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A Very Different Extruder

Posted by rq3 
Re: A Very Different Extruder
February 16, 2022 08:16PM
Quote
MarksAlot
I've been working on a similar idea, kind of inside-out. Just have to machine a few more parts.
By inside out, do you mean using an outrunner motor, or something different? I look forward to seeing it. I just finished constructing my outrunner idea that I wrote about several posts back. Check it out! [reprap.org]

Quote
rq3
Thomas Sanladerer of YouTube fame just did a segment on the new E3D hot end, including measurements of just how much force it takes to squeeze molten plastic out of a nozzle. It's not as much as I thought, and the Schnekenstruder has a mechanical advantage of about 21:1.
Thanks for the heads-up, I hadn't seen that video yet. Brilliantly simple way to measure extrusion force. That integrated nozzle/heatbreak design does look great for eliminating the possibility of leaks between the heatbreak and nozzle, but I think the patent will ensure that regular threaded nozzles remain the standard.

What exactly do you mean by 21:1 mechanical advantage? I thought it would be a leadscrew type calculation. In the case of mine with 288 steps per mm, that gives a lead of 400/288 = 1.39mm per revolution, so 1Nm torque should give 2pi/.00139 = 4520N linear force. According to the Sanladerer video it only takes about 1kg to extrude, so that's only 2.2mNm. And the NEMA 11 is rated for 15mNm, so it probably is indeed enough, especially since you don't need microstepping.
Re: A Very Different Extruder
February 16, 2022 10:51PM
I'm looking at something a little closer to a Uhing rolling ring drive,
I've done miniature versions of the Uhing on 1/8" piano wire as a linear actuator. Somewhat more than 20 lbs of thrust.
I'll have to support filament a little better if I can get it to work.
Re: A Very Different Extruder
February 16, 2022 11:13PM
How do you go about getting sufficient grip should the filament change diameter?
rq3
Re: A Very Different Extruder
February 17, 2022 11:32AM
Quote
dekutree64
Quote
MarksAlot
I've been working on a similar idea, kind of inside-out. Just have to machine a few more parts.
By inside out, do you mean using an outrunner motor, or something different? I look forward to seeing it. I just finished constructing my outrunner idea that I wrote about several posts back. Check it out! [reprap.org]

Quote
rq3
Thomas Sanladerer of YouTube fame just did a segment on the new E3D hot end, including measurements of just how much force it takes to squeeze molten plastic out of a nozzle. It's not as much as I thought, and the Schnekenstruder has a mechanical advantage of about 21:1.
Thanks for the heads-up, I hadn't seen that video yet. Brilliantly simple way to measure extrusion force. That integrated nozzle/heatbreak design does look great for eliminating the possibility of leaks between the heatbreak and nozzle, but I think the patent will ensure that regular threaded nozzles remain the standard.

What exactly do you mean by 21:1 mechanical advantage? I thought it would be a leadscrew type calculation. In the case of mine with 288 steps per mm, that gives a lead of 400/288 = 1.39mm per revolution, so 1Nm torque should give 2pi/.00139 = 4520N linear force. According to the Sanladerer video it only takes about 1kg to extrude, so that's only 2.2mNm. And the NEMA 11 is rated for 15mNm, so it probably is indeed enough, especially since you don't need microstepping.

I tend to agree on the Revo nozzles. Not enough benefit to justify the hassle and expense.

The roughly 21:1 mechanical advantage comes from the tangent of the 15 degree roller angle (3.73, or the standard leadscrew "inclined plane" equation), and the ratio of the drive roller diameter and the filament diameter (10/1.75=5.71). In other words, it takes 5.71 revolutions of the drive carrier to get one drive roller revolution, multiplied by the inclined plane advantage.
rq3
Re: A Very Different Extruder
February 17, 2022 11:40AM
Quote
MarksAlot
How do you go about getting sufficient grip should the filament change diameter?

The schnekentruder has a knife edge drive roller that bites into the filament far enough to deal with any diameter variation. In fact, as the diameter of the filament gets smaller, the effective pitch diameter of the drive roller gets larger, so that it automatically compensates for volumetric extrusion based on filament diameter. The effect is not linear by any means, but it's within about 5%.

