The top layer is a piece of pyroceramic glass. It can withstand huge temperatures and supports very well abrupt temperature changes. This also means that it doesn't change shape at all when heated. This is the most critical requirement of a high end build platform for a 3D printer. If the base isn't perfectly flat (I mean down to 0.05mm precision)the prints will come out wrong.
My first builds were done directly on the heating PCB, but the results were somewhat horrible. I had to go through great lengths to keep it perfectly flat despite the temperature spikes and the few times that I managed to do it right, the prints would fail for some other reason.
This new design fits on the Prusa Mendel wooden Y-axis carriage sold by Makergear, but it can easily be tweaked to support other frameworks. I have already published all my design files on Thingiverse, so feel free to grab them and hack it.
To draw out the exact requirements, I used FreeCad at first, but quickly ran into a bunch of issues when exporting to DXF. FreeCad is very useful for 3D designs, but when it comes to 2D, it is somewhat neglected and lacks some polish. I decided to use good ol' QCad instead and got the blueprints done in no time.
If like me you don't have a laser cutter at hand to do this precision work for you, there are other ways. I have ordered the glass from One Day Glass. They do custom glass orders which they can get delivered within a week. Very friendly staff as well.
The second layer is the heating PCB. It is made by Makergear and runs on 12V. The power is managed by a RAMPS v1.4 board, which I may document in a later post. For those of you who are not familiar with build platforms on 3D printers, this prevents the bottom of the print from cooling at a different speed than the other layers by maintaining a certain temperature close to that of the extruded material. Doing this will prevent what is called "warping", which distorts the final printed object slightly.
Lastly is the plywood layer. It only serves to give some rigidity to the platform at a reasonable weight (and for cheap).
To hold it all together, I have used bolts fitted with small springs.This prevents the printing nozzle from ramming too hard into the build platform, if that should happen, and thus prevent the glass from shattering. If you use that trick, make sure to use springs that aren't too hard to offer too much resistance, but enough not to make it wobbly. It must remain stiffly in place but yield under a reasonable weight.
That's it. I was hoping to test it out, but I've burned one of my servo motor driver. Now I have to wait for a couple more weeks before I print anything again. Stay tuned!