Variable orifice nozzle on Hot-End

[Evan Lee]

Hi All, 

I've been kicking this idea around in my head for a while. 

I want to prototype it, but I think it needs some more thought before I actually go make it. I wanted to throw it out here where there are some engineers who would provide feedback (Ryan, et al). 

Basically a nozzle with a long slit in it and a slide mechanism that can function to expand/contract the extrusion hole in the nozzle. This is not purely my idea, the first I thought about this was an 'aperture' idea mentioned from Chris Norman of Kraftwurx/Digital Factory. I took his idea and tried to think of a way it could actually be made. 

The only thing I want to say that I would have a hard time rendering would be that this whole nozzle/hot end scenario would be on a small stepper that could rotate it, much in the way of a drag-knife for a CNC cutter. So, it's not purely 'one way is thin, one way is fat', it could extruding fat any direction, and could be extruding thin any direction. The point is obviously to speed up infill, and to be able to add big fat layers where needed. 

Feedback is appreciated!

-Evan 

The renderings below show what I'm thinking about:

[Evan Lee]

Oh, and Ryan, I see you're in Houston; So am I. If you're interested we should meet up and talk 3d printing. You have some very cool ideas. 

[Ryan Carlyle]

Hmm, biggest challenge is going to be getting a seal around the "gate." Extruders can exert a huge amount of pressure, and plastic will want to leak around the mechanism. You need some kind of seal there.

[whosawhatsis]

Just don't try to do it the way these guys are: https://www.kickstarter.com/projects/865631972/3d-printer-xhead-extruder

In the discussion on G+ (https://plus.google.com/+Whosawhatsis/posts/H6QWFh8LkCM), we started speculating about how to actually do this. The best idea I came up with was to use a silicone nozzle and carefully regulate the pressure to control dilation of the orifice (extrude faster to make the nozzle wider). The real-time flow modeling you'd have to do would be a nightmare, especially with retraction factored in.

I've also considered the rectangular nozzle approach. With rotation of the nozzle, you could soft of control the effective extrusion width, though it would have interesting effects in tight corners. The other option is to not turn the nozzle and just close it up to a 1:1 aspect ratio for perimeters then widen it for infill. Is that would allow you to fill spaces faster, but you'd need very responsive dynamic control of the width to keep it within oddly-shaped perimeters. I've considered this (minus the perimeter part) in looking for a way to do raster deposition printing, but the mechanism was too complicated for what I was trying to do.

On Wednesday, April 29, 2015 at 11:36, Ryan Carlyle wrote:

Hmm, biggest challenge is going to be getting a seal around the "gate." Extruders can exert a huge amount of pressure, and plastic will want to leak around the mechanism. You need some kind of seal there.

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[Wing Wong]

+1 regarding plastic getting around...

Anyone ever see one of these dispensers:

Basically, the sliding block will be in a channel. The edge would have a raised lip that is the same height as the endstop for the channel. The top of the channel is flush with the gate lip and the endstop. By sliding this back and forth, you would be able to control the aperture, though it will be a rectangle or oblong with rounded corners, if using round ends.

Instead of flexible steel, a rigid bar could be used. Though once again, molten plastic could potentially wick/push through the sides. Also, the larger mass of the metal and raised channel represents alot of heat that would be exposed to the layer of plastic. That and ooze/retraction issues when the aperture is opened and closed.

W.

[Ryan Carlyle]

Hmm. Here's a bad idea. What about something like a calligraphy pen? A split "nib" that the plastic sticks to, and spreading the two sides of the nib expands the size of the bead laid down? Might not work super well for thermoplastics, but maybe for a UV-curing resin extruder?

[Evan Lee]

That is interesting, my original approach to this was a needle that was embedded in the hot-end and could push downwards into the nozzle in a similar fashion to a technical pen, with it's needle that is inside the nib: 
https://s-media-cache-ak0.pinimg.com/originals/90/f5/a3/90f5a33dab495a47ac22640e69e04302.jpg

[whosawhatsis]

That's what the kickstarter I linked to above is doing: https://www.kickstarter.com/projects/865631972/3d-printer-xhead-extruder

Problem is, that will restrict flow (making it harder to push filament out) but won't change the outer diameter of the orifice, which is what matters.

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[Evan Lee]

That does seem to be what they're doing, would you look at that! (sorry I didnt the first time, doh!)

Guess it didnt get funding. 

I don't think it is the answer -- it was just my initial thought. I think my option presented up top would be difficult to implement because of those pesky leaks it will definitely have a habit of creating. 

 

[whosawhatsis]

I didn't notice that they had canceled it. Must have finally understood what I was saying when I told them why it wouldn't work.

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[Evan Lee]

LOL