Cross slide feed nut slop problem

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Cross slide feed nut slop problem

This topic has 19 replies, 14 voices, and was last updated 8 March 2014 at 16:09 by Mark C.

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6 March 2014 at 10:00 #146145
Andrew Evans
Participant
@andrewevans67134
Hi All. I have a Denford Viceroy lathe with a problem. There is so much slop between the cross slide feed screw and feed nut that I can rock the slide back and forth by about 0.01". I can work around backlash but the problem is that unless you push the slide right back before each cut it can move back as soon as the cut starts and you end up losing position. The lathe isn't worn elsewhere, just this nut.

Is it worth trying to slit the nut and adding a couple of screws to squeeze it? On the off chance does anyone have a spare nut knocking around? I have seen the idea of making one from Delrin by heating around the screw.

Any help or advice would be great.

Andy
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6 March 2014 at 10:00 #17326
Andrew Evans
Participant
@andrewevans67134
6 March 2014 at 11:18 #146155
Ady1
Participant
@ady1
it can move back as soon as the cut starts and you end up losing position

Put a cross slide dro on and you'll be fine, they are good to 100th of a mm when you shift position

Mine cost a tenner

A cross slide DRO is probbly one of the most useful mods you will ever make to an old lathe

Don't buy any old vernier

The ones I have switch themselves off after 60 odd seconds and keep the measurement stored, and use poundland shop AG13 batteries.

Edited By Ady1 on 06/03/2014 11:24:10
6 March 2014 at 13:34 #146165
Bazyle
Participant
@bazyle
Delrin nuts are getting good reports on other forums. I've got myself a bit of Delrin for this but haven't worked out how best to attach that to the slide which is my excuse for not getting on with it.

Some lathes have a nut split part through to form a hinge which might be what you were thinking of. The problem with this is that the movable bit ends up at an angle to the thread so is only partly in contact and wears more rapidly. It also means the working part of the nut is shorter. So it may be better to turn a very short new bit of nut to fit on the end.making sure you know where the cross slide is when this extension is about to drop off the end. Also making a short nut will give you practice on making a new full one if you decide to.

If you find your screw is also worn making a new one might seem a bit daunting. You could consider just taking a shave off the thread flanks of the unworn ends of the old one to bring it all to an even pitch. It doesn't matter that the thread valley is wider than spec as your adjustable nut will take that out. (you weren't thinking of making a screw/nut pair with half a thou backlash with no adjustment were you?)
6 March 2014 at 13:53 #146167
Ady1
Participant
@ady1
The other problem with older lathes is that the feedscrew is far more worn in the middle than the ends, so the distance it travels varies upon which part of the screw the feednut is at

A DRO eliminates this problem, ensuring that you only move the distance required

I fitted one after 2 years latheing, wish I'd done it within 2 months

Delrin is a good temporary fix but only lasts for 1-2 months if you do a few hours a day, I've found aluminium quite easy to work and it wears better

Edited By Ady1 on 06/03/2014 14:10:05

Edited By Ady1 on 06/03/2014 14:12:36
6 March 2014 at 16:58 #146188
Metalhacker
Participant
@metalhacker
Are you sure it is the feedscrew in the nut? My Boxford had this problem which persisted after a brand new feedscrew and nut, The problem was the thrust bearings and packing washers. When tohse were corrected to take up the slack allthe play disappeared. The DRO route is really good too. Decide which is less hassle and see what suits you!

Andries
6 March 2014 at 18:06 #146203
maurice bennie
Participant
@mauricebennie99556
Hi all Just a thought,Andre Citroen over come the rattling of gears by having two gears ,of the same size running side to side ,a slot cut in both and a strong spring in the slot , forcing the teeth apart ,so that when put together one tooth was pushing on the left side and one on the right side of the tooth that they were driving. could this also be done with two nuts and a spring between them,forcing the nuts to push on lt. and rt. of the screw thread? one nut being on the slide and the other nut screwed up to it with a spring between them so that it is not able to turn but able to slide a small amount..If only I could draw it .Does this make any sense?

Maurice
6 March 2014 at 18:27 #146206
Tim Stevens
Participant
@timstevens64731
One problem with Maurice's ingenious suggestion is that in both directions of movement, the slide is held against a spring, and not firmly. So, if cutting brass, for example, the tool could be drawn into the work the full travel of the spring. What might work better would be two nuts which could be moved apart by a positive mechanism – more complicated than a spring, but more secure. I wonder if there is room for this?

Another result of the spring idea could be to increase the wear which is the cause of the problem – movement in either direction would involve more friction against the spring load.

Cheers, Tim
6 March 2014 at 19:22 #146218
Russell Eberhardt
Participant
@russelleberhardt48058
I split the crosslide nut on my Atlas to fix the 20 thou backlash about five years ago. I've had a new nut waiting in the cupboard for four years now but the backlash is still no more than 4 thou after my bodge.

