my models keep getting knocked off. what to do?

Hi, I’m new to printing. I got myself a Kobra 2 and it was printing fine when I got it. But recently it started to knock the prints off at random times. I have done several recalibrations, adjusted the Z offset up and down. What I have noticed is that all of these models seem to have a small overflow of material which I’m guessing the nozzle is bumping into. But I have no idea what causes it. I’ll post the latest print that failed, there the extra material is more pronounced than usual. Any suggestions what I should adjust? (Btw I’m using Octoprint)

https://lm.boing.icu/pictrs/image/64e90560-402f-45d4-bcef-18ae3c79289f.jpeg

MangoPenguin,
@MangoPenguin@lemmy.blahaj.zone avatar

That first layer looks really rough, although it’s hard to tell for sure from the photo.

In my experience the most common reason for prints getting knocked off is a poor first layer, so the print lifts off slightly and then the nozzle hits it.

feecoomeeq,

In my cade it was eSteps calibration and flow cube print calibration. After setting this up (flow 91%), issueless prints

IMALlama,

Post a picture of your first layer, or just the underside of this print. It looks like your nozzle is quite a bit too high, but it’s hard to tell.

Since you said you had good adhesion before (with the same filament, right?), here are some things to look at:

  • clean your bed! If it’s removable, dish soap works well. IPA also works well, but you want the 90% or 95%
  • first layer squish. Too much will give you elephants foot. Too little will result in poor adhesion
  • have you changed your bed and/or first layer temperature?
  • have you changed your first layer speed? Slow is good
ScottE,

You can try adding a brim (or a raft if that doesn’t help) and see how that goes - tall and skinny models can require some extra bed adhesion to be stable, and that can affect the very top if the model is moving enough for the extruder to hit it. Worth a try…

admin,

This already had a brim but it is quite ugly. The thing is I had the same failure while printing a bigger object like a Stormtrooper helmet. Randomly popped off the bed after like 2.5 hours

watson387,
@watson387@sopuli.xyz avatar

The only time I’ve ever had the extruder knocking down prints is when the bed was out of level.

IMALlama,

I’ve had it happen when I partially lose adhesion and the print starts to warp.

skilltheamps,

First thing to try would be cleaning your bed with alcolhol / soapy water. Grime and fat from your fingers prevents good sticking of prints.

Then, what happend to your first layer? Is it supposed to be cylindrical at the bottom too? It also looks like the first layer height is way to high: the filament is just laying around like spaghetti, not adhered to the bed

admin,

I have cleaned the bed already with alcohol and microfiber cloth. Yeah the brim is supposed to be cylindrical but it obviously isn’t :D . Is that a modification I should do in Prusa Slicer? For the first layer height

Evilschnuff,

You may want to calibrate your z height. The first layer should have a slight squish to it in profile, like a cat tongue biscuit.

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