New light extruder concept out of bolt

Update: video here: vimeo

First test complete.

TLDR: IT WORKS!

The NEMA-17 motor has adequate torque!
The filament moves through the extruder without twisting!

Video will be available via Vimeo in about 45 minutes.

Next I will need to change the settings in the firmware and pull the jumpers off the controller board to eliminate microstepping and calibrate the steps/mm, then mount it on the printer with the hot-end and see how it will handle printing.



Edited 1 time(s). Last edit at 02/02/2014 04:28PM by the_digital_dentist.

Great ! contragulations ! I expect to see the video soon !
Have you done a test with a both side cutted filament to see what's happenning with the torque?

You can't have one side twisting without the other side twisting the same amount or the filament will twist apart. It doesn't.

I mounted the extruder over a scale, limited to about 5kgs, and ran the filament down onto it. It overloaded the scale so I backed off a bit to capture the force at about the limit of what the scale can measure- 5.2 kg or about 51 N. There was no evidence of torque slip in the motor or of the nuts chewing deep grooves into the filament. I think it can push a LOT harder.



I think it's time to test it with a hot-end and see how it prints.

Congrats
I love the looks of it.

I would like to see a line drawn on the filament with a fine permanent marker, zoom up close and post a vid.
It will be interesting to see if it can feed 100's of feet of filament without twisting.

Have you thought about how to swap out the inverted-worm to switch to a different filament diameter?

Print herringbone bevel gears, might help with the backlash.

With a high extruder force you might be able to use a smaller stepper motor NEMA 14, or how about a NEMA 8

Hmm, interressting concept, but i can`t see the real benefits of this type compared to a "normal" geared extruder ?
a Printer with a geared extruder can also make 500m/s (movement), and most ABS/PLA isn`t even good enough to print with this speed.

pro: alot of force, but is so much really necessary?

con`s:
-slow acceleration -> slow retract
-large design (bulky) , even with built with a nema 14 (nema 8 is not much lighter than nema14)
-changing filament would take very long ?
- if the filament diameter is changing too much it may slip or stuck ?

Chri

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Quote
A2
Congrats
I love the looks of it.

I would like to see a line drawn on the filament with a fine permanent marker, zoom up close and post a vid.
It will be interesting to see if it can feed 100's of feet of filament without twisting.

Have you thought about how to swap out the inverted-worm to switch to a different filament diameter?

Print herringbone bevel gears, might help with the backlash.

With a high extruder force you might be able to use a smaller stepper motor NEMA 14, or how about a NEMA 8

Thanks!

Swapping filament sizes should be easy enough- just make another set of tubes with gears/bearings/nuts. My redesign, the green version seen in the video, is designed so the top cover can be removed without dismounting the extruder from the printer. Just take off the 4 screws and it will be open. The bearings/tubes/gears fit into the cover and base easily. The bearings and gears have to be pressed onto the tubes so once put in position, they will stay put.



I think for 1.75mm filament that will be much easier to twist, the nuts should be located as close to the hot-end as possible. Move one nut to the bottom of the extruder instead of both being in the center of the extruder. It would be best if both nuts were at the entrance to the hot-end but that would take concentric tubes and special gears (and $$). This way is simple and cheap.

I don't think backlash is going to be a problem. The gears have to turn 1.26 revs (453 degrees) to move the filament 1mm. If there are a few degrees of backlash the error in movement of the filament will be small. Even if backlash does affect print quality, Slic3r has provision for backlash built in to accommodate Bowden tube extruders, so tweaks during slicing should fix any problems that occur.

I'm not concerned about 100s of ft of filament twisting. If the filament is coming off a spool within a couple feet (depending on the size of the printer, mostly) of the extruder there isn't going to be any way for the filament to twist (at least, 3mm filament- don't know about 1.75mm filament). The only time twisting will be a problem is when the spool is empty and the last couple feet of filament are off the spool and waving in the breeze I am more concerned about the load on the motor as filament shape and diameter vary. Another potential problem is filament dust accumulating inside the top tube. I may need to put some holes in the tube right above the nut to allow any dust created by the process of the nut chewing on the filament to spill out. That is a simple modification. Putting the nut at the top of the extruder instead of in the center will also prevent dust accumulation in the tube.