I've done good work on a lathe with loads of backlash. You only have to make sure you turn the handle back enough to clear the backlash before applying feed. The tool will not be drawn into the work with a correctly shaped tool.

Russell.
6 March 2014 at 19:34 #146222
John Haine
Participant
@johnhaine32865
Er, why does it move back when the cut starts? Usually, whether it's wear in the nut or play in the thrust bearing, setting the cut moves the slide forward and takes up the backlash. Something very funny must be going on here!
6 March 2014 at 20:39 #146231
Andrew Evans
Participant
@andrewevans67134
Thanks all. Helpful suggestions. John – the slide can be rocked back and forth slightly by hand. unless the slide is pulled towards the user before starting the cut the force of the cut pushes it back by up to 10 thou. Its definitely play between the screw and nut.

Andy
6 March 2014 at 21:52 #146240
John Haine
Participant
@johnhaine32865
I'm sorry but I think that is wrong! Every slide can be rocked back and forth through its backlash, but usually when you apply some feed in order to take a cut the act of putting on the feed takes up the backlash. From what you describe I think the nut is moving with stiction in its housing. When you withdraw the slide it moves the nut backwards, it binds, then when you feed forward there is enough stick for it not to move but the slide moves. But the cutting force pushes the slide back relative to the nut because it is larger than the stiction force. I would check how the nut is clamped into the cross slide myself, you could take all the play out of the nut and bearings and it would still exhibit the same symptom.
7 March 2014 at 00:41 #146254
Ady1
Participant
@ady1
unless the slide is pulled towards the user before starting the cut the force of the cut pushes it back by up to 10 thou.

John could be right, the nut may be moving about inside the carriage
7 March 2014 at 08:04 #146263
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Ady1 on 07/03/2014 00:41:46:

unless the slide is pulled towards the user before starting the cut the force of the cut pushes it back by up to 10 thou.

John could be right, the nut may be moving about inside the carriage

.

I am not familiar with the details of the Denford Viceroy, but

… this previous thread may be relevant.

MichaelG.
7 March 2014 at 09:07 #146273
WALLACE
Participant
@wallace
Strangely enough, I knocked up a locking nut for a Union tool grinder yeyesterday which worked a treat – it’s the split type with a cap head bolt to lock it up. I’ll do a photo later today.
However – you will need a tap – presumably lh acme to make it. I didn’t as somewhere along the line, the leadscrew had been swapped for a rh metric one which I had a tap for.
Also – if going down this route -use a vice or similar to clamp the nut first so it’s a tight fit. Over enthusiasm with the cap head can crack the lock nut at the sharp edge where it’s been machined away ! (I didn’t swear too much as it’s going to replaced with the correct acme one when I get a chance. ….. …)

W.
7 March 2014 at 10:24 #146288
robert mort
Participant
@robertmort83504
The Delrin/Acetal approach is the best. It eliminates backlash and lasts far longer than a bronze replacement.

I've made one for my Raglan lathe. Fitting it needed some thought due to the limited space, but in the end was quite easy. See my photo album
7 March 2014 at 13:17 #146312
Ed Duffner
Participant
@edduffner79357
I'm making a cross-slide at the moment and decided to use Delrin for the feed nut. Below are a couple of photos. To remake it in the future would be a bit time consuming so I might make another sort of cage in brass which holds a simpler Delrin square-section with the thread running through it.

Regards,
Ed.

Edited By Ed Duffner on 07/03/2014 13:19:31

Edited By Ed Duffner on 07/03/2014 13:20:20
8 March 2014 at 10:42 #146393
Andrew Evans
Participant
@andrewevans67134
Thanks all – in the short term, so I could finish off a job, I did a bodge by squeezing the nut in a vice and that has reduced backlash. In the long term I might try the acetol approach and will experiment first. Definitely the nut itself isn't moving about, it's locked to the slide with a ball bearing that is forced out with a grubscrew.

Andy
8 March 2014 at 12:58 #146408
Richard Greening 2
Participant
@richardgreening2
Hi all,

just looking at subscribing,

I could not help but see this problem "Backlash" !!

I have only ever seen it cured on CNC machines with recirculating balls and adjusted finely,

they work very well !

A lathe , Miller, no nut split or otherwise will ever eliminate this, you can only take out the backlash by screwing back prior to putting a cut on !

thanks for listening

MY opinion only

Rich
8 March 2014 at 16:09 #146433
Mark C
Participant
@markc
It probably won't fit in this job but the split nut method mentioned above works well and I have that mod on my miller long feed screw – I just added the details to the thread I started on mods to my Elliot mill.

Mark
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