First attempt at a heated bed

In short.... Complete failure.

Since I will be printing quite large parts I need the bed to be absolutely flat, therefore the ideal material would be glass. Having failed to print on cold glass I tried a number of things. Firstly I sourced the glass from an old cupboard sitting in the garage (hope my girlfriend is not reading this blog or I'll be in for it) cut it to size making 4 equal sized bits that fit nicely on the bed. The idea was to change the glass for a quick turn-around.

Firstly I stuck some nichrome wire to one side of the glass using kapton tape and placed a second bit of glass on top on the first. Needless to say after around 10 minutes the bottom glass cracked. (3 bits of glass to go).

Second attempt was similar to the first but with a thin sheet of steel (0.3mm thick) sandwiched in between to diffuse the heat better..... Same result, bottom glass cracked.

Third attempt saw 2 casualties (glass wise that is) the first slipped off the work bench and I guess you already know what its fate was. The last bit of glass was placed on top of the piece of steel. The steel (same 0.3mm thick) had nichrome wire taped to the bottom side. Preliminary tests looks promising with the glass reaching a temperature of 110C, 90C around 2 inches from the edges and 60C at the edge. I was quite please with that so I ran upstairs, fetched a piece of insulation material from the loft (at this rate the house is going to fall apart soon) and taped it to the bottom the steel were the nichrome wire is.

I also constructed 4 "Z" shaped brackets to hold everything in place and solve the issue of the print nozzle hitting the bed mounting bolt since the actual print bed is now elevated. I therefore proceeded to mount everything on the Reprap, aligned the bed and switched on the power supply for the heated bed.

I monitored the glass temperature for a while and when it reached 100C I turned down the current on the power supply in an attempt to keep the temperature constant. This seemed to work after a number of adjustments.

Excited, I fired up the Mendel to run a test print..... Clicked on "Home all" and...... crack!!! :-( the vibrations from the machine were enough to shatter the glass. Puzzled and disappointed I disposed of the glass.

I guess the vibrations and the pressure from the "Z" brackets was a bit too much for glass.

Glass bed idea now scrapped.