Build plane sudden shift in alignment

[hks]

I have a new machine, run eight builds and half have developed the same shifting problem. First thought it was the glass shifting so made some little rubber wedges to take up space between the glass and the guide pins on the table. Did two good builds after that but yesterday the problem resurfaced. It appears that the belt on the X axis shifted a tooth or the motor jumped some steps. Checked belt tension and appears good but tightened a little anyway. It appears to have shifted to X left about .050. Other than that wondering where to look. Anyone else seen this?[img]

20150325_114914.jpg

Build plane shift, 9 hrs total, shifted at 6

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[insta]

Are you using Z-lift or Z-hop? (different slicers call it different things)

I bet you're not, and the nozzle is colliding with little bits of the previous layer that are sticking up.

[hks]

Would Z lift cause the entire build plane to shift or just cause a blob at the contact point?

[insta]

Neither, Z-lift is an intentional step of the slicers that causes the part to drop a small amount (usually 1-2 layers) below the print area, so as the head moves to a new part on the print, it doesn't come into contact with anything underneath it. When the head arrives at the new location the 1-2 layer drop is removed and printing resumes. It can have a small, nearly imperceptible impact on print quality (slightly degrades it), but if it lets you actually print without issue then it's a net win.

[hks]

Thanks, I could try that and see what happens, my builds are long (8-20 hours) and I'm loosing half of them at this point. On the bright side I usually catch them before the whole job is done. My Simplify setting is at "0" and I understand they recommend ".5" mm if you set it.

[insta]

I run 0.32, but yeah you'll notice an immediate change in the number of prints with shifted layers.

Incidentally, this also means you are slightly overextruding, or under retracting. There is further calibration to be done, but Z-hop is a big rug to sweep those niggling calibration issues under.

[PcS]

I had this problem recently and turning down the print speed fixed it for me. Default was 4800. Lowered it to 4000.

[jimc]

4800 isnt really fast for the printer to move. the questionable default speed setting in s3d is the 18000 xy movement speed. i think thats borderline of what the steppers can move. that combined with 3000 default acceleration in the right circumstances can cause a skipped step. in addition to what insta said about the overextrusion. all those combined i think are the biggest causes.

[PcS]

You are right jimc . Forgot about the x y.

[Bratag]

I regularly print above 4800 (or 80 mm/s as I prefer to work in) Haven't seen this kind of shift. I would be looking at hitting or the part as mention here. I do generally run with z-hop - but mainly for parts where the head is going to be passing over a mass of plastic repeatedly. If its primarily a shell you can really open the M2 up and it performs very well.