It also makes calibrating the steps per millimeter of the whole thing interesting, as the answer depends on the filament diameter. I started with a calculated 2775 microsteps per millimeter, and after calibration with PLA and PETG have settled at 3000 steps per millimeter. I attribute the difference to mechanical imperfections and drive roller slippage, i.e., it's not 100% efficient.

I have some flexible TPU filament on order, and will be very interested to see if the schnekenstruder can deal with it at all.

Edited 2 time(s). Last edit at 02/17/2022 11:45AM by rq3.
Re: A Very Different Extruder
February 17, 2022 12:21PM
To me, an ideal extruder would measure both diameter and travel, calculate volume dispensed, and use that to close the servo dispense loop.
Thermwood does similar with their pellet extruders.
They do a pressure condtrol loop with the screw, the melt then flows through a gear pump to meter/measure the flow into the nozzle, and nozzle velocity follows melt volume dispensed.
We could do similar. A strain gage for pressure control, and a filament encoder+diameter gage right at the cold end entrance. I know all have been done seperately, but not sure volume metering+ pressure control+ nozzle velocity following + predictive/adaptive/lookahead has been rolled together outside high end pro-level printers.
rq3
Re: A Very Different Extruder
February 19, 2022 03:08PM
Quote
dekutree64
Ah, I'm glad I didn't bother with magnets yet then. I recommend using coarse thread screws if you're screwing into plastic. Fewer turns to take them in and out, and at least in my experience machine threads in plastic tend to wear out more quickly.

I have unloaded mine once, and with some gentle turning back and forth by hand I was able to get the lumpy end of the filament through the rollers without having to unscrew the mount. Probably would be better to do it while the filament is still warm so it puts less pressure on the rollers, but it will take some experimentation to find the right time window when it's soft but not sticky. Another option would be to retract part way and then reach in with some nippers and cut the filament between the rollers and heatsink. Then purge the remnant through the nozzle when loading the next filament.

My two-post mount is very nice in terms of usability, since it gives such a clear view and finger access. The long screws support the upward pressure from extrusion just fine, but a three-post mount or full cylinder like yours may be better for high lateral acceleration, to better resist whiplash in all directions. You only really need finger access from one side since it's so easy to turn, but loading and unloading is twice as fast when you can use both hands to spin it.

I look forward to the results with your NEMA 11. My guess is that it will be a bit underpowered. The NEMA 14 seems just right, with enough headroom that you can run cool without worrying about missing steps. Though with an aluminum carrier, a heat-tolerant mounting surface, and no bowden adapter epoxied to it like mine, the stepper should be fine running a little hot.

I still want to try the outrunner design I posted before as well, especially now that we know the anti-torque device is unnecessary. But I won't have a place to put the bowden adapter, so I may have to do it on my other printer. The design is a little mechanically iffy since it puts the extrusion force pulling upward on the roller screws, and pulling upward on the rotor so the shaft retainer clip will have to be shimmed just right so there's no wiggle room. But it should be about as lightweight as you can get.

To unload, I'm finding it easiest to heat the nozzle, clip the filament where it enters the motor shaft, and just lift the whole motor and drive assembly off. Then I advance the motor 20mm while holding the end of the filament that came out of the nozzle. To load, just put the motor back, ask for 20mm of extrusion, and stick the filament into the motor shaft. The entire process takes about a minute. I don't even have finger access to the drive mechanism anymore.

Next month I'll be trying the NEMA 11 motor with a CNC machined 7075 aluminum drive carrier.

And here's a REAL shocker. I've never used any kind of flexible filament before, on any printer with any extruder. So I ordered some 95A hardness thermoplastic urethane (TPU) from Matterhackers. I was VERY surprised at just how soft and rubbery this stuff is, very much like well cooked spaghetti. It turns out that the VDE-100 Schnekenstruder LOVES spaghetti, especially when printing an I-Phone case at 20mm per second, 100% concentric skins, 50% gyroid infill, and 50% cooling.

No anti-torsion mechanism of any kind. I am very pleasantly surprised. Photos attached.

