Backlash in crossfeed handle, small bench lathe.

[Gas_mantle.Participant @gas_mantle]

Hi all,

I'm trying to minimise backlash in the cross feed handle on my Chester DB8, the machine is only 2 weeks old and works well, overall I'm happy with it.

However the crossfeed handwheel has what I would regard as excessive backlash, it reads that it's fed 0.3mm before it actually reaches biting point and starts moving the slide.

I realise it's not the end of the world and a skilled machinist can compensate for the slack but to me it does seem excessive and ideally I'd like to reduce it.

I've adjusted the gibs and the slide itself operates smoothy without any sloppiness so it's really just the handwheel that I need to improve.

Anyone got any ideas ? What you consider acceptable levels of backlash in the handwheel travel ?

Many thanks

Peter.

Edited By Peter Nichols on 13/06/2015 12:39:13

[Gas_mantle.Participant @gas_mantle]

[JasonBModerator @jasonb]

If its like the Warco ones then the nut is split and has a couple of grub screws to stretch it and take out play in the nut/screw. Wind the slide back towwards you and you may be able to shine a torch in to see the slotted grub screws which can be turned with a long screwdriver. But may be easier to remove the slide to do.

Also worth checking if its end float in the screw, get a firm grip on teh cross slide and try to move it in and out watch near the handwheel dial to see if the gap opens and closes. A thin shim washer will help to cure it by filling the gap

[Gas_mantle.Participant @gas_mantle]

Hi Jason,

Thanks, I can't see split nut so I'm guessing it's not the same as a Warco.

What happens is when I turn the handle anti clockwise to pull the slide the wheel is flush but when I change direction and screw the slide away the wheel initially moves the 0.3mm or so away from the slide before it reaches it's biting point and moves the slide.

There is a central allen bolt in the wheel but it seems to make little difference and doesn't appear to allow removal of the wheel in itself.

I did wonder about packing the gap with a washer and I'll probably end up doing that but to my mind the current level of backlash is excessive and the machine itself should be capable of taking up the slack with proper adjustment.

Peter.

[Gas_mantle.Participant @gas_mantle]

Hi Jason,

I've had a fresh look, there are 2 cross hed bolts at the bottom of the main nut.

Is it now just a case of tightening these ?

Mind you I think I'll end up having to remove the slide to get to them.

[JasonBModerator @jasonb]

Yes just a small turn and see how it goes.

[Gas_mantle.Participant @gas_mantle]

Hi Jason,

Many thanks, done that and the problem has reduced, I'll see how things are over the next week and possibly try a shim behind the handwheel as well.

Peter

[AjohnwParticipant @ajohnw51620]

There will be back lash so the aim is to work around it using the dials. Say 2mm of outward movement is needed. The tool is wound out 2mm plus backlash and plus some more and then wound back in to the correct reading. Then if there is a need to move the tool in further back lash has already been taken out.

Things are the opposite way round when boring.

0.3mm is nothing and you may find that adjustments just close up the nut and as there will still be some play you might finish up bottoming one thread with another – not a good idea. 0.3mm might concern me on a slide that used a 1mm pitch lead screw as it represents 30% play but that wouldn't make the lathe unusable, just indicate significant wear or a poorly produced item.

There is an arrangement usually called jam nuts – 2 nuts and their spacing can be adjusted. Rare and not of much use really as some play is needed for lubrication.

One aspect that is worth looking at closely is if part of the play is actually down to the handle / dial moving backwards and forwards. This is adjustable on some lathes but I have seen it "built into" some Chinese lathes.

John

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Edited By John W1 on 13/06/2015 15:21:52

[JasonBModerator @jasonb]

Adjustment does not close up the nut, works more like jam nuts where the srews alter the distance between two threaded parts similar to this nut

[Gas_mantle.Participant @gas_mantle]

Thanks,

The problem is certainly better after tightening the nut, as yet I haven't been able to figure out how to remove the handwheel to place a shim behind it. The central allen screw when removed allows more 'in – out' travel but doesn't seem to allow removal of the wheel completely. As it's a brand new machine and I'm a novice I'm reluctant to force it incase there is something else retaining the wheel.

John, I'm reassured after you saying 0.3mm isn't excessive, I initially thought it seemed a lot of play but maybe it's the norm.

I guess the reality is, it's more of a minor annoyance than anything else, if I want to make a precise cut I'll use more accurate ways of measuring than crude handwheel scales.

Peter.

[JasonBModerator @jasonb]

If its anything like my 280 then once you have undone the allen screw you can pull the handwheel off. Its just on a plain shaft with a keyway and key to stop it rotating. Once off you will be able to see the thrust bearings, put your shim washer between the bearing and handwheel boss. Though I think I machined a bit off somewhere to get the same effect but best not do that as yours is so new.

[AjohnwParticipant @ajohnw51620]

Jam nuts usually have the same thickness so that the same number of threads take both forwards and backwards thrusts. That should help maintain equal wear.

Where handle play is adjustable it's usually some sort of threaded bush some where and some means of locking it in place. I say somewhere as I have a feeling I have seen it in the actual handle on a lathe.

John

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[Gas_mantle.Participant @gas_mantle]

Many thanks for the help guys.

I've now fully rectified the problem, I managed to get the feed handle off and make a shim to go behind it. Fortunately the thickness was ideal and it now operates perfectly.

It feels so much more precise and responsive compared to all the slack that was in the system

Cheers

Peter.

[Ady1Participant @ady1]

A digital cross slide eliminates backlash issues, you can still have a jiggly nut, but can compensate accurately because it records the actual-distance-moved-by-the-slide

This is especially useful when you are say, screwcutting since you lose the tool position when you withdraw the tool for each cut and you only want to depth a few hundreds of a millimeter deeper for your next cut

One of the best mods you will ever make, once you finally make it (Three years before I saw the light)

 

Edited By Ady1 on 14/06/2015 12:17:07

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