Comments on RepRap: Blog: Pinch Wheel Extruder Prototype

American Science and Surplus has a few geared moto...

2009-01-16T08:17:00.000Z

American Science and Surplus has a few geared motors that are close - 4-7 rpm at full voltage, and under $20.

Item 37739 on http://www.sciplus.com/category.cfm/subsection/18/category/172 looks promising.

A gear meant to mate to a worm drive may have smoother output - no diameter changes, profiled to mate to a round object, and avg cross-section of the filament should be consistent due to helical hashing.

As for the question of filament diameter and adjustment, if you put the skate/idler bearing opposite on a shaft long enough to put strong springs/elastics like section of surgical tube stretched as a rubber band from either end of the axle to pins near the motor, it should self-adjust, no?

Looking forward to playing with this myself when time allows.

I think I would be a bit worried about the radial ...

2009-01-15T21:51:00.000Z

I think I would be a bit worried about the radial force on the motor bearing. I assume that it must be pretty high to press the cog into ABS. In which case I wouldn't expect the bearing to last very long. I think it would need something hefty like a skate bearing.

laser cut pinch pulley extrder

2009-01-15T21:09:00.000Z

laser cut pinch pulley extrder

laser cut pinch pull extruder in progress:http://p...

2009-01-15T21:08:00.000Z

laser cut pinch pull extruder in progress:

http://prometheusfusionperfection.wordpress.com/category/hercules-extruder/

Zac, I've posted details of another motor option f...

2009-01-15T11:42:00.000Z

Zac, I've posted details of another motor option for you that would be perfect for the pinch-feeder. ( on the builder blog) I've seen these in person, and they are a great little unit.
Buzz.

Corwin, neat idea, but I'd guess that you'd need a...

2009-01-15T07:28:00.000Z

Corwin, neat idea, but I'd guess that you'd need a nozzle valve with that setup, as the tubing and the extra length of plastic filament under compression is going to compress like a large spring, causing a lot more ooze and startup delay than normal. MIG welders have very stiff tubing, stiffer filament, and almost no nozzle pressure.

But hey, give it a shot and see how it works - that's the real test!

I was looking at the builders blog post on a comme...

2009-01-15T06:43:00.000Z

I was looking at the builders blog post on a commercial pinch wheel setup from a welder and a thought occurred - we've kept the extruder motor on the toolhead, but it doesn't have to be there. The welder feeds its wire up through a tube so that the operator doesn't need to carry the heavy motor and pulleys around. It seems like something along the lines of aquarium tubing or another plastic/rubber tube could do the same thing for us. The biggest problem would probably be the transition to a new spool of filament, but if the tube ID is close enough to the filament diameter the new filament will be able to push the remainder of the old down the line. If it works, it would have the added bonus of making the extruder on the bot smaller, which would make it easier to double up to add a parallel head with a larger extrusion size.

example of tube that could concievably work: McMaster part number 5733K54 is a hard, clear (so you can see the filament) tubing with a 4mm ID, minimum of 1" bend radius, rated to 500 degrees F (260 degrees C). $2.65 a foot.

Zach: the semi-fork(not as in a seperate project, ...

2009-01-15T03:35:00.000Z

Zach: the semi-fork(not as in a seperate project, but a sub-type of darwins using this as a design mod) was originally planned to create a semi-miniaturised version of the system in which beginning with 2, then later maybe 4 smaller sub-areas would operate on the same stepper motor control drivers working in parallel where the movement on one stepper would be transmitted to 2 or 4 extruders. Each "cell" would have shared walls or corners to reduce parts but the stepper motor driver would push each cells extruder along the X,Y axis at the same time. The idea being that the production volume would be much reduced, but it would be large enough to produce parts for a normal sized machine(bar perhaps the main carriage on the X axis). Basically it was a system for increasing the replication rate of normal machines. I was going to call it "the motie" version(after the sci-fi species that reproduces like crazy). Only the extruder would need to be replicated.

i.e Darwin slowly makes a motie by making parts one by one. Motie makes darwins very fast by building 4 copies of a part at once. A Motie is like a miniature darwin that is much better at mass producting darwin parts as opposed to actual objects. It was brought about after I gave a presentation on repraps at a sci-fi con and had a dozen people asking me for printed parts.

