My MakerBot is making stuff again! Yippee!
The new .5mm barrel/nozzle seems to work well so far. The only problem I had, was some serious warping on an object I tried to build. The size of the raft is 50 x 60mm, so it’s not the largest object I’ve ever built, but it’s obviously big enough to make problems.
After 3 or 4 aborted prints I dug out a project I was planning since some weeks now, but never got around to do it: A heated build platform.
After reading about successful (i.e. warp free) prints on a heated build platform, Jordan Miller built at Hive 76, this seemed to be a solution for my problems and much easier to build than a heated build chamber (well, that’s another project I plan for weeks now…).
So, please put your hands together for the heated build platform:
I had this aluminum plate lying around for a while and always thought, that it would look nice as the base of a build platform.
It’s a little too big, but since I don’t have the right tools to do a clean trim, I just leave it at its current size for the time being.
I bolted an original MakerBot acrylic build surface down to the aluminum:
From the back, I drilled the same holes as on the original build platform for the bolt heads of the y stage and for the magnets.
I simply taped the magnets into the 4mm holes. Then I bolted three resistors (2.2 Ω, 25 W) to the plate and taped a thermistor directly on the aluminum.
The resistors are placed around the y stage, so the built platform still fits into the MarkerBot. However, the front and back resistor are blocking the maximum/minimum movement of the y stage. I’ll have to find a way to rearrange them on the plate so they don’t block the stage’s movements. Don’t be afraid, I already have an idea… :)
I did a first test of the heater and used a spare extruder controller v2.2 to drive the resistors and to read out the thermistor:
Although it took about 10 minutes to reach the target temperature of 60°C, the test was quite successful. Thanks to the 5mm aliminum base, the build platform nicely heats up very uniformly.
This left me with the problem how to drive the heated build platform inside the MakerBot.
Fortunately, MakerBot Industries was so kind to include three MOSFETs and some spare I/O pins on the Extruder Controller v2.2. So I use one of the MOSFETs (A+A-) to drive the build platform heater. Then, I made a small circuit/connector dongle…
… and use this to connect the thermistor to one of the Arduino’s unused analog pins (A6):
On the hardware side, the only thing missing is an ingenious connector for the 4 wires from the extruder controller to the build platform. Right now, I use an insulation screw joint (luster terminal) for the connection. But this means loosen 4 screws each time I want to remove the build platform more than 15 cm from the MakerBot.
I dream of a connector like the MagSafe connector on my MacBook Pro, build right into the y stage/build platform. But that’s another project…
On the software side, the extruder controller firmware needed some work in order to handle the additional heater element/thermistor.
These changes were easy enough, since only the extruder controller firmware need to be changed. The motherboard firmware can stay untouched.
I implemented the second heater section in a way, that it’s automatically initialized with a target temperature of 60° C. So whenever I switch on the MakerBot, the build platform starts warming up and hold the target temperature until the whole system is switched off.
Since it takes a while to heat up the build platform (around 10 minutes), it’s ok to start early with the warm up cycle.
Of course, it would be nice to have control over the built platform temperature without the need to upload a new firmware version each time. I already implemented all needed functions to read the current temperature and set the target temperature thru Replicator G. But this needs changes in Replicator G (including the UI). I’ll do that as soon as possible.
Finally: Does it work?
It’s amazing to see large rafts staying down on the build surface, as if it were the most normal thing on earth.
Here are two parts I printed today. Guess which one I printed before having a heated build platform and which one after…