Carriage slipping

Looks like a bowed leadscrew. I can only repeat what I suggested before.

Edited By Bandersnatch on 09/09/2018 18:26:25

Will try what you suggest Bandersnatch. Will it not be better to buy a new leadscrew?

When my Myford was doing exactly the same thing, I chased around trying to figure out what was wrong and I thought it was the lead screw as well.

It turned out to be the saddle gibs that needed some adjustment, once that was done the problem disappeared.

Take a firm grip on the saddle and see if you can feel any movement when you try to twist it on the bed.

Phil

What I suggested takes 30 seconds, Charlene .... why not try it first and then consider further options.

All I can tell you is that when I had my minilathe, whenever I had the same kind of machining pattern that you show, the 30-second fix .... well ..... fixed it. If the leadscrew is permanently warped, as opposed to a misalignment induced warp, you could consider a new leadscrew or removing the original and straightening it.

Could be a Chester, but there are others that colour.

How smooth does the cut surface feel - often they look worse than they actually are.

Adjusting the saddle, cross-slide and top-slide gib strips for smooth, shake-free movement will help finish, as will oiling them!

Neil

I have actually tightened the saddle as well as the cross slide and I think that helped to solve the problem as well. I will try what Bandersnatch is suggesting next.

Neil, the surface is not as smooth as what I know I can get, but it's better than previously achieved.

Yes, it is a bit difficult to identify. The bloke I bought it from told me he bought it from someone in The Czech Republic, although I don't believe a word he says. He also told me that he bought it new at the beginning of July and it was damaged on arrival, that is why he was selling it. It was definitely not new, but I got it for a good price.

Thanks again guys. I will try the outstanding suggestions next weekend as I don't get time during the week to work in the shed.

About 15 min in he shows how to set up the leadscrew so it wont bind .

You want to go back and forth doing this adjustment a couple of times and once you are happy with that loosen the two cap screws that hold the saddle onto the apron and let it settle( half nuts still engaged ) before re tightening them , the allow the apron to settle so it is not pulling or pushing the leadscrew in or out . Another very important setting is the leadscrew end float - in the video he sort of touches on the subject but with the way his machine is set up you would have to shim the nut out so the pin hole lines upand there is no end float . My sieg has a long nut with a grubscrew in the end to lock it and that is much easier to work with .

If you mean the rack and pinion gear set up that allows you to move the saddle along the bed with the handwheel is jumping teeth i'm sure the mounting holes for the rack gear are slotted so you can loosen the cap screws and allow the rack to drop a little to engage the pinion better , IIRC my lathe had an issue where the pinion would rub against the lathe bed and this was fixed by skimming the end of the pinoin gear .

If after all that you still find the halfnuts jumping the only solution is to remove the apron assembly and take a look at the half nuts and their operating mechanism , the nuts could be partially stripped out or maybe they are not closing fully .

I can highly recommend Neils book - if you are new to machining with these little lathes it is well woth the purchase price and also a couple of others from the workshop practice series that are dedicated to the mini lathe .

Edited By XD 351 on 10/09/2018 04:19:50

Edited By XD 351 on 10/09/2018 04:33:39

Edited By XD 351 on 10/09/2018 04:38:03

Edited By XD 351 on 10/09/2018 04:38:23

Loose headstock bearings can make funny rings like that too. Try tightening up the adjuster nut on the end of the main spindle.

Also it would be worth trying a different tool bit and see if the problem persists. Carbide tips in small lathes can sometimes do funny things.

I’m not a mini-lathe enthusiast, but does it screw cut, or slip? I suspect the finish is a combination of loose gibs and the cutter is hanging back, and then cutting coarsely alternately.

Does it do thevsame with a sharp HSS cutter?

Is the top slide tight, even locked down? You have a fair bit of tool overhang with that toolpost. Carbidevtooling may be exacerbating the effect.

Charlene, it looks very much like one of these on ebay, so that may provide a starting point for further research.

There's several that look similar if you follow This Google Search

Good luck with your new machine; roughly whereabouts in the world are you, as you might find a local willing to assist.

Bill

Edited By peak4 on 10/09/2018 11:52:43

Edited By peak4 on 10/09/2018 11:53:07

Looks like a mini lathe of some marque.

Have you checked that the (probably plastic) gears are: 1) Intact - No broken teeth or torn keyway)

2) That the keys are present in all the gears from Mandrel to the Leadscrew, (otherwise you are relying solely upon friction to provide to drive to either the Leadscrew, or the pinion and the Saddle)

If the geartrain includes a compound gear as an Idler, there should be a key long enough to unite both gears, and similarly, the key on the Leadscrew should be long enough for both the gear on the leadscrew and the spacer

Without the spacer, the gear could float and not drive continuously. The gears should mesh over their full width.

With regard to ,meshing, there should be just enough backlash on each mesh to allow a strip of paper to pass through, no more and no less. (The Banjo and the Idler stud(s) are all clamped up properly, are they?)

One of the gears is not running eccentric is it?

DAMAGE reported: ANYTHING bent, Leadscrew, shaft in the Saddle, (might account for the "slipping on the rack" Not the tumbler reverse?

As suggested, maybe you need to ask if anyone local to you would be preared to come and have a look to see where the problem lies, and what might be done to solve it.

Howard