Sunday, April 29, 2007


Aluminum Barrel Refactoring

After fighting with software and firmware all day, I decided to take a break and tackle something I'm comfortable with, something real. I had a couple incremental improvement ideas I wanted to try out on the aluminum barrels.

First off, I have a step bit, which is a triangular bit with varying diameters on it as you go up. I wanted to enlarge the inlet hole on the extruder barrel. My thinking is that it if the filament fed into the barrel comes in slightly wrong, then it might get jammed. if we make the orifice a bit bigger, then it should just guide the filament in properly.

Also, I noticed that the bolts werent going all the way into the acorn nut, creating a cone shaped gap between the bolt and the nut. This was causing the plastic to pool. So, I used my dremel and ground off the first 'row' of threads on the bolt. that way it sticks out a bit further and should cut down on that pooling.

Finally, I wanted to try a different strategy with wrapping the barrel. Previously, I was using tape to mark how far the nut goes in. This was not quite optimal because the marking could be off and then the heater wire may be too far up the barrel. Also, i wanted to concentrate the wire closer to the nozzle. Instead, I wanted to use the nut itself as the guide to where the wire should be wrapped. To accomplish this, I wrapped a plastic bag around the tip of the bolt, then threaded the nut onto the bolt, then pulled the plastic around the nut and taped it down. The plastic allows me to use jbweld without worrying about permanently attaching the nut to the bolt. After it dries, you simply unscrew the bolt, then peel the plastic off the jbweld. Nice, huh?

See more on Flickr...

This looks really great, Zack.

A few comments/questions:

1. I wonder if you could add a washer right above the acorn. If you tighten the nut against this washer, should give you additional surface area to transfer heat to the tip where it is needed (rather than just thru the bolt.

2. In conjunction with 1, could you add several layers of JBWeld and nicrome to direct heat to the washer?

3. Is the pooling of plastic in the tip really that bad? I can't see how it would affect the extrusion -- does it affect the ability to remove the tip?

4. Where do you imagine the temperature sensor would be placed? Did you have any thoughts on getting it as close to the extrusion hole as possible (to more accurately monitor the actual temp of plastic, vs temp near the heater?)
hey, sorry about not responding faster.

1. i think the energy transfer is pretty darn good between the barrel and the nut. if anything, it needs insulation to keep the heat in. it does the job pretty well as-is though.

2. i dont think jbweld conducts heat well... it can just withstand it.

3. not really. it doesnt affect removing it at all either... the plastic forms to the threads and the tip is just a cone shape.. check the flickr to see what i mean.

4. i was going to place it on the nozzle, and if you see the extruder instructions Adrian is working on, he drills a small indentation in one side, and then jbwelds a thermistor in the spot. pretty cool!
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