Z axis would not run after crash

Just had a crash on my 3-axis router as a result of the Z axis position being about 5 mm lower than expected. Crash came after a tool change, so it is likely that I messed up the Z touch off (spindle has an ER collet so I set Z height by touch off after every tool change). But the weird thing is that, after jogging the Z axis up to get the tool out of the material, the Z axis would then no longer move. At that point, Z axis did not respond to jogging or MDI commands. There was no indication that the Z axis motor was trying to move and the Z axis position did not change on the display. (I am running step and direction mode with no position feedback, so it is possible for the display to show a change in position without the motor actually moving.) I was able to jog and command moves normally in X and Y. Problem was resolved by loading another program and then reloading the original program. The original program then ran normally.

For what it's worth, the program I was running is my first attempt at using sub programs and fixture offsets. Before the crash happened, I had interrupted the program about halfway through the first set of sub programs in order to skip ahead to the next tool change. The crash occurred immediately upon resuming after making the tool change. Also note that I have interrupted this program in this way a number of times and have not had this problem before today.

I am wondering if there are steps I should be taking after interrupting a sub program or after interrupting a program that uses fixture offsets. It would be good to know what best practice here.

Any ideas what caused this problem and how to prevent it from happening again?

Thanks,
adh

 

If you interrupt a program, you loose S, F, M3, G43 (if toollength from tooltable is used) and it falls back to a certain offset, mostly G54. If you want to to restart from a line, its safest to enter there a line with all the required gcode, and start from there, as G0 G55 S7000 M3 G43 F888 and proceed carefully with initial machine movement, watching DTG in dro. If using many subroutines, sometimes it may not succeed to restart from a line, and restart into a subroutine will fail and is absolutely not recommended to try.