Same file, same pattern, is my z axis bad ? Or is it termistor? Speed is the same. Two shells. Should I go slower? There is small shift of to one side when model have something uncommon like hole or end of the top surface -but then the shift disappears and then it comes back . Any ideas ?
A set screw coming a little loose would cause a shift. Wouldn’t think it would get corrected unless after some josseling it gets rewedged.
Had this issue a while back on my Printrbot. Swapping out the G2 belts fixed it.
Are both pulleys with teeth per chance?
Looks like a backlash type issue. You’ll often see temporary shifting like this at geometry changes.
Could be some binding of some kind. Are your bearings well lubricated? Slower print speeds can often eliminate the shifting you are seeing. What speed are you printing at?
It’s definitely not a problem with the z-axis, what orientation was your print done in?
this is makerbot rep dual ext clone, its 20mm/s Everything in the printer is fine, except for the rob connecting the pulleys, I think it is slightly bend, because I might tighten the belts too much one day, I think maybe it is related to retraction ? There is so many possibilities
@Adam_Steinmark I will look into it, I have those belts for more than two years now, I used to have one problem in the past with SD card not being read and one print was left overnight with the stepper motor going over the limiters to one side maybe it scraped off some tooths, but that was ages ago. Thanks
@Dan_Collins yes they are, why ? I did not have this issue before, it came out recently I thought maybe my z axis is going mental since the bed got some abuse last time I was trying to pull of one of very well stuck prints
@Jeff_Parish 20mm per second per second, so quite slow but it have too heads so it is heavier -I have to keep it slow as possible. The lubrication - I use teflon all weather bicycle oil to keep the moisture out. heh. uk.
@Ryan_Carlyle okay I heard Thomas Sanladerer saying something about backlash, but he did not mention how to get rid of it l; is it managable in Simplify 3d maybe >? or adjustable mechanically?
@Duncan_Gunn what do you mean orientation ? the designed orientation of course XD thicker base lower thickness to the top , all perfect very easy to print, except for this weird artefact, I am fitting PCB inside so I have to file that down a little , in 8 units.
the only clue that I know is that it just happens sometimes, and it is repeatable, like I am creating perfect conditions for that artefacts to occur with certain load of material/temperature/acceleration/pressure maybe? but how to not do this, I do not know yet I will attempt tomorrow slower print and we ll se what happens
@Piotr_Sitko My guess, was belt was just loose enough and the skips seem to line up to point of acceleration perhaps. Maybe jerk and acceleration caused a tooth jump. Just a guess though.
@Piotr_Sitko backlash is a hardware issue – looseness in the belts, wrong kind of belts, loose belt clips/clamps.
You had the belts for 2 years? Lifespan is normally 1 year. I think I replaced mine it a year and a half. Were these printed simultaneously or separately?
@Piotr_Sitko It looks like you have a problem with either your x or y axis. Since you say it’s only some of the time, are your drivers running too hot?
@Ryan_Carlyle would you say this is a good backlash test - https://www.thingiverse.com/thing:2256550 ?
i`ve had this exact same problem appear a few times with a new x drive train, only to disappear without any trace.
it looks exactly like backlash should look, but none of the tests i could find come back positive (including the one above - which prints perfect).
@Adam_Steinmark separately , the belts are low quality and old, I hope those are the problem. Drivers are not excessively hot i think they are ok. I will get new belts ! 
thanks
