Lathe cutting fault finding strange thing happening

I have a Denford Easiturn and recently when taking a cut near the chuck instead of the cut being flat... it is wavey. The ballscrew is 25.. diameter x 5mm pitch and the cut mimicks the ballscrew e.g. it goes in for 5mm and the out for 5mm (or it get larger in diameter for 5mm then smaller in diamter for 5mm).

Attachment 30298


Has anyone any idea what causes this? Worn ballscrew? Worn bearings?

thanks

Have you tested to see if there's any vertical movement on the cutting tool? looks like something you might see if the tool was moving away from the center of the workpiece.

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Originally Posted by AndyCD

Have you tested to see if there's any vertical movement on the cutting tool? looks like something you might see if the tool was moving away from the center of the workpiece.

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Hi, thanks for the reply. Sort of... I can't see any movement as such with a dial gauge, however I perhaps should have mentioned this only happens for the first 40mm (ish) from the chuck face. If I use a thicker bar with a tailstock and make a cut 70mm from the chuck face the cut is as smooth as a babies bottom - which why I was thinking worn ballscrew (coupled with the ballscreww being 5mm and the tramlines also being 5mm.

thanks again for th reply.

do you see the same behaviour (moving in & out from the workpiece) if you mount a DTI to your cross slide?
just trying to rule out spindle play as well

Hi, no the cross cuts are perfect.

thanks again

apologies, I meant run a dti down the length of your workpiece, as though you were taking a length cut
I'm just trying to see if the behaviour is coming from the z screw or from forces being applied to the spindle

Ah - cracking idea - will do.

thank you

If the carriage assembly is tight on the ways, then the ballscrew shouldn't affect the cut in that way.

I'd be putting a DTI on the main carriage, and giving it a good lever to check for play.

I can't think of the exact setup on the Easiturn, but it could be something like a slight wobble in the ballscrew, which combined with play, is enough to move the carriage on the ways.

Yes, it moves with a clock on the main z-axis... going to check the main carraige and the fixing to it next.

:encouragement:

You have wear in your ways close to the chuck, this kind of artefact is common in worn manual lathes.

Can it be fixed or is it a case of a new apron/lathe?

thanks

A bed re-grind and carriage re-fit should sort it out.