Friday, November 5, 2010

Aug 20, 2010 third... fifth... ugh, sixth times the charm

So I have been playing around with the hot end of my extruder for weeks.

Every time I thought I'd make a post of "it works!", it failed. I've been considering renaming this blog the repstrap fail blog. The extruder hot end design I have come to is a confluence of better skill and craftsmanship through failure, and some design ideas I played with to work around my lack of Kapton-fu.

I added a nut on either end of the 3 hole washer to hold the brass barrel reducing the structural stress on the thermal barrier. I also drilled a tiny hole in the top nut to accept the thermistor. This
moves the thermistor out of the way of the nichrome wire and washer, which I was having trouble taping around. Second, it also allows for quicker troubleshooting and repairs. On the end is nichrome wire wrapped around
the bare brass barrel, except for a strip of Kapton tape going up the length of the barrel. I've found that Kapton tape sticks to it's self better than it does bare brass. The strip of tape is three times as long as
needed. I left the unattached, longer amount out over the nozzle while I was wrapping the wire. I double wrapped the nichrome closer to the nozzle and folded down that length of tape down to hold everything in place, which of course covered the nozzle. Then kaptoned it down and covered it in ceramic tape, more Kapton. And finally cleaned up cutting where needed with an Xacto blade.
The Thermistor was a much simpler installation than it ever was previously. I put it in the hole and Kapton taped around the nut and Thermistor. done. I'd like in the future, maybe the next heater barrel
I make, to have two thermistors at different locations on the barrel. Should be simple to implement, a hole in both nuts and a couple lines of code on the Arduino. I'm not too sure on the host software though.

Heating this for the first time, I'm excited to see it work much MUCH better than the other things I had tried. With the added nuts the thermal mass seems greater, but it could also be that the thermistor is about 1cm from the end of the nozzle instead of right on top of it. But it does seem to hold heat longer and plastic extrudes easier and more consistently than anything before.

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