Hello,

I own a kbc three axis with a centroid m-15 controller. The mill boots up and finds home fine but every once in a while, once called, the z-axis will make full speed jogs into the up or down limit switches. When this happens, the axis looses count, will not follow the feedrate override and will only come to a stop once it hits either limit. The only way of temporarily solving the issue is rebooting the machine. Any help would be greatly appreciated.

i would expect it to be an encoder problem,loose wire or just going bad,check the encoder for loose connection or wires,maybe they are being pulled on,the servo will run away at full speed once encoder signal is lost

you could also swap the z axis board with the x or y,just to rule out a faulty drive card see if the problem moves with the board

same goes for the motor if all three are the same,swap it with another,but only try one thing at a time,swapping is the best and faster way to debug a problem like this

just make sure you have your hand on the estop button so not to crash somehting
and sorry for multiple posts,good luck

I will second SORCHEROR's encoder diagnosis, and motor swap recommendation.

If it were a problem with the servo drive, the control would continue to count position accurately as it ran away (and it would stop sooner, with a "position error" stall message).

If the problem is fairly persistent (you can reproduce it reliably in five or ten minutes of jogging around or making short moves) then swapping motor connections at the back of the console will work. For example, if you exchange the X power and encoder connections with the Z power and encoder connections, then whenever you press an X axis jog button, Z will move (and vice versa). If you do this, and the Z motor still runs away (even though the control thinks it is X) then the problem is in the motor or the motor cable. If, after you swap, the X motor runs away (which the control thinks is Z) then the problem is inside the console box.

Be very careful doing this, as the Z limit switches won't stop a runaway on the X axis output.

If the problem is too intermittent to positively identify this way, then I would physically swap motors. I.e. disconnect the cables at the X and Z motors; dismount them; swap pulleys if necessary; and trade places. Then you can run indefinitely with X moving X and Z moving Z, but with a different motor in each place.

When all is said and done, you will probably find you have a faulty encoder on the Z axis motor. I can sell you a replacement for $160 plus shipping, but will need to know the back shaft diameter where it is mounted (probably 3/8", but not guaranteed).

Do you know the model year of your control?