B'Struder: Universal Bowden 1.75mm Extruder

by tempo502, published

B'Struder: Universal Bowden 1.75mm Extruder by tempo502 Mar 6, 2015
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The B'Struder is an entirely new Bowden extruder design. It fits all common stepper motors, and all popular pinch gears. Variants are available for several common tube connections.

YOU PICK THE EXTRUDER HARDWARE! All you need is a few M3 screws/nuts, a suitable ~3/8" or ~10mm spring, and three 623 bearings.

Unlike most extruder designs, the B'Struder filament path runs entirely through the spring idler arm. This accomplishes two unique things:
1) Makes the filament path alignment very tolerant of different pinch gear diameters
2) Makes tension on the Bowden tube (due to filament pushing force) mildly assist pinch gear grip

This requires very specific geometry for the hinge, idler bearing, output fitting, and pinch gear contact point.

This is a new design, and feedback is welcome. But it's working great in my Delta so far. I'm running very aggressive retraction settings without any issues. Let me know how it works for you!

[UPDATE 11-13-15] Performance has been consistently awesome. I have two of them running with a lot of hours on each. The only real changes I have in the "to do" list are:
1) Widen filament inlet a bit
2) Add more fitting options (eg E3D pushfit insert, M4 tube back to the drive gear for flexibles) -- SEE REMIXES FOR MORE OPTIONS


Print the arm at 0.1mm with >50% infill and good print cooling. PLA should be fine. No supports required if printed "upright" as the STLs are oriented. May require minor cleanup of bearing pockets or filament path with a hobby knife / drill depending on your printer.

Stick an M3 nut in the nut pocket, insert a 623 bearing into the bearing slot, and screw a 12-14mm M3 screw into the nut to capture the bearing. Stick two more 623 bearings in the hinge pocket. They should be a snug fit.

Print the plate with whatever settings you want as long as it's strong. No supports required. I recommend ABS if you run your motor hot. (I'm using PLA with motor current not maxed out, but that's risky.) For NEMA 17 motors, align the hinge pivot hole with the motor bolt pattern. For smaller or geared motors, align the slots with the motor bolt pattern and break away the supports in the hinge pivot hole to expose the M3 nut pocket.

Bolt the plate to the motor. Bolt the arm hinge to the plate snug, but not so tight that the bearings bind. (A dab of thread locker is a good idea.) Install the pinch gear on the motor shaft and confirm alignment with the idler. Insert spring.

Compatible steppers:
Pretty much any common extruder stepper with a centered shaft and 22mm "pilot." Should include:
Any NEMA 17, geared or ungeared
Most NEMA 14s, geared or ungeared

Compatible pinch gears:
Should work with pretty much anything from 9mm to 12mm diameter
Tested: TriDPrinting.com 8mm bore hardened pinch gear
Tested: Makerbot Mk7 gear
Tested: Random eBay mk8 gear
Tested: QU-BD Raptor

Other hardware required:
3x 623 bearings
1x M3 screw 12-14mm long (idler bearing shaft)
1x M3 screw 20-25mm long (arm hinge, length depends on motor)
2-4x M3 screw 5-8mm long (motor mount)
2x M3 nuts
4-6x M3 washers recommended
1x spring approx 3/8" or 10mm diameter, ~25-30mm long (to compress to ~15mm in use)

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This unit works not so well, the spring does not keep adequate tension. I will possibly try a more aggressive spring.

Spring force is pretty important. You can try a stiffer spring, or you can try one of the remixes with adjustable spring compression.

Hi, i'm confused. Which files should I use for mk7 and which ones for mk8? Thanks.

The arm design doesn't change with drive gear / hob. Pick the arm to suit the fitting style you want to use.

Any mounts for Rostock Max v2s?

Can anyone recommend a spring available in the UK or ebay that ships here.

Also wouldn't this be stronger is printed lying down?

Sep 25, 2016 - Modified Sep 25, 2016

I've been using these for a while, and had to re-print one today that broke. Something I noticed this time: the arm, if printed upright as in the STL, does need supports in one spot if you want a perfect print: Take a look at the vertical hole through which the filament passes. Where the filament emerges from the arm to make contact with the gear and then goes back into the arm, there are un-supported horizontal overhangs on either side of the vertical hole where it re-enters above the bearing/gear.

Also, I would suggest tapering the inlet hole on the bottom, to make filament loading easier.

Yeah, you're right. My assumption is that people will do a little cleanup with a hobby knife and ream out the filament path to size. That gives the tightest possible fit around the filament to avoid buckling with more flexible materials. If you print with 0.1mm layers, the mess there is minimal.

I personally prefer to print it upright so the bowden fitting threads come out as clean as possible, and was surprised to see how many people choose to print horizontal instead. I might have added some bespoke support to the bearing pocket if I had known people would prefer that.

