Plywood Tip Assembly for Huxley

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Who and why may need this?

This extruder tip assembly was designed (by AlexRa) for use on a Huxley reprap (purchased from TechZone). Since the Huxley feeds filament through a Bowden cable (which does have its disadvantages!), there is no provisions for mounting the extruder drive on top of the extruder tip assembly.

My design goals were:

  • Ensure that the whole thing can be made at home with minimum tools (CNC mill, lathe or laser cutter would make things much easier, but are not required);
  • Avoid using hard-to-get materials (such as PEEK plastic);
  • Make the extruder tip assembly very robust and sturdy.
At the time of writing this, this extruder tip assembly has been made, installed and successfully tested. It appears to work well, but has not seen much use yet, so its long-term performance is not known.

Required materials

When possible, I tried to use materials easily available from a hardware store:

  • Some 6mm plywood
  • A 30mm wide strip of 2mm-thick aluminium
  • A bronze or brass M6 bolt (could be bought on eBay)
  • Some PTFE tape (the thicker the better, the one I got is 0.2 mm and it works ok)
  • Some 5min epoxy

Some pieces were taken from the stuff that came with the printer (TechZone's Huxley):

  • a piece (about 70mm) of the PTFE tube (the "Bowden cable")
  • a piece (about 5 mm) of the PTFE cylinder used as the tip holder in the original design
  • 25cm of insulated nichrome wire for the heater. The wire that comes with the TechZone kit is just enough for making one heater, so you may need to buy more, or you may prefer to use one of the existing solutions based on a resistor.

Required tools

  • Some carbide PCB drillbits for the nozzles (at least 0.5mm)
  • A Dremel with a drillstand
  • A regular power drill, a drill press would be nice but is not required.
  • Drill bits: 2mm, 3mm, 6mm and 16mm
  • Hand taps (M6 at least)
  • A jigsaw.

Making the extruder tip

The hot tip in this design is just a drilled-out brass bolt. The tip provided with the TechZone's kit would be adequate, except that its outer threading is M7, and finding any matching M7 parts proved to be difficult. Anyway, being able to make your own tips (with whatever desirable nozzle diameter) is a good thing. With proper tools (such as a metal-working lathe or a CNC mill) making the tip is trivial:

  • cut a piece of about 25mm from a brass bolt or a threaded rod (search for "M6 brass threaded rod" or "M6 brass bolt" on Google or eBay ),
  • drill a 3mm diameter hole through most of the length, leaving 3-4 mm for the nozzle,
  • machine the tip into a cone and finally drill a 0.5mm nozzle.

What follows is the beginner-level instructions how to do the same without proper tools, using a Dremel with a drill stand and a regular power drill. Get yourself a good set of carbide PCB drill bits for the job. A lot of those are available on eBay ("carbide PCB drill bits"). You will need at least a 0.5mm bit (with some spares, because they do break easily!). I also used a stronger 1.0-1.5mm bit to start the 3mm hole, but that's optional.

You may encounter several difficulties drilling deep holes in the brass bolt:

  • As the hole gets deeper, the bit tends to overheat, get stuck and break. Solution: drill in the oil! Screw a plastic cap (e.g. from a water bottle) onto the bolt and fill it with WD40. While drilling, lift the bit often so the oil can re-fill the hole. The free bonus is that you get to watch the brass filings convecting with the heated oil!
  • It is difficult to start the 3mm hole at the exact center of the bolt. Solution: start with a smaller diameter! Use a magnifying glass if necessary (on eBay: "Third hand tool w/magnifying glass"). Make the first pass with a 1.0-1.5mm carbide bit, then drill out using a regular 3mm bit. Note that a high-speed rotary tool (such as a Dremel) works well with fine carbide bits, but is no good with larger diameters where you need more torque and less rpm. Do the drill-out with a normal power drill.
  • It is difficult to keep the hole parallel to the bolt's axis. Solution: use a drill stand with your Dremel and make a rig as shown on the photo.

After a few hours spent on this and a few broken drill bits you are likely to have a quite usable extruder tip. After that, it would take you about half an hour to make another one.

Making the tip holder

Assembling the thing