X-Axis Shifting

Hi everyone.

I'm configuring a newly built Prusa Mendel with RAMPS board. Having an issue with the x-axis shifting during printing. The parts start off without issue and after approximately 30 mins the x-axis begins shifting. The image shows how the layers begin migrating after a period of time. The belt has been tightened and the gear is firmly on the stepper motor (the shaft has been flattened).

Has anyone else run into this problem? Any help is greatly appreciated!

Can you do a bigger picture to show your X axis belt?

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Waitaki 3D Printer

As requested. Does this show the x-axis belt well enough?

I was interested in the x ends and where the belt runs over the idler bearing and motor. BTW, have you checked the voltage on the pololu?

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Waitaki 3D Printer

Another thing to check is the current setting to the X axis motor. Too much current and the stepper won't step properly. To little current, and it will miss steps and shift.

If you're not sure, rotate the little variable resister for the proper driver, all the way down or to the left. Use Pronterface to move the axis. If it doesn't move, or just whines, turn the adjustment up only a bit, less than an 8th of a turn. Try to move again.
Once you get to the current level where it moves cleanly, turn the adjustment up one 8th more and you should be good.

I got the same problem, i changed the motor current and tried several other settings but non of them seems to work.
The motor is not missing any steps nor does the head got stuck. This you can usually hear this pretty good.

What i do noticed is that when the shifting occurs, this usually is after 30min+ working, the motor-driver has some strange behavior.
When it happens I stop the printing, but leave the motors on. So they fixed, when i push a little on the y-axis it is fixed til at some point the y-axis suddenly moves easy and smooth, then it fixes again. Like 1 or 2 seconds in both directions.
Smooth means really smooth, so not like the there is no power. This happens to the X and Y axis.
Again i played with the motor currents there was no change in this behavior.
Can it be that the electronic-driver is oscillating?

Do you have heat sinks on the stepper driver chips? I bet you don't.

This sounds like the chips are going into thermal shutdown when they get too hot. They shut off, cool, and turn back on, all within a very short time, but long enough for steps to be missed.

Yes, that was my problem.

I added a heatsink to every motor controller and a placed a fan directly at the motor controllers.
That made all the difference. Now i can start printing again.

On the site of Melzi they claim that you can do without heatsink bud that is not true in my case.

Thank you, Lounhkb