Any idea why this lathe is chattering? Spindle bearings?

[SteveT]

In a past post you commented that you dropped the head, if you have a crack in the casting your would be able to set up the bearing okay but under load would get the reported chatter.
Worth checking I think .

[Fergus OMore]

At the risk of being very wrong, might I pen a few thoughts? Going back to the beginning of getting your Boxford, did you ever test it under power to do precisely what you are doing now? Or did you buy a 'basket case', scrape it or whatever? None of us ( ?) have that information.

It may well be that your spindle/headstock assembly was either worn or incomplete. Could you inform of this, please?

Regards


Norman

[hermetic]

if you did put a tailstock centre in, and the situation immediately improves, you will have proved it IS the spiundle bearings.

[loply]

Hi guys,

Fergus - I did test it before I launched my little rebuild, and it was similar to now, ie chattered a lot.

Steve - yup, I'm concious of that, I can't see any cracks but if I do order new bearings I will fit them to the spare head just in case.

Doc - when you say the chuck is 'sprung' what do you mean sorry? Are you referring the the jaws not being parallel?




So I've just been out and done some more tests. I managed to tighten the spindle bearings more by extending the spanners to give me more leverage, I think the rear bearing is too tight a fit on the spindle, as it took a lot of force, but doing so has reduced the end play to half a thou and got rid of the bearing noise. Also, it has introduced a bit of drag and for the first time the bearings are getting warm.... I can still deflect the spindle nose by about 0.01mm by pushing on a 200mm test bar though.

However, I think I've got to the main cause of the issue. The chuck just isn't rigid on the spindle nose.

I confirmed the shoulder on the spindle nose (which the chuck butts up against) is running true, and has no burrs, nor does the back of the chuck where it hits this shoulder, but the chuck body can easily be deflected up and down by several thou just by pushing on a 6" workpiece.

Putting a tailstock centre in makes it turn perfectly, I can suddenly take a 1mm cut on a steel bar and get a good finish.

The issue seems to be therefore that the workpiece is wobbling because the chuck isn't rigid on the spindle.

I checked the chuck was bolted tight to it's back plate, and inspected the spindle threads really carefully, can't see what the problem is though  Surely if the chuck is butted tight up against a true-running shoulder on the spindle, and there are no burrs, it should be tight and rigid? Unless it's just the small amount of deflection in the bearings being amplified?

[chipenter]

what the problem is though  Surely if the chuck is butted tight up against a true-running shoulder on the spindle, and there are no burrs, it should be tight and rigid? Unless it's just the small amount of deflection in the bearings being amplified? or is it butting up agains't the end of the threads somthing else to check .

[SteveT]

Sounds like you are getting close to the problem  but I note your comment that the back support bearing is tight on the spindle, in my last post I mentioned cross location i.e the spindle and bearing have no room to expand so preventing free expansion of the bearing arrangement. The back bearing should be a light transition fit on the shaft or the housing, if that back bearing is locked in position you can have a multitude of problems including short bearing life.

 

[philf]

e... in my last post I mentioned cross location i.e the spindle and bearing have no room to expand so preventing free expansion of the bearing arrangement. The back bearing should be a light transition fit on the shaft or the housing...

Steve,

The normal arrangement of two taper rollers is fail-safe in that, as the spindle expands with the heat, the inner races move apart thus increasing clearance.

I agree the rear bearing shouldn't be a tight fit on the spindle.

Phil.

[Fergus OMore]

Apologies but I may be quoting the  obvious but a screwed to spindle chuck does not depend on the thread but to the register- or the backplate if there is no register.


Cheers


Norman

[seadog]

I was in the middle of posting a reply, but beaten to it by Norman. The regsiter on the spindle must be identical to the opening in the backplate. The thread is just to hold it onto the spindle.

[loply]

Thanks for all the input guys, few more things to check.

I don't suppose somebody with a similar sized lathe could chuck up a 6 inch bar, put an indicator on the chuck body and see how much the chuck deflects by when pressing by hand on the end of the bar?

[John Rudd]

The normal arrangement of two taper rollers is fail-safe in that, as the spindle expands with the heat, the inner races move apart thus increasing clearance.

I agree the rear bearing shouldn't be a tight fit on the spindle.

Phil.

As Phil says.......
The inner races on both bearings should be a good fit without being too tight else you wont be able to set the bearing pre load correctly

[bertie_bassett]

Thanks for all the input guys, few more things to check.

I don't suppose somebody with a similar sized lathe could chuck up a 6 inch bar, put an indicator on the chuck body and see how much the chuck deflects by when pressing by hand on the end of the bar?

I can see what I get on my viceroy tomorrow if I get a chance, mine needs a lot off attention but does actually turn out fairly good work.

have also got nearly all the drawing for the 4.5 and 5'' lathes, might take some digging to fine the headstock drawings but I'm sure they are there somewhere

[loply]

Thanks mate, would really appreciate that.