Edited 3 time(s). Last edit at 02/19/2022 04:02PM by rq3.
Attachments:
open | download - Schnekenstruder_Flex.jpg (691.8 KB)
open | download - Printing_Flex_TPU.jpg (650.4 KB)
Re: A Very Different Extruder
February 19, 2022 06:50PM
Excellent! I've never used flex filaments either, but it's nice to know this extruder type doesn't have any limitations.

My outrunner version should be able to use that same loading procedure, by loosening the set screw and pulling the rotor off. I definitely need to make an aluminum carrier for it. The plastic shaft hole just doesn't hold the rotor stable enough. I haven't quite worked out the machining procedure to get the roller shafts angled and spaced just right, but I'll get it. I could possibly make the stator mount as well, either using a thread mill or manual die for the threads. But plastic should be ok as long as it doesn't get too hot.

Quote
MarksAlot
I'm looking at something a little closer to a Uhing rolling ring drive,
I've done miniature versions of the Uhing on 1/8" piano wire as a linear actuator. Somewhat more than 20 lbs of thrust.
I'll have to support filament a little better if I can get it to work.
Oh, so having the filament pass through the inside hole of the bearings? Interesting indeed! It would be nice if you could get bearings without the edges chamfered, so the edge could function as a blade. But in my experience only the 2mm and smaller sizes have a sharp edge on the inner race. I just checked my 4x8x2 and 5x8x2 bearings and both have very slightly rounded edges, which slide smoothly against PLA filament even when tilted to scrape the edge against it. But with 3 of them positioned to intrude into the 1.75mm diameter just a bit so the filament is bent slightly from one bearing to the next, it will probably grip well enough. But variation in filament diameter or changing to stiffer or more flexible filaments may cause trouble.
rq3
Re: A Very Different Extruder
February 21, 2022 02:28PM
Quote
MarksAlot
I'm looking at something a little closer to a Uhing rolling ring drive,
I've done miniature versions of the Uhing on 1/8" piano wire as a linear actuator. Somewhat more than 20 lbs of thrust.
I'll have to support filament a little better if I can get it to work.

I'll bet you can do this with just one bearing, with a hollow sleeve press fit into the bore. The center of the sleeve would have the knife edge, the entire bearing would be canted, and the outer race would be driven to rotate. A single bearing Schnekenstruder!

Here's a bad cross section of the sleeve, with maybe a 2mm bore in the knife edges:
-----------
-----\/----

-----/\-----
------------

I'm off to the lathe!

Edited 10 time(s). Last edit at 02/21/2022 02:47PM by rq3.
rq3
Re: A Very Different Extruder
February 21, 2022 09:02PM
Quote
MarksAlot
To me, an ideal extruder would measure both diameter and travel, calculate volume dispensed, and use that to close the servo dispense loop.
Thermwood does similar with their pellet extruders.
They do a pressure condtrol loop with the screw, the melt then flows through a gear pump to meter/measure the flow into the nozzle, and nozzle velocity follows melt volume dispensed.
We could do similar. A strain gage for pressure control, and a filament encoder+diameter gage right at the cold end entrance. I know all have been done seperately, but not sure volume metering+ pressure control+ nozzle velocity following + predictive/adaptive/lookahead has been rolled together outside high end pro-level printers.

That would be ideal, but can you do it under, say, 70 grams? winking smiley

As Richard Feynman said, "There's plenty of room at the bottom".

My goals with the VDE-100 Schnekenstuder were:
1) Will it even work?
2) Will it save weight?
3) Will it be accurate and repeatable?
4) Can it be duplicated by anyone with a 3D printer, and maybe a drill press?

So far, it's checked all the boxes, and thanks to you kicking me in the head, may get even simpler, lighter, and easier to fabricate, but it's going to involve another entire series of trial and error.

I've also just received notification that the CNC'd aluminum drive carriers, which I wasn't expecting until mid-March, should be here this week. Same with the NEMA 11 motors, perhaps. Tracking says they're in Jamaica. I'm hoping that's Jamaica, New York.

