Y axis skipping

Ok. I have been running my prusa i2 for a while now and have an odd problem. The y axis appears to skip on longer prints, but not all of them. I am using white lithium grease on the rods, and it even does it right after I disassembled and greased the bearings. I am considering adding code to the g code to home the axis every several layers to help correct any alignment issues.

Does anybody have any suggestions on what else might be wrong?

I am using marlin firmware. And when the prints finish without skipping I am happy with the results.

Insufficient stepper current or the stepper driver is overheating.

By far the most likely is a driver that's getting *way* to hot. If they get close to melting, the shut down to protect themselves. If that's what's going on, you need to roughly cut the heat rise on the driver in half. Usually it's a combination of fans /heat sinks / adjusting current.

Edited 1 time(s). Last edit at 12/25/2013 06:17PM by uncle_bob.

I.ve been having the same issue with my prusa for a while now. I am using Marlin and pronterface with slic3r. My board is a RAMBO. it doesn't skip every layer, just the odd once in a while. Tried increasing current to the y axis stepper, no change.

Mike

After reading some more, thought I'd try setting the print speed to about half it had been to see if I've been over driving it.

So far it is behaving very nicely... Too bad, the last printer I built handled speed no problem. Time will tell.

Mike

I started having this issue (as well) yesterday.

It's not stepper driver overheating, nor the stepper, i wasted more than a day fiddling with that. It sounds a bit like the belt skipping. I have GT2 belts with high quality pulleys, and belt is about the same tightness.
I was able to print at speeds well above 200mm/s before this started, larger prints are far more prone to this as well. Now even below 100mm/s speeds it eventually skips *sigh*

It is yet another design flaw on Prusa. The basic mechanical design is simply flawed. Will tighten the belt and design a proper belt tensioner and/or redesign the whole Y-motor bracket the get proper grip on the belt, need to get more teeth touching it.

Using RAMPS + Sprinter.

well I'm printing at 30mm/s now and have two shifts in the print. I've tried swapping boards, same effect.

mike

so you have replaced all but the actual stepper now?

On the guy with the belt problem - try reducing the acceleration. I found that helped on some prints.
May help the original poster as well - it may be that the acceleration is overcoming the torque of the
stepper causing skips.

One of my largest issue that I recently fixed. Fix it mechanically. It's the bearing. aside from the prusa having y-axis design flaw, the friction from all the moving parts in the bearing is the cause.

Switch to metal on metal bushings with lots of grease. Less noise and no friction or gouging the steel rod like with the bearings.

Should look something like the picture attached.

Prusa finally printing reliably and clearly. I had noticed some slack in x belt and tightened it. I changed the Y axis stepper. Y was still a problem so increased amperage in firmware. This cured the Y axis skipping.

Was using the ecksbot quick change extruder body on the ecksbot X carriage. This became loose and the idler could never stay tight. It turns out that my J-Head was overheating the underside of the carriage and extruder body. This caused the body to warp. I changed to an older style ecksbot extruder body and a j-head clamp stacked either side of x-carriage to keep the jhead rigid

Extruder stepper would occasionaly skip as well so increased its amperage to 1 amp as well.

Can turn out impecably clean prints now. Currently testing speeds to see where the prints will start to fail. so far 55mm/sec is fine at .14mm layer height.

Printer is an Ecksbot style prusa running on latest Marlin. Control interface is Printrun with newest Slic3r.