[tk59]

I am trying to get a new Chinese 6040 machine set up. Not have any problems with the Y or X axis, but cannot solve the problem with the Z axis. A search of the forum revealed a number of threads on lost steps in the positive direction, but nothing about loss in the negative direction.
As I run test cuts using Mach 3 and the supplied roadrunner.tap Gcode, each progressive cut becomes shallower until after several movements, the end mill no longer contacts my material at all. I have ruled out most obvious problems such as a loose end mill.


The problem becomes worse at slower rates and lower accelerations. There is an occasional but noticeable catching or "clunking" only as the z-axis lowers. Repeated movements at high rates accelerations don't seem to cause the problem.


Given that it is only a problem during descending movements, an underpowered stepper or bad bearing on the ball screw seem unlikely too. Any suggestions on what to check next?

[awerby]

Check for a mechanical problem in the Z axis assembly. What might be happening is a setscrew on a coupler came loose, that's spinning on the shaft as the motor pushes it into the material. Mark across all the screw/coupler connections with a Sharpie, rerun the program, and see if any of the marks show signs of disruption.

[tk59]

The problem doesn't seem to be the coupler as I the problem occurs even when I run the router without cutting anything so the shaft should have little to no load beyond the friction in the bearings. The slower the z axis run in a negative direction, the rougher the movement. At higher speeds everthing runs very smoothly. Could the problem be a bad stepper or an issue with the current at lower speeds?

[awerby]

If your motors are running rough, it might be something that can be addressed in Motor Tuning. Try reducing acceleration by half in the Z axis and see if that helps. It's hardly ever a bad stepper, although it could be that your power supply isn't giving them enough voltage to overcome their inductance. Or that the drivers are total crap, which is not uncommon in those machines.

[tk59]

Thanks for your suggestion. Turns out, it's not the motor or tuning problem. I decided to swap the Y and Z axis drivers. I made the appropriate changes in the dip switches on each driver to make sure I was using the original settings. The z-axis now runs properly and the problem has moved to the y-axis. This suggests to me that it's either a problem in the dip settings, the stepper driver or the voltage as you mentioned. Unfortunately, they did not provide any schematics or internal setting recommendations so is difficult for me to determine if the dip settings are correct.

[ericks]

I had so many issues with my 6040 when i got it. It used to "stall" often. Installed leadshine motor drivers and screened motor cables. For three years i have had zero problems. Show us a pic of your motor drivers if you can.