Just started a print on my Mini, and while the bed was extending outward to its farthest position to be prepped, the belt that drives it started slipping. Made a horrible ratcheting noise, and wouldn’t stop till I cut the power. I tried twice more with the same result.
I can’t see anything caught in there. Any suggestions? Is the belt maybe worn out, or is it possibly a calibration issue?
Mini 1 or 2? For either check belt tension.
On the 2, check the sensorless homing sensitivity.
Thanks for asking: it’s a Mini 1. So how do I check or adjust belt tension?
Check the OHAI website for Mini 1.03 and 1.04 assembly instructions. I would think there would be belt tension instructions there.
Thanks, I’ll check it out.
So on closer examination, I don’t think the bed drive belt is loose. It seems to work just fine making small adjustments on the Y-axis.
The problem occurs only when it gets to (or very close to) the home position, fully extended out front. That’s when it starts juddering endlessly.
Is there some sensor that tells the bed that it’s reached the home position? Or some way to recalibrate the bed’s actual position? I tried reducing the Y-axis length settings from 154mm, but it didn’t help.
The belt is not slipping, the ratcheting sound and jerky motion are from a broken stepper motor shaft inside the stepper motor.
The broken shaft can catch and function periodically or eventually just stop moving. The motor shaft is broken internally behind the support bearing so it is not evident unless you disassemble the motor, and the motor assembly pressures the shaft to exhibit periodic function.
I have had 2 of these stepper motors break on mini 1’s. Chalk it up to poor or nonexistent heat treatment of the motor shaft or just low quality steel that sheared from excessive alternating rotational torque stress.
I recommend replacing the steppers on the y and x axis at the same time, replace the z axis steppers only if they break, they have a different torque load.
Thanks for the tip. As it turns out, I had to relocate my Mini to another location, and the act of moving it seems to have fixed the problem.
Who knows, maybe there was some dirt or dust caught somewhere that made it slip, or the bed was slightly misaligned and got nudged back into true. Whatever the cause, it’s working again, at least for now. If the problem returns, I’ll take your advice and look into replacing the steppers.
Until that day, this Mini’s still going strong on original parts after seven years.
Your problem is the limit switch was not stopping the bed and it hit the front bearing and caused the motor to stall. look and make sure the switch is not coming unplugged, or has shifted/moved.
That makes sense, thanks for the tip. Though it’s been working just fine since I moved the printer physically to a new location, so whatever might have shifted must’ve shifted back. Go figure.