[WIP] Bowden extruder

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dognotdog
Posts: 181
Joined: Tue Sep 04, 2012 9:22 pm

[WIP] Bowden extruder

Post by dognotdog »

So, I'm working on a bowden extruder arrangement to print with multiple filaments.

Here's the first, untested prototype of the feeder mechanism:
Image

I don't know if the rubber band tensioning is going to work, but there's only one way to find out. Hopefully I can finish the X axis carriage and make some first tests this weekend.

Kjetilei
Posts: 334
Joined: Fri Mar 16, 2012 8:26 pm
Location: Stavanger, Norway

Post by Kjetilei »

Thank you for sharing the design dognotdog :)

Please report back when you know if the rubber band tensioning works. I fear that the tension will get worse fast, but it sure is worth a try! If you use filament with pretty consistent diameter I think you would be better of with a bolt solution (you should not even need any spring/curly washers).

Have you looked into the micro extruders available on thingiverse? I bet :)

Have you been able to test if the bowden tube is kept in place securely? You could also try to look into the Pneufit connectors (e.g. http://reprapworld.com/?products_detail ... =1595_1616)

It would be great if you could provide a photo of the extruder mounted to the frame. Have you planned the location of the extruders (you where thinking about four if I'm not mistaken)?

An idea: If you rotate the feed direction around 30-degrees inwards (with the tension arm side being defined as outside and the bearing supporting the stepper shaft being on the inside) you might be able to include space on the inside for guiding several Bowden tubes. That way you should be able to stack the extruders tightly together on top of each other (although I'm uncertain if this would require a too steep bend and the stacking could cause overheating issues).
4_bowden_extruders.png
Keep on experimenting! :)

dognotdog
Posts: 181
Joined: Tue Sep 04, 2012 9:22 pm

Post by dognotdog »

Alright, so the first test run shows that the rubber band tensioning isn't very good. Though it does create a lot of force, due to the "long" reach of the rubber bands, it also results in the insert really digging into the filament if it jams, even for a short bit, thus leaving little chance for the filament to move on by itself.

The more prominent problem is oozing, though. I'm currently trying to tune the Marlin firmware's "advance_k" parameter, to see if that helps.

Kjetilei
Posts: 334
Joined: Fri Mar 16, 2012 8:26 pm
Location: Stavanger, Norway

Post by Kjetilei »

Sorry to hear about the problems, but they should be fixable :)

Usually I experience the insert piece digging into the filament on small jams when it has not been tensioned enough. Is that what you mean or have I misunderstood you?

Do you experiencing oozing when dual extruding (with one extruder remaining "passive" for a longer period) or oozing in general? Have you changed the retract length setting?

kennethagiusmosta
Posts: 27
Joined: Mon Jul 16, 2012 6:43 pm

Post by kennethagiusmosta »

Hey dognotdog,

We are miles apart and we're thinking the same! I like your Bowden extruder but I think the rubber bands are too weak.
Below please find two photos of my Mig feeder mechanism. Should be of inspiration...basically the concept is the same and reliability is a guarantee.
a7.jpg
a6.jpg
I have also found some cheap wire grommets and "basic" pipe which I hope will work on my design. Photos below;
a2.jpg
a1.jpg
I have also thought of a 26x40mm hotend which could house 4 nozzles. This should be bolted under felix's x axis easily. Obviously some modification are needed. Photos of the design below;
a3.jpg
a4.jpg
Sorry about my very bad technical drawing (really :) ).

In a few words its a sandwich of an aluminum plate which will serve as a heater, a heat insulator plate and a final cooling down aluminium plate. In between the grommet and the nozzle a ceramic tube or drilled wood dowel to further increase filament slip to the nozzle. Something like that! :D

My playing time is limited so you I posted my ideas hoping to be of some inspiration to your designs.
Be free to comment..

Thanks
Kenneth

kennethagiusmosta
Posts: 27
Joined: Mon Jul 16, 2012 6:43 pm

Post by kennethagiusmosta »

Correction:
Played with Sketchup trying real scales.. Alu plates must be 42x42 and not as stated ie 26x40
Will post more details....and a sketchup model/file of my 4-nozzle-concept-hot-end.

dognotdog
Posts: 181
Joined: Tue Sep 04, 2012 9:22 pm

Post by dognotdog »

Nice work so far!

Surprisingly, the rubber bands are strong enough, that's not the problem. I've printed a test piece, and while it looked like crap from the oozing, there was no significant slippage on the feeder. Problems only occured at feedrates of 300-500 mm/min while extruding manually for testing.

The bigger problem is the stiffness of the filament. I have about 50cm of tube and I can easily push 1cm back up the tube by hand, without the tube itself doing any flexing. It seems to be just the flexibility of the PLA & space inside the 2mm inner diameter.

I'm not sure at this point which kind of tensioning is better: high rate of stiffness change (setscrew) or low rate (rubber bands). The former seems to have the advantage of not digging into the filament in case of temporary stalls, while the latter should handle uneven filament better, in theory. All I can say at this point, is that I don't like the "new" official design, as it's a pain to take the stepper off, and everything twists around in unpleasant ways. I have something coming up soon that will require a dual extruder setup, and I think I might just build a non-bowden dual extruder setup for that, as the bowden seems to also introduce a lot of uncertainty which I don't have time to iron out.

Also, that MIG feeder mechanism has the advantage that welding wire is a lot stiffer than PLA. Though that mechanism is also known to be very sensitive to fine tuning, and slippage is not unheard of. Higher quality feeders often use two driven rollers, making a total of four.

Kjetilei
Posts: 334
Joined: Fri Mar 16, 2012 8:26 pm
Location: Stavanger, Norway

Post by Kjetilei »

dognotdog: sorry to hear that the Boden cable experiment didn't work out as hoped. I just can't fathom that the filament can be pushed 1 cm inside the tube :o Crazy! If you need a non-Bowden dual extruder setup and would like to try my WIP, just let me know. The current setup holds the hot ends very tight. I just haven't had the time to work on it/test it more for the last week :(

stratogavster
Posts: 120
Joined: Tue Jul 17, 2012 9:04 pm
Location: United Kingdom

Post by stratogavster »

Nice experiment......has there been any further progress? I'm quite fond of the benefits a Bowden extruder offers, but wondered if anybody has managed to retina the benefits of a direct extruder yet?

Also would be great to see sample print images :)

dognotdog
Posts: 181
Joined: Tue Sep 04, 2012 9:22 pm

Post by dognotdog »

No further progress. I've tried lurking in IRC to find out more about bowden designs, but have yet to come across a remedy to the stiffness problem.

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