Since my previous post on the stubborn clog on my Stratasys FDM 2000 support extruder, I made a rather shocking discovery. But first, what I managed to accomplish before said discovery…
The first step was removing the Torlon inlet buffer from the extruder tube. John‘s inlet buffers are a very nice tight fit to the tube itself – unfortunately, removing it pretty much requires destruction as a result (sorry, John!). I figured I could just break it off, but I’d be left with the ‘nipple’ of the inlet buffer still embedded in the tube. So I used a heat gun to warm up the tube to loosen the material that had leaked out between the tube and inlet buffer while trying to twist off the buffer itself.
Apparently I got things a little too hot, as my gloved hand left imprints in the sides of the Torlon buffer when I finally broke it off.
Unfortunately, I also left a good bit of Torlon stuck inside the inlet, just as I had feared. At this point, I stuck the extruder tube in a jar of MEK for a good long time and sloshed it around every so often to help soften up the material still inside the tube. I also occasionally would use a pick to dig out chunks of the Torlon.
My plan at this point was to model the extruder tube in CAD so that I could conceivably machine a replacement in case this one was entirely ruined by internal buildup, gouges, or some other problem. Alan C. was kind enough to share his FDM 2000 nozzle model and drawing, so I didn’t need to do any work on determining the nozzle threads. I’m guessing that the threads are actually 9/16″-24 rather than 14.22mm-24tpi, but Alan used a CMM in doing the reverse engineering and his custom made nozzles work perfectly, so who am I to argue with success? I also noticed that on my 2000’s support nozzle, the central 0.154″ protrusion on the back side of the nozzle actually sticks out by a few thou, whereas Craig noted his is dead flat with the outside ring surface. There may have been some loose tolerances at work during manufacturing, especially in light of what I found on the extruder tube.
When using some short lengths of wire (old solid core phone wire worked well) as a pseudo pipe cleaner to push/pull out softened polymer goop from the hole that runs through the center of the extruder tube, I noticed something rather odd – the wire would tend to ‘catch’ when I pushed it through from the nozzle end. It was almost as if there were a constriction in the extruder tube. After digging out the last bits of Torlon from the inlet side, it still looked like there was some buildup on that end of the extruder.
After trying to clean it up further with a pick, and looking at it through a lighted magnifying lens, it became quite clear to me that it wasn’t buildup at all, but aluminum – the extruder tube was poorly made in the first place! Here’s an image showing exactly how this extruder tube would appear if you sliced it in half:
The extruder tube appears to have been turned on a lathe before having the 90 degree bend done, with the central hole having been drilled through from each end (1/16″ drill from the nozzle end and 5/64″ from the inlet end as best as I can determine). Apparently one of the holes was drilled just a few hundredths of an inch too shallow, leaving a nice conic restriction just past the inlet. No wonder the blasted contraption had been jamming like crazy! Pushing a .05″-ish diameter wire though the fully functional model extruder showed that there was no such restriction. I can’t think of a single reason why you could conceivably want such a restriction in the first place, so I can only assume that this was extremely poor quality control on the part of Stratasys (apparently the horror stories of people returning malfunctioning heads for replacement only to get back used heads with just as many problems are not at all unfounded). I’m at once really disappointed in the manufacturer yet relieved that the problem and fix is so blindingly simple. My solid model probably won’t be needed after all as reference for creating a new hot end, but in case it would be useful for anyone else, here’s the .sldprt as well as an IGES model and a measurable eDrawings .eprt: FDM2000 heater tube (includes the manufacturing defect just in case I’ve been entirely wrong)
Now, where did I put my number-sized drill set….