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Flexible shaft - the best of both worlds?

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Posted · Flexible shaft - the best of both worlds?

Aha. Should have looked at your ym first...

See you work on it for some time now. Understand what it is to have a lack of time sometimes.. if you could find time it would be appreciated if you could share your experence so fare. .. did you already reach good print quality?

You also say its rather costly. What are the expensive components? Are the gears so expensive?

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Posted · Flexible shaft - the best of both worlds?

Well, first a not-so-small disclaimer: I live in Croatia, so I cannot source virtually anything locally. Which means shipping, import taxes, VAT (an insane 25% here, which is paid for the postage price also, which in turn is twice as insane) and of course, waiting a long time for any single part. That's what makes the whole thing very expensive for me. For someone in the US for example it would probably turn out relatively cheap. :)

Worm gear sets are pretty costly and not all that available. I currently use the Modelcraft 1:20 set from Conrad which is around 13 Euro, and the only thing I could find, but the worm is a 4mm bore so it needs to be machined to 5mm to fit the 5mm NEMA11 shaft, which is some extra money. The motor will set you back for around $20 + shipping and taxes.

Also, since the current needed for a motor like this is pretty low, I found they work cooler and more reliably with a dedicated low current driver like the DRV8824.

I found that the best way of designing a drive bolt for this is to integrate it with the shaft which holds the worm gear - makes for a much simpler and more reliable setup, also easier to assemble. I never managed to find a local shop who wanted to do this, so I had to source them from Germany which cost pretty much, although the quality is outstanding.

And lastly I burned through kilos of filament for this thing, the thing in the photo is something like the 40th iteration. I have 2 shoe boxes packed full of prototypes, haha. There are three main versions I made with different gear/motor orientations and the rest of the prototypes branch from those. All of them work but I'm still not 100% sure which one is best.

The extrusion quality is good, and on some prototypes plain awesome, but currently I'm waiting for new belts since the ones I have are completely worn and as soon as I get them I will try to post some tests. It has good extrusion speed, stringing is nonexistent and retraction is almost too fast to notice.

The weight of the completely assembled extruder is currently around 180 grams which is pretty good, but I'm working on making it much lighter still. The last 20 iterations of the extruder mostly printed themselves out, since I have only one printer, but due to all the modifications I did to my printer over the years it's all messed up from a hundred (dis)assemblies, so it's not really a good benchmark. I hope the new belts will make a difference here, and I'm planning to make a whole new frame since my original one looks like swiss cheese ATM.

When I started with the flex shaft extruder the whole thing was only 4x4x3cm (most of it hollow), but as soon as you have to stick a motor in there it gets much more complicated if you want to keep it small.

All in all I'm due a very long blog post about all of this, but just can't find the time. If there is more interest in this, I'll start a new thread, to keep this one flex-shaft oriented. :) And sorry, I talk too much when provoked. :p

 

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Posted · Flexible shaft - the best of both worlds?

Thanks for this thread - I am now too drooling all over the idea to have this in/on my UM2.

 

  • stringing non existant
  • retraction too fast to see
  • easy filament swapping
  • no more pieces of filament stuck in the bowden tube
  • no more weird orientations of filament to fit the extruder/bowden tube entry

OH HELL YES!

 

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Posted · Flexible shaft - the best of both worlds?

And for those who have live the experience: no more excessive humidity buildup in the bowden tube due to Nylon filament (got that just yesterday).

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Posted · Flexible shaft - the best of both worlds?

Great, as every of foehnsturm's creations - I'm a fan of it, therefore please excuse the question "what if I need a second head supplied??"

I know, room for engineering and thinking but this I think will be the next level needed...

B.t.w. Greetings from hot and "hot" Las Vegas - I love vacation :-)

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Posted · Flexible shaft - the best of both worlds?

chopmeister;

 

Please do start a new thread on this, will follow your progress closely as it seems to be the best option sofar for flex fillaments. You say you changed to a motor driver better equiped for low current, any idea if it would be a problem to use the nema11 on the UM2, looking at its "all in one" electronics?

 

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Posted · Flexible shaft - the best of both worlds?

I'm keeping a close eye on this topic. The results almost sound to good to be true.

 

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Posted · Flexible shaft - the best of both worlds?

I'm keeping a close eye on this topic. The results almost sound to good to be true.

 

Don't tell anyone.. ssstt.. :)

 

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Posted · Flexible shaft - the best of both worlds?

Rev2 is printing rev3. This will be a "naked" version with improved fine tuning possibilities. I had a little too much play in one of my parts which resulted in inconsistent extrusion every now and then (can be seen in the top part). Don't worry about the ripples in the lower part, the hotend mount was loose ...

gallery_5589_458_474031.jpg

 

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Posted · Flexible shaft - the best of both worlds?

