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Yet Another Worm Extruder

Posted by damonb 
Yet Another Worm Extruder
May 09, 2010 10:49PM
After about a years delay from my previous attempt, I finally got around to making another extruder. This time based on a worm drive. The worm drive and gear are from sd-spi.com and give an 18:1 gear ratio. This gives 3600 steps per turn.
My stepper is rated at 53in-oz holding torque. So the with 18:1 I get roughly 950 in-oz holding torque. Not sure what dynamic torque would be, but it is way more than what I had before.
I did get some extrusion from the barrel, but now I am running into problems with
slipping in the drive wheel. The drive wheel is currently aluminum and the thread teeth are deforming some. I think I will switch over to steel, which should give a little better bite without deforming. I will provide updates as I get things figured out.
open | download - 2010-05-09 21.35.40.jpg (456.2 KB)
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open | download - 2010-05-09 21.36.00.jpg (441.1 KB)
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Re: Yet Another Worm Extruder
May 10, 2010 12:47AM
It looks like you have a great mechanical setup, how ever in the words of nophead the heat zone has to be small.

My guess is under 15mm where it looks like your heat zone is spread across a good 30+.
Re: Yet Another Worm Extruder
May 10, 2010 09:04AM
Shortening up the heat zone is something I can try. I also noticed, in my rush to see the whole thing working for the first time, that I forgot to put any insulation around the windings.
Re: Yet Another Worm Extruder
June 06, 2010 10:52PM
I finally have gotten a successful extrusion on my extruder. The one mentioned in the earlier posts did have problems with plugging up as was suggested might happen by freds.

My first variation was to switch to a lower section of brass and an upper section of .148 diameter .01 wall stainless steel tubing. Still had the plugging problem.

I knew from my previous attempts that that all brass led to a lot of heat being conducted up and making the base of the drive almost too hot to touch. It also drew about 10-15 Watts to power.

After taking a little bit of time to do some thermal resistance calculations using all stainless steel and about 3/4 of an inch long, I decided to build a stubby extruder barrel. Nozzle diameter was drilled to .012 inches or about .3mm. The tip is still about 1/8 inch of 1/8 inch brass, silver soldered to the end of the stainless steel barrel.

This works fantastically. Also my power required to get extrusion came in at about 5 volts and .7 amps according to my power supply. I could not get exact temperatures because my thermocouple started messing up. I blackened some of my ABS.

I ran the new design for about 10 minutes and found very little heating of the extruder drive mount. Unfortunately I had some problems when I drilled my hole and it did not come out circular. So the plastic initally wanted to curl all over the place until there was enough weight to pull it straight down. I did not get exact values of the extrusion rate, but it was somewhere between 10 and 20 mm per section. I am thinking I can get more, but with the thermocouple not reading correctly, I decided not to push it with the temperature and power.

Pics of the new extruder barrel attached.

I will build another barrel that will not have a messed up extrusion hole and has a new thermocouple so I can do more detailed tests.
open | download - 2010-06-06 21.25.09.jpg (372.4 KB)
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open | download - 2010-06-06 21.24.42.jpg (344.9 KB)
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