The stock MakerBot Cupcake kit comes with an acrylic build platform – nothing fancy, just a square of orange plastic sandwiched on a square of wood.
The Cupcake prints 3D objects by melting ABS plastic on to the build platform, layer by layer. When the molten ABS hits the room temperature acrylic, it cools rapidly. Like most things, ABS shrinks when it cools. Unfortunately, when you lay more melted ABS on top of that cooling ABS, it tends to curl up at the edges.
One first solution to this is to print using a “raft” – a series of lines put down on the build platform, on which the part itself is printed. The idea is that the raft, which is printed slowly, so the lines are thick, really sticks to the build platform and resists curling. For small parts, this is somewhat effective. For larger parts, curling is still likely.
The second solution to the problem is a heated build platform, which replaces the acrylic for a circuit board and aluminum plate. The circuit board is covered with traces that get hot when a voltage is applied to it. The aluminum plate helps spread out the heat and make it even.
The heated build platform is heated to 110 C, which is about at the softening point of ABS. This slows down the cooling and keeps the ABS from curling. It works quite well, and in theory it is not necessary to print with a raft. It is often still useful because the first bit often screws up and it’s better for that to happen on the raft than the object itself.
The heated build platform is $50, and most of the time you need a relay board as well, which is another $20. The relay is needed because the mosfet (switch) on the extruder controller can’t handle the current drawn by the heated build platform. The relay powers the heated build platform directly from the power supply.
Honestly, the heated build platform is probably worth the $70. But it always seemed a bit of overkill to me. Once the first several layers are slowly cooled down, I suspect the build platform doesn’t actually need to be heated. The heated build platform by default is kept at temperature throughout the entire print, which is wasteful.
I’ve been thinking that there might be an easier (or at least cheaper) solution. I noticed that the second print on the acrylic build platform always comes out better than the first. I assume this is because the acrylic retains some heat from the melted ABS of the previous print.
Race car tires don’t work so well when they’re cold – they get all slippery and don’t “stick” to the racetrack. In Formula One (and presumably other auto racing series) the crews keep tires warm by wrapping them in electric warming blankets. A standard heating pad costs about $15 and is big enough to fold around an acrylic build platform. Maybe it could work? If it worked, you could alternate two build platforms – print on one while heating the other.
Saturday I was having trouble with the CRASH Space MakerBot Cupcake, so I spent time working on two other Cupcakes that I need to get printing. Last weekend, we built Mk5 Plastruders for each. I also have a Heated Build Platform and an Automated Build Platform (which is also heated) to put in them, but I haven’t finished them yet. So I decided to try the heating pad on the acrylic build platform.
I turned a heating pad on high, folded it in half, and put the acrylic build platform inside. After a few minutes, the platform was much warmer than after a print. The test print was a relay board mount, which lets you mount the relay board on top of one of the stepper controllers. It’s a large object – with the raft it nearly covers most of the build platform. There was absolutely no curling at all. The raft stuck to the platform so well that it was actually difficult to get the print off it after it finished. After it came off, the part came out perfectly flat.
The raft probably isn’t necessary. There is an optional Raftless plug-in that prints the first layer of the object slow and thick, similar to a raft, so that it sticks to the platform well. It can also start printing off to the side of the object so that it has enough time to stick to the platform. This sacrificial “tail” can be later cut off. I’ve had good luck printing with the Raftless plug-in on a heated build platform, and I bet it would work for a heated acrylic build platform as well.
Each MakerBot at CRASH Space will have a dedicated heated platform, so this isn’t terribly useful. But it’s nice to know that if for some reason the heated platform isn’t working, the heating pad works nicely.