Strange problem with position loss

[Derek]

This has been going on for a while and I’m finally getting around to asking about it. Like a for sure a couple of years or more or perhaps even longer and I just never noticed it.
I have two knee mills that run UCCNC and have identical hardware.

UC300 USB 5LPT
HDBB2 BOBs
DG4s 16035 drives
US digital 500 line encoders
Kelling servo motors.

When I start the machines up I run a warmup Gcode program on the X and Y. Basically it runs them back and forth a bunch of times. It’s the same program every time. After it runs the Y axis returns to within .0005” - .001” every time. The X axis on the other hand drifts on both machines. It never drifts the same amount and it has drifted as much a .300” more than once. After the program completes I zero the X axis DRO and run it again. It may drift a little more but usually it comes back to within .001. Now here is the the really strange part. After the X axis stops drifting it’s rock solid the rest of the day.

As a point of reference one of the mills used to have a CNC4pc C32 and a M44 and it had the same issue with that BOB as well. I just finished switching it out with the HDBB2 and 5LPT and I have the same issue. The first run the X drifted about .020”. After resetting the DRO I have run the same test 10 times and it comes back to within .001” every time. These are older mills with a lot of milage on them so .001” is amazing to me.

Warming up the machines isn’t a bad idea and like I said when it’s done drifting it’s very stable but I would like to get it figured out if I can.

Thanks
Derek

[Vmax549]

Hi Derek, Have you tried changing out the encoder for X axis ?

How about swapping X and Y axis to see if teh problem goes to Y ?

(;-) TP