The point of my original post of course, is that it won't be needed at all, since this extruder design looks much more amiable to running in parallel. I can just combine 2 or 4 of these (as seen in the original post on the design) and make parts really fast once I get a controller board thought up for controlling multiple systems at once. The issue is currently moot for me, given I'm being driven insane by getting my bits from bytes machine working.

update: the gearmotor is 265g w/ the aluminum pull...

2009-01-15T01:45:00.000Z

update: the gearmotor is 265g w/ the aluminum pulley attached. by comparison, the GM3 is 30g, but its also mostly plastic.

if anyone can spec a similar motor (12v, 2-3 RPM, etc) that would be excellent.

forrest: yes, the motor weighs quite a bit. its a...

2009-01-15T01:20:00.000Z

forrest: yes, the motor weighs quite a bit. its also total over-kill. we should be able to find a suitable motor that weighs half that but is still torquey enough. i'm going to attach it to my RepRap machine tomorrow and we'll find out if it is indeed too heavy or not. bottom line is that this filament drive system is drastically superior to the screw driven style. finding a proper motor is easy.

adrian: no need for a groove in the gear. infact, i bet filing down the teeth would decrease its ability to drive filament. the reason it has such good filament driving capabilities is that it actually presses matching tooth profiles into the plastic and then uses those to drive it.

no idea on the torque, but the motor has no problem driving filament. i'm going to try and spec a smaller, lighter motor and we'll find out if that helps or not.

finally, the idler wheel (you can find all this info in the design files, btw) is in a slot cut in the acrylic. it can be moved towards and away from the pulley wheel, and when you get the proper tension, you tighten it down into place. its *very* simple to adjust, and can easily accomodate various filament thicknesses. it might not handle filament with a varying size on the same strand, but if thats the case... you should get better filament ;)

Brilliant Zach :-)Gear groove - might be possible ...

2009-01-14T18:49:00.000Z

Brilliant Zach :-)

Gear groove - might be possible to spin the gear in a Black and Decker then simply hold a rat-tailed file against it. It'd spread the teeth a bit, but I expect they'd still grip.

Any idea what sort of torque you need? Clearly quite high, but I was wondering if it could be driven by a geared-down small stepper.

Is the idler pinch-wheel floating and sprung against the drive? That might be a way to accommodate variations in the filament.

Beagle,I read the SKU# off of the pic in Zach's ar...

2009-01-14T18:43:00.000Z

Beagle,

I read the SKU# off of the pic in Zach's article and then looked it up on the Kysan site.

http://www.kysanelectronics.com/Products/datasheet_display.php?recordID=2055

Mind, Zach has one in-hand that he can look at and weigh himself. It's possible, I suppose, that Kysan list the shipped weight on their data sheet. I doubt that, though.

Where did you find the data sheet?From what I'm re...

2009-01-14T18:35:00.000Z

Where did you find the data sheet?

From what I'm reading, it's about 200 grams - http://www.kysanelectronics.com/Products/Detail.php?recordID=6987 shows a 1.5 rpm model.

Um... this is all wonderful stuff, but I was look...

2009-01-14T15:16:00.000Z

Um... this is all wonderful stuff, but I was looking at the data sheet for that Kysan gearmotor and although draws zip in the way of current it weighs in at half a kilogram. By the time you got the rest of the extruder parts assembled I suspect you're talking about a finished extruder weighing in at anywhere from 750-1000 grams.

Now that can probably be made to work on a Tommelise positioning system or one like Ed is currently designing at Bath university, but that is a LOT of inertia to put on Darwin's xy positioning rig.

ps. my SDP-SI order arrives today!!!!

2009-01-14T14:34:00.001Z

ps. my SDP-SI order arrives today!!!!

ed: yes, also the idler wheel is in a slot, so it ...

2009-01-14T14:34:00.000Z

ed: yes, also the idler wheel is in a slot, so it can be moved back and forth before tightening it down. The rubber on the idler wheel gives it an extra bit of springiness.

letsburn: why fork? just contribute to the project directly. all ya gotta do is publish your modifications. =)

I like this idea, given it's much easier to create...

