General granule extruder design concepts

nophead Wrote:
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> I think flourecent lighting has enough UV in it to
> turn ABS yellow.
>
The cases I'm referring to were in my office where only incandescent lighting was used. From what you've said and my own experience, I think the stuff just gets old and fragile on its own with no radiation enhancement.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

A couple of random thoughts:

1. The auger designs I've seen have had the auger extend into the heated zone. Since the auger tends to conduct heat, the thermal break is compromised. What would happen if the auger stopped on the cool side of the thermal break? Would it still be able to push the granules ahead of it or would you tend to get packing problems?

2. The main problem with a piston design is the pause while it reloads. What about 2 pistons working alternately (1 loading, 1 pushing). Too complicated?

degroof Wrote:
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> A couple of random thoughts:
>
> 1. The auger designs I've seen have had the auger
> extend into the heated zone. Since the auger tends
> to conduct heat, the thermal break is compromised.
> What would happen if the auger stopped on the cool
> side of the thermal break? Would it still be able
> to push the granules ahead of it or would you tend
> to get packing problems?


I'm not sure whether this would work or not. I think it's got some merit. The worst that can happen is the auger can just spin around instead of pushing. I think I'll try it first.

> 2. The main problem with a piston design is the
> pause while it reloads. What about 2 pistons
> working alternately (1 loading, 1 pushing). Too
> complicated?

I think the real problem here is valving in the hot zone. With the piston, it honestly just makes more sense to have a large enough piston to print one entire layer and reload after each layer.


With either a piston or an auger based design, we need a thrust bearing. Now, as I understand these, they're just two washers with ball bearings between, one attached to the outside, one to the inside.

In the case of the piston, the "inside" is a nut which we crank to move the piston. In the case of the auger, the inside is just the auger shaft.

Take a look at Forest's captured nut design.

[www.3dreplicators.com]

You could have the motor stacked horizontally on top of the drive piston which could simply be a cap on the threaded rod.

Then use skate bearing like demented did for his extruder on each side of the drive nut.

[builders.reprap.org]

Does anyone know how much axial force a skate bearing can withstand?

Annirak Wrote:
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> Does anyone know how much axial force a skate
> bearing can withstand?

No but I stumbled across ceramic bearings with a 180C rating that might strike some idea's here.

[www.shopping.com]

Here's some bearing spec's.

[www.hchbearing.com]

Looks like thrust bearings can be had for <$10 from ebay.