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Cross slide backlash

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Paul Liddle22/04/2019 10:32:16
5 forum posts

Hi.

I an new to model engineering and just bought a Myford super 7 and the cross slide has some backlash. I stripped everything down cleaned and adjusted everything and its reduce the backlash but there is still some play between the nut and the casting walls. Should there be any shim in there (or would it be a good idea to put some shim in) ?

KWIL22/04/2019 12:31:31
3106 forum posts
56 photos

Paul,

There are two locations to look for to minimise backlash.

1 Between the leadscrew and the nut.

2 Between the leadscrew and the End Bracket.

When setting the Gib, detach the End Bracket and adjust the Gib screws such that the cross slide moves by hand easily but firmly without snatching, over the normal front to back movement.

Edited By KWIL on 22/04/2019 12:31:55

not done it yet22/04/2019 13:14:22
3167 forum posts
11 photos

As Kwil, there is backlash (within the change of direction of screws in threads) and end-float.

End-float should be eliminated with shims, or other means; backlash is always there to some extent and operators live with it without losing any accuracy in their work.

Jon Lawes22/04/2019 13:17:32
avatar
313 forum posts

**LINK**

This modification is available for the ML7 (I'm aware you are referring to the super 7), I wonder if something similar could be done. I used the bearings listed for my ML7 and it improved things drastically.

KWIL22/04/2019 13:25:02
3106 forum posts
56 photos

Out of interest, both my S7s have a thrust bearing fitted on the leadscrew to "minimise" the leadscrew/bracket backlash. Home brewed not kit.

Paul Liddle22/04/2019 13:54:15
5 forum posts

Thank you all for the answers.

Ive checked again and I think the nut or the thread is worn.The end bracket is tight and the locking collar is well adjusted, nothing moving there. If i remove the top slide and look through the hole I can see the thread moving in and out of the nut when I push and pull the cross slide.

A thrust bearing on the locking collar sounds interesting

Jon Lawes22/04/2019 15:18:55
avatar
313 forum posts

If you turn the handle side to side to expose the backlash you can see the whole thread moving back and forth. That's what indicated to me that was where the problem lay. I suspected it wasn't the nut in my case as the lathe hadn't been used much

SillyOldDuffer22/04/2019 15:42:04
4536 forum posts
971 photos

Most lathes have a bit of backlash and it doesn't matter much. It has no effect whilst cutting pressure is applied.

The usual problem is when you reverse the tool out, have a think, and then go in for another cut forgetting the need to compensate for backlash. But provided you are in the habit of reversing out a little further than the backlash, then the dial will realign correctly before the tool reaches the job with the calibration still correct. Not difficult to do when the backlash is small, but easy to mess up when the backlash is very bad. How big is your backlash?

Beware of obsessively minimising backlash. Often done by tightening everything up beyond the point severe wear is caused. Sometimes it's best to leave well alone.

Dave

Paul Liddle23/04/2019 15:32:10
5 forum posts

Ive just measured the backlash/play in the nut and its 0.330 mm. is this too excessive?

I was looking on the myford site for a replacement nut and leadscrew and there is a choice of 2. I think i have a powered cross slide (does that mean when I engage the lever thingy the cross slide drives out? blush)

The leadscrew for a powered cross slide is matched to the nut for accuracy so my 0.330 is looking pretty poor.

Once again thanks for helping

John Haine23/04/2019 15:53:09
2577 forum posts
133 photos

The power crossfeed is engaged by a button that you pull out. The lever engages the longitudinal feed. 0.33mm is a lot. The feedscrew on a pxf lathe is larger diameter, 5/8 in if I remember right. And it has a longitudinal keyway machined along it that engages a key in the drive pinion. If you can post a photo of the apron it's easy to confirm if your machine has pxf.

Hopper24/04/2019 00:36:09
avatar
3651 forum posts
72 photos

Backlash of .3mm is more than it left the factory with but it won't affect the operation of the lathe particularly. It's about average for an elderly used lathe such as you have. It will not contribute to rough finish or inaccuracy in turning to size etc. You just have to be sure to always wind the tool out past the backlash point when screwcutting etc then be sure to wind it back in the correct amount.

And when taking a fine cut, if the cut is say .002" too deep, you don't just move the dial out that .002", you wind it out past the backlash point then bring it back in to the mark where you want it so the backlash is taken up. Standard operating procedure even with new leadscrew and nut as they always have some working clearance even when new.

Howard Lewis24/04/2019 09:45:43
2156 forum posts
2 photos

0.33mm (0.00129" ) is not an unusual backlash in a even a moderately used machine. I live with a machine with 0.020" backlash, without much problem.

As has already been said, you retract by more than the backlash, half a turn to be safe, and then return to the setting that you require. You work within the peculiarities of your particular machine. Make yourself familiar with your machine, and the controls, and how they affect its operation.

If you are new to the hobby, and machines, join a Model Engineering club where you will receive help and advice, and learn form contact with more experienced machinists. Continue to read this Forum and ask questions, you will learn a lot.

You will be amazed by the work that people do on quite modest machines.

Howard

Emojis!!!!!!!!!!!!!!

Edited By Howard Lewis on 24/04/2019 09:46:37

John Haine24/04/2019 10:08:50
2577 forum posts
133 photos

Um, .33 mm is about a third of a millimetre, and a millimetre is about 40 thou. The number should be 0.0129 inches, 13 thou.

Howard Lewis24/04/2019 20:17:43
2156 forum posts
2 photos

Thanks John!

That's what I meant to type, but left the fat finger too long on the key, and was more concerned with editing out that stupid emoji. Forgot to put a space before the final bracket!

Howard

fat fingers again!

Edited By Howard Lewis on 24/04/2019 20:18:17

Paul Liddle25/04/2019 13:20:18
5 forum posts

Thanks for taking the time to reply and all the advice. I've not used a lathe for the last 35 years and that was only at school and as part of my apprentice training. I have a couple of small projects to start this weekend.

I'm looking to join my local club and to visit the exhibition at Doncaster.

Regards

Paul

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