Shifted prints

I've got my new Prusa Mendel working for the most part.

I had problems with layers shifting so I lowered the firmware default_accelereation to 1000.

That works for the most part, however when I print more than one part or a part with separate points, I still get shifting.

It happens in both the x and y directions.

I've included an example.

Any suggestions?

Are your pololus hot? If you can't touch them, they're too hot.

When they get too hot, they go into a self-protect mode that looks just like skipped steps. For me, at least, this is the problem 95 times out of 100. If (when?) you find that they are, adjust your trimpots counter-clockwise to reduce the power/heat they take on.

Or add a fan to help cool the stepper drivers.

Check for loose pulleys too.

I gave this a try. I retuned my stepper drivers and tried another print.

This time, it shifted in the X direction. The stepper heat sink was fine. I could keep my finger on it no problem.

Its always when the print head is making a big move across the print bed.

I guess I can go lower on the accel? I'll give it a try.

Its just weird as the accel is down to 800 on my firmware now. I'm using a RAMPS 1.4 with Marlin. The stepper motors are from Ultimachine (Kysan's)

The belts were the first thing I checked before posting. They are pretty tight now.

Shifting usually means skipping steps. It can be mechanical or electrical. Just because your belts are tight doesn't necessarily mean it's not mechanical. Look at pulley slip, as noted above or anything else that could cause slop or backlash. If you rule out mechanical try swapping stepper drivers and see if the problem follows the swapped driver.

I will check the pullies, however I'd be suprised if the problem is there. The motors have a flat end and the nut in the pulley is against it. I imagine I would hear some nasty sound come out of it if it slipped.

I will try a stepper driver swap and see what happens.

I do appreciate the advice in troubleshooting this!

So new theory and it seems to be working....

I re-calibrated my stepper drivers and the problem actually got worse.

I noticed that the shifts never occured mid-layer - only at the begining of the next layer.

So I was wondering if the head was moving fast in a direction to get back to the starting point for the next layer, perhaps the momentum of the head assembly was actually pushing the stepper motor a couple extra steps because perhaps the holding torque was too low due to lack of current.

So I dialed the stepper drivers about a 1/4 turn more and everything seems to be working for the current print.

Just curious if any of those more experienced think my reasoning is sound?

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Just curious if any of those more experienced think my reasoning is sound?

Indeed...I just got my Prusa i3 going and ran into that issue straight off. I was simply that my Y-axis stepper didn't have enough current.

Having to adjust the current is normal. Good to see you have it working.