Hi Markku,
good luck with your trials!
I am in the process myself, with the following configuration, source and cost included for anyone who might need the info:
1) 5mm aluminum bed, ?40.-
Local lasercutting shop
2) silicone heating pad, 200x300mm, 400w, 220V, thermal element type J, ?75.-
http://www.freek.de/produkte/flaechenheizelemente.php#nr8113) controller to match, ?195.-
http://www.pohltechnik.com/product_info.php/info/p140_Temperaturregler-Tischger-t-Schaltlast-bis-10A.htmlObservations so far (ran up to 76?C setting/70?C effective aluminum surface:
>Need about 10min preheating time for even temperature distribution.
>Heat distribution is reasonable, about a 4?C deviation across the mat area, about 8C deviation outside the mat area.
>Z calibration needs to be adjusted for every temperature level.
>Blue painter tape is not adhering good enough to print ABS without raft at 70C. PLA raft at +6 helps.
>At 70?C, the heat is not dissipating into the structure of the bed moving mechanism.
>70C is not enough to prevent ABS warping on larger parts.
I will continue to increase temperature to find a good setting for larger parts.
BR
Peter