X-Axis stuttering

Hey, all,

I just got calibrated and started running first samples. Right away noticed a problem with the X-axis binding up. Tried running four jobs and they all failed early after a few dozen X passes. I can hear the stepper grind and stutter. The model features get laid down offset in the X-axis only. No problem with Y-axis.

If I shut off power, I can manually slide the print head assembly side to side in the X-axis and it feels okay for a few cycles of back and forth travel, but then I can feel it seize hard. The belt return roller on the side opposite the X-axis stepper motor appears to be rotating freely. Good solid "twang" on the belt, and I don't see any skipping of the toothed pulley on the stepper. Flats of the shaft turn with the pulley okay. When the print head does seize during manual pushing, applying pressure on the corners of the print head doesn't seem to release it, so I am guessing it is not that the linear bearing guide rods are misaligned or cocked. Could it be the X stepper itself?

Added a pic of the 5mm step cube with features offset in the X-axis. Not that it probably helps much, but....

Any help on how I can troubleshoot this?

Thx.

 

It could be possible you have your belt too tight and you're binding the stepper motor. If the carriage has a great deal of resistance when you try to move it by hand it's too tight.

It sounds like you did all the basic troubleshooting with the pulley, drive shaft, etc. It is certainly possible to x motor is bad but it's hard to know for certain until we troubleshoot the belt.

 

Okay, I tried relieving some of the tension by unloading the spring tensioner on the belt and the head assembly still seized up.

I finally pulled the cover off, took the belt off the pulley and spun the stepper shaft/geared pulley all by itself by hand. Sure enough, it seizes up. The head assembly glides freely when I push it back and forth, so it is almost certainly not the X-axis linear bearings.

Thanks for the troubleshooting feedback, Mike! Guess my next step is contacting the Robo3D guys.