I put the nuts at the center of the extruder to ensure that it would be easy to load filament. I can see if the end of the filament is getting to the second nut properly and can even guide it if need be. It turns out that doing it that way worked as predicted and I haven't had to touch the filament to get it into both nuts, even though they aren't well centered on the tubes. If the nuts are separated very far the filament may need some help getting into the second nut- that could be tricky if the nut is at the bottom of a tube. The alternative approach in that case is to open the cover and manually twist both tubes/nuts onto the filament then put it all back into the extruder. It would be nice to have some sort of "funnel" inside the tube to guide the filament to the hole in the nut.

The whole thing can be shrunk a bit by putting two of the bearings in the center, next to where the nuts are now, or using smaller gears. I didn't know how far to space the bearings so I just randomly picked a value I thought would work. If left in the current configuration, the bearings could be placed closer together and the tubes shortened to shrink the thing a bit in the vertical dimension. I'm not 100% sure that two bearings are needed for each tube.

I don't know how fast a stepper can be driven. If 300 rpm is the maximum for example, this thing could move 238mm of filament in one minute. That's about 4mm of filament per second. That translates into about 300 mm/sec print speed with a 0.35 mm nozzle. That's more than fast enough for me, but I don't know if the stepper can be driven that fast. It can certainly be driven at 100 rpm which translates to about 100mm/sec print speed, which is still fast enough for me.

Quote
Chri
Hmm, interressting concept, but i can`t see the real benefits of this type compared to a "normal" geared extruder ?
a Printer with a geared extruder can also make 500m/s (movement), and most ABS/PLA isn`t even good enough to print with this speed.

pro: alot of force, but is so much really necessary?

con`s:
-slow acceleration -> slow retract
-large design (bulky) , even with built with a nema 14 (nema 8 is not much lighter than nema14)
-changing filament would take very long ?
- if the filament diameter is changing too much it may slip or stuck ?

Chri

Usually if I have a problem printing it is a filament issue. Geared pushers are great until you strip the filament or it gets kinked after the hobbed pulley. For me this has the potential to provide a great amount of force, reduce the filament deformation (nice for bowdens), and support the filament all the way to the extruder.

This is a great first stab. It is probably unfair at this point to compare it to refined existing designs. (My side rant for today is that we would all be driving cars with Wankel engines if they would have been invented first.) The acceleration and size of the design can be morphed greatly with different design choices. (I feel like I could make this more compact and faster with standard spur gears and just require the nuts to be pressed into nut traps instead of soldered on tubes.) The filament diameter variance will have to be tested.

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Quote
Chri
Hmm, interressting concept, but i can`t see the real benefits of this type compared to a "normal" geared extruder ?
a Printer with a geared extruder can also make 500m/s (movement), and most ABS/PLA isn`t even good enough to print with this speed.

pro: alot of force, but is so much really necessary?

con`s:
-slow acceleration -> slow retract
-large design (bulky) , even with built with a nema 14 (nema 8 is not much lighter than nema14)
-changing filament would take very long ?
- if the filament diameter is changing too much it may slip or stuck ?

Chri

You have some good points. My experience with direct drive 1.75mm extruders is that when the hot-end jams, the drive gear chews a divot into the filament and then it can no longer push. When the hot-end clogs I find that I can usually manually push on the filament and get the plastic to start flowing again. This is the #1 reliability issue with FDM printing. I don't know what causes the hot-end jamming- I'm not sure anyone really does. I see lots of hot-end designs that claim to overcome the problem but when you read forums like this one you find out that the problem persists. That tells me what is needed is a method to provide more push force without chewing up the filament and losing grip. This design is intended to provide a big push force. In extruders where the drive gear pinches the filament against a bearing, there is a small drive area and a lot of force- that's why the gear chews a divot in the filament. It is better to have less pressure on the filament spread out over a larger area. With this design, the nuts can be made arbitrarily long. With the right selection of tubing ID you could thread the entire tube.

