Just like anything else, there are benefits and drawbacks to everything, and such is life in the word of fused deposition modeling (a trademarked term, btw) and what plastics to use. The most common for a MakerBot CupCake CNC is ABS plastic, the same material that LEGO bricks are made from. The material melts easily and consistently, it’s durable when finished, it’s widely available, and it’s relatively cheap.
Of course there has to be a drawback. While printing ABS in this layered fashion, it’s common for the different layers to progressively cool down while printing, and without a ‘hack’ to fix this, the object will frequently curl up and potentially pop off the build platform.
The ‘default’ fix for this is to print on ‘raft’ – a grid square of plastic put down first, the hope being that this stays adhered to the base and tries to keep your print flat:
As objects get wider and thicker, even the rafts have trouble staying perfectly unless stars are aligned. Over the last few months various users of MakerBots and RepRaps (and other similar devices, some entirely hombrew) have been working on creating a heated build platform. Operators have found that by keeping the model warm, the plastic won’t warp.
Low-tech solutions have included hairdryers, space heaters, heat guns, and various enclosures, but since the community has experience with heating via nichrome wire, this became the common route. Two of the first setups were by Jordan Miller and Eberhard Rensch. Jordan Millers design became the “MakerBot Hotness v1.0″.
As is common, the evolutions of the idea were helped along by many people including the MakerGear guys and a second version was finally produces and sold by MakerBot Industries: Heated Build Platform 2.0.
The MakerBot Heated Build Platform v2.0 requires some surface mount (SMD) soldering, something we’d never done before. We got a hot plate, solder paste, and got to work:
Words of warning: our “Aroma” brand hotplate worked well on low, but you have to watch for hot spots. If possible it would be better if you put a piece of aluminum over the hot plate, but under the board.
We sanded the kaptop top sheet to make things stick easier:
When wiring the HBP up according to the wiki, the MOSFET on the extruder board would shut down after just a few seconds. After checking our board for any shorts, we tried again to no avail. We installed a heat sink on the MOSFET for the HBP, but this only increased the runtime slightly before it would reach thermal overload. The wiki suggested being able to wire the HBP up to power directly.
We saw the following results:
- 5v Power: temp went to 68°C and stabilized
- 12v Power: temp went past 140°C and kept going, we unplugged it
Since the target temperature is 110 to 120, neither solution was ideal. We worked out how to wire it up with a relay:
The relay is wired as follows:
85: goes to extruder controller “A-” port
86: goes to 12v positive (constant)
87: goes to the red wire on the HBP
30: goes to 12v positive (constant)
The black wire on the HBP goes to ground, not on the relay. The relay we used was a small Hella relay, probably for a car horn.
The extruder controller provides constant power, and switches ground.
With this installed and working, we were able to print a large flat item, raftless without any curling at all!
And as a note, the HBP has red LED’s all the way around it that show when it’s being powered: