Crazy Extruder Nozzle Idea

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Dear Pegasus Glass,

I have a question about the cost and minimum order size of custom glass pieces, and would be very grateful for your assistance. I've attached a drawing of the necessary part. I don't have any previous expertise in glass drawing, so I'm not sure whether this part is easy or difficult to make. Unlabeled dimensions are not critical, but the overall length of the tube should be somewhere between 40 and 60 mm, and the narrow needle end should be as short as possible (less than 4 mm if possible). The length of the transition zone is not important, but a reasonable length is 10 mm. I have not been able to find any off-the-shelf parts that are similar.

For a part like this, what would you estimate the minimum order size to be, and the per-unit cost?

For some background: I'm currently building a "RepRap" (Replicating Rapid Prototyper, www.reprap.org ), which is an open-source affordable 3D printer meant to be built by hobbyists. One of the major points of failure for the RepRap is the extruder nozzle. This is a chamber that heats up 3mm plastic rod to its melting point and extrudes it through a narrow hole, creating a fine molten plastic filament to print objects. The RepRap has a very large online community.

Many designs have been proposed for the extruder nozzle, but none have had truly satisfactory performance. A typical nozzle is made from an M6 brass screw drilled through at 3mm, with a dome nut screwed to the end, and an 0.5mm hole drilled in the nut. Heating wire is wrapped around the outside of the screw. One problem with this design is that the high heat conductivity of brass causes the entire extruder to become heated, meaning plastic melts in undesirable locations. Also, it is difficult to drill a fine hole precisely, and there can be leakage problems from plastic extruding through the screw threads. When a jam occurs, it is difficult to tell why, because the tube is opaque.

I believe that a borosilicate glass tube would be far superior. The greatest benefit would be the ability to see the conditions inside the extruder nozzle, to verify that the plastic is melting properly, and check for jams. The thermal conductivity of glass is much lower than brass, meaning that the melting zone could be confined to one end of the tube. The end could be drawn into a fine needle without drilling, creating a smooth change in internal diameter.

If the minimum order quantity is small, I would certainly order some parts like this and encourage others to do so as well. If the minimum order is large, I would recommend a part like this to one of the RepRap parts vendors (such as www.makerbot.com or www.reprapstores.com) for resale.

Thank you for your help,

Jacob Bayless
Engineering Major, University of British Columbia