Wednesday, December 24, 2008


Extruder Madness Part Deux!

I've been kicking around an alternate extruder idea for a while now and have finally gotten around to putting it down on "paper." Ah, the joys of late night caffeine to clear up a headache!

The goal was an extruder with no specialty parts. Everything can be obtained from your local hardware store which is exactly what I did. The only tools I used was a cordless drill, a vice, a bench grinder, a small bastard file, and a 10-32 tap. Keep in mind that this does not include the heater barrel which is a separate problem that I'm addressing.

So, here's the extruder. Yes, it extrudes quite well. Put a couple feet of 3mm ABS through it with no problem. Hadn't even bothered sharpening the threads yet but that would certainly help also.

This is basically a take off of the lasercut extruder design, the 608 bearings and such, but without any need for the specialty parts. The design isn't as heavy as it looks though it does have a bit more weight than the Mk II. For my machine it wouldn't be a problem though ymmv.

Here's how I put it together. Very little text from now on.

Cut head of of 5/16-16 x 5" screw.

Assembled the 608 bearings (Drive Bearings 1 and 2) on the drive screw.

Took a 1/2" aluminum cable crimp, drilled and tapped it 10/32 for two set screws and drilled one end to fit the extruder drive screw and the other to fit the GM3 gearmotor shaft.

Next I took three small L-brackets (maybe one inch on a side) and bent them as follows. I then drilled out their holes to fit an M6 shoulder bolt. This along with a shoulder bolt and some washers makes up the Pressure Bearing assembly.

I then assembled the frame to which everything mounts from two 3" L-brackets.

Then came the attachment clamps for the drive screw Drive Bearings 1 and 2. Drive Bearing 1 is held by plumber's tape and a piece of steal and Drive Bearing 2 is held by a pipe clamp. I would only make the plumber's tape ones in the future. It held better.

And that's it, your done!

Keep in mind this is not a finished extruder design but simply a starting point for better designs and more detailed builds. I test this by clamping it to the desk and hooking up the GM3 gear motor. Worked like a champ. Total cost for all parts was something like $20 US. Total time to build once all the holes were drilled and the pieces were bent was about one hour.

Adjustments concerning the height of the 608 bearing form the drive screw--the one that presses the filament into the threads which I call the Pressure Bearing--can be made by "shimming" the 608 bearing held by the pipe clamp--Drive Bearing 2. I did this by inserting small pieces of scrap tin between the frame and Drive Bearing 2 so that it pushed the drive screw incrementally closer to the Pressure Bearing. This works very well and is very quick.

Please, if you have a good idea for improvements, fixes, etc., then please let me know.


I notice that the "exotic" tool - the 10/32 tap - is only used on the motor coupling. The McWire design uses short pieces of rubber fuel line. I tried that on my extruder and found that it slipped under high torque. But that was easily fixed by a couple of pieces of tie wire, essentially clamping it in place.

This modification would eliminate the tap, and make this something that anybody who has a drill could build.
Nice concept! Now run it in reverse and attach the filament to a bucket. Weigh the bucket and keep adding weight to the bucket till the GM3 stalls. That will give you an idea of how much force it can generate. Divide that by the cross-sectional area of the filament (~7 mm^2) and you will get an idea of what sort of extruder barrel pressure you can achieve.
@John Gilmore

True. I just happened to have a 10-32 tap on hand and figured everyone could get one at the hardware store but if they don't need too, then why? Is a good point. However, I have used the tube couplings on my McWire and there is a sever backlash issue. Now, on the extruder we don't need precise control, but we do need to be able to back that thing up so as to reduce pressure and ooze at the end of a line segment. With the shaft encoded gearmotor setup now becoming prevalent, this isn't going to be a problem. However, I have a Gen 1 electronics setup so I have no option for a shaft encoder.

Good point for those who don't have a tap though. Less tooling is better.


Wow, is all that really necessary? I'm just kinda eye-balling it. I suppose I can run that experiment though. I'm really interested, however, in an extruder that doesn't require a crap-ton of pressure to get extrusion to happen. As it is, this module puts out enough pressure to equal what my MK II puts out so I, at least, can extrude with it.

Right now I have it torn down--due to documenting the build--and will need to rebuild it before I can test it out. I also want to make a few improvements, tighten things up, and sharpen the threads. After I get that done, I'll do the testing you suggested, Forest. Can't hurt to know.

heh. looks familiar. I like the skate bearing idea-- It works well:
Hey demented! Could I prevail on you to edit some of the white space out of your posting? Thanks. :-)
By the way Demented, since no one mentioned it yet, this is brilliant:)

Sure. When I was writing it, the pictures would all line up in a row and the text would sit beside them so I put a bunch of returns in there to get it below them...No need for it I guess. I'll get rid of it.



Hey demented....made any more refinements on this? I've just about got a working xyz bot working but no extruder. (seem to have a ground loop fault I can't find.) I'd like to get started on the extruder and yours would keep me from having to buy/make/scrounge one from someplace. Couple of years ago I made one from wood. Managed to extrude about a foot of filament by hand. It's still in the closet somewhere and will be cannibalized for whatever I do.
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