Cross slide backlash Mini lathe

I have just bought a dial indicator and I actually measured the backlash on my Warco Super Mini Lathe. It seems to be around 0.2mm and you can 'just' see it move and hear a small clunk at each end.

I have been fooling around with those three screws on the slide and I understand, from several on line sources, that you can minimise the backlash by 'tilting' the nut on the lead screw with the outer two and they rock the nut about the smaller middle screw. I have tried various combinations and, at times, the slop is just over 0.1mm and can be very much worse, too. How is the system supposed to operate?

I'd love to learn of a nice iterative and convergent procedure to improve the slop. It's a very popular topic with lathe owners but perhaps a member here could help me to get a proper answer.

Cheers
Andrew

Personally, Andew ... I wouldn't bother

If you do manage to reduce backlash by that tilting method, the nut will soon 'bed-in' and backlash will re-appear.

Much better anti-backlash arrangements are available [albeit considerably more complex]

MichaelG.

To echo MG; ignore the online "experts" and stop worrying about it. My industrial lathe has a proper split nut anti-backlash arrangement. But it's pretty worn so the cross slide backlash is about 0.5mm. Simply doesn't matter though; I can still routinely hit 0.02mm tolerances.

Andrew

Backlash can also be a product of feedscrew endfloat , while winding the feed handle in and out take a look at the gap between the dial and backing plate to see if it opens up or closes . On some lathes this is adjustable and on others shimming ir required .

Backlash is more of an issue with a milling machine than it is with a lathe where all of cutting is only in one direction - ie you are feeding the cross slide in to turn the OD or you are feeding it out to bore a hole .

I personally would be more concerned with gib adjustments on a lathe rather than backlash .

Andrew,

I have a CJ18 mini-lathe which is almost identical to your Warco Super Mini.

The cross slide backlash on mine is 0.1mm and the top slide is 0.13mm and like Michael and Andrew I dont worry about it. When I got the lathe (my first) I did worry a bit about it but from reading and youtubing soon realised that adjustment can reduce it but not lose it altogether.

Following up on feedscrew endfloat, when I got my first lathe (a 1908 Drummond) I was horrified to find 10mm of backlash in the cross slide... Thinking where do you get parts for a 110 year old lathe, panic. On closer inspection majority of it was in feedscrew endfloat. Couple of spacers and thrust bearings backlash now tolerable. May try a Delrin feedscrew nut sometime but at the minute too busy learning how to use the lathe. John

My view is that you are better off adjusting the nut for a nice even feel when the cross slide is wound right in.

If you round the end of the nut to match the slot and recess the end of the cross slide so it can overlap the leadscrew mount you can get up to about 20mm of extra travel.

Not a lot of people know that

Neil

Thanks for all those useful opinions.

The reason for my concern is that I am chasing the dreaded chatter. The cross slide movement is just one thing that could be contributing. The way I'm grinding the tools could be having an effect perhaps; I have minimal length of tool projecting and I make sure the (original) tool post is tightened well down.

One thing that I find annoying is the way that, when I take of the drive to the feed and the machine is doing no work, I have to pull the cross slide away pdq and backlash delays that. The top slide is far better behaved, I find with a light feel to the feed screw and no noticeable backlash.

On the subject of adjustments, I would also like to know the best way of adjusting the change gears when I go back to the 20/80-20/80 setup. The gears seem to chummer a lot and, when in neutral, I can't always turn the lead screw end wheel backwards cos the gears seem to 'bunch up'. Adjustment is a bit of a pig, with that nut in behind the gears that sets the position of the intermediate pair being hard to get to and allows about 15 degrees of spanner movement. The gears are steel, unlike the majority which seem to use plastic. Could they just be pool made?

Cross slide leadscrew backlash will not cause chatter, generally speaking. My old Drummond has over .25mm backlash on the cross slide and regularly cuts to accuracies within .02mm with nice smooth finish. Ditto just about every lathe I have used at home and work for several decades. Gib adjustment is more important.

