Makerbot Heated Build Platform - Build and first use summary

After being unsuccesfull in printing the main part of the Printruder II printable plastruder i needed a way to print large part.

I could print about 15 layers before warping kicked in. Which in general isn't bad considering allot of people get warping almost instantly (some even on the raft).

At 14ish layers the left front corner of my printruder head started to curl up. I had hoped the warping would be contained to one corner and was praying for a good outcome. Needless to say (and judging by the picture on the right) the warping had become so bad that the print head ended up outside the object and was crashing into it repeatedly. I quickly stopped the build, afraid my extruder could become damaged from crashing into a fairly thick wall already.

So i ordered a Makerbot Heated Build Platform v2 and assembled it.

The build
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Putting the HBP together was a bit overwhelming at first, because i had never SMT soldered before. The whole hot plate thing sounded a truckload of work (and allot of money to spend for something i'll probably only use once). Luckely i could turn to an electronical engineer at work who said you can SMT solder by hand without a hot plate. You just need a good soldering iron and good quality solder. He showed me how to do it, and behold - i SMT soldered ALL the components perfectly without prior experience and WITHOUT a hot plate :)

If you follow the manual on the wiki it's all very straight forward. There's no pitfalls - just take your time, solder in a very well lit environment and use magnifiers (those come in handy!).

Take note of the orientation for the leds, the green markings are horribly small.

When everything was assembled i sawed off the tips off the nuts. Next time i'm in a hardware store i'll search for screws i can sink into the metal so nothing sticks out on top. But sawed off i don't loose any build space either.
Setting It Up
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I read allot of messages from people saying their mosfet overheated quickly. Some people report 1-2 minutes, others report as little as 5 seconds before the mosfet shuts down due to overheating. A fan is a solution - but not adequate... so are heat sinks. On heavy (or long) loads any chip (not properly cooled) will eventualy shut down from overheating.

Hooking the platform directly to the power supply for power is an obvious solution. I mean - the PSU is just sitting there with very little to do. Good thing about open source: a bunch of people have done all the work for us already. Hooking it up to 12V directly makes the bed heat up, but keeps heating up. We want to be able to control the temperature, so let's use a relay.

John Abella's blog has a nice write-up about how to install a relay and the right way to connect the wires. I also used a 12V-30A car horn relay that cost me no more then 5euro. The 30A is a bit much but that one was on the shelf! For visual clarity i added a schematic to the left on how the wires go. A few people are confused about where the black wire from the HBP goes to. Well it goes to the black wire on one of your black wires on the PSU. Yellow wires on your PSU are +12V, black wires are -12V (also called 'ground'). My PSU had a 4pin 12V connector i could never use on the makerbot so i cannibalized it for the 2 +12V connections (30, 86) and 1 ground (black wire from the HBP).  What's important is to use a diode between 86 and 85 to stop back EMF from destroying your mosfet. Read about it here.
Note: A+ on your extruder board goes nowhere! It is normaly used to feed the HBP if you don't hook it up directly to power.

The wires can be soldered straight onto the relay, but you could use isolated crimp-on connectors like i did. They in turn can be soldered or just crimpped depending on how lazy you are ;)
Also comes in handy if you ever need to take it appart.

Keep the wires as short as possible, and away from the motors.

Printing with a HBP
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Allot of the HBP users feedback mentions firmwares 1.6 and 1.8 heated build platform. I had v2.0 installed, tried one test cube and noticed the whole thing behaving weird - so immediatly flashed to the lower firmwares. I'll test it out with the new firmwares later when i printed some necesary parts (z wobble arrester, printruder II). Right now i'm concerned about making good quality builds and the older firmware combination works.

I haven't figured out how to print raftless. Building on the HBP with a raft requires some cleaning up when it's done. The raft doesn't always come off that easely, but i get nice builds so far - so raftless is something i'll worry about later.

Since i'm printing with (red) ABS for now, the HBP is heated to 120°C. I noticed i have to give it 123°C to make it 120°C. My prints stay pink untill i remove them from the bed, then they turn red - which indicates me the object stays nice and warm and doesn't suffer as much from inter-layer cooling.

Next will be to test my black PLA. I had briefly tried it but my extruder needs more tweaking to be able to print it succesfully. My attempts cause the filament to strip out almost instantly eventhough i was heated up to 230°C. Some research showed that the heater barrel needs to heat up to 150°C at the tip to be able to print PLA correctly. So that's something i'll have to figure out in the future.
For now i'm happy with my red ABS.

Check out a video i made while printing the z wobble arresters:
z wobble arrester printing
Originally uploaded by kling3r