Tommelise AEM Extruder 1.0
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Making the extruder barrel
The first thing I did was to use the conical end of a tap set to dimple the copper cap for the extruder barrel.
After making the dimple in the copper strip you bend it as shown so that the extruder cap seats snugly onto the end of the 5/32 inch hard copper tube.
After I put the dimple in the 0.025 inch copper strip I carefully bent it and secured it to the 5/32 inch hard copper tube with a large alligator clip as shown.
I then made a small loop of copper/phosphorus braising rod and put it around the 5/32 inch tube where it met flush with the dimpled 0.025 inch copper plate. While I am sure that there are several makers of this sort of braising rod I was able to get a plastic package of three rods by Bernz-O-Matic at my local hardware store. A package of three rods costs under $3. After it was rigged on the vise I applied a hot flame from my propane torch shown here making another extruder barrel.
First note that the flame goes under this table. Also note that the light blue cone of the combustion zone of the flame is kept away from the joint being braised. You need a fairly substantial flame for this operation because you want the melt to happen fairly quickly.
It is very easy to see when the joint is properly braised. The braising rod melt forms a fillet all the way around the joint and the colour of the copper changes rather dramatically. The copper/phosphorus braising material is a silvery colour, something that becomes obvious when you clean and trim the extruder cap afterwards with your Dremel abrasive wheel. A #76 wire guage drill bit is hair thin and wants careful setting in the drill chuck of your Dremel hand tool. It's good to do this operation over a piece of paper because if it slips out of your fingers and falls on your floor, especially on your carpet you will have seen the last of several dollars' worth of drill bit.
I've cut off the excess copper flange material with a few strokes of a hacksaw leaving a rectangular extruder head with a protruding dimple that you saw made in the first operation shown in this tutorial. Here is my extruder barrel after drilled the extrusion orifice and cleaned it up a bit more. The orifice that I drilled is clearly visible. I put a drop of coolant on the end of the extruder before I drilled. I had drilled a test hole before through that thickness of copper without incident.
With fine wire gauge drill bits you want to use a method of driling called "pecking". This entails lightly tapping the drill bit on the extruder head and almost immediately pulling it back out of the hole so that the microscopic metal chips can clear from the bit's fluting and the bit can have a moment to cool off. It is very easy to snap one of these drill bits, especially when you finally drill through the 0.005 inch copper cap. It takes a deft touch and a lot of patience to do this sort of work by hand. Plan on snapping a few drill bits learning the technique.
After that it was a quick matter to slide the brass mounting plate over the extruder rod followed by the 0.5 mm copper support flange and braise that as well.
With that done it was a quick matter to braise the back copper support flange to a short length of 3 mm ID copper tube to act as a guide out of the polymer pump and into the PTFE thermal break. WARNING! If you use your vise and let the flange rest on the iron vise the flange will not heat properly and the braising rod won't melt or adhere properly to form a solid joint. Always leave some distance between what you are braising and a good heat sink like a cold vise.
It's not elegant but it works.
After this was done I cleaned and trimmed the extruder barrel assembly with my Dremel hand tool set with an abrasive wheel.
Painting the extruder barrel with flame resistant BBQ paint is a simple matter of finding a venue. I put the extruder barrel assembly in a cardboard carton bottom left over from Christmas and set it in an ornamental cypress outside and sprayed it.
I applied about 4 coats allowing an hour between sprayings for the paint to dry and harden. Afterwards I cut two, 14 inch lengths of #32 glass and silicone insulated nichrome 80 wire. Each length is rated at 12 ohms and will deliver 1 amp heating at 12 volts. I wrapped them in parallel around the extruder barrel and applied 4 more coats of BBQ paint to set the wire firmly on the barrel.
I kept most of the heating element at the end of the extruder barrel so that polymer filament going through the barrel would see most of its heating just before it got to the extrusion orifice.
Warning!
You see me braising things on a vise clamped to my worktable. Let me warn you that you NEVER, EVER point the butane torch at the worktable. I always point it parallel to the table or under it where neither the flame nor the wash of superheated air hits the table. I also keep a fire extinguisher within easy reach in case I make a mistake.
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