BNBSX Extruder and TPU  

RE: BNBSX Extruder and TPU

A bit more progress

RE: BNBSX Extruder and TPU

Not as pretty as my PETG prints, but no retractions with TPU.

RE: BNBSX Extruder and TPU

TPU tree frog is even nicer at 20 mm/sec print speed and 20 mm/sec retraction. Yes, BNBSX can handle TPU.

What better use for this than spiders? Intentionally printing here with retraction off to get maximum stringiness.

Bunny Scientists Testing on Little Bear...

RE: BNBSX Extruder and TPU

Do they seem real enough, Little Bear?

"MORE testing is required," bunnies.

Fearless bunny scientist

Bunny Scientists are, of course, unaffected by fear

RE: BNBSX Extruder and TPU

If you reduce the distance between extruder gears and nozzle to an absolute minimum and use high-quality Capricorn PTFE tubing, you'll be able to print TPU much faster and with far less retract. That's what I like about the Skelestruder, it does an excellent job at this due to its very short distance.

It's a pity it's so ugly 😀

RE: BNBSX Extruder and TPU

Yes, the Skelestruder has the filament path about 2 mm shorter than the BNBSX.

That's approximately 57 vs 55 mm filament path. The difference is smaller than one might expect, because BNBSX is already a short body extruder  like an MK3S as opposed to the Bear from which it was derived.

Best strategy on a BNBSX is to trim the PTFE longer and chisel shaped to tightly intercalate into the Bondtechs. The entire path below Bondtech can be PTFE.

RE: BNBSX Extruder and TPU

Posted by: guy.k2

Yes, the Skelestruder has the filament path about 2 mm shorter than the BNBSX.

That's approximately 57 vs 55 mm filament path. The difference is smaller than one might expect, because BNBSX is already a short body extruder  like an MK3S as opposed to the Bear from which it was derived.

Best strategy on a BNBSX is to trim the PTFE longer and chisel shaped to tightly intercalate into the Bondtechs. The entire path below Bondtech can be PTFE.

 

Hmm, are you sure? I did a quick'n'dirty comparison and it seems the distance from Bondtech gear to E3D heatsink throat is in fact 6.5mm longer in the BNBSX compared to Skelestruder.

And that's significant - I remember reading that the ability to feed stubborn materials diminishes with the cube to distance pushed. So in this case this would make a whopping 40% difference (55 vs 61.5mm).

(Not slamming your extruder here, guy-k2, it's my favorite in fact 🙂 But it can't beat the shorter path of a Skelestruder when it comes to flexibles 😉 )

RE: BNBSX Extruder and TPU

My measurements could be off. I only have CAD for the BNBSX. There isn't an equivalent CAD for the Skelestruder from which to get accurate measurements. I can only estimate for the Skele based on the sizes of the filament cap piece. I agree the Skelestruder will always be a bit shorter path. BNBSX intentionally follows filament path dimensions of the MK3S so it can run with stock firmware. 

If someone has accurate measure of vertical distance from top of E3D aluminum to height at center of Bondtech, we could have an accurate comparison. 

Here it is for the BNBSX. 15.5 mm from Bondtech center height to E3D aluminum top.

You can see the advantage of cutting the PTFE longer and chiseled as opposed to the shorter PTFE in this pict. By doing that, you can fully constrain the filament below Bondtech.

Ugh. Thanks forum software for the geometry distortion. Click on pict to get full size, undistorted view.

RE: BNBSX Extruder and TPU

Got a good measurements for the Bondtech center to end of PTFE filament path distances using actual E3D and BNBSX and Skelestruder.

BNBSX = 48.4 mm

Skelestruder = 42.6 mm

Yes, the Bondtech PTFE path difference is 6 mm (12%) shorter on a Skelestruder. 

RE: BNBSX Extruder and TPU

If we really want to be correct, we'd compare the distances the unmelted filament being driven by the Bondtechs. That would be distance to melt zone which is up to another 10 mm

BNBSX 58.4

Skelestruder 52.6

That still leaves the Skelestruder a 10% advantage in handling flex filaments.

RE: BNBSX Extruder and TPU

Or 37% if you take the cube. Don't worry, I still like the Bunny more 🙂

Super-short-ears Bunny extruder for flexibles soon? 😀

RE: BNBSX Extruder and TPU

Super-short-ears Bunny extruder for flexibles soon?

Probably not. That would break compatibility with fan shroud, stock firmware, and fail printer setup wizard. If Bunnies were going to really optimize flexibles, it would be a completely different extruder with the shorter Mosquito hot end sans adapter. Course, that means only custom firmware would work and require people acquiring a Mosquito and tungsten carbide nozzle. Is it worth the weeks of design work?

What is going to make practical improvement without breaking so many things, is a tighter constraining PTFE cutter for the BNBSX. 

RE: BNBSX Extruder and TPU

> That would break compatibility with fan shroud, stock firmware, and fail printer setup wizard.

Not necessarily. I could design some super simple gapped cylinders that clip onto the smooth rods near the top to reduce Z travel. You're right about the fan shroud tho. But it would definitely work without a custom firmware.

Those willing to flash custom firmwares could instead enjoy 5-6mm more Z build space, in addition to better flexibles handling 😉 I think that alone would be worth it.

> a Mosquito and tungsten carbide nozzle

The Mosquito works with any regular nozzle too, no need for something so fancy.

RE: BNBSX Extruder and TPU

Any ways, back to BNBSX work. A fairly radical PTFE cutting jig is being printed now that more accurately sculpts the PTFE with curves to fit the Bondtechs very tightly. Depending on how accurately cutting with that goes, it may even be possible to have a single, continuous PTFE tube all the way from the top of the BNBSX down to the bottom of the hot end. The only cuts into the continuous PTFE would be where the Bondtechs actually engage. At the very least, the entire path below the Bondtech grip will be constrained in PTFE.

New PTFE Shape Works

The extra constrained PTFE shape works. By extending the PTFE further up and sculpting it to hug the Bondtechs, BNBSX flex performance is improved.

First thing I noticed is idler tension can be as tight like PETG and polycarb. That's usually with head of tension screw flush with extruder. Before today's experiment, I had to set it to just grab filament and little tighter. Any tighter and flex filament would wander off path below the Bondtech. No more of that happening with idler tension.

Here 4 cm diameter cylinder in TPU is being printed at 0.2 mm layer height, 4 perimeters, 150% speed on front control dial, PrusaSlicer perimeter speed 100 mm/sec, and volumetric max 2.0 mm3/sec.

This is NOT 150 mm/sec. It is limited by volumetric limits, but you can definitely see TPU is being handled at decent speed.

New PTFE cutting jig will be released after a bit more refinement.

Here is how the PTFE looks with new sculpted shape. Notice how far up it extends relative to the Bondtech. The tips are nearly level with the Bondtech axes.

RE: BNBSX Extruder and TPU

Here is the TPU cylinder after completion. The spiral (seam) isn't terribly pretty at that speed.

RE: BNBSX Extruder and TPU

PTFE Sculpting guides are now available at https://www.thingiverse.com/thing:3819794

RE: BNBSX Extruder and TPU

@ guy-k2

Have you tried a piece of capricorn XS tubing?, it is even better constrained than most PTFE as well as has less friction inside, both ideal prerequisites for flexible filament.

https://www.captubes.com/specs.html

I use this on my skelestruder and also as a reverse bowden feed to same.