Sunday, March 09, 2008


Blow your nose and clean your teeth

Ed and I have been experimenting with various strategies to improve build quality. One problem is bits of polymer sticking to the head and then dropping onto the build and messing it up. Another is the fact that if you run the acorn-nut nozzle (left above) too close to the surface it smears the molten polymer all over itself, and then re-deposits some of that later where you don't want it.

I made up the nozzle on the right. It is 1.5 mm diameter at the end, with an 0.5 mm diameter through hole. With this in place of the acorn nut, you can run the nozzle over the surface to sweep it flat without pushing the polymer where you don't want it.

It is a bit more complicated to make than the acorn-nut nozzle (which just needs you to drill one small hole in an off-the-shelf part, of course). But it works significantly better.

To clean the new nozzle, we've added a toothbrush along with a nose-wipe cycle to the host software. This keeps the crud off the nozzle by wiping it back and forth at the start of each layer.

Now. How do we clean the toothbrush?...

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Since I rebuilt my extruder with an acorn nut shaped to a point with a conical outlet hole I get much worse performance than my old one piece nozzle. I was thinking of doing pretty much what you have done.

I think the end of the nozzle should be about three times the filament width.

The hole should not be too shallow either. Making it shallower reduces the extrusion pressure and the die swell but also makes the extruder more incontinent. With a conical hole such that the edge is only about 0.1mm thick the extruder overrun is about 40mm!

Presumably your hole is as long as the nose, or is it opened out behind? Have you noticed a change in the overrun?
Regarding cleaning the brush, I find any bits that get stuck get knocked off on subsequent wipes so you probably just need a little pot underneath to catch the dross.
Wacky idea: What about the tip from a mechanical pencil? They're roughly the same shape and usually have a 0.5mm diameter. Might be a bit too delicate, though.
To clean the toothbrush, just forget about it. All you have to do is print a new one and recycle the old. viola!

Presumably you'd want a clean brush at the start of each printing job, right?

Also, making a toothbrush takes some work with staples and a polishing wheel, in addition to the plastic molding. It might be worthwhile to learn how to reuse one.

I see and support your point completely. I was just trying to stay in the whole mindset of the project. It is definitely a much better thing to figure out how to clean a brush instead of just throwing the old one away
Might help to spray an incompatible oil (maybe silicon or teflon?) onto the toothbrush. Something to keep the polymer from sticking then when it cools successive passes would flake it off.
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