Wednesday, April 25, 2007
JBWeld Nozzles: Busted
In my recent quest to find the 'perfect' extruder barrel, I've tried a variety of things. I've recently become obsessed with JBWeld, a widely available high temperature epoxy. I first starting using it to attach the nichrome (heater) wire to the heater barrel. It works really well for that. So, I thought.. what else could i use it for?
One of the things I really want is for the barrel to be as easy to make as possible. I'm using a 3/8" bolt with a 1/8" hole drilled through it for the filament to pass through. This allows the nozzle to screwed on and be replaceable / interchangeable. Borrowing the from both Forrest's and Vik's nozzle design I came upon an interesting idea: use JBWeld as either the nozzle itself, or use it to attach a thin metal piece to at nut which would then form the nozzle. For the thin metal piece, I simply drilled a hole in an old penny.
As it turns out, this doesn't work at all. The barrel heats up, the JBWeld loses its 'gripping' strength and it falls apart. Note that the JBWeld on the barrel holds up very well: theres no stress on it. Its the JBWeld that holds the penny to the nut. On the plus side, the plastic melted quite well, so I'm confident in the barrel design.
Another problem I had was that I was using steel bolts and they were RIDICULOUSLY hard to drill out. I basically trashed two 1/8" drill bits trying to drill through them (and i was using lubricating oil too.) So, basically the whole method needs to be changed.
Seeing how steel was hard to work with, not a very good heat conductor, and quite heavy I had to come up with an alternative. I did some internet searching for a softer metal and found some VERY interesting facts. I found a metal that is very soft (easy to work with), very good at conducting heat (melts plastic well) and is decently cheap. It is also something that one could cast in their backyard if they were so inclined. Can you guess what it is yet? Aluminum is the answer!!
I did some further searching on www.mcmaster.com and found that they sell hex head aluminum bolts. They are a tad pricey (~$0.75 / bolt) but they will work well for me and only one is needed per extruder. This was nothing revolutionary, but rather a rethinking of the working material for the extruder barrel.
The tough nut to crack was the nozzle tip. Basically, I need something that can screw onto the extruder barrel, and also cover it. Nuts are a logical solution, but they are open on two sides... you basically have to weld/braze/solder a cover on it. After more searching, I found an AMAZING substitute that works so well it made me jump up and down. It is called an 'acorn nut' and it is basically a nut that is closed and rounded at one end! Infact, McMaster sells them in aluminum, and they are also similarly cheap (~$0.25 /ea) I ordered some and they should be here by the end of the week. I'll definitely be posting the results of this excellent find this weekend.
once i get my extruder controller setup, i should be able to control the temperature more precisely (right now i'm just hooking it up straight: 12v & 10ohms)
even still... it didnt seem like this was something that would work. the jbweld is trying to hold the two pieces together... with an acorn nut, the whole thing will be metal and the threads on the bolt will be keeping it on... really securely.
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