Forgot to insulate the corners from the heatbed! DOH! Thought of it, realized I needed to, a few test prints is all... was what I was thinking just before I forgot... this was after maybe 12-15 hours of printing with the bed too hot at 65c didn't even need it really, 45c or so would have done the job I needed. PLA box 150mm x 120mm and tall enough to take 10 hours (duet case on .14 going for a super nice surface). Noticed bad layers but it was still actually printing reasonably well, as the motors pivoted skyward...
Live and learn :) this DIY was first of all to teach me about this, I learned something so still on the right track.
For now the insulation plumbers use to put behind pipes they are brazing might do the job nicely. Plumber told me about it once related to another project but from the description, thin sheet that resists the heat from a blowtorch to preserve wall building materials, it might be really good for this at totally isolating the heat zones of bed and motors.
I need some of that to try out, anyone tried it already? Looking on Amazon... 1000c resistance 'felt plumbers pad' showing the stuff with a blowtorch on it, but over 15 hours how much heat transfer? Buildup of heat? Will it break down? various materials available... any recommendations besides felt plumbers pad that is cheap? I think I have seen cork used... is that a good material? does it burn or char over long term use? I plan on using some fans on the motor side of it all, tight fitting insulation against the bed. Sound ok or is there a better method?
going to loose build height, 10mm or so, but sort of no choice if I want to print anything really big and tall and have a flat base. 5 hours no problem but 10 hours at 150mm wide with no heated bed and the corners will lift, ever so slightly to 'omg NOOOOOOO YOU UGLY HORROR!!!!' it's a bit random but it just won't lay flat reliably to prototype versus troubleshoot.