I’m assuming you can’t actually see the carriage stopping but only a regular banding along the length of your workpiece. I think the is not uncommon – from time to time I’ve seen it on work I have done. I think most likely reason is some harmonic frequency. I just try and reduce the visual effect by using a tool with a reasonable radius on the tip rather than a real point. Of course after making sure gibs are adjusted. I think it only shows on the finish rather than leaving ridges. Also worse with ‘finishing’ cuts.

Steve

Banding usually as Steve says, but if the carriage is visibly hesitating I suggest looking for:

• Half-nut or lead-screw worn or very dirty (which Paul's check makes unlikely)
• Half-nut not engaging properly – an adjustment
• Slipping clutch (if fitted!), either worn out or needs adjustment
• Missing gear teeth (check all the gear wheels)
• Slipping belt (worn-out, age hardened, oil-contaminated, or maladjusted)

+1 to speedy's broken sheer pin. It happened to me, most confusing!

Dave

Edited By SillyOldDuffer on 09/10/2022 08:39:35

Try cleaning the carriage rack and the pinion on the end of the hand wheel.

Additionally when trying to diagnose a problem on an imperial lathe this are more obvious when measuring in the same system of units. You say 3 to 4 mm. Is it actually 1/8 inch which is the pitch of the leadscrew, so you have an immidiate clue.

regards Martin

I don't have a modern Myford so not sure of the drive – is it by the rack or a very slow screw thread? Is the leadscrew imperial and the marking actually every 1/8 inch ? Or does it correspond to the pitch of the rack?
If the latter then it firstly points to a bit of swarf in the drive gear.
If the former and it uses a slot in the leadscrew to drive the rack gear (as on Boxfords) the sliding key inside the worm may have a burr or swarf catching on the edge of each pitch of the leadscrew.

On my Boxford I once found the weight of the sticking out handle part of the carriage handwheel as it went over top dead centre caused it to take up the gear slack and make a mark if everything was very loose.

Seems like everything has been suggested, but I would check if the leadscrew rotates smoothly by itself without any end float and shows no sign of being bent. You could try different leadscrew gears if you have any and see if the pitch of the banding changes. Suspicions of the pitch of the leadscrew matching the banding have already been posted.

Keep us up to date with results as you go, the information is valuble.

Whilst I agree with Martins assessment of dirt/swarf in the handwheel pinion causing a tight spot (that does happen on occasion) it would be unlikely to create such a 'banding' every 3-4mm. Swarf there would, and is, felt every time the saddle is moved by the handwheel too.

Paul,

your initial post states that your lathe has 'started ' to "stop, start and hesitate" – are you saying this is new compared to previous use?

You also sate that the leadscrew nut is clean and appears to be okay. If this is the case then the issue is elsewhere. A new nut will not necessarily cure the problem.

As I said previously if the carriage stops moving then there has to be delay in drive transmission somewhere – when in drive any backlash is constantly taken up so with several leadscrew pitches in contact with the clasp nut it is unlikely to be between the two. It is more likely to be something that is impeding the leadscrew drive allowing the tool to dwell in as the saddlle stops.

If you can't feel the banding nor measure it the it's probably the oft seen 'banding' as a result of fine cut and feed that sometimes occurs. It's usually a direct copy of the leadscrew pitch though.

EDIT – Well done, new one on me but one well worth remembering. Keep on turning

Edited By Ramon Wilson on 09/10/2022 16:33:36