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SnakeBite extruder for 3mm 3D printing filament

by the_digital_dentist, published

SnakeBite extruder for 3mm 3D printing filament by the_digital_dentist Mar 1, 2014

Description

This is an experimental, high mechanical force 3mm filament driver to push the filament into the hot-end of a 3D printer. It uses counter-rotating 6-32 nuts to drive the filament.
Video of operation here:
vimeo.com/87940579
Update: IT WORKS! It will need some tweaking...
vimeo.com/89471876
vimeo.com/89471877
Here it is on a large print: vimeo.com/89872411

Recent Comments

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I just tested it with 30 tooth drive gear on the motor and 20 tooth gears on the nuts. This allows the assembly to be reduced in size and theoretically increases maximum print speed. It also increases the load on the motor, and recent test results indicate it increases the load too much. The NEMA-17 motor I am using doesn't seem to have adequate torque to push even one of the 20 tooth gears with the filament in the nut. I'm going to go back to the 30/30 gear device and see if I can get the retraction to work better. More testing this week...
That is soo cool, any developement on the project?
There is a lot of work still to be done. In the video I have the nuts located in-board, so there is a pretty long distance from the entrance to the hot-end. Having the nuts in-board allows for very easy loading of the filament as you can see in the video. I have another version where both nuts are outboard, but had some trouble with those nuts not gripping right, so the one that worked is the one I am testing. Those nuts were made on lathe then tapped by hand. They fit over the ends of the tubes and lined up perfectly.

It remains to be seen how this design handles variations in filament diameter/cross section shape. I am looking into threading a collet from a dremel tool to serve as a nut with adjustable tension.

I think printed gears may not be strong enough for this application, but who knows? Metal gears would allow the size to be shrunk even further, but they tend to be very expensive. The gears I used are actually for 3/16" shaft but its so close to 5mm it works fine and they hang onto the motor and brass tubes tightly.

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Instructions

Printed on MegaMax with 0.35mm nozzle, coex3D green ABS filament, first layer 0.35mm, remaining layers 0.2mm, no support material, 30% infill, 2 top and bottom layers, 2 perimeters.
Use NEMA-17 motor, 6-32 screws to hold cover on base, 8-32 screws to mount on printer carriage, M3 screws to motor.
One nut is left hand threaded, made by tapping mild steel with left hand tap, the other is standard 6-32 nut. Both are soldered to 5mm ODx 0.45mm wall brass tubing. 625Z bearings (5x16x5mm) are pushed onto tubing. Gears come from American Science and Surplus or ebay, also pushed onto tubing.
That is soo cool, any developement on the project?
I just tested it with 30 tooth drive gear on the motor and 20 tooth gears on the nuts. This allows the assembly to be reduced in size and theoretically increases maximum print speed. It also increases the load on the motor, and recent test results indicate it increases the load too much. The NEMA-17 motor I am using doesn't seem to have adequate torque to push even one of the 20 tooth gears with the filament in the nut. I'm going to go back to the 30/30 gear device and see if I can get the retraction to work better. More testing this week...
There is a lot of work still to be done. In the video I have the nuts located in-board, so there is a pretty long distance from the entrance to the hot-end. Having the nuts in-board allows for very easy loading of the filament as you can see in the video. I have another version where both nuts are outboard, but had some trouble with those nuts not gripping right, so the one that worked is the one I am testing. Those nuts were made on lathe then tapped by hand. They fit over the ends of the tubes and lined up perfectly.

It remains to be seen how this design handles variations in filament diameter/cross section shape. I am looking into threading a collet from a dremel tool to serve as a nut with adjustable tension.

I think printed gears may not be strong enough for this application, but who knows? Metal gears would allow the size to be shrunk even further, but they tend to be very expensive. The gears I used are actually for 3/16" shaft but its so close to 5mm it works fine and they hang onto the motor and brass tubes tightly.
I really like this. Since the feed rate isn't dependent on the diameter of a hobbing (and the varying engagement of the
hobbing into the plastic), there's one less variable to account for when calibrating the printer.

Also, since there is no longer a need for a gap between the filament feed exit and the hot end, the slight chance of misfeeding/filament buckling can be eliminated. Well done!

A couple of thoughts (not critique, just curious/brain dumping):
Does the threading create any burr or swarf in the plastic?
I'm thinking the plastic should be soft enough to form rather than cut the threads. That would be ideal anyway, since any plastic debris buildup may cause problems, and would (probably) make calibration less accurate.

The gears look like they could be modelled with involute_gears.scad (from MCAD). It might make it easier to fit/center the nuts if you can customize the centers of the gears. Not sure how printed gears would work for bevel gears, but I think it's worth a try.

A couple of cross braces should take care of the wobble, but i suspect it might not even be a problem once the nuts are centered well.

I'll definitely try this approach once I get my current projects out of the way.

/Andreas
That's a great idea!!!
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