Set your change gear clearance by running a piece of paper through the gears between the teeth then tighten up the stud nuts. This gives you a clearance of the thickness of the paper: about two thou (inches) or so. Gears often have tight and loose spots if not machined perfectly, so set your clearance with paper on the tight spots. Bit of extra clearance on the other teeth will not get in the way.

Chatter is more likely to come from loose gibs or even a poorly adjusted spindle bearings, but don't dive into adjusting the latter unless you are 100% sure they are out of adjustment.

The plastic gears come in for a lot of moaning (but they rarely seem to fail - I'm the only person I know who has managed it, by running the saddle into the headstock or something like that) and have the benefit of repeatable accuracy so backlash setting is less critical.

Driving the train backwards is always hard as it is geared at 16:1. I made a simple clutch that swings the banjo out of engagement with a lever projecting out the front of the gear cover.

I made a long front-tightening nut for my banjo which makes this easier.

Some other ideas fro Mini Lathes HERE and HERE.

Neil

I agree with Neil about the cross slide back lash. "Tilting" the nut is the "offical" i.e. manufacturers way . However it cannbot be got rid of totally and it is always good practice to feed in from one direction so back lash is removed from the calculations shall we say.

However you say that your main problems is chatter. The advice concerning gib adjustment is good. Buy a set of those cheapy diamond laps and I used the middle one, cut back the plastic to a sharp edge and then you can remove high spots from the dovetails. It will make a difference.

I had one of the yellow Clarkes lathes for many years as a back up machine but all of thes lathes require tuning up to give good results. Mine was almost impossible to part off with, so I bought Dave Fenner's books on the mini Lathe (they are all about the same despite branding). Two things were apparent over the chatter and the inability to part off. Firstly the bearings of the headstock had worn (they are not good new even as they are basic ball bearings). They were changed for taper roller SKF bearings, and its not a hard job I hasten to add. By the way the original Russian design of this lathe specified taper rollers it was only the Chinese sharpening their pencils on costs (cheep cheep) that caused the proliferation of poor ball bearings.

The biggest improvement was changing the shears that hold the saddle in place. The Chinese method of a cast bar with push pull screws is poor to say the least. I changed mine to solid steel bars bolted in place with hexagon head screws. When you dismantle your machine you will understand why this is useful. Then shim them exactly like the Myford (most other quality manufacturers) Tips are take your measurements as the loosest part of the travel and then use the diamond lap judiciously along the UNDERSIDE of the ways until there is an even sliding fit along the whole length. The rear one is critical get this right first then work on the front. This is matter of feel and you may find that shims will have to be changed as you go along. It can be achieved but patience is the key. I was subsequently able to part slices of 2" dia mild steel with some ease.

As this lathe finally died I am starting again with Chester Superior.

Hope that helps a bit

regards

Ian

Edited By The Oily Rag on 22/09/2018 09:26:35

Wow - more fab information there!

I have read about the questionable finish on the gibs and, bearing in mind I want to do things one at a time, rather than a major rebury, that's something I can go for soon. Those diamond laps sound useful. When I last look at them (on a stand at a past Boat Show) they seemed quite expensive but, if there is a cheaper source, I could go for some of those. I just acquired a 7mm spanner for gib adjustment and that saves a lot of bad language with a small adjustable.

I like the idea of a clutch on the banjo. As Wayco have gone to the trouble of giving me a wheel on the lead screw, I may as well make use of it and it's only 'half useful' at the moment. That banjo adjustment is a pain and I may take a ring spanner and going it down to fit in that limited space. No excessive torque required.

I looked at images of a Derlin style anti backlash nut. Looks clever and a mod could be possible but it could affect the range of movement without some more effort.

Most of the backlash is not caused by the screw, It is movement of the two fixing screws that the instructions tell you to just nip up to tilt. Ignore this. Wind the slide fully back. loosen all three screws. gennly tighten the centre one and then tighten the other two,gradually in turn until they are tight. This will prevent any movement of the screw nut when winding.

Keith

As you've found Andrew there's loads of info describing how to improve mini-lathes. As a beginner myself I was tempted to leap in and start applying all the good ideas immediately. With hindsight I don't think it helped!

