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Hobbymat Lathe - Play on Cross-slide

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Martin Dilly01/08/2011 18:04:57
2 forum posts
I've found that my Hobbymat lathe has about 0.15mm play on the cross-slide, such that when I push and pull on the dial (at right angles to the lathe bed) there is visible and audible movement relative to the saddle. I've adjusted the backlash to no effect.

I suspect wear either on the threaded rod controlling the cross-slide movement or else in the female thread in the saddle casting. Does anyone have any suggestions for a cure please?
Steve Garnett01/08/2011 19:51:32
837 forum posts
27 photos
The only thing you can do is to start over, I'm afraid. The screws on Hobbymats aren't Acme ones, just 'ordinary' threads, and as such aren't exactly optimised for the job. If I was going to replace mine, I think I'd attempt to redo everything using Acme threads, with a backlash adjuster on the cross-slide, and also I'd use proper thrust races - much easier to adjust, and much smoother in operation.
 
But there again, for myself I'd seriously debate whether doing all this for a Hobbymat was worth all that effort. If it's your only lathe and all you have room for, and it's otherwise adequate for your needs, then that's a different matter of course. But it will be quite a bit of work, and you'll almost certainly need access to another lathe to complete the work - unless you are very ingenious!
 
Should also mention perhaps that whilst this is annoying, it doesn't actually stop you using the lathe. As long as you advance the cross-slide towards the cut you are making so that all the backlash is taken up, it shouldn't affect your cut. What you don't want to be doing is setting the cross-slide position by moving out and then cutting - that will cause you problems. You need to take up the slack first.

Edited By Steve Garnett on 01/08/2011 19:57:01

maurice bennie01/08/2011 21:13:30
164 forum posts
1 photos
Hi Martin ,Is there a nut in the middle of the handle that can be tightened to take up the slack in the bearing at the end of the screw that pulls and pushes the cross slide.mine has .Hold the wheel and tighten the nut ,not too tight or you will not be able to turn the wheel .hope this helps..good luck
Maurice.
James Scott01/08/2011 21:36:46
3 forum posts
Hi im having the same problem with my MD65 as well as the jibs loose and i cant move the carrige by hand if i find a anwser ill let you know
 
James
Steve Garnett02/08/2011 01:20:31
837 forum posts
27 photos
I've spent ages setting up the gib strips on my Hobbymat - they really aren't that easy to adjust. One thing that makes it a lot easier though is to replace the original grub screws with hex-socket screws; this makes holding the position whilst you do up the lock nuts a lot easier to achieve.
 
Also, as supplied the strips themselves aren't that wonderful. I honed mine, and then polished them. This made moving the slides a lot easier. I say slides, because I did both the cross-slide and the compound. As I said earlier, I'd contemplated proper thrust races for the wheels, but since I needed the lathe to work accurately rather than be wonderfully smooth, I didn't go that far with it.
 
Posted by Martin Dilly on 01/08/2011 18:04:57:

I suspect wear either on the threaded rod controlling the cross-slide movement or else in the female thread in the saddle casting. Does anyone have any suggestions for a cure please?

I should have added earlier that it's not too difficult to tell which is worn. If you have the same amount of backlash throughout the travel, then probably the casting thread is worn, but if the backlash varies, then it's much more likely to be the threaded rod that's the root of the problem. If you get a combination of slack everywhere, but worse in the area mostly traversed, then possibly both are worn. If it's the saddle casting, then the only option is to bore it out and put in an insert with a fresh thread in it. This isn't going to be easy though, because the threaded part of the casting isn't detachable; it's an all-in-one casting with a tapped hole in it.

ady02/08/2011 10:43:46
612 forum posts
50 photos
If the casting leadnut hole has a rear entrance, ie goes all the way through to the back then maybe you can make up another lead nut and tap it in via the back entrance.
 
Sounds like one of those pain in the neck jobs, but once you get it sussed you have yourself a hobbymat with a replaceable leadscrew nut system.
 
Don't expect zero backlash from a hobby lathe, that's a mistake IMO
You need to take any wobble into account when you do a job and tighten up when really necessary, don't expect Hardinge toolroom lathe quality, adapt for the job being done.
A locking nut mod on the slides can also be a useful mod for light milling work.
 

Edited By ady on 02/08/2011 10:48:19

Steve Garnett02/08/2011 14:50:02
837 forum posts
27 photos
Posted by ady on 02/08/2011 10:43:46:
If the casting leadnut hole has a rear entrance, ie goes all the way through to the back then maybe you can make up another lead nut and tap it in via the back entrance.
 

 
I'm pretty sure that they are all tapped right through - you don't really have a choice about putting a complete insert in, either replacing the original thread, or preferably replacing it with something a little larger, and more Acme-like!
 

A locking nut mod on the slides can also be a useful mod for light milling work.


The manufacturer beat you to it - all slides and the saddle can easily be locked on the machine ex-factory. This is because there's a standard milling attachment for it.

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