Layers drifting/offset north causing "stairstep" effect (Page 1 of 2)

Guess it'll take a few posts before I can post a picture.  If you're looking to help and want to see, ask me (HunterGreen) in the IRC channel (chat.freenode.net #Solidoodle) for the link.  (If you do, maybe you can post it here for me.)

By "north" I meant towards the back of the printer (so along the X axis, in what shows in Repetier's manual control as +Y).

The stepping is not that gradual; it printed several layers fine and then jumped all at once, and did that again about six or seven times, rather than constantly drifting by small amounts.

I have had this happen a few times. I found that the filament on my roll overlaps sometimes and the print head cannot move forward. Then the filament releases and it continues. Other things to check include the belt tension on the x and y axis.

Make sure the filiment is not binding up.

Actually, I just measured it, and the shift this time was just over 5mm.  That is, one layer is offset from the next only in the y axis and by just over half a centimeter.  This really seems like it's more than the kind of "drift" that other threads seem to be talking about, or that these solutions could address.

I'm going to try running another go and this time I'll attempt to video-record the entire build with my cell phone in hopes I can catch what's happening at the exact moment of the jump.

Nope, it let me go through the motions of attaching but the attachment seems like it vanished along the way.

Here's a try at posting it as an image.  Maybe the forum finally trusts me.

The object I'm trying to print comes from here.  I just loaded the STL into Repetier, sliced it, and tried to print.

I just watched it in slow motion and that extruder jumps(vertical) a large amount like something caught... so if there wasn't a big ball of plastic under the tip then either the wiring cable to the printhead caught on something or the filament did.

Make sure if you are using a spool like the one pictured below that you trim off any extra filament that sticks out the side and could catch on the back of the printer or something while printing because this will cause losing steps in the direction you are experiencing.

EDIT: I see in earlier posts that you made sure the filament was not tight and had ample slack... so .... the next most probable culprit is the wires going to the carriage either the big wire bundle on top or one of the wires going to the stepper or limit switch is snagging the bed or something???

Hunter, Being a machinist cnc in another life, looks like belt skipping to me! Measure one tooth, and one space on the Y belt, I bet its the same space on your step. Belt may be too tight, or too loose!

Just ran another print and tried to stare at it the whole time to catch it in the act of jumping so I could see why.  But the skips are a fraction of a second long, and I would have to be staring intently at just the right spot.  Though I see at least a half dozen skips in the print, and I heard thumps at least that many times, I never actually saw anything suspicious other than the extruder head itself seeming to jump up and down.  I wish I had a half-dozen camcorders I could fix pointing at every part of the printer and leave running during a print, because how else am I going to catch it in the act other than just getting lucky?

There were no wires catching anywhere, to the best of my knowledge, and I was watching for it.  The big bundle of wires that leads to the extruder does sometimes brush against the Y-axis belt on the left (as I look at the front of the printer), causing the top of that belt to flip a bit, but it doesn't actually bind up at all when this happens.  The wire leading to the X-axis motor doesn't bind up on anything.

I made absolutely sure the filament wasn't binding.  I left lots of slack and periodically checked it and made sure there was still plenty left and the loops weren't catching anywhere.

I'm pretty sure the glass plate didn't slide.

This time there were a large number of smaller skips instead of the 5mm-in-one-hop skip I saw the last few times.  But that could just be because I let it go all the way through this time.  The first skip was definitely one of the biggest.

How tight are the Y-axis belts?  If I push on them with a fingertip with as much pressure as I can apply just using the finger itself, without actually putting my arm into it, the low point is a few millimeters below the level of the shaft it runs parallel to it.  Here's a picture of me pushing it down to that point.  Hopefully this gives a sense for how tight it is, so someone can see "oh, that's way too tight" or "oh, that's nowhere near tight enough".

I think I'll also try that perfect circle calibration again because, while I never saw the axle stick out to either side before doing it, I seem to see a bit of that now.

I really hope someone chimes in with something specific because I'm getting nowhere tracking this down.

Three failed attempts at printing the "0" since that one success.  The fourth try is going now.

Every time I catch it skipping, it's making a long move (typically to position for another layer or a different region) and the extruder bumps into the object itself.

Hmmm.. good luck, hope this is not a normal thing with solidoodles...

Aha, what grease should be used?