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Y-axis movement problem.

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Hello everybody, I have encountered a problem.

The printhead moves normally in x-axis, but struggles to move normally in y-axis. It looks like it hits an invisible obstacle from time to time, therefore, when printing, models are not scaled correctly. Belt tension seems to be normal, there are no strange sounds from stepper motors as well. Re-installing standard firmware did not give any results (I use custom firmware for heated buildplate).

Previously this day, the printhead has hit a part of a print, due to my lack of attention. After that everything was ok for a few hours, then the problem appeared.

Can it be a motor failure, do I need to get a new one?

Thanks in advance.


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Try powering down the motor, and move the print head by hand, by pressing lightly on the sliding blocks. How does the movement in the Y direction compare to movement in X?

Also closely inspect the belts, and rods to make sure that everything still looks square, and level, and the belts are all running smootly.


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Thanks for such a quick response, I guess I have figured out, what the problem is. The motor runs smoothly, but the pulley doesn't. So, either it is loose, or broke down. I need to disassemble the machine a little and check.


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This is a common problem but with many causes. The most common is slipping pulleys. There are 6 pulleys on the Y axis. If you are anything like me you probably only tighted the 4 obvious ones but missed the 2 on the short belt. Tighten the hell out of those 2 pulleys (as well as the other 4 pulleys).

Consider marking all 6 (all 6! Even the one on the motor) pulleys and their shaft so you can see which one is slipping. Also the UM came with higher quality set screws (versus the ones that are already inside the pulleys). You might want to replace the 2 on the short belt with the better set screws.

Also sometimes the Y belt is rubbing against the wood. It is very subtle and difficult to see or hear. You can tell it's rubbing because the belt twists a different way each time it changes direction. If you see this, move the motor pulley as close to the motor as possible without touching (about 1/2 mm) and you probably also have to add washers under the 4 plastic spacers. If the Y belt is rubbing it causes this slipping also but usually not sudden like you describe - usually it causes missing steps on the motor and it's more of a tilt to all your printed parts.

There are other potential causes but do this first.


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