Chatter/finish problem

Hi all

Warning - over enthusiastic novice alert!

Ever since I got my lathe a couple of months ago, it has had a finish issue. I presumed that it was my lack of experience, and I tried lots of cutting bits, different speeds and feeds, modifying the cutting point on lathe cutting bit et cetera. But nothing really made any difference. When I got the lathe, it was bolted to a piece of plywood, so I presumed that vibration was the issue, and I got hold of a proper stand, beefed it up with a piece of 6 mm steel plate as a table, and installed the lathe on it.

I then went through the process of adjusting all of the gibs, aligning everything, measuring the different run out, aligning the tailstock et cetera.

Same problem, worse in fact. See pic.

That was supported by the tailstock.

I had it to bits to change the V-belt, so I’m now familiar with the main spindle and the associated parts. Once the main spindle was reinstalled, there is no perceptible lateral movement, and the dial indicator does not measure any runout. However, I did discover that there is about 0.5 mm of longitudinal play. It seemed to me that that could easily be the culprit, and should be resolved anyway. The funny thing was, when I did some facing cuts, there did not seem to be any finish problem.

The race bearing (?) all seems fine. The bearing that the spindle sits in are lined with a brass sleeve, with a hole for oil and an indent for a grub screw to stop them moving about, and then obviously a bolt to set the overall tension. When running, I’ve managed to adjust it so that’s the brass sleeves do not rotate with the spindle, and the overall temperature of the bearing area is “slightly warm“ after running for 10 minutes or so.

on the far end of the spindle, there is is thread and a collar which screws onto it. This seems to be the way the longitudinal play is controlled. It is secured by a grub screw (which doesn’t seem to go all the way through ?!). But if I screw it up tight enough to eliminate longitudinal play, the spindle will not turn.

And it doesn’t look as though that collar is designed to run against the face of the second bearing (which is painted). So I’m not really sure how to secure the longitudinal travel of the spindle correctly.

questions…

Am I barking up roughly the right tree? Or is it like to be a different problem?

Am I doing this correctly?

How to fix the longitudinal travel issue?

cheers

Steve

There was no end-float while facing, hence the better finish. End-float should be very close to zero, if not zero.

.

It looks like there is a thrust bearing assembly missing !

You mention a painted surface … could that possibly have been a ‘touch-up’ paint job ?

MichaelG.

I don’t think so. I think it only has a thrust bearing (if that’s the race bearing parts) at the chuck end. The gears end just has the brass sleeve. I’ve watched some YouTube videos of others refurbing the headstock of this lathe (Zyto) and it is the same as mine. And I am 99% sure the paint is original…..

End float is the usual suspect. You don't say what type the lathe is , if you don't know post a pic of the entire lathe. Some small English lathes have a bronze washer as a thrust bearing others have a needle roller. If it's the washer type a conversion to needle roller is often an easy fix and worth doing.

If you are cutting longitudinally towards the head stock, then I don't see there being any end float either.

Is the spiral pattern a 'spring cut' effect whilst winding back the tool?

.

Fine … it was only a guess, based on the available evidence

It all looks wrong to me; but sorry I cannot be of any assistance.

MichaelG.

No, good call Michael, thanks for the input.

Steve

Steve,

what material is it you were cutting on the picture?

Or - other words - do you have the chatter also with softer materials like brass or aluminium?

Is the tool sharp and exactly in the middle?

You are using a (revolving) centre as a support in the tailstock I suppose?

Regards
Gerhard

I rebuilt a machine similar to yours and when i adjusted the collar you show a much more experienced friend instructed me to put a 0.001” feeler gauge between the cast face and the collar face then tighten the locking screw. This allows the spindle to run free but with minimum end float.

Work just fine for me.

Good luck.

Hi Gerhard

it is brass

I get similar results with all the tools I’ve tried (many completely new)

yes, a revolving centre, but I get the same results with a short piece of stock simply in the chuck

Steve

With a zero top rake HSS tool you should get a fizzing noise and a shower of tiny chips when cutting. Some brasses will dig in worse than others especially if there's a lot of backlash available to snatch the tool in.

That’s exactly what I get, and they go everywhere.

Looking at your stand and the description of adding an additional 6mm steel plate I think there shouldn't be much vibration from this side. Your stand looks like being made for a much larger machine. Probably you have some bearing problems as others wrote above.

Size (and weight) of the lathe is of course also a factor. I started on my fathers Emco Unimat sl, a rather small machine with round bars as a bed, vibrations were always present, especially with harder materials. From there I went to an Emco Compact 5 (35kg), which was heavier and had a much better bed than the sl, vibrations got better. After 35 years with the Compact 5 I upgraded to a Chester DB8, and again - a much heavier machine (113kg), and much better results.

Do you have a photo of your tool mounting and stick-out etc please?

I think Dave above is thinking you may have too much tool stick out. It is a possible cause of chattering and should always be minimised. Another thing to try to achieve is to have the point that is cutting over the cross slide so that it is positively supported. Sometimes these can be hard to achieve at the same time but should be achievable on a plain piece of bar. So if the compound slide is sticking out wind it back and if the tool is sticking out reposition it further into the tool holder to support the point as much as possible.

Martin C

I don’t have a photo of the tool setup, but the “stick out” was minimal and the tool post was supported by the carriage, all the gibs were tight etc. I read a lot about those causes of chatter and tried to eliminate them…. 🥺

That’s really interesting. Looking at mine closely, it isn’t quite like that. The bronze or brass “sleeve” in the bearing is actually slightly wider than the bearing and so protrudes by about 1mm on both sides. The edge of the “collar” is actually chamfered, so it doesn’t ever actually contact the cast iron, if the sleeve is secured properly by the grub screw.

see pics

I wonder why this is….. is it different to yours?

steve

I've not watched thes, and you may already be aware of them, but there's a series of Youtube videos covering rebuilding a Zyto. May be something about the endfloat adjustment in there.

Links to https://www.youtube.com/watch?v=bET-ooQffz0&list=PLDOK2EUenGuqFq4RGcpuVs90D6IbMEafL

Rob

I think the trouble with machines of this age is that they have had many modifications over the years. Mine had a number of mods so its possible that he headstock is not as original, but it seemed to work fine.

Just watched a Zyto rebuild where he rebuilds the headstock, looks like he tightens the locking ring a gentle finger tight then looks the grub screw.