This design is essentially a gear reduced driver, like the Wade's extruder. Instead of using gears to multiply the torque produced by the motor, I use a nut that has the same effect. My green gears are the first gear and you can view the nut as the second gear (or is the filament the second gear?). For every rotation of the first gear the filament is only moved about 0.8mm.

Slow acceleration and retraction- Yes. Not nearly as fast as direct drive, but able to provide a lot more pushing force to keep the plastic flowing out of the nozzle.
Large design- this is a prototype to test the concept - it was done using low cost (about $20 total) off the shelf components and was intended to be cheap and fast to build. The design can certainly be shrunk.

Changing filament requires reversing the motor until all the filament is backed out of the nuts, then feeding the new filament into the thing until it engages both nuts. That would take a minute or so. I don't think it's a big problem, but it does require that the hot-end be already heated up because the firmware won't let the extruder motor run unless it's hot.

Switching between 3mm and 1.75mm filament should be pretty quick and easy. You can have two sets of gears/tubes/bearings with different sized nuts. The prototype is design so the cover and all those parts can be removed without detaching the extruder from the printer. It would take just a minute or so to convert from one filament size to another- unscrew the cover, pull out the bearings/gears/tubes/nuts for 3mm filament and pop in the same for 1.75mm filament then replace the cover. Easy-peasy!

The issue of filament diameter variation is the biggest potential problem. Someone suggested that the nuts could be replaced by internally threaded collets that would allow adjustment of bite. It might be possible to spring load such a collet to allow it to follow variations in filament diameter without intervention. I'll have to run a bunch of filament through this thing to really know how big a problem shape and diameter variations will be.

In case anyone is interested, here are the parts I used:

Gears:
[www.sciplus.com]

625ZZ bearings:
[www.ebay.com]

Brass tubing 5mm OD, 0.45mm wall:
[www.ebay.com]

6-32 left hand tap:
[www.amazon.com]

I had the NEMA-17 motor from a QU-BD extruder (ugh!) and the rest was 3D printed.

This is a great!

With counter rotating drive force, I can't see twisting is an issue. It would be interesting to try running with just one drive nut even.

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I've been following this discussion for a while now and have been working on my own 1.75mm designs. It is hard to get an adequate feed rate. This is a two fold problem: 1.75mm filament already requires higher motor speed since there is less volume per mm of length, and smaller threads have smaller pitches requiring more revolutions to get 1mm of extrusion. This can be solved with additional gearing. Either directly in the bevel gears or before the bevel gears.

I think M2x0.4 thread will work for 1.75mm filament. The pitch diameter of M2x0.4 is 1.75mm.

Quote
nicholas.seward

Usually if I have a problem printing it is a filament issue. Geared pushers are great until you strip the filament or it gets kinked after the hobbed pulley. For me this has the potential to provide a great amount of force, reduce the filament deformation (nice for bowdens), and support the filament all the way to the extruder.

This is a great first stab. It is probably unfair at this point to compare it to refined existing designs. (My side rant for today is that we would all be driving cars with Wankel engines if they would have been invented first.) The acceleration and size of the design can be morphed greatly with different design choices. (I feel like I could make this more compact and faster with standard spur gears and just require the nuts to be pressed into nut traps instead of soldered on tubes.) The filament diameter variance will have to be tested.

My intention is not to make something bad at the very beginning, i just wanted to give some objective feedback from my experience with (lightweight) extruders, for sure it would be interessting how this concept will work when its developed to smaller dimensions
If i sound a little bit rude its just because i`m not so good at english ^^"

From my experience with 1,75mm ABS material there is not alot problem with backpressure, for sure it may depend on the used hotend.
I equipped serval printers with a Nema14 Geared extruder, and even the model with bowden was printing at very high speed.
Even changing the filament will only take about 5-10? seconds.
What i often don`t really understand is that problems of printing are often solved the more complicated way, so instead of reducing the backpressure at the hotend, the extruder will be made stronger,
With a Nema17 at the moment this design isn`t really "light" and i thought that would be one of the goals, as i read the thread the first time.
but maybe with a Nema14 and a transmission it may work as well

Quote
This design is essentially a gear reduced driver, like the Wade's extruder. Instead of using gears to multiply the torque produced by the motor, I use a nut that has the same effect. My green gears are the first gear and you can view the nut as the second gear (or is the filament the second gear?). For every rotation of the first gear the filament is only moved about 0.8mm.

