Easiturn backlash

[diverjohn46]

I seem to have excessive backlash in the 'x' axis on the easiturn lathe. Ive taken off the cross slide and there seems to be little backlash in the ballscrew, but, the ballnut seems to have a lot of play in it.
Is it possible to adjust the ballnut at all?
I see that there are three caphead screws either side of the casting, is the nut adjustable? The backlash seems in the region of 40 thou.......
The resistance when you move the nut on the ballscrew feels 'spongy' as though there is a spring inside?

The lathe cut very nicely but getting accurate feed is an interesting exercise and ultimately fruitless!

Any ideas anybody?

JOhn

[diverjohn46]

Managed to adjust the ballnut to give almost zero backlash on the cross slide - not the easiest thing to do and I do now need to take the whole thing apart to modify the screw holes to enable the three cap head screws to go back in again.....

But, the lathe was very good yesterday with the adjustment made and is cutting to a repeatable size, surface finish is nice too!

Thanks Darryll for the helpful suggestions, next job will be getting the spindle encoder(s) working to allow some screw cutting and to have decent spindle speed control.

[diverjohn46]

Managed to adjust the ballnut to give almost zero backlash on the cross slide - not the easiest thing to do and I do now need to take the whole thing apart to modify the screw holes to enable the three cap head screws to go back in again.....
For those who haven't done it the three cap head screws holding the ball nut(s) to the central casting need to be undone and the ballnut screwed in slightly to take up the backlash. Unfortunately, this then means that the screws will no longer go into their holes.......
Getting the screws out while the nut was in situ was a pain, but better at least in this initial 'get it going' and learn' stage than taking the whole of the x axis drive apart to extract the ballscrew and nut.

By the way, whoever hand scraped the cross slide - your handiwork is very neat and evident! Lovely Job!

But, the lathe was very good yesterday with the adjustment made and is cutting to a repeatable size, surface finish is nice too!

Thanks Darryll for the helpful suggestions, next job will be getting the spindle encoder(s) working to allow some screw cutting and to have decent spindle speed control.

[diverjohn46]

Well, had another look at the backlash issue- The ballnuts are knackered! I took the topslide assembly off and removed the pulleys and stepper motor from the rear of the saddle assembly. Getting the ballscrew out wasn't a problem and I then removed the ballnuts. The balls were in a very sorry state!

I have replaced the balls with 3.5mm (the ones I took out measured about 0.135") which seems to have sorted the problem out, though re-loading the ballscrews was fun............
Still got a small problem in that I wrecked one of the ball return caps which means that I only have two runs of balls in one of the two nuts, but, backlash seems to have gone and as I have now 5 working ballruns in the two nuts that should probably do until I can get new nut and screw!

Just for interest, I also replaced the drive belt which was a reference 150 xl 037. This came from e-bay at a price of £5.50 which seemed quite reasonable. The replacement balls were from simply bearings and cost £22 for 500.......

[diverjohn46]

OK, made a few small changes.
The re-loaded ballnuts have now given me a huge difference with almost no backlash at all.
I've also updated my stepper drivers and transformer.

I've got 70v 5.2A stepper with a 48v toroidal transformer. Rectified and smoothed (100 v 1 farad capacitor) this feeding 62 volts DC to the stepper.
Working with the EaziCNC programme and their serial card, this is giving a pretty good rate of rapid feed and allows some fairly useful screw cutting too.
The difference between the old transformer/driver combination at 32 Volts and the new at 62 volts is huge. The (original) Parker stepper motors now get warm, but certainly not hot and the traverse speeds are a huge improvement!

Now it works I can get on a learn to use it (though I do need to make that tool changer.....)