by makeme

The Search for a COTS Nozzle

In Uncategorized on 10, Feb, 2011 at 16:16

For anyone interested in improving existing 3d printer designs, or creating new ones, the extrusion nozzle is a real issue. The biggest problem is that the nozzle can’t be made out of the same material the bot prints in; it will either liquify at extrusion temperatures or bond with the material being extruded. Additonally, the nozzle has to meet very particular standards of size, shape and strength.

It’s entirely possible to machine a custom nozzle that does the job quite well. That’s what everyone has been using so far. But the level of machining required is prohibitive. Just try drilling a 0.5mm hole if you don’t believe me.

What we need to find is a Commercial Off The Shelf (COTS) nozzle that is already being mass-produced for some other purpose. It doesn’t necessarily need to be a drop-in product, a little light machining (like tapping threads) would be fine, but it does need to be:

  • Resistant to heat. ABS is extruded at around 220*C, and some people run a little bit higher.
  • Rigid. It needs to resist quite a lot of pressure from the extruding plastic.

Also, it would be nice if it was:

  • Cheap. Duh.
  • Interchangeable. Some preexisting threading or method of attachment.
  • Doesn’t stick to molten plastic. Infrequent, if any, need for cleaning.
  • Variety. A range of nozzle inner diameters would be great.

I don’t think anyone’s found anything like this yet, at least not with an inner diameter under 1mm, but here are some ideas that might work.

  • Graphite Ferrule. These things are used in gas chromatography. They’re described as “soft” but they are manufactured with a range of diameters in appropriate sizes and are made out of pure graphite, so they don’t melt until 450*C.
  • Capillary Tubes. These things are used in liquid chromatography and other advanced stuff. They can be made out of all kinds of different materials.
  • Ceramic Tubes. More of a range of things. What’s important is that they tend to be manufactured in sizes down to and below 0.5mm inner diameter.
  • Needles. Again, a range of things. But a few examples for different purposes like veterinary medicine, dispensing materials, and inflating balls.
  • Flow Control Orifice. These are used to control the flow of liquids or gases through pipes. They’re all made out of brass or steel, they’re tiny, and they’ve already got pipe threads.

If we can’t find anything that works as-is, then we have to move on to additional steps that take a COTS nozzle from almost right, to totally right. Some examples might be:

  • Solder. High-temperature solder (usually lead free, possibly with silver in it) could be used to close up an overly large inner diameter, and then an appropriate hole could be drilled through the solder.
  • Cement. Some sort of fireable clay, mortar or concrete type stuff could, once set, resist the temperatures (and maybe the pressures) involved. Maybe it could even be formed around a wire of the appropriate diameter, so when it sets the hole remains and no drilling is necessary.
  • Multi-part. Perhaps machining appropriate grooves (.25mm-1.5mm) in two matching surfaces, and holding them together, would work.
  • Tapping. Threads are great for attaching one thing to another, particularly if you might want to detach it in the future.
  1. I was talking about this to a guy at work a while back, and he suggested I look into motorcycle jetting. That is a tiny screw-in piece with a tiny hole in it that is designed to let fuel or air into a carburetor. They seem to be sold using all kinds of different numbering systems, but at least a few are sold by the size of the hole in thousandths of millimeters. Also look into carb jet reamers. They seem to be designed to make tiny holes. The first one I found was for .49-2mm

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