Here's a recent discussion about trial and error heated bed PCB design:
http://forums.reprap.org/read.php?2,293302,319336#msg-319336
Some tips for making a heatbed from nichrome wire powered by wall (mains) power, as used in the BerryBot:
http://forums.reprap.org/read.php?178,311911,311911#msg-311911
I haven't searched the archives to see if anyone has ever proposed or tried etching traces directly on the back of a glass build plate as used in automobile rear window defrosters, but it seems like a tangent worth exploring if it can generate enough heat for ABS.....
http://forums.reprap.org/read.php?2,293302,319336#msg-319336
Some tips for making a heatbed from nichrome wire powered by wall (mains) power, as used in the BerryBot:
http://forums.reprap.org/read.php?178,311911,311911#msg-311911
I haven't searched the archives to see if anyone has ever proposed or tried etching traces directly on the back of a glass build plate as used in automobile rear window defrosters, but it seems like a tangent worth exploring if it can generate enough heat for ABS.....