Typical heatbed temperature gradient for an MK1 PCB?

I am getting a quite dramatic temperature dropoff on one side of my MK1 PCB. Here's a video showing the dropoff after it's been on for about an hour.

[www.youtube.com]

I've managed to reduce the dropoff with some insulation and a strip of space blanket, but it is still pretty dramatic. I'm a bit baffled to why it is happening. Maybe the PCB copper for the section of the board is not the same thickness as the rest of the board.

btw. This is running off a X360 powersupply that's 12V 200W. After fully warmed up it's drawing 8.5A @ 11.97V. Traces up with 2.5mm glass + Monokote. The PCB has a cold resistance of 1.9 ohms.

Edited 1 time(s). Last edit at 11/27/2011 02:52AM by billyzelsnack.

I think that gradient is actually very good - looks to me its way better than it should be. I was expecting alot more dropoff at edges compared to middle. I hope you did not expected it to have same temperature all the way, did you - it could not happen.

My assumption was that the entire PCB would be able to maintain at minimum of 105C.

I think I'm going to get a thin copper sheet and see if I can spread at least 105C to to the edges.

I assume you want it for abs so i'll resume to relate my little experience with that.

From time to time i use for abs, a copper cald double layer sheet with some kapton but leaving copper on all sides ~1cm or so. Is good but 1,5mm thickness not rigid enough and i had some really huge parts which warped together with the cald pulling it above from clamps. Funny. Also the cald itself can bend a little from heat. Dunno about gradient or anything but i would expect that it probably lowers the overall temperature because the heat exchange with the environment gets actually improved with copper surface. Which is not too bad because the air near the piece ought to be as hot as possible to mitigate warping.

For abs really huge parts (10*10cm) i have 2 slates of 4mm glass, but both are craked from one side to the other and only kapton holds them together, but i use them like that since i dont have else. Had few other glass pcs cracked in all directions, but the ones i use now one is cracked transversally, the other longitudinally. I couldnt figure a way to use glass with abs temperatures on my bed without it cracking. Funny, again.

If i would of had other surfaces like a sweet 3-4mm aluminium one or else, i would of rather used those.

If you want more heat overall, thats another story and i think only way is with a higher voltage supply, probably 14-20V one which would let it draw more current. I use a regulated ~20V~30(-ish)A supply which i made with a transformer from a very old ups unit, but i also use a hb etched myself so no clue how would that relate to the official hbp.

I have access to FLIR thermal cameras here from time to time. At the moment, I have one that only delivers counts (no temperature calibration). This should produce a good image of the heat footprint for my beds. I'll try and post results here when I can.

Just as an aside, I have discovered that there is an optimal temperature for ABS to stick to glass, with minimal warping and peeling off. For me, it's around 110'C. It's not the only parameter. Fill%, size of the part, and the number of parts being printed also play a role.