Friday, 4 July 2014

Heat bed

posted 2 Apr 2014 23:45 by David Taylor

A quick update that I've been meaning to post for a couple of weeks now on my heat bed.
I've used a Printed Circuit Board (PCB) based heat bed. More specifically I got my hands on a RepRap Mk2A bed. I am able to heat this bed to 110°C but during printing it's only able to maintain about 97°C at best.
The image above shows a fairly consistent heating profile for my bed. The downside is that at the moment I only have ABS filament. With PLA, we should be able to get going in about 6 minutes and should also be much easier to maintain the temperature.
The MK2a also support 3 point mounting which I did go for. As you can see from the image below, my aluminium print surface sits snugly against the back two posts.
Having washers between the screws and the PCB Heat bed required that I cut a space for them out of the aluminium heat bed with my Dremel to ensure that the print surface plate sit snug against the PCB at all times.
I've also installed a cork backing to the bottom of the heat bed to minimise heat loss in that direction. so the entire assembly, with Cork, PCB Heat bed, Aluminium Print Surface covered in Kapton tape is shown below.
With all of the above, I was still battling to make parts stick long enough to finish printing. I tried Hair Spray (although I think I used the wrong type), but in the end I am super impressed with ABS Juice.
Basically I take about 10ml of Acetone, drop a couple of small reject ABS parts in and wait for it to dissolve. Once I have a slightly thick white smooth liquid, I pour it onto the heat bed and smooth it out with a small paint brush. Once this is dry, I can print just about anything without it ever coming off the bed. It actually makes it quite hard to take it off even afterwards, but with a bit of gentle persuasion, it pops free without breaking the part you just printed.
Tip: I lay another cork tile on top of the heat bed while heating it up. This reduces the heating time by about 15%. I've seen guys using cardboard, news paper and boxing to do the same. Effectively, just give your heat bed a blanket and remember to remove it before you start printing ;-)
Those of you that have been following my tweets where I've been saying that I want to print my quadruped leg would have noticed that I have still not done that. The universe seems to be holding me back: Power outages and Thunderstorms are to blame. (For those of you in the UK, thunderstorms in South Africa require unplugging all electronics and internet connections... ;-)

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