A few years ago my school bought a Rapman 3.1 from bfb. After it was constructed they quickly realised that the print wasn't that good and so it was neglected in the corner. When we found it we had to repair many things on it and we also decided to upgrade it with a heated bed. We searched for a good solution but with no avail. This guide will show you step by step the construction of our heated bed and hopefully you can make one too.
Step 1: Optional - Housing for Arduino
What we first did was to create a housing for the micro controller (arduino). We used laser cut acrylic to create this housing and stuck it all together with tensol. This part is just for aesthetics but I highly recommend it to limit the risk of short circuits from open connections as the arduino is quite sensitive. Also it makes everything neater and makes sure that the wires don't interfere with the printer.
Step 2: The Print Bed
In order to create a heated bed for abs we needed to duplicate the acrylic print bed provided but in aluminium as acrylic isn't a good conductor of heat when compared to aluminium. We traced out the shape of the old bed with a scorer and made the big cuts using a guillotine. We use multiple drill bits to create the inner and outer holes and then filed the rest off to give a smooth finish. Next we covered the top with Kapton tape so the abs would stick easier and also to get the top nice and smooth. Lastly we used the thermal adhesive to stick the resistors and temperature sensor to the back of the aluminium taking care to space the resistors out evenly.
Step 3: Supplying the Power
We managed to find an old computer in the depths of the ICT basement and so we took out the psu out of it. In order to switch the power supply on we found the green wire and the corresponding black wire( normally the one next to it) on the main motherboard plug and we attached a small toggle switch to prevent it being switch on by accident. Next we took the molex connector (the one pugged into either your hard drive or optical drive. It's normally a translucent white) and used both the 12v line (the yellow and the agacent black wire) to power the resistors and the 5v line ( the other red and black wires) to power the arduino/micro controller. We finally connecting both grounds together.
Step 4: Arduino/micro Controller
We used an arduino to control the whole bed. We hooked up the temperature sensor(tmp36) to 5v, gnd and A0. The two Leds were hooked up to pins 11,12 and to gnd and the switch was hooked up to 5v, pin13 and gnd with a pull down resistor on the signal line. Finally we hooked up the relay shield to 5v, gnd and pin 10.
Now for the programming...
In essence what's happening is that the arduino is turning on the heated bed until the temperature reaches a certain point (for pla:~60c for abs:~110c) then it will switch off the resistors until the temperature goes too low then it will switch the resistors back on.
If temp >110
Turn resistor off
Turn resistor on
The switch on the interface would switch the heating process on and the LEDs one would show if the arduino was on while the other would show whether it was ready to be printed on ( it had reached its target temperature).
Step 5: Final Results
Now here's one we prepared earlier :p
But on a serious note the bed worked really well and it improve the print by a mile.
Finally I would recommend this project for any budding enthusiast as its a fairly simple project only needing a few skills and although we had access to the schools machines e.g a laser cutter, remember this is a guide not a rule book you can do it anyway you like.