Wednesday, January 17, 2007
Making the 2 amp extruder barrel...
After I discovered that I couldn't braise brass without a Oxy/Mapp rig I went back to an old design notion that I had. That was to make the barrel, cap and a support flange of copper and thread it through the brass support plates. That worked just fine. It's not as elegant, but you can do it without a lot of drama.
The first thing I did was to use the tap set on the end of a thread die to dimple the copper cap for the extruder barrel. This was not something I did with the 1 amp test extruder barrel. I went ahead and drilled it for 0.5 mm as well. That went very smoothly.
It was also a total waste of time.
I set up the cap for braising just as I did with the test unit.
It braised beautifully. The copper/phosphorus braising material flowed into the extruder orifice, however. What's worse, the copper/phosphorus alloy is a lot harder than the straight copper so the plug was the devil's own job to drill out.
I pulled out my trusty #75 wire gauge drill bit and pecked at it for the better part of a half hour without making a lot of progress. I was getting tired and shaky what with the second day after surgery always being worse than the first, so I got the bright idea of using the broken #76 drill bit that had broken off with one turn of drill fluting left when I broke through the .5 mm cap on the test extruder. That turned out to have been a brilliant idea. The broken bit had hardened at the break and being shorter was a lot stiffer than a regular bit. It cut through the copper/phosphorus plug like it was butter in about 15 seconds.
The lesson is that if there is any fluting at all left on a wire gauge drill bit when it breaks don't throw it away. It can be very useful mostly because if you break it again you haven't lost anything.
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.
Now the extruder barrel and brass mounting flange are ready for trimming, painting with BBQ paint and wrapping with #32 nichrome wire. That's for another day, however.
One big word of 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 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. PAY ATTENTION TO THIS WARNING!
and my fire extinguisher has been sitting next to my rep(st)rap since the day I plugged in the circuit board!
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