Why exactly does a Core X Y Z printer loose tram ?

kcress

I have a Troodon printer. I've replaced the original controller with a Duet3 and 6. It has a fixed bed and four Z steppers for the four corners of the gantry which provides all the three dimensional motion.

Whenever I turn off power, or really annoying, reboot the Duet3, I can see the gantry's right rear corner drop about 2mm. Whenever this happens I have tram three times to converge back on to a reasonable levelness. This takes a painful amount of time. Does anyone know specifically why gantries drop and if there's anything I can do to prevent it or reduce it?

Thanks.

droftarts

@kcress I would think that the gantry isn't square (in the sense of the two Y axis extrusions are twisted relative to each other), which forces one Z stepper down when it is not powered.

The Troodon is basically a Voron 2.4, so you should be able to loosen of the gantry frame, level it, then re-tighten it to make it square.

Ian

Nurgelrot

@kcress Perfectly normal and expected that you should tram the gantry before every print with this type of printer. They all move when power is lost to the steppers even if you don't see it. Your bed.g should have looping built in to get it down to some acceptable tolerance and call it in your normal start print procedure at bed temperature.

dc42

@kcress said in Why exactly does a Core X Y Z printer loose tram ?:

Whenever I turn off power, or really annoying, reboot the Duet3, I can see the gantry's right rear corner drop about 2mm.

It appears that the detent torque of the motor driving that corner is insufficient to prevent the motor from turning under the load. Is it the same type of motor as the other Z motors? How does it drive the Z axis: leadscrew, ballscrew, belt, or something else?

kcress

@droftarts Hi. I'm going to find some machining reference blocks and see if I can detect something out of square.

Thanks.

@Nurgelrot Hi Nurgelrot, Yes, I realize that and expect needing a tram. Thinking back, the original Troodon HW didn't seem to do that. Though, it may have worked a tram in I wasn't recognizing. It's been a few years since I converted over to the Duet 3. I sure never saw it do the corners then the whole gantry jerk to a new plane.

I need to figure out how to put an automatic converging tram into bed.g

@dc42 Hey DC, All four motors are identical. They're all driven from the HC6 so they stay ordered. I'm not sure I'm following you though, as the gantry stays trammed as long as the power remains ON and the Duet never restarts due to a config file update. You're not talking about detent torque of an unpowered stepper? Or, are you?

This thing is all belts 400mm x 400mm x 500mm

dc42

@kcress yes I am talking about the detent torque of an unpowered stepper. When you turn power off or reboot the Duet, all 4 Z motors become un-powered. If just that corner of the bed drops then that suggests that either the detent torque of that motor is lower than the others, or there is a twist in the bed or bed frame so the motors have to apply force to overcome that twist and keep the bed flat - and when that force is released, the bed resumes its natural twisted shape.

droftarts

@kcress said in Why exactly does a Core X Y Z printer loose tram ?:

I need to figure out how to put an automatic converging tram into bed.g

You can do this simply by just repeating the levelling section a number of time in bed.g. However, a better way would be to put the levelling in a meta gcode loop, so it repeats until the deviation is within the limits that you set. There's an example of using a loop here: https://docs.duet3d.com/en/User_manual/Connecting_hardware/Z_probe_auto_levelling#examples

Meta Gcode reference page: https://docs.duet3d.com/en/User_manual/Reference/Gcode_meta_commands

Ian

kcress

@dc42 I did not know that. I bet all my tinkering may have torqued the axis beyond the original, that didn't seem to need tramming. I've likely exceeded the detent torque now.

Thanks.

kcress

@droftarts Ian, Thanks for the link. I've implemented automatic tramming into bed.g

Thank you!