PCB MK1 Heater

Instructions

In order to make flat plastic parts you will need to heat up the surface that you print on (heatbed). There are at least 3 common ways to accomplish this.

1. Nichrome wire attached to the bottom of the print surface.
2. Power resistors attached to the bottom of the print surface.
3. A PCB that has been etched on one side.

I chose the PCB as a heater.  It's low profile, the work has already been done, simple design, effective at heating, and at about $25-$35, it's cost effective.

Attach 12 gauge wire to the contact points (I'm told 3 feet).  Once I know for sure how long the wire should be, I'll be heading to a hobby store to purchase battery pack wire sold by the foot.  The reason is it has a very high number of copper wires inside, a high temperature silicone sheathing, and thus very flexible.  This is exactly what you want because the bed will be moving.  You will also want a thermocouple so that the temperature can be measured, 2 surface mount diodes, and a 1k resistor.

There is some debate which is better the MK1 or MK2.  The MK1 is from Prusa himself, the MK2 is not.  Just don't buy a hot bed with thin copper, it won't be able to hold the amperage and burn out.  I hope the one I ordered will be OK.  It is my understanding that there are a lot of Chinese boards that use the copper layers under 35 microns (and cheap).  One way to tell is to ask.  Another way is to look for solder in the thru holes (that's bad).

Keep in mind that I wanted to be able to print in ABS.  ABS temps demand that the bed be real hot, like 107 degrees C.  After a lot of effort I built the heat bed.  MDF wood for the bottom, MDF on the top with cork gasket around the perimeter with standoffs.  As far as I know, I'm the only one doing this (so far).  This keeps a nice area for air to not circulate, which makes for the best insulation to get the bed real hot.  I originally had the PCB with the wires facing down, but that wasn't getting hot enough, so I have the wires facing up and the pyrex on top of that.  This setup allows the bed to hit 100C pretty quick, and can get as hot as 112C.  A pictures worth a thousand words...