extruder drive screw

is there any previous discussions online about the decision to move from a rigid drive shaft to the flexible one in darwin 1.0? from our experience it was quite difficult to get the flexible shaft working right, and the benefit seems minor when using a flexible CAPA feed.

There was a bit of discussion. Adrian wanted to be able to have the Mk II design handle rigid rods and in order to do that he needed to get the gearmotor out of the way. The flexible shaft let him manage that.

Of course, nophead has found in his work (http://hydraraptor.blogspot.com) that the flexible shaft tends to store energy in the direction of rotation by tightening up the braid of wire. What that means is that if you stop the extruder the stored energy continues to turn the shaft for a bit making starting and stopping extrusion in real time a bit problematical. It also causes trouble if you need to run the polymer pump in both directions.

I haven't shifted over to the flexible shaft concept myself largely because I am using continuous, flexible HDPE filament so it doesn't get me anything. I know, however, that it could become an issue when I go on to less flexible filament materials like solder eutectics to print circuits.

Hello all,

I was grappling with the same problem (and flexible wire). If the feed screw is conically tapered then the motor axis can be inclined out of the way of the feed material, one trouble is that this screw must be machined.

An easier prospect is to employ a wide diameter feed screw and recalculate the rpm/pitch parameters, this has the drawback of requiring yet higher gearing.

Toby

Not wanting to offend the Mk II designers, or anyone else, but exactly what kind of stiff filament with 3 mm diameter are you going to use with the present extruder?
Designing a tool for hypothetical future uses seems a not so good idea to me. Darwins job is to print plastics, and most of them can be made to a flexible filament.
OK, there

hey karl,

the main reason is to print with PLA. vik oliver has done a bit of work with this... look on the main blog for more info.

the cool thing about open source is that all the old designs are still available... the v1.0 extruder with the old style mounting brackets will always be available on sourceforge. if it turns out that this version of the extruder is more trouble than its worth, then it should be fairly simple to revert back. also, the only thing that really changes is the motor mount, so if people really want, we could make up some direct mounts for the motor and they can use it just like in the old version.

i'm going to be doing alot of extruder experimentation in the next few weeks, so hopefully i'll be able to report back with a fuller knowledge of the subject.

Hi Zach,
as i understand, the trouble with the Mk I extruder driver was that it slipped too easily, especially with CAPA? Thats why the thread-drive was introduced for Mk II / Darwin. What I haven

Are you looking for a reason other than being able to use stiff plastics? I don't think I've ever heard any other justification. At this stage, everyone is still experimenting with different materials to see what will work well. The flexible drive doesn't seem that extravagant to me.

I just dropped by usplastics.com, they sell rigid 1/8" x 48" welding rods of ABS, PVC, and CPVC (they also sell PE and PP in coils). I don't have a clue how much you can bend the rods, maybe they could bend around the motor without binding. With the current design I don't have to worry about it.

emf Wrote:
-------------------------------------------------------
> Are you looking for a reason other than being able
> to use stiff plastics?
>
Plastics don't tend to be that stiff. I think Adrian was thinking more along the lines of accommodating wax as a filler material and eutectic alloys such as Woods, Fields and Rose's metals.
>
> I just dropped by usplastics.com, they sell rigid
> 1/8" x 48" welding rods of ABS, PVC, and CPVC
> (they also sell PE and PP in coils). I don't have
> a clue how much you can bend the rods, maybe they
> could bend around the motor without binding.
>
1/8-in diameter is, for practical purposes, not much bigger than the 3 mm rods that we use, though it isn't interchangable. I've got some 3 mm x 48-in HPP welding rods. I can also buy that in coils. All that stuff coils on about an 18" diameter. No big deal.

I would really suggest branching the current 'thermoplast extruder', reverting the darwin 1.0 extruder design to use the previous mkII bracket and creating a 'rigid thermal extruder' which would have more reason to use the flexible drive shaft. If the darwin instructions are based around using flexible CAPA, i don't see much advantage to introducing the problems associated with using the flexible drive shaft. this would also mean that a rigid feedstock extruder could be developed without regards to the effect it would have on the flexible stock.

> All that stuff coils on about an 18"
> diameter. No big deal.

Looks like I jumped to the wrong conclusion there, I must've been remembering thicker rods. D'oh.

I'd wondered if a you could make a 1/8" extruder that would handle 3mm filament as well. Seems like it could work, but I'm not ready to take a drill to mine yet.

Karl,

I think you are confused about versions. There was a MK1 extruder with rollers that did not grip very well. Then the MK2 used a threaded rod connected directly to the motor, then it was modified to have an offset motor mount and a flexible connection.

The link to the MK1 has rotted.

This is the direct drive one
[www.reprap.org]

This is the offset drive
[reprap.org]

I built a mixture of the last two, offset drive with the old nozzle. IMHO this is the worst of both worlds. I would recommend the opposite cross, direct drive with the new acorn nut nozzle.

The reason I don't like the flexible drive is not that it is hard to make, it isn't if you used JB weld, but that it winds up, stores energy and unwinds again.

---

[www.hydraraptor.blogspot.com]

now that i'm setup with molds and stuff, i'll see about making 2 sets of molds: one with the offset and one without. that way people can use whatever version they'd like, without much effort.

i'll be doing some work in the lab with this this weekend. hopefully it goes well!

nophead Wrote:
-------------------------------------------------------
> Karl,
>
> I think you are confused about versions. There
> was a MK1 extruder with rollers that did not grip
> very well. Then the MK2 used a threaded rod
> connected directly to the motor, then it was
> modified to have an offset motor mount and a
> flexible connection.
>
> The link to the MK1 has rotted.
>
> This is the direct drive one
> [www.reprap.org]
> ruder
>
> This is the offset drive
> [reprap.org]
> rmoplastExtruder
>
> I built a mixture of the last two, offset drive
> with the old nozzle. IMHO this is the worst of
> both worlds. I would recommend the opposite cross,
> direct drive with the new acorn nut nozzle.
>
> The reason I don't like the flexible drive is not
> that it is hard to make, it isn't if you used JB
> weld, but that it winds up, stores energy and
> unwinds again.