Sunday, February 19, 2006


Saturday afternoon filament extruder experiments

I ran more experiments today using my 1/4th inch (6.35 mm) ID screw pump. I began with the metal drill bit that I hadn’t used in yesterday’s experiments.

Metal drill bit

Maple syrup

As you recall, water did not pump well at all in the rig. Adrian suggested that syrup should pump better than water. He was correct. Maple syrup did pump rather well in this configuration.

Semolina grains

I tested the configuration with uncooked semolina grains. The metal drill bit pumped that media wonderfully. I tried putting my fingertip over the end of the barrel. The semolina collected behind my finger and the drill bit was thrust back out of the rear of the barrel with considerable force. A very solid plug of semolina grains were packed in the barrel. I had to literally drill that plug out.

CAPA 6800 pellets.

I fed polymer pellets into the “t” junction. The metal drill bit tended to chop these up and pump them to the end of the barrel. Most, however, of the pellets were thrown back out of the hopper. The pellets that emerged from the barrel were mangled rather than chopped into proper bits.

Visual inspection indicated that the pellets were considerably larger than the helical passage in the metal drill bit. The pellets had to be deformed or chopped until they could be fitted into that passage.

Wood auger bit

I repeated the experiments with semolina grains and polymer pellets. The wood auger afforded a considerably larger passage than the metal drill bit did. Both semolina grains and polymer pellets were pumped effectively. The polymer pellets were not mangled as they had been with the metal drill bit.


Considerable torque forces are being developed when tough polymer pellets are being cut and mangled. Hanging on to the barrel with a spanner is not practical. A frame holding both the barrel and the drill is needed.

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