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foehnsturm

Flexible shaft - the best of both worlds?

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I had to try it out as the bowden tube for sure has some drawbacks: very limited choice of certain (flexible) filaments, high retraction distances, a considerable time lag during retractions, less than perfect extrusion control due to the springy character of the filament within the bowden tube ... But I wanted to retain the lightweight print head.

As far as I know the idea is anything but new to the reprap community. However the (rather expensive) Flex3Drive comes as a plug and play unit for certain printers. The key for a highly precise and reliable operation might be the high 1:40 gear ratio it uses so the shaft has to handle only very limited torque.

I made a plug and play component for my modular print head. What's nice about it is that the 1:40 gear ratio together with the 12 mm knurled wheel give approx. a fourfold increase in steps per e compared to the UM original. So I just changed from 1/16 microstepping to 1/4 and steps per e already were 98.5% on target.

The worm gear can be adjusted for zero backlash. Torsional deflection of the shaft looks to be less than a 1/8 turn which corresponds to approx. 0.1 mm filament feed.

This is the very first print:

 

 

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Very impressive. :cool:

I also thought once about implementing a flexible shaft for the very same reasons. However, it was just a general idea, never mentioned somewhere and I never built it as it is quite some work to relocate part of the feeder to the print head. So, congratulations for being the first one... :-P

I'm pretty convinced that we will soon see quite a few 3D printers using this mode of operation. Most probably, a company from Brooklyn will try to patent it soon... :sad: So it's very good that you let us all know about it! Thanks!

 

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I know I read about people suggesting this a long time ago, but IIRC what was said then was the torsional deflection that you mention would be a big problem. Looks like you proved them wrong! :) That retraction speed looks like a huuge time saver for large, retraction heavy prints.

£95 + £15 shipping (to Europe) is the price I found if anyone is interested.

 

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I think the high gear ratio is truly the key. First I thought about adding a bigger wheel to the motor-shaft coupler to make it easier to turn by hand. But as I noticed even fast extruding is accomplished by turning the coupler easily just between two fingers.

Retraction speed is just stunning. The whole retraction process feels "digital": on/off instead of time-consuming pulling and pushing of filament within the bowden tube.

The next iteration will be a spring loaded extruder arm with quick release functionality.

 

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feohnsturm, I love this! There have been threads about this on the umforum a few times (eg. here) but up until now most people have just tried with dremel type flex shafts. I also like the reuse of your modular print head. Will you be sharing the design? With all the hot end options you keep making, it can become a UM standard.

Can you describe the flex shaft provided by Mutley3d, how heavy, how long, how rigid? Is there any appreciable resistance to head moves that tighten the bend radius?

 

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Love that idea! Thought about it a year ago, but never realized it. Small worm gears are hard to source. Looking forward to see your design. Don´t know if worm gears might be printable with nylon or sth. like it. We print normal gears, so maybe. Would be great to get some more details about the design. The results are great, but Mutleys prices are a "little" too high.

 

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Look pretty nice. I dont quite understand the difference between this and the use of the current feeder. Is it because there are 2 sets of gear driving the filament at each end of the tube?

Don´t know if worm gears might be printable with nylon or sth.

I dont see why not. Screws can be printed so its pretty much the same. I guess it will depend on the required size and depth. That lloks like a nice challenge :)

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I thought about using a dremel flex shaft for a test with a "paste struder" , it never occured to me it could be used on a "real" extruder... but this seems really brilliant!!

I'll be following this.... and probably buy a kit if there would be one.... very insterested if you share your design !! Would like to get a head with an interchangable nozzle on my UM2 anyhow, so this could be the option ....

 

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@jhertzberg

If mounted correctly (it looks like the supplied shaft "likes" a 270° turn) the resistance for head moves is much like the bowden. And I'm still using the Merlin hotend.

Right now the gearbox is incorporated into the hotend-specific part of the printhead because I want to be able to switch back to the bowden drive without disassembling the crossbar and the sliding blocks. However, if I stay with the flex drive the gearbox should be incorporated in the part which holds the linear bearings.

I'll post some pictures tomorrow, then I'm away for 10 days. Files will follow thereafter.

 

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To my shame I have to admit I still don't have a clue. :???:

 

I guess it's a pretty smart idea to use a flexible shaft (like the one driving your speed and tacho gauge on a motorbike),

to keep the steppermotor stationary and away from the printhead to reduce the mass.

When supplied with the gears and bearings and printable printhead. It's worth the try :).

 

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Nice looking extruder there foehnstrum! :)

I had a working prototype of this exact same setup some 2 years ago, but using steel RC worm gears (1:20). It was abandoned due to hysteresis ruining the prints. It was clearly visible that movement of the head introduces small twists to the flex shaft, which in turn gives imprecise extrusion, especially on larger prints. Obviously with a higher gear ratio, that effect would lessen but still be there. So I'm really curious what is your experience with it so far? And what's the weight of your printhead?

After that I still retained the 1:20 worm gear setup but instead drive it with a tiny NEMA11 motor, which I think is a "best of both worlds" solution. I'd love to have a chat with you and compare some of the stuff I've made for my extruder. Drop me a PM when you get back! :)

 

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If you mean the NEMA11 based one, the concept is explained https://www.youmagine.com/designs/nanoblock on my YM profile, although there are no files to speak of, since I've been constantly changing the design for a very long time now, and it's too much of a hassle to update the files all the time. It currently https://drive.google.com/file/d/0B6N3xYq4GumKYXVUQm5ERlhjZm8/edit?usp=sharing

 

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