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I have measured .05mm (approx 2 thou) backlash on the X axis of my SX3. I have adjusted the gibs and checked the stepper shaft coupling and there has been no change. I thought that given there is a double ballnut there would be some way of adjusting the backlash there but it is not obvious to me how to do it.
I have attached a photo of the assembly. With the unit assembled as shown there is a small but easily detecable amount of play between the two halves of the ballnut if you hold one and twist the other. Can anyone advise me if/how this can be adjusted and any other things I might do to improve the backlash.
kenealym I've got similar 'twistability' in my ballnut and with the gibbs adjusted as they are now, I measure 0.03MM of backlash (just a smidge over in reality). Mine might be tighter than yours or it might not even have any effect on the backlash at all, difficult too say.
Certainly my thrust bearings are where I managed to reduce it a fair bit from what it was. The factory ones just weren't running right for some reason and I managed to get my hands on some replacements. Would've been a lot easier and cheaper if they'd used the more popular, larger size ones...or maybe the smaller ones just aren't commonly stocked in the UK.
IGG1e, thanks for your post. Did you just replace the bearings at either end of the lead screw or did you replace the whole ballnut assembly? Do you have any part numbers?
(After this I need to attend to the Y axis which has slightly less backlash and Z axis which has considerable backlash - did you do any work on either of those?)
It was just the bearings at the end by the stepper motor, ball screw left alone. It could possibly be a case of the lead screw to stepper motor coupler flexing a bit that adds a small amount of backlash, not tried a different type.
In general though I'd say your machine replicates what I found. The Y axis seemed to suffer from too tight thrust bearings and re-shimming those actually made it smoother and reduced the backlash to match the 0.03 of the X. The Z had about 0.08 - 0.1 I think. I couldn't seem to make it any better and it is a pain to work on that axis mechanically. Doing my counterweight system rather than the gas struts, whilst not removing backlash, has certainly removed almost all of the 'head nod' on a direction change.
Thanks for that. I am getting about .1mm on the Z too. So from your experience I may not be able to better that and it does look like quite a job to get at it.
I don't think the X problem is in the coupler. If I set the jog to steps of 0.01 I can see the coupler and the screw moving but get not movement of the table itself until I have "moved" 0.05mm.
I will have a look at getting a shim between the nuts on the X axis and see if I can improve that and report back.
Thought I'd update this as I've just measured them again.
Axis ---- Measured MM
X ------- 0.036
Y ------- 0.045 (not so great)
Z ------- 0.039
Short of running the X and Y very loose on the gibbs, not sure of a way to reduce it.
I have had a look at the bearing and there does not appear to be any way of adjusting it.
I can't seem to get any better than 0.05mm on X and Y although that is just within tolerance for advertised ballscrew setups with C7 accuracy such as below. (0-0.05mm)