Edited 1 time(s). Last edit at 02/21/2022 09:15PM by rq3.
Re: A Very Different Extruder
April 03, 2022 05:00PM
@rq3 would a hollow shaft stepper like the OMC 17HS13-1504H be an option? ID of the shaft is 4mm, I'm thinking of a PTFE tube insert (OD 4mm/ID 2mm) to constrain the filament better ...
rq3
Re: A Very Different Extruder
April 04, 2022 09:25AM
Quote
oliof
@rq3 would a hollow shaft stepper like the OMC 17HS13-1504H be an option? ID of the shaft is 4mm, I'm thinking of a PTFE tube insert (OD 4mm/ID 2mm) to constrain the filament better ...

The shaft is 8mm in diameter, which is too large to provide clearance for the bearing shafts on my current design. And it weighs almost half a pound! I've run the latest Schneckenstruder on a 28 gram NEMA 11.
Re: A Very Different Extruder
April 04, 2022 05:22PM
yes it is heavy, but one has to work with what one has. the 8mm OD shaft is breaking the bank though, I will likely need to plan differently.
Re: A Very Different Extruder
August 22, 2022 10:26PM
very cool to see how this design has progressed. Hope to see it continue to compact down, and hopefully not get stolen by anyone. Keep up the great work
rq3
Re: A Very Different Extruder
August 27, 2022 05:34PM
Quote
OutcastZeroOne
very cool to see how this design has progressed. Hope to see it continue to compact down, and hopefully not get stolen by anyone. Keep up the great work

At this point, the Imperial version of the Schneckenstruder is permanently mounted on my go-to delta printer, and is the only extruder I use. And it's open source, so it can't be stolen.
The fact that I've publicly provided the design means that it can't be patented, either, at least in the US.

I've received a few "threatening" e-mails regarding patent infringement over the years, but when I sternly point out that if they'd like to sue me over, for example, an Archimedes screw over 2000 years old, and they'll not only lose the suit, but also any possible patent protection they think they currently have, they all quickly lose interest. Addressing real infringement does NOT start with an e-mail. Patent trolls disgust me.

On several occasions I have filed, and then intentionally abandoned, patent applications expressly so that the idea CANNOT be patented. The filing is a public disclosure, making further attempts to patent the same idea impossible. At least in the US. These days, it is cheaper just to disclose the idea publically on the internet, which legally can serve the same purpose.

On two occasions, when an idea that I had previously disclosed publicly was subsequently patented by someone else, based demonstrably on my disclosure, I myself have acted as a "patent troll" and demanded payment from the guilty party, with the implication being they could pay me a reasonable sum now, or a much larger sum to a bunch of lawyers to protect an idea that they had obviously stolen. They payed me now. I don't consider this trolling. I consider it monetary punishment for gaming the broken US patent system, by using the broken US patent system. Apparently they agreed. The sums were not large, but sufficient to convince the offending parties that patenting something that someone else has brought to commercial practice is not a wise, or profitable, idea.

Invent madly, and tell everyone what you've done. It's the only way forward
VDX
Re: A Very Different Extruder
August 27, 2022 06:02PM
... we've made the same here in Germany (or EU) IP-range -- filed a patent and abandoned it shortly after, so no other party can "block" our open-source development with a similar claim


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
rq3
Re: A Very Different Extruder
August 27, 2022 08:38PM
Quote
VDX
... we've made the same here in Germany (or EU) IP-range -- filed a patent and abandoned it shortly after, so no other party can "block" our open-source development with a similar claim

In the United States of America, any public disclosure now qualifies. I am glad to see that also appears to apply to the European Union.
Re: A Very Different Extruder
September 02, 2022 12:16PM
I may have to give this a go at some point. With how my custom printer is set up I’m pretty sure I can fit one of those over my custom water cooling setup for a nice light direct drive system.
rq3
Re: A Very Different Extruder
September 02, 2022 02:20PM
Quote
OutcastZeroOne
I may have to give this a go at some point. With how my custom printer is set up I’m pretty sure I can fit one of those over my custom water cooling setup for a nice light direct drive system.

Here's a new video from Tom Brazier showing his printed version, and how he grinds the knife edges:
[www.youtube.com]
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