng]

Ace

It could be the cross-slide that's loose rather than the bearings. Did you lock down all the parts (like saddle & top slide) that you weren't changing ? Was the gib on the cross-slide firm ?

If not. your back TP use would lift and twist the saddle, X-slide, top-slide assy and, perchance, break the parts you have.

Maybe ?

[chris vine]

Hi Ace,

To check the main bearings for play is easy if you have a dial indicator (clock) of some sorts.

Simply set the indicator to read on the top of a chuck and put a piece of stoutish wood on the bed and under the chuck. Using the piece of wood as a lever, attempt to lift the chuck, gently but firmly!! you should not find the chuck lifts by more than about 1 thou. That is free IE easy lift. if you pull hard on the piece of wood you will continue to find movement but this is just parts of the lathe flexing.

As for the bearing caps, I think on the ml7 (but am willing to be corrected) that they tighten down onto shims so that they should be "fairly" tight. IE within reason, tightening the cap bolts will not adjust the bearing.

You could check the end play of the spindle with a clock as well. Again much more than 1 thou would be too much.

(If you put a clock reading tenths on a bar in the chuck with the clock stand on the bed, you will find movement of a tenth or so, just by leaning with gentle hand pressure on the tail stock.)

Others are correct as well to point you in the direction of other play. You may well find that a much higher speed will help. For example I would use around 2000 rpm on 1" mild steel using a indexable carbide parting blade on a super 7: a bit more rigid spindle than an ml7.

Chris.

[Noddy]

When I first tried my ML7, it chattered like hell, a friend suggested adjusting end float in the spindle (just loosen the allen grub screw in the collar at the end under the change wheel cover, tighten up snug by hand and tighten the allen screw again.) It worked, I check it regularly now.

I've never tried taking the bearing caps off to look at the shims, and I've heard it is really easy to drop them in the grit and swarf if you do...

Hope this helps
Keith

[ivanp]

when i first got my S7 i had all sorts of trouble parting off.
in fact i avoided it when i could .
what really changed every thing was when i had the bed re-ground and the saddle fitted my myford at the same time.
This really made a big difference the only other thing i did was invest in a Dickinson tool post.
but as far as i remember it was the correct fitting of the saddle to the bed that made all the difference .
parting off is not a problem now.

[Tel]

Slow speed has never worked for me - spin it as fast as you dare, with light feed

[ace]

Hi Tel

Slow speed didn't work for me either! I have a fear of higher speeds after last year when the bugger jammed and shattered the blade sending shrapnel in to all directions including my left arm. I have since tried a few things as others have suggested and managed to part off two 1/8" X 1" dia stock without trouble although I did flood it with cutting fluid this time. I am using the short cross slide now instead of the longer one, don't know if that has made the difference .


ACE

[pendembu]

If you buy the ML7 manual from Myfords it gives clear instructions regarding adjusting the bearings by removing shims.The capscrews on the bearings should be tight.
Parting off problems on small lathes are nearly always down to lack of rigidity in the build of the lathe and headstock and the ML7 is no exception.I recently had my 1969 model bed reground and new hardened mandrel and p/bronze bearings from Myford.It solved the parallel turning and parting off problems but at a cost of £600,more than the cost of a new small chinese lathe and the same as the cost of a second hand CVA for sale locally which I should have bought instead of refurbishing the ML7!