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Snardo
(@snardo)
Eminent Member
Strange print head travel

I started a print this morning and then had to leave for work soon after. The first layer looked good before I left. A while later, my wife sent a picture of the print - see below. This was supposed to be a simple, rectangular bin with an open top. It looks like the print head traveled beyond the boundary of the perimeter of the print in several places. Any idea what might cause this type of behavior. This is the first time I've seen something like this and I've printed this same file successfully once before.

Opublikowany : 11/03/2019 4:36 pm
RH_Dreambox
(@rh_dreambox)
Prominent Member
Re: Strange print head travel

I think it looks like the drive pulley on the Y axis is not tightened properly.
Check that both the X and Y axles drive pulleys are correctly mounted and tightened.

Bear MK3 with Bondtech extruder

Opublikowany : 11/03/2019 5:05 pm
vintagepc
(@vintagepc)
Member
Re: Strange print head travel

also try disabling your filament sensor.

https://github.com/prusa3d/Prusa-Firmware/issues/1522

Opublikowany : 11/03/2019 5:23 pm
Snardo
(@snardo)
Eminent Member
Topic starter answered:
Re: Strange print head travel

While the github link does show an issue similar to mine, I'm not seeing how it is connected to the filament sensor. Can you explain further?

Opublikowany : 11/03/2019 6:38 pm
vintagepc
(@vintagepc)
Member
Re: Strange print head travel

The theory is that the filament sensor is causing a false "out-of-filament" reading, which makes the printer lose its planning buffer. It then restarts from the last gcode, which, if it was a long straight infill line, will take it off the edge of the print bed. This causes a crash detect, which *should* rehome and recover the print as best as possible.

If it happens and the last gcode was a small step or change in direction, it will likely just manifest as a layer shift instead, if it's even visible at all.

Opublikowany : 11/03/2019 6:45 pm
Snardo
(@snardo)
Eminent Member
Topic starter answered:
Re: Strange print head travel

Thanks. Any idea why this might suddenly manifest when there has been no change in the firmware since I built the machine 6 weeks ago?

Opublikowany : 11/03/2019 7:01 pm
vintagepc
(@vintagepc)
Member
Re: Strange print head travel

The sensor is known to have issues with some types of filament (shiny, especially black PETG, and transparent ones). I suspect the issue doesn't happen nearly as frequently, but it can still happen with other colours.

Opublikowany : 11/03/2019 7:05 pm
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(@)
Illustrious Member
Re: Strange print head travel

... like Vintage just said ...

Opublikowany : 11/03/2019 9:35 pm
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