Bad vibrations; is it in my head?

[liveaboard]

Yesterday I started getting these spiral chatter patterns in my work; all my work.
I took the carriage off and cleaned everything, oiled it, no change.
Tightened everything, no change.
I used different cutting tools, other material, other chuck, all of which gave good results until yesterday. I even found the pattern in a simple bore that was tight against the chuck.

I think the only thing left is the head bearings; they're not loose.
There might be a rumble, it's hard to tell because the machine is always noisy when it turns.

Anything else I should try before serious dismantling?

[John Hasler]

Does the pattern vary with spindle speed? Z feed rate? Depth of cut?

[armscor 1]

A rumble in the spindle bearings gives a clue.
Taper roller bearings, sleeve bearings?

[NP317]

It's caused by that coronavibrous-19.
RussN

[liveaboard]

No change with differing spindle speed, feed, or cut depth, or different tools, different mounting [long with tailstock bearing or short puck in the chuck... This started from one minute to the next.

I don't know what kind of bearings it has. I suspect roller bearings.
There is zero information to be found about this lathe, Zalenda UZ4.

[John Hasler]

That sure makes it sound like something in the spindle.

Put DTI on the inside of the taper?

Put a test bar in a collet, run the lathe at slow speed, grab the bar with your (oiled) hand and see what happens when you push and pull in various directions?

[liveaboard]

Thanks guys;
I've tried lifting and pushing the chuck with an indicator on it; normal degree of movement I think, around .05mm The rear end of the spindle is about the same.
But to feel it with my hand on a rotating shaft is a new to me, I like that idea.
I'll report on results as they come in.

[curtis cutter]

I cannot really tell, and this is most likely a foolish question, but are you hitting the material at the center line. Although it is probably an illusion, the first picture it looks to be low.

[liveaboard]

Very centered; I cut across the end face first.
The boring tool used for the other part is also set at the same place it always was, and that didn't have any problem before.

So I chucked up a 1" stainless rod and let it rotate as I pulled, pushed, lifted and depressed it.
I can't feel anything weird.
I used a long round file with handle against my ear to listen to the bearings; there's a rumble, but again, I can't pin anything down. I don't know what it sounded like before.

I chucked up a chunk of 30mm black steel rod and cut it a little with a sharp tool near the chuck slow; the cuts appear faceted instead of lined.
I'm more inclined towards the bearing theory.

This machine is older than some rocks; I'm not looking forward to taking it apart.

[BadDog]

Have you checked end play? I have no experience, but in my head, the only thing in the headstock that could do that (steady frequency) would maybe be loss of preload.

But to me, that makes me think loose in the tool stack. And I think that looks like a pattern I got when the tool block was not fully seated. In my case, when I brushed off before installing the new block, I missed a piece of swarf That prevented full lock on the face. Since it happened with 2 of yours, I doubt it's that simple, but could the tool post be damaged or somehow no longer locking up like it should? Or anything else going down the stack. Compound rotation mechanism left loose? Lost preload on the cross slide? Something got under the saddle causing it to be able to rock? Just throwing stuff at the wall.

[armscor 1]

Roller and ball bearings can give you false readings checking for play, I remember my Brothers HD shovel engine having a bad knock coming from the bottom end, pulled it apart and checked big end play grabbing the conrod you could not feel any play giving you the impression it was OK, but carefully rotating the conrod on the journal we found play in one spot one of the rollers had a flat spot.
The flat on the roller had to be in perfect alignment between journal and big end to feel movement.

[liveaboard]

I did not check the end play specifically; I suppose I should.
I checked the up down play at each end of the spindle.

I tightened the head bearing without any improvements and then loosened it off again because it was too tight.
As said above, I took the carriage off completely, cleaned and oiled it first thing.

I have a heap of other work to do before I can pull the lathe apart.
I'm reassembling my hedgecutter after a lot of modifications and the hedge is a total mess.
Then I promised to paint the house. Not a small job single handed.