Before rebuilding the lathe I'd look at the tool. Assuming that the material is steel the tool angles are wrong. Fine for brass, but not for steel. The top of the tool needs to slope away from the work by far more, say 15° or so.

Andrew

The appearance is a, 'Cyclic' chatter and no doubt emanates from the lathe spindle bearings or end float. Further check of belts etc to see if they are stiff from being in one stopped position for a long time. Tool geometry does not cause this type of chatter. Tools need at least 12 deg. clearance and back rake, the simplest tool angles. Refinements in angles to suit the materiel being turned. Most lathes in good fettle will turn quite well with any tool with clearance.

Clive

A few obvious things to check;

• Tool height is critical. The point should be set as close as possible at the mid-point of the rod, 9 O'Clock. (The tool looks high in the photo and may be rubbing);
• Tool should be sharp.
• motor in forward rather than reverse (the chuck should spin anti-clockwise).

Any chance of a better photo? The camera has auto focussed on the slide, leaving the rod blurred. Holding a sheet of paper close under the rod should force the camera to focus on the chatter.

That two lathes both have the same fault suggests bad luck or the same 'mistake' when setting up. The 'mistake' may simply be what your test rod is made of. I've had bad experiences trying to turn random scrap and now buy new metal specified for machinability.

Dave

Edited By SillyOldDuffer on 31/07/2017 09:52:24

The tool looks to be too far to the left of the cross slide to me. I would set it up so that the carriage was getting as far to the left as possible without the chuck hitting it. Then set the tool post on the slide in a position that allows the required cut to be made. That way the forces on the tool tip are less likely to be trying to lift the right hand side of the slide up.

Martin C

Try this, set up the Dti, on the lathe body so that the plunger/lever is lightly resting on the spindle. Get a bar and using as a lever attempt to lift the spindle by leverage. All being well the reading should be minute.

Then place Dti. with plunger against the should of the spindle and again using a lever try to move the spindle axially, again minimal deflection. This sis just to satisfy the spindle condition, reading does not matter as you are only trying to see if it will move.

Clive

Another simple suggestion. A 4-jaw chuck will chatter if two jaws end up doing most of the holding because the other pair are slightly loose. The slack jaws allow the work to 'flap' under tool pressure as the chuck rotates. I suppose a damaged chuck might cause the same effect.

Andy: you seem to be focussing on the spindle, but haven't said what other checks you've done. Forgive me for asking but are you the kind of 'engineer by trade' who knows about lathes? I ask in case I'm telling granny how to suck eggs. I once found myself explaining 3-pin plugs to an Electrical Engineer. He thought it was hilarious; I was embarrassed…

Dave