Yes this design is capable of two gears, the second gear is very high, so it may work great with a "direct" driven first geard nema14 as well

Quote
You have some good points. My experience with direct drive 1.75mm extruders is that when the hot-end jams, the drive gear chews a divot into the filament and then it can no longer push. When the hot-end clogs I find that I can usually manually push on the filament and get the plastic to start flowing again.

then when the hotend will clog and you have much more force on the extruder, what will break first, the hotend or the extruder ?
I see the drivegear chewing more as savety feature when something goes wrong to prevent more damage..

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Usually if I have a problem printing it is a filament issue. Geared pushers are great until you strip the filament or it gets kinked after the hobbed pulley. For me this has the potential to provide a great amount of force, reduce the filament deformation (nice for bowdens), and support the filament all the way to the extruder.

the "kinked" problem after the bolt is because most of the printed extruder designs have just a too large gap between the bolt and the filamentguide.
For me i use a extruder with 3mm bore and put a custom made brass insert into it which is really really close to the bolt, so it has no chance to slip away.

Chri

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I am dead in the water. My ATMega2560 controller board is toast and can't be seen by my laptop or desktop machines. I think the 16U2 chip is blown. I will continue testing after I get a new controller board.

New controller board has arrived. Testing will resume this week.

Nice

i was looking for a cone-gear generator to make some tests with a smaller version, but didn`t found any

Chri

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Quote
Chri
Nice

i was looking for a cone-gear generator to make some tests with a smaller version, but didn`t found any

Chri

You mean a bevel gear? Do you have access to a CAD program? Simple bevel gears aren't hard to make.

No i don`t have access to a professional CAD program, i`m working with sketchup.

Chri

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[chrisu02.wordpress.com] Quadmax Intel Delid Tools

Check out DesignSpark Mechanical- free CAD, similar to Solidworks. http://www.designspark.com/eng/page/mechanical

You don't have to make the gears. If you make/print them you have to worry about strength as well as some means to affix them to the tubes/shaft. The gears I used, which can press fit onto a 5mm shaft/tube, are available on ebay or from American Science and Surplus very cheaply. I used gears with 30 teeth, but you can get the same gears with 20 teeth that are quite a bit smaller.

I`m already very skilled at sketchup so i want to stay there for now (designed 4 Printers and couple of extruders and other stuff there)

i`m from europe so there would already be the frist problem in getting those gears, and second reason is that i want to try a construction with smaller gears, the mounting and strengs is not the problem there.

Chri

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If SketchUp has a Loft feature, you can make simple bevel gears. I can provide instructions on how I do it in SolidWorks. Or if we can talk about the dimensions/constraints in your design and I can make and send you the models.

Edited 1 time(s). Last edit at 02/13/2014 11:36AM by PvtDBJackson.

I have a Plugin installed called "curviloft" , but don`t know if this would do the trick ?

edit: holy sh`t , just found a gear Plugin that also can do helix and bevel gears

Chri

Edited 1 time(s). Last edit at 02/13/2014 03:18PM by Chri.

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While waiting for some parts to arrive I decided to address some of the less desirable features of the extruder.
- using smaller gears to turn the nuts to reduce overall size and speed up extrusion (let's hope the motor has sufficient torque for the extra load)
- using smaller bearings to shrink the size (went from 5x16x5mm to 5x8x2.5mm)

The previous iteration size, excluding motor, was 100mm long x 42mm wide x 56mm high
The latest is 68mm long x 42mm wide x 35mm high

My web hosting service seems to be down- all the images have disappeared from my previous posts.
You can see pictures of the new stuff here: https://groups.google.com/forum/?fromgroups=#!topic/milwaukeemakerspace/a0oRcWwJNDU

I finished fabricating the nuts and assembled everything today. Test printing will commence tomorrow if everything works. There are more photos of the assembly here:

Extruder cover assembly
Extruder side view
Extruder assembled

The small gears, tubes, drive nuts, and bearings all come off the unit by removing the four cover screws, without taking the extruder off the printer mounting plate. That means it might be possible to change filament sizes by simply having a second cover assembly to swap in. You'd still have to tweak the steps/mm in the controller board, either via a firmware update or by using the menu on an LCD controller interface.

