Sunday, January 04, 2009
First Extrusion with New Extruder Design.
I've just extruded my first filament, using a new extruder design (short heated zone, composed of stainless steel, aluminum, and brass.) I've only built the heated parts of the extruder -- and fed the welding rod by hand. Nevertheless, I was able to extrude both ABS and HDPE. Details (and photos) are available in my latest blog entry. More photos are available in my picassa public gallery. But here is one photo of my first extrusion from the new heater-barrel assembly:
A problem with the other metal heaters to date is that once the heater is turned off, the melted plastic forms a solid plug which doesn't melt even when the heater is turned on again. Has that been a problem with this design?
Also, fiberglass insulation is very irritating. Is the ceramic insulation you're using also irritating?
I just ran a quick (before work!) test, and my extruder started up and extruded again this morning. I also tried a couple-minute pause (per Nophead's comment on my blog) and extrusion resumed OK. Not sure how long a pause is typical. I'll need to do more careful measurements, but I *think* my solid/fluid transition zone is ~10 mm, about the length of my reduced cross section in the stainless steel stem.
You're either a mind reader -- or great minds think alike....
I have the (big, TO-3) heatsink already tapped (3/8"-16 UNC) for the stainless stem. Unfortunately, I didn't account for one of my insulated standoffs for the nichrome. That's currently in the way; I *think* I can modify things so it will all fit together. Fingers crossed.
With a heat sink, I may be able to make the transition zone even narrower, though at the cost of some electrical power for the heating coil.
Looks like you are onto something there!
To me it looks like you have the following:
1. Thermal mass with the Aluminum heater barrel.
2. Narrow melt zone; that is enforced by the stainless guide to wick away heat and keep the main fiber from melting until it is advanced.
3.Changeable brass nozzle to have different sizes of nozzles and vary the depth of the melt zone.
A suggestion that I have would be to add a sleeve machined out of PEEK to go around the stainless steel guide to reduce the heat transfer to mostly just the face of the guide.
I guess the next question is was is the maximum extrusion rate it can keep up with?
First posted on 19 January 2007.
It should theoreticaly be possible to anodise your aluminium section. (at home even)
This would act as a temperature conductive, high temperature, electrical insulator to allow you to do away with any PTFE insulation and keep the filament in close contact with the heated section.
Just skim off with your wonder paste.
I'm a pragmatist -- I'll use what works best. If that's something different than my (messy) mixture, so be it.
I just picked up a DC supply that should be suitable for anodizing small parts. (I've had good luck using craigslist and freecycle.) Hard anodizing seems to need low temperatures -- I have literally *piles* of suitable coolant to either side of my driveway. I need to hunt up a source of Aluminum wire; then I could try anodizing.
I'm also interested in the flexible mica; another reprapper just send me a sample to try.
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