Tuesday, 13 June 2017

A new bed

I rather obviously need to get a new bed to replace the broken glass. I started looking at places that will do aluminium sheets and quickly found metal-fachhandel.de, which has lots of options. Particularly confusing is the choice between "gefräst" (milled), "gewalzt" (rolled), "gegossen" (cast), and "hochfest" (high strength). There also seems to be some difference in exact composition, between AlMg4,5Mn, AlZnMgCu1,5, and AlMg3. I guess milled and cast are rougher than rolled

I looked at a few posts around the subject, and found the choice of aluminium over glass is not as simple as I hoped for. Longer discussion here.


  • Can use the distance sensor on the whole plate
  • Heats up faster
  • Doesn't break if you foolishly drop the print head from really high
  • Can do away with the clamps
  • Possibly warps (though some special mounting trick might fix that)
  • Could get scratched if the hotend runs into it
  • Could generally scratch over time, leading to prints that are hard to get off
Trying with an alu bed for a while cannot be that bad, though, I can always change it if I want the glass advantage. Ordered a 5mm sheet from Stahljunge GmbH / Team Heavymetal (heavymetal-aluminium.de) Tuesday, it arrived today - that's pretty fast! And nicely packaged, as well:

Before doing a test print, I wanted a shot of the tip of the hotend, to see if it had taken damage. This is the kind of shot where my DSLR shines, though holding it right was a challenge.

I think that might be a piece of glass up there, I should extrude carefully at first. But other than that, I think it doesn't look too different from a fresh one (modulo scratches).

Calibrating by hand shows that, of course, the new bed is a lot higher, about 4.8mm current Z offset. I tried to update the firmware to use a more appropriate Z height, but for some reason it couldn't upload it. Annoying, but no deal-breaker, I'll just start my calibration cycle with G0 Z6 instead of G0 Z2. Once I've figured out how to hook up the proximity sensor, it'll be a moot point anyway.

Trying to push the apparent piece of glass out by extruding a bit didn't work. I managed to break off the remaining piece of filament trying to push, so now I'll have to take apart the extruder to get that out. It's also possible that my attempt at doing a cold pull with too little filament to pull on caused fusing of melted filament to some part of the extruder.

In the end, I had to take the whole extruder setup apart and do a cold pull together with some needle poking on the standalone (or rather hangalone) hotend. After putting it together again, I calibrated to 5.2mm Z offset, had to change the initial GCode to not go to Z5 while heating. The bed doesn't heat through very fast, even at print start it's lukewarm to the fingers.

I'm trying at first without any hair spray and a relatively high Z offset. It's not sticking at all. Tried with hair spray, still no good. Lowered by 0.1, still no good (but the hairspray was old). Tried with hair spray added after the bed got heated, it at least sticks a bit, but the print ended up with lifted corners despite the filament being clearly squeezed tightly:

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