Erratic Z Movement

[terrycheney@bigfoot.com]

I am using a older PR machine. As we were cutting it would lose it's elevation and begin to cut deeper. This change would happen during the z up and down process. It would cut fine for ten or twelve z-up's and down's and then the z motor would pause for just a second and when it came back down it would be off. (usally to deep.) When we would change the cable from the z driver board to the y driver board, the motor didn't seem to hesitate any more and definately had more stregnth. We talked to Shopbot and they suggested that the z board was at fault (we agreed) and so we replaced it. This did help, but did not totally solve the problem. While substantialy cutting down on the "pausing", it will still happen before a file is over, everytime. (Note: We still have the old small motor on the z. The x and y motors have been upgraded) So we decided to hook up the new z. When we hooked it up it also would pause. It would move for a distance very smoothly and then it seemed like the motor would start to fibulate, if you know what I mean, and move slowly backwards. (We also tested to make sure the cable was not damaged by hooking up another one - no differance)

So, any ideas on where the problem lies? Or what the next steps are in diagnosing the problem?

Terry

[windsor@muskoka.com]

When you say that you changed the Z did you mean that you changed the stepper motor ? --or did you get a new R&P Z axis ? ---I started having all kinds of problems with my ball screw Z axis . ---mainly dust ( use Bostic dry coat on it before every file to lubricate it ) , but later on after a lot of wear I tightened the bearings on the rails to get rid of the slop , and the alignment of the screw went off causing it to bind and loose steps . Have you tried moving the screw by hand with the motor off ? ---This summer I got the control box upgrade , and the whole machine got a lot more powerfull . even the little motor on the Z axis overcame a lot of rough spots on the screw were it would have lost steps before .

[ctoddh]

I had the same problem and mine was caused by the black box where the ball screw passes through. I could not figure it out for the longest time until all the ball bearings just fell out one day. It seems the groves just wore out. Once I replaced the black box everything was fine.