The nuts have been moved outboard. With the bearings moved inboard, there was no other way to make it all fit. It should be fine for 3mm filament, but I'm not sure you could get away with that for 1.75 mm filament.

Edited 2 time(s). Last edit at 02/23/2014 09:44PM by the_digital_dentist.

Looks great!
I'm curious what are your thoughts about the optimal I.D. and pitch for 1.75 mm, and 3.00 mm filament.
Tks for posting pics!

I think the ideal pitch is one that results in a whole number of steps per mm of extruded filament, but that will also depend on the gears you use. I have 30 and 20 tooth gears and I used a 32 tpi taps to make the nuts because they were cheap, readily available, and about the right diameter. With these gears, one rev of the motor will turn the small gear 1.5 times, which will move 1.19mm of filament, which translates to 168.07 steps per mm without microstepping. That's really close to a whole number, and much less than 1% error if you used told the controller that it's 168 exactly. I think the diameter/volume of the filament varies by at least that much, so it may not matter. At these small sizes, making nuts by turning internal threads would require some special tooling.

I tried a 7/64" drill bit but after tapping,the hole was too big and the filament slid right through. So I went to 3/32" (~2.38mm) and it bites a little too much, which is good- it's easy to make a hole a little bigger. I used a tiny rat-tail file to open the threads up a little, until I was able to twist the nuts onto 3mm filament with my fingers. It might be better to use a slightly larger drill- maybe 2.5mm...


I have no idea what sizes would be good for 1.75mm filament, but standard taps at that size (M2) are finer than 32 tpi, so you might need to use a larger drive gear or smaller driven gears. There is a 40 tooth gear among those I bought, so you could get a 2:1 gear ratio that would help keep the speed up. With 1.75mm filament you have to move almost 3X as much filament as 3mm filament for the same extruded volume.

It remains to be seen whether the motor can provide sufficient torque to drive the filament with the gears I am using and what happens over the range of filament diameter tolerances one would find in the wild. Considering the push force I was getting with 1:1 gears, I don't think torque will be an issue.

I have no idea what maximum value of steps/mm is acceptable in Marlin. If anyone knows, this would be a good time to speak up!

Nut problems! The drill size I started with doesn't seem to work right. When I file the tapped hole larger to bite the filament less, the force required to spin the nut doesn't drop until it suddenly drops too much and the filament starts slipping. I think the nuts are going to have to be made by tapping a small collet so the final diameter can be adjusted. I'm going to fall back to the original, larger extruder for first print testing.

The problem you may will have is that the filament break inside the nut : it will be horrible to remove. It's why I choose to thread with screws instead of nuts.
Thank you for keeping us in touch of your progress.

If the filament breaks inside the nut, you could chase it out with a small drill or even a tap pretty easily. I can't think of anything that would cause the filament to break inside the extruder. If one side were turning and not the other you could develop some pretty big force on the filament, but if that happens, you have bigger problems anyway since both nuts are driven by gears. I suspect that the nut would start to chew up the filament the way the current pinch-wheel designs do if there was enough force to prevent movement of the filament.

Getting closer! I did another redesign to reduce size a bit, printed the parts, tested operation pushing filament back and forth, bolted to a mounting plate with a Budaschnozzle hot-end, uploaded files to thingiverse and video to vimeo and put blog post at the Milwaukee Makerspace site.

I will be printing with it tonight or tomorrow and will make video of success or failure for all to enjoy.

Vimeo: [vimeo.com]

Thingiverse: [www.thingiverse.com]

[milwaukeemakerspace.org]

Tks for the video!

It appears that the inverted worm drive would have a lot axial force.
The delta printers would be very interested if the weight could be reduced.

Do you think you could drive the filament with enough force, and speed with a NEMA 8, 11, or 14 stepper motors,
using Dia 1.75 mm filament?