Thank You for this design!

I have an e3d pushfit connector and I only can screw in half connector. Can you make a remix 5mm taller so I can screw in all the connector?
And, if I can abuse a version that have M10 thread on both sides
Thanks in advance!

I really like this design, well done! Currently I'm printing my third one for a diamond hotend, can't wait to see how it turns out.
I was wondering though if you'd be willing to make a variation of the M6 idler so that it has a bowden coupling on both sides.
This is because I want to make a sealed plastic box that contains my plastic and I'd like to run a bowden tube from that box to the extruder

I uploaded a double-ended M6 fitting version. Let me know if it works!

Should be pretty straightforward. I'll let you know if I get a chance. Feel free to try it yourself as a remix -- you'd just need to take the M6 outlet version and copy the threaded section to the bottom, and probably add some additional material around the base to get some strength around the threads.

That would be very nice indeed. Currently I'm using a compact bowden extruder (also here on thingiverse) with bowden fittings on both sides of the feeded. I love that setup as it will prevent wear on the filament en extruder from filament touching the entry hole. Unfortunately though I'm not too satisfied about the compact bowden extruder as it designs allows the idler arm to twist, which seems to worsen over time.

Made this and it rocks man! Great job! Rocking it on my Kossel XL!

How are mounting this to your delta?

Bolt it to the 2020 column. Check the remixes for lots of mounting options.

MakerToolWork's extruders use an M5 bolt and T-nut to apply pressure to the spring, so that it's adjustable. I might try and modify your design to allow this.

Also; my hobbed bolt has an OD of 8mm. It came from e3d. Do you think the design will be easy enough to adjust for that?

This design is for hobbed gears that mount on a motor shaft, not hobbed bolts. I think you'd need some pretty significant modifications to turn it into a hobbed bolt style extruder.

Oh. Sorry. I have a hobbed gear. I didn't realise there was a difference. From the looks of it the main thing I'm going to have to modify is adding a channel where the set-screw extends outside the diameter of the gear.

Yeah, space for a bigger set screw is just about the only thing the design needs for better drive gear compatibility.

I have a bag of http://www.mcmaster.com/#9657k291/ sitting around -- will they work?

Looks a little short/fat. But I suspect you could probably bend the spring ends to a smaller diameter and use one of the adjustable-compression remixes (B/Mod and Shy Rockabilly) posted here.

Thanks -- I just saw that you listed more details further down in the instructions. I was initially looking at the summary.

I found http://www.mcmaster.com/#9657k306/ which matches the desired dimensions better, but I suspect what really matters is the spring rate which is a result of the diameter, length, number of windings, wire diameter, and metal type (I've been dealing with springs a lot lately while 3d printing a Curta calculator -- wudev.digitaltorque.com if you're interested). That one on McMaster-Carr is rated for 8.2 lb/in which is around 1.46 kg/cm. Does that sound right?

Honestly, I typically just pull a few candidates out of my box of assorted springs, and try a few until I find one that feels right. After building a whole lot of extruders, I can kind of eyeball the spring and estimate whether it's stiff enough or not.
Probably more stiff than it needs to be: http://www.thingiverse.com/make:200447
Looks about right: http://www.thingiverse.com/make:176763
Looks a little weak: http://www.thingiverse.com/make:156324

Err on the side of longer/stiffer when buying unknown springs. If it's too stiff, you can cut off a wrap or two from the spring to loosen it up a bit.

I would guess that a ~25mm long spring rated ~8 lb/in should be in the right ballpark once compressed to ~15mm. The force applied at the idler is roughly double the spring force, so that would give somewhere around 6 lbs force on the filament. I would think that's acceptable...? If not, you can always print one of the adjustable bases and tighten it down.

It's on my to-do list, but I haven't yet created a calculator to relate idler pressure to drive gear stripping :-)

B'Struder: Universal Bowden 1.75mm Extruder
B'Struder: Universal Bowden 1.75mm Extruder
B'Struder: Universal Bowden 1.75mm Extruder
by Heffa

Just wanted to say the this is the most elegant and well-executed extruder I've seen. Thanks for sharing!

I love that! That's sad it isn't OpenSCAD design, so I will need to remade this to be able to adjust - but still amazing!

Please post a remix if you do it in OpenSCAD :-)

Just curious, what would you want to adjust?

of course i'll post it :)
These are main things I want to adjust:
1) i want bowden to go through whole "arm" of extruder for it to be better an printing ninjaflex
2) i want to publish it under disserent license (i want it to be non-commercial), which i'm unable to do by modifying original file because of its ShareAlikeness

Love the design overall. What motor are you using? Not a fan of fixed spring setups though (I like to be able to adjust the idler pressure without buying a new spring).

I'm using a Kysan 1040229, which is a 5.2:1 geared NEMA 17 stepper rated 1A.