The good thing about modifying a new lathe is that you learn all about how the machine is built. Unfortunately, for the beginner there are many pitfalls. As you haven't learned to use the lathe yet, you don't have a good sense for what's OK and what isn't. For example, you want to twiddle nuts to reduce backlash when the forum advice is that backlash doesn't matter much; also you assumed (not unreasonably on the face of it) that reducing backlash might reduce chatter, which is unlikely. In engineering best not to fix the wrong problem, and, if it ain't bust don't fix it.

Chatter can be caused by several things one of which is loose gibs. But, unless you've got some experience, it's also caused by common learner mistakes. How well I remember when learning to drive a car that they were all fitted with faulty engines that stalled, kangaroo petrol, a defective clutch, and poorly arranged pedals, mirrors and seat-belts.

I suggest getting several hours experience with the lathe using known metal (not random scrap) and known tools (shape appropriate to the job, sharp, and mounted in the toolpost correctly), also with feed-rate, rpm and depth-of-cut in the right ball-park. Experiment.

Once you've done that, you'll be better positioned to decide if the machine needs work or not. When I first had a mini-lathe I wasn't impressed. After I'd learned how to drive it and dumped the awful scrap I was practising on, most of the 'faults' disappeared and it turned out to be very capable...

When in doubt ask, the forum is brilliant at answering questions.

Dave

Edited By SillyOldDuffer on 22/09/2018 11:22:03

@SillyOldDuffer
Yes - you are right. I did read in several places of the need to tiffle a mini lathe, as delivered, so I was not sure. That is until I came across this Forum which seems to be pretty well informed. Moreover, there seems to be a general consensus about most of these things here. As they say "Twenty million flies can't be wrong" so I tend to believe you.

You are right about the learning process. Things are getting better for me already. I haven't actually broken anything yet and I've learned to be careful. I promise I will not pile in and change things willy nilly. The dial gauge measurements I have done have been impressive, in general and most things seem to be pretty firm. Parting off is still a bit scary but, again, i have heeded the advice about procedure and things seem to plop off the end with very little fuss. It's just that I am taking ages on every cut. I couldn't earn any money at that rate of work but I don't need to.

I do have one big problem, though. My son in law (lovely bloke so no pressure) did two apprenticeships at Ford and is now responsible for managing production of thousands of engines with sub micron tolerances in places. It's a high standard to be aiming at!

Edited By andrew lyner on 22/09/2018 11:39:04

Are we all assuming you have locked down the other axis (and top slide) when cutting? That alone can tell you plenty about whether any chatter is caused by any particular part.

That's a good point. I have both held the carriage wheel tightly and also engaged the half nut (gears in neutral) and things definitely do change. (Is that the "locked down" you refer to or can I lock the carriage some other way?) For instance, when parting off, a tiny movement of the carriage can increase of reduce the chatter and the position of the blade in the slot can be seen to waver (slot gets wider on the way in). This is another bit of technique I'd like to sort out and I have found that lateral force from the tool seems to cause a force along the main axis. I can't think why this is happening but, looking with a loupe, there seems to be a definite effect on the gaps either side of the tool. Could it be to do with the squareness of the blade? Something for me to investigate.

No, I mean locking down to prevent any movement. Most lathes (and mills) have that option but I don’t know whether yours does. I always lock the carriage while parting off.

Ahh, locking down the carriage. The mini lathes that I know do not as standard have this ability. The closest is on the Clarke where there is a grub screw (socket headed) in a tapped hole each side of the saddle front approximately centred on the top of the VEE. One had been tapped through and early on I thought great the saddle can be locked. Don't be tempted into this as logically this will lift and jack up the saddle against all its tolerances off the VEE when in fact you need to clamp the thing down onto the ways. I have not found a sound commercially available product but there are a number of simple designs around to clamp the saddle down onto to its ways.

regards

Ian

Edited By The Oily Rag on 22/09/2018 19:44:12

I used a flat piece of aluminium bar bolted to the saddle, with a thru bolt to a clamping plate running underneath the slideways...

I'll take a picture tomorrow and post here