The Heated Print Bed Saga!

So i installed a piece of glass that i re-appropriated from work into my printer as the print surface, it was about 240mm by 310mm by 5mm thick armored glass. ( Woot )


I suspended it over my Y rails with springs and adjusting screws to level it out. this worked great, i turned the screws over so the threaded posts pointed up and an nut and washer pushed down on the bracket this adjusted the bed for leveling and squaring, once  had it square i attempted a print, having not read enough blogs as i should have, my plastic refused to stick to the bed, a quick chat with a few peoples (i think they were peoples, if not they were polite and helpful alien) i found that i needed to heat the bed hotter to get my ABS to stick to it. so a quick search on the web i found me some cheap ceramic power resistors and some thermal double sided tape from jaycar.

And the fun began....



A Quick read of the blogs and wiki i find a number 75'c to get the plastic to stick. so i look at the box of power supplies i have in my junk room, and surface with several 12volt @6.6amps SMPS units, armed with this, my power resistors and my thermal tape i set out to do a heap of ohms laws calculations, i ended up with a spreadsheet that did all the simultaneous equations for the various combinations of 32 1 ohm resistors and 5 PSU's. i ended up at one point with 3 psu's all pushing 5amps plus in to resistor chains, burning my fingers, my desk and even a toe.. but i got it to 77'c!! GOAL.

so i though :( turns out that i didn't read enough of the blog that  i got the 75'c magic number from, and that was for PLA.. turns out ABS needs 110'c so back to jaycar and my junk room, and i have several more attempts to heat a slab of glass up to 110'c.. at onw point i had two 500watt ATX PSU's struggling to give me what i demanded!! all that they had and then some.. i had 4 12volt chains pumping 9 amps each and 2x 5 volt chains pumping 5 amps each... (found that the guy on the net actually knows what he was talking about, you need to load up or use the 5 volt rails on a ATX supply to get the full 12volt Amperage) this was the best i could do and got the glass to 100'c.. Would it be enough to get the ABS to stick...


No... Fail

all i managed to do was to make the resistors glow!! oh and burn my fingers again....

i will try and find a pic of the resistors glowing, but after that test i found that i had destroyed the resistors, they actually split in half.

to control this i simply had all the PSU's running off the one power strip with a switch.. as i couldn't get it hotter than i needed there was no need for the MCU to control it..