Now running rev3. I ordered some flexible filament. In the meantime I'm feeding all the old filament I couldn't use with the bowden tube anymore (too brittle, too short BTW: never order a sample pack with a bowden feeder ... as the samples are quite short you have to throw away some 20%).

gallery_5589_458_580060.jpg

 

 

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Posted · Flexible shaft - the best of both worlds?

Right now I'm printing with the same speed settings I used for the bowden (outer shell, inner shell, infill: 40, 60, 90 mm/s at 0.15 layer height) which are very safe settings for the Merlin hotend with most filaments. I'm more focusing on retraction performance and evenness of extrusion.

Due to the high gear ratio the stepper could push even more than the already somewhat overpowered UM original feeder. The limiting factor should be filament slipping.

 

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Posted · Flexible shaft - the best of both worlds?

No issues with 150 mm/s @ 0.15 mm.

 

Great stuff foehnstrum! Do post the pic of the finished print, I'm super curious to see the results. :)

Also how come you haven't greased the worm gears? From what I've read worm gears shouldn't run dry or they wear much too fast.

 

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Posted · Flexible shaft - the best of both worlds?

Also how come you haven't greased the worm gears? From what I've read worm gears shouldn't run dry or they wear much too fast.

 

I am using worm gears (not related to 3D print) and I found that Delrin/Acetal gears are moving very smoothly without grease. I would be afraid to grease them because grease would catch dust and act as sandpaper on the gears...

But my usage is much less intensive and I can be wrong...

 

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Posted · Flexible shaft - the best of both worlds?

I've read in various engineering books that all worm gears should always be lubricated, due to the way they transfer power. But here's an excerpt from SDP/SI webpage:

 

"Worm meshes have relatively high sliding velocities, which induces a high temperature rise.

This causes a sharp decrease in strength and abnormal friction wear. This is particularly true of an all plastic mesh.

Lubrication of plastic worms is vital, particularly under high load and continuous operation."

It's up to you to keep them dust free in the process I guess. :)

 

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Posted · Flexible shaft - the best of both worlds?

@chopmeister

Exactly what I've learned. ActualIy I greased them (it's white grease and not that much, so it's not clearly visible on the picture). Before that I sometimes noticed some creaking sound and even some white wear of friction. But I should add that this was also due to a bad adjustment.

Although this is the stringy 2013 ColorFabb PLA, retraction settings could still be optimized. I found out that with my Merlin hotend I sometimes get uneven extrusion close the the point where the print starts after a retraction when retraction speed set to 60 mm/s and more. This could be related to some properties of the flexible shaft but I would also assume that pressure build-up and release within the melt-zone just isn't possible with both: infinite speed and control. But to be honest I have no feeling about the acceleration and jerk settings on the e axis. What are your experiences?

gallery_5589_458_623238.jpg

gallery_5589_458_2769694.jpg

 

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Posted · Flexible shaft - the best of both worlds?

To be completely honest, I have none. The prototypes I used were abandoned after the first few tests in favor of a small motor based approach, which I'm developing ever since.

I've never tried a 1:40 gear set, because all I had available at the time was a 1:20 set. And with that the prints were a complete mess. At one point we measured the angle at which the worm turned when manually moving the head from the front left corner to the front right, with the extruder off, to check hysteresis. And it was a lot, but I can't remember the angle, it was ages ago. In the end that influenced the quality of the walls too much.

But seeing your results I'm almost certain the flex shaft I used was the culprit. The difference is simply too big - I wouldn't say your prints look twice as good due to the higher gear ratio, more like 20 times as good. :) The one I had was a pretty big thing, more of a Dremel type. Unfortunately that was also the only flex shaft I had access to.

 

Well, that and a combination of me not having a guide tube for the filament. At that point in time I had very limited experience with head-mounted feeders and thus had no idea how big of an impact a guide tube makes.

Darn it, to think I could have been there 2 years ago makes me want to slap myself. :D

 

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Posted · Flexible shaft - the best of both worlds?

Oh and yes, the retraction is a problem with flex shafts due to the winding. There will always be some backlash there, since they are generally manufactured to work either clockwise, or counterclockwise. I have heard of some specialty shafts which can handle both, but don't know much about them.

There was also a patent I found for an anti-hysteresis flexible shaft for use in surgery. I even remember how it looks, but I've never actually seen shafts like that manufactured.

 

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Posted · Flexible shaft - the best of both worlds?

I stand corrected...

 

Yes, but bear in mind that is for "heavy loads and constant operation". It's safe to assume driving an extruder classifies as both, while your application may not. ;)

 

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Posted · Flexible shaft - the best of both worlds?

Arrgh... I'm just trying to print Ninjaflex with the Bowden. It's not fun. I could really use the flexible shaft right now. Unfortunately I would need the version for the dual extrusion head... (I thought it couldn't hurt to mention this for the case foehnsturm is bored and looks for another challenge... :lol: )

Thanks for sharing the design, foehnsturm! Great work!

 

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