[rotorhead]

Hi loply,

I helped my son dismantle his Viceroy a long while ago, unfortunately I've forgotten its configuration, but I did download some original files from Denford, I'll include them for you.

If these are helpful I'll see what else I've got..

[DavidA]

Loply,

Have you joined the Denford machine forum ?

If not, you should.  I just registered and there is a whole lot of stuff on all their machines. You could save yourself a lot of grief by going to the people who are using the same machine as you.

I can't think why I didn't do it sooner.

Dave.

p.s. check your PM.

[bertie_bassett]

with a bit of bar about 6 inches or so hanging out my chuck I can read about 1 thou of deflection on the side of the chuck, if I pull fairly hard toward me.  that's on a badly maintained viceroy tds

id second joining the denford forum, loads of info on the site. a member there called dazz did a full strip down of his a few years back including a vsd conversion. pics are still there I think
plus they have all the original drawings

[loply]

Thanks for that Bertie. I'm getting about 2 thou in the same situation, just pushing hard with the fingers of one hand.

I presume you took the reading off the end of the chuck nearest the tailstock?

I might just go ahead and try some new bearings out of interest as much as anything. Seems about £45 for a pair.

As far as I can tell the bearings fitted aren't high precision or anything, just standard timkens as used on wheels and other things.

[bertie_bassett]

sorry ment to add a pic of my set up but forgot



as you can hopefully see I was measuring between the headstock casting and the rear end of the chuck. pushing quite hard wit my hand I was getting 1 thou deflection either way.

things to  note though:  iv never adjusted the preload on this lathe, its got fairly thick grease in it and takes a little while to get up to speed when cold. the chuck jaws are definitely belled out,  generally in need of an overhaul.

[loply]

Success 

Thanks for all the advice folks, think I've got this sorted.

I ordered some new spindle bearings which gave me the confidence to go to town on tightening the old ones. As I mentioned earlier, the rear bearing is a stupidly tight fit on the spindle - instead of a sliding fit like my other Viceroy, it's a tight press fit (presumably a factory error?).

I put a 2ft extension bar on the spanner and cranked down on the rear bearing nut... nothing for a while, then crack, it turned an eighth or so... Half expecting that I'd cracked the casting I checked it, ran it for a while, then tried again... Literally giving it all my muscle, in fear of knocking the lathe over if I slipped, it moved another eighth or so. I backed the nut off then snugged it back up hand tight.

End play disappeared completely, and play on the spindle nose came down to about 0.001mm (down by a factor of ten). The bearings are getting pretty hot but I can keep my hand on them (although not by much). The chuck is still deflecting though not quite as much (but it doesn't seem to matter).

On that exact same steel bar from the first video I can now take a 0.4mm deep cut without a single bit of chatter! Turning 100% parallel too... 0.00mm taper in 4 inches.

Couldn't be happier! The lathe is now performing exactly as I'd hoped. Thanks for all the advice everyone.

Video - this is at 1800rpm, 0.4mm DOC -

[awemawson]

Excellent news 

Always good to hear of a satisfactory conclusion to these things 

[lordedmond]

If the bearing get to hot slack the nut off a hair ,with a hide mallet give it a clout on the end opposite the chuck to move the spindle in a little to take off the pre load a little.

But if it was me , but it's your lathe I would take out the spindle and polish the journal so the bearing is a rightish slip fit then you will be able to set it up easier


Anyway glad you have it sorted a cheap laser temp gun is handy look for 20 to 25 degrees C above ambient as a guide

Stuart

[Pete.]

If the bearings are getting hot that should ease the pre-load though it's not an ideal situation. To release some of the load I would back off the clamp nut until it's loose, spin it up until barely touching and put a piece of soft ally flat across the back of the spindle then give it a good hard crack with a large ball-pein hammer. Either that or extract the spindle and clean up the bearing diameter a bit to ease the fit.

Now you mention it I recall the (floating) rear bearing on my machine was really tight on the spindle too.

[DavidA]

All this hammering on the bearings sounds rather brutal to me.

Surely best to remove the spindle and fix it properly.

Dave.

[John Rudd]

Well I did say, the bearing inner races ought to be a tight sliding fit on the spindle

I've changed standard bearings to tapers on several machines....to find I had to polish the journals to ensure a good fit.....no hammer used or big spanners to set pre load....

Excessive tightening will cause the bearings to overheat....but you know that already...

If you have changed a wheel bearing on a car you will know what I mean...

[DavidA]

John,

The front wheel bearings on rear-wheel drive cars is a good example,

I also have changed many of these taper roller assemblies. Th inner part (inner race) being a light interference fit, and the outer part just slides onto the stub axle.

And just nipped up with a enough force to stop the play on the wheel.

No brutality needed.

Dave.