Stepper motor locking up on Z up

[rbach]

For some reason out of the blue yesterday my z drive locks up when trying to jog up at full rate. It sounds as though its getting pulses to go in both directions and if you hold the jog up button down you can actually see the spindle slowly move in a downward direction even though the DRO is still coutning up.
It moves down fine and if I set the jog rate to slow jog rate to 90% it will work fine but nothing more than 90% and it will lock up again.
It does this when trying to run a program as well when the machine attempts to move to rapid clearance height it will lock, the DRO will get out of whack and the program is shot.
Running Mach 3, did an upgrade yesterday to see if that would fix it, no help. full reboot and shutdown of all systems no help.
Have made no changes since thursday when the machine ran fine.
Any suggestions on what the issue may be and some trouble shooting tips.
Thanks
Randy

[photomankc]

Your Z is too heavy for the stepper it sounds like. You'll either need a counter-balance to take up most of the weight of the head, do a pully reduction on the motor output, or get a bigger stepper to be able to pull that weight up.

[vger]

I had a similar issue with my Z... Maybe a little tacky, but I streached some large rubber bands vertically on the Z to decrease the load in the up direction. The one advantage of the rubber bands is they don't add much mass. I also found that ambient temperature made a bit of difference. When really cold, I think my Delrin nuts are just a bit tight.

Steve

[MadMachines]

For some reason out of the blue yesterday my z drive locks up when trying to jog up at full rate.
Randy

Can you run the motor disconnected from the machine?, try swapping over motor connectors on the driver and run the z as another axis(for testing purposes), you could even try swapping the motors if they are the same. Has anything happened since you last used the machine? bumped, knocked etc. You could try removing the spindle to lighten the up load and see if it functions properly, however it sounds as though a problem has developed as the machine was running fine before. Yes? As with any diagnosis, it is usually a process of elimination. Good luck.

Cheers