It’s taken me almost two months to get around to writing part 2 of this series, opps! However this is because I have actually been using the printer, and working on a project for a friends rally car (watch this space).
Now where were we… ah yes, the heated bed. In the previous article I explained why a heated bed is a good upgrade for a 3D Printer, especially one that uses high temperature plastics such as ABS. Installing one is
easy straightforward, however my little machine required a few modifications along the way.
To convert your printer to use a heated bed first you’re going to need, you guessed it, a heater to heat the bed.
1. Sourcing a Bed Heater
I chose to use a 12V Silicone Bed Heater. These are easy to get from China and come in an array of different sizes to suit your needs. As I write this, doing an ebay search brings up 47 of them from a range of manufacturers.
Truth be told I took this route because its what everyone else does, however there are some major benefits to this style of heater. Firstly they are simple to wire (4 wires, with feedback), they are relatively thin and they can be driven straight from most standard firmware.
Most common printer PCB’s have the ability to drive a 12 or 24 volt heated bed directly, however I opted to use an external power supply. My heater is rated at 350 watts, so at 12 volts it can draw up to 350/12 = 29.1 amps! I was not willing to push that through a thin PCB, no matter how much the manufacturer says its
marginally spec’d to that ampage.
In hindsight I probably should have gone for a higher voltage heater and then wouldn’t have had to flow as many amps to achieve my desired bed temperature; especially given the fact my power supply has to drop down from 240 volts! A smaller step would have been more efficient. In fact 110V heated beds are available, their just less common.
2. Wiring the Heater
The heater has four wires, one pair is power/ground for the heater itself and the other pair are attached to a thermister embedded in the heater. The thermister wires were attached directly to the control PCB and this allowed the software to measure the temperature of the bed while printing. The power wires went to the external power supply via an automotive relay (12v 40amp). The relay was switched using the heated bed control off the PCB, which is usually used for driving the bed directly. This giving a lovely 12v output to charge the relay coil and switch on the bed.
I ran the power switch and thermister lines through the case via some two pin connected. Initially I wired theconnectors straight to the aluminium printer chassis but soon realized one of the pins ground through the outer thread! This mean’t I had to print some little top hats to make sure the signals didn’t ground. Printing parts for the printer; it’s 2016.
Once this was all wired together surprisingly it worked straight away (well once the above earthing issues were fixed). This gave me closed loop temperature control of the bed, ensure a nice consistent temperature.
3. Fitting the bed
It wasn’t all straightforward. The Chinese manufacturer neglected to give any dimensions when listing the heater, so I had no idea how thick it was going to be. I had a feeling it was likely going to cause issues with the self leveling system, as this requires the bed to bottom out when being installed to get under the sensing probes.
Low and behold once I installed the heater the aluminium bed no longer fit. Fortunately I had my non-heated bed on hand and I used it to print taller probe mounts. Magic.
So that’s it for this installment. In part 3 i’ll go through building an enclosure and the tricks I’ve learn’t when printing ABS.
A closing thought and something to consider before getting one of these machines. The more I have used the printer, the more I have come to realize that it is as much a piece of workshop machinery as a lathe, mill or welder. It requires maintenance, care and cleaning to remain consistent and usable. In my experience, few people have the patients for this.