Fair point on the spring adjustment... shouldn't be hard to add that to the next rev.

Aug 27, 2015 - Modified Aug 27, 2015

Would you consider making a version of the arm for 3mm filament with with the 10mm fitting?

I'm sure it could be done, but it would take some work to re-arrange parts to make room for the fitting. It's kind of on my to-do list, but I don't think I'll be able to get to it any time soon. (The sketchup source files are attached if anyone wants to take a stab at it.)

Thanks for the reply, I would give it a go but I'm not very good at Sketchup. I might try to replicate it as 3mm in another program sometime.

Could you make a 608 version?

No, that's too big, the 3mm bore bearings are necessary to suit the M3 hardware and NEMA 11/14/17 form factor. Switching to 608s would require a major redesign of the idler fixing and arm hinge.

Is there any particular reason you want to use 608s?

Yeah, I figured it'd be a pretty major change. The biggest reason is 608's are extremely common. I'll have to order 3 of the necessary bearings.

623s are quite common as well :-)

I have used this for around 4 months now and it has been almost perfect. Easy to feed new filament and even without a geared stepper, using mk8 I have plenty of torque. Never a problem with regular filaments.

The only down side, and this is common for any bowden it seems, is that it doesn't work 100% with flexible filament. I use a simi-flex that is not as flexible as ninjaflex, its more like oxygen tubing. But it will still pop out and get jammed enough that it cant print about half the time.
If the top hole was brought a little lower or if it had a little more support around it I think it might do the trick.

That being said. Tempo, if you could make this work better with flexible filament this just might be the perfect extruder, and I have tried a bunch.

I agree. My fear is that if I bring the filament outlet close enough for the mk8 to print flexibles, it will stop fitting the mk7 or other drive gears. And so on. That precision of fit is really hard for a design to accommodate multiple drive gear sizes.

The only good solution I've thought of is using the M4 nut version of the arm, and bringing the PTFE tube all the way back to the drive gear so you can adjust the spacing to suit each drive gear.

I might try that. I did drill out the hole a bit and put a small length of PTFE in between the drive bowden tube. It was only slightly successful. But I think I had other problems with my hot end causing more pressure in the tube than normal which bound up things.

Hi, perfect design. Best extruder-setup for bowden I ever had. My settings:

  • MK5 drivegear
  • Nema17 stepper 1.7A set to 1 A
  • 80 cm bowden.

No slipping or other problems.!!!

Do you think this extruder works with this gear : http://www.ebay.com/itm/For-Reprap-3D-printer-Feedstock-Wheel-Extruder-Gear-Hobbed-Gear-Drive-Gear-/361297222385?pt=LH_DefaultDomain_0&hash=item541efe1af1

I tried with normal MK8 extruder gear and the grub screw doesn't goes all the way in and it bumps into plastic part. Also 22mm spring is not long enough for this gear.

The linked gear looks like it will fit with the large part next to the motor, but it might be necessary to cut a pocket out of the underside of the spring arm to get the hob groove fully aligned with the filament path. The source is attached to this Thing if you want to do that.

The MK8 should fit fine once you put filament in between the idler and gear -- the extra thickness of the filament stands the arm away from the set screw. Unless you are using an unusually long set screw... you can always try a smaller one. McMaster has a good selection.

I agree, 22mm spring is not long enough, unless you're using a very large diameter drive gear to push the idler arm more.

For people using M10 pushfittings, I have created a version of the arm part with a M10 threaded hole for the pushfitting:

B'Struder: arm for M10 sized pushfittings

Pretty nice and compact design! Would it be possible for you to export to a stp/step file from Sketchup?

Hmm, off the top of my head, no step file export, but I think I can do a 3d AutoCAD DWG that Solidworks can import and convert? I can try it later when I get a chance, if you want.

Mar 17, 2015 - Modified Mar 17, 2015

I like how streamline your design is, very nice! How long is your teflon tube to your hotend? Have you tested the limits on it and how much torque does your motor have?

I'm using a ~400mm tube with ~2.5mm retraction @ 100mm/s right now. Works quite well.

The motor I'm using is a 5.18:1 planetary gearbox NEMA 17, Kysan 1040229. It's got tons of torque. I haven't really tried pushing it yet though.

Where did you source your spring from? I just got some springs from a major online company...they were supposed to be 3/8" O.D. but ended up being only .28" O.D.

I think it came in a multi-pack from Home Depot. The springs people often use for Replicator 2 extruders should work.

Nice design. What push-fit connector are you using?

I'm using a 4mm tube by M5 straight thread fitting sold by TriDPrinting.com. I also uploaded a version of the arm that fits an M6 straight thread fitting that McMaster sells.

Hey, looks fine.
Nee to try this.
Thanks for sharing !

I think I finally found the extruder for my printer project! Thanks man!