PVA burning 75% into print, repeatedly

dmahalko · November 24

I am slowly coming to the conclusion that the UM3E firmware is not properly maintaining the BB Core printhead temperature during the course of a long print job, and the cause of this is likely the heated printing plate, which at first heats the glass, but then continues on to radiantly heat all the other surfaces inside the UM3E body.

I have decided that since the failures are repeatable, with the PVA burning at nearly the same spot each time, I will just keep trying the same project over and over until it succeeds, damn the waste of filament. I have been gradually turning down the heat to see what happens.

Also I am using a PVA raft, and that has absolutely no problems whatsoever, looks clean, no faults. It's only right near the end where the printhead is getting to be too hot, the PVA chars, and plugs the printhead.

Model source: https://www.thingiverse.com/thing:34277

"Deer Head detailed" by Takeshi Nov 11, 2012

Uniform scaling 36.51%

PLA Green in AA 0.4

Natural PVA in BB 0.4

Profile: Fine 0.1mm

Speed (default) 70mm/s

Generate Support, using Extruder 2

Build plate adhesion: Raft

Build plate adhesion Extruder: 2

Enable Prime Tower

Wipe inactive nozzle on Prime Tower

Ambient room temperature: 73 F / 22.7 C

1. Drop print temperature from 200C to 190C. No apparent effect. Prime tower contains small black blobs of PVA. Cleaning printhead BB hot push cleaning: lots of black charred gunk strings out

2. Staying at 190C, drop printhead standby temp from 100C to 80C. PVA gets further along before failing. Prime tower contains small black blobs of PVA. hot push cleaning: lots of black charred gunk strings out

3. Staying at 190C, drop printhead standby temp from 80C to 60C. PVA fails at about the same spot yet again though a little higher before it failed. Hot push cleaning: far less black charred gunk, it's now just a light brown and a tiny tip of black charring. The interior of the prime tower looks much better, and no more black PVA blobs.

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So.. how low can I go for the printhead standby temp? I am going to try for 40C / 104F next. Can it be set to turn off completely?

Also through all this I have not changed the print speed. Lowering the temperature has had no effect on PLA print quality for Fine mode.

Once I bottom out the standby temp, I will probably start dropping the print temp to 185C and then 180C while maintaining Fine print speed to see what happens.

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So anyway, it seems the PVA BB core is not maintaining correct temperature through the course of a print job, and eventually gets too hot and burns the PVA.. But the PVA works completely fine at the start of the job when the print bed has not had time to radiantly heat up the printhead assembly...