Thursday, January 18, 2007


2 amp extruder barrel complete

I finished wrapping the 2 amp heated extruder barrel and setting the windings with several more coats of BBQ paint.

I wondered why I was able to do the winding so well and finally remembered that when I was about 4 years old my father, an avid fisherman, taught me how to set guide loops on new fishing rods with thread and then set the thread windings with fingernail polish.

I've loaded most of the heating capacity up by the orifice and only a little further back. I also made the extruder barrel a bit longer. The theory is that the rear end of the extruder barrel will stay cooler and not cause the filament to melt at the entry to the barrel, something I'd seen happening when I tried to extrude polycapralactone at too high a temperature.

This evening or this weekend I plan to trim the threaded rod for the polymer pump and then assemble the Mk 2.1 for testing.

looking great! i cant wait until you get it up and running.
Me either. :-p
just wondering... can you get bbq paint at a regular old hardware shop like home depot or is it more complicated?

also... new tools arrived today! reciprocating saw, vice grips, and a nice digital caliper ($15)

i <3 harbor freight!
I honestly can't remember whether I got mine from the Ace hardware outlet about 6 blocks off or the bigger Orchard Supply hardware store over in Sand City a few miles away. I've seen it in both. I expect Home Depot ought to have it.

What I bought is black Krylon BBQ & Stove Paint in a spray can. It's rated up to 1200 degrees F.

There doesn't seem to be anything complicated about getting it, unlike a lot of the stuff we have to track down.
I do remember. I got it at Orchard Supply at Sand City.
BTW, black paint accelerates heat radiation. If the paint is silver, it will help reflect the heat back into the mass of the extruder barrel.

This minor detail may not matter much. One could always wrap an extruder that is too cold in a layer of aluminium foil after painting.
You have to be careful not to generalise about colour and heat radiation. A surface that is "black" or "silver" in the visible range can easily be something very different in the 1-20 micron IR range.
Thats interesting, I was wondering if the paint you used might have a certain property relating to heat reflection. BBQ paint would work best if it looked black but could still reflect the heat back in, so that would make sense....

I suppose it could be tested with an IR diode and sensor pair, if it's very reflective compared to some other surfaces... :)
I have an IR thermometer which is a bit of a more sensitive version of what you suggest. The only problem with that approach is that the field of view of the sensor is a bit wider than the extruder barrel at any reasonable distance, so you wind up taking some average of the temperature of the barrel and part of the background, too. :-(
Humm... could a mirror set right behind/beside the extruder be used to trick it? If it saw the extruder and it's reflection it would have a slightly better average reading no?

Silliness... ;)
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