2009-01-14T10:50:00.000Z

I like this idea, given it's much easier to create massively parallel systems with this design. I'm planning a minor project fork and this design can pretty easily be altered to mean you can fit either 2 or 4 extruders in parallel without having the redesign the whole axis system.

Ah yeah! Nice zach, nice. And the rubber must be a...

2009-01-14T10:18:00.000Z

Ah yeah! Nice zach, nice. And the rubber must be a bit more forgiving on irregular diameter filament than the nut idea Steve and I've been trying.

enrique: yeah, the problem with those ratchets is...

2009-01-13T19:06:00.000Z

enrique: yeah, the problem with those ratchets is that they are too thin, with funky mounting holes. i submitted some quote requests to gear makers to see if they will make us some custom gears

geo: yes, with encoder feedback we will be able to slow it down, but you can only slow it down so much before the motor stalls out or becomes jerky. i think its best to design so it works ideally within your range, then use the encoder for precision control within your desired parameters.

So the reason for wanting a smaller diameter pinch...

2009-01-13T14:41:00.000Z

So the reason for wanting a smaller diameter pinch wheel is because the velocity of the output shaft, yes? And you are going to have encoder feedback?

If you are going to have encoder feedback, then it doesn't really matter if the motor is too fast! What matters is the resolution of the encoder, and the torque the motor can produce. The whole idea of a closed loop control is that you can change the dynamics of the system without changing the actual system.

By the way, we should be trying to mount the encoder on the motor shaft, not the output shaft. That will solve lots of problems. If you had even a 24 ppr encoder on the motor shaft, that gives you 14400 ppr on the roller. You could drive that motor well below a 0.1 rpm and still have excellent control.

If that is the case you can change from the tiny roller 12mm to a 30mm roller and still have the ability to go slow, and fast! Both speeds will feed with awesome regulation.

For ratchet wheels, toward the bottom of the catal...

2009-01-13T06:25:00.000Z

For ratchet wheels, toward the bottom of the catalog at:
http://www.ofrei.com/page_6.html

you can buy the 12 mm ratchet wheel, the CLK-7850R-12.0, for $8.00.

Another place to get em is from the timesavers:
http://www.timesavers.com/catalog/index.htm

in the Gears, Cams and Wheels catalog at:
http://www.clock-keys.com/pdf/Categories/
gears%20cams%20&%20wheels.pdf

the 12mm No. 19844 is available at $4.50.

Unfortunately the ratchet wheels are really thin, for example the No. 19844 is only 2 mm thick.

enrique: yup, i got a couple of gears, and a coup...

2009-01-13T05:22:00.000Z

enrique: yup, i got a couple of gears, and a couple of the pulleys. i'll post an update with what works best in a few days.

wade: yes, the idler wheel is on a slot... you can easily adjust it closer or further from the drive gear

geo: the ratchet profile is actually *exactly* what i need. unfortunately for us, they don't make them small enough. we need metal ratchets that are 12mm in diameter or smaller. can anyone find me one or a source for one? ideally it has a 6mm bore and a set-screw. might be tough to find...

If you are planing on making an order to Stock Dri...

2009-01-13T05:04:00.000Z

If you are planing on making an order to Stock Drive Product/Sterling Instruments I strongly suggest purchasing a set of ratchet wheels. Like part number (A 1B14-24024). They may only drive well one way, but hey, they should have no problem driving any polymer, they just have the right shape. There are lots of us working on a pinch wheel extruder right now.

he Zac, I've posted some pics of a commercial vari...

2009-01-13T03:51:00.000Z

he Zac, I've posted some pics of a commercial variant of what you've just made, which is designed for "wire", as I thought it might inspire you/others to keep up the good work!

That looks pretty sweet! Is there a way to adjust...

2009-01-13T03:38:00.000Z

That looks pretty sweet! Is there a way to adjust the tension for different filaments or gears? I suppose you could just cut out a few different sized idler wheels on your laser cutter. I knew I should have asked for a laser cutter for Christmas!