Has anyone thought about or explored the use of a silicone rubber nozzle, or in particular, just the orifice area of the nozzle? I was thinking that you could start with a very small orifice (say 0.1mm) that could stretch to a wider diameter at higher extrusion rates, essentially giving you a variable diameter nozzle based on the flow rate. Of course, you'd have to figure out a geometry (and metal backing structure) that would allow the orifice to stretch without bulging downward appreciably. But it would be great to be able to print really fine details just by slowing down. In theory, you could even have a zero diameter orifice (i.e., a hole made with a needle) that closed off completely to prevent oozing.

Edited 2 time(s). Last edit at 11/18/2018 09:32PM by LoboCNC.

That is a great idea, get on it.

Something tells me you’d have issues with heat transfer to the filament with a silicone nozzle considering there are a lot of silicone items available as an insulator because it doesn’t transfer heat or at least doesn’t transfer heat well.

I am also guessing, but I don't think lack of heat transfer would be much of a problem as the plastic should be substantially up to temperature before it reaches the nozzle - the lack of heat loss from the nozzle due to it having a relatively low thermal conductivity could be an advantage.
In the end, the best way is to try it to see if it works.

Mike

This is a terrible idea from a control point of view.

If you do this, the nozzle diameter is linked to extrusion pressure. Pressure is linked to extrusion speed, which is in turn linked to print head speed. therefore, you need to extrude faster in order to print faster, but you also need to take acceleration into account, so this means that your nozzle will be getting smaller close to the corners, or the edges of the infill. Until or unless you can command instantaneous movement of the print head with no acceleration to speed, this isn't going to work. you'll also need to be able to do the same thing with the extruder, going from zero to full pressure instantly. No way this will end well.

You're also adding compliance to the nozzle position. There will be a tendancy to "drag" the actual extrusion point behind the centre of the nozzle. This is going to decrease accuracy, so you're probably better off just using a larger nozzle in the first place.

You're probably better off with a dual extruder, using a second one with a larger nozzle for infill. Actually, you're DEFINITELY better off doing it that way, since all of the provision to do that is already in place with firmware. With a large enough nozzle, you can also then do the "combine infill" thing to only have to do it every second or third layer.

---

MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Quote
SupraGuy
This is a terrible idea from a control point of view.

If you do this, the nozzle diameter is linked to extrusion pressure. Pressure is linked to extrusion speed, which is in turn linked to print head speed. therefore, you need to extrude faster in order to print faster, but you also need to take acceleration into account, so this means that your nozzle will be getting smaller close to the corners, or the edges of the infill. Until or unless you can command instantaneous movement of the print head with no acceleration to speed, this isn't going to work. you'll also need to be able to do the same thing with the extruder, going from zero to full pressure instantly. No way this will end well.

You're also adding compliance to the nozzle position. There will be a tendancy to "drag" the actual extrusion point behind the centre of the nozzle. This is going to decrease accuracy, so you're probably better off just using a larger nozzle in the first place.

You're probably better off with a dual extruder, using a second one with a larger nozzle for infill. Actually, you're DEFINITELY better off doing it that way, since all of the provision to do that is already in place with firmware. With a large enough nozzle, you can also then do the "combine infill" thing to only have to do it every second or third layer.

It might not be as complicated as you think. The line width is a function of the extrusion rate, not of the nozzle diameter, so you should be able to print with normal slicing parameters and have everything work out. The tricky part is that you want the slicer to be able to actually generate thinner lines in the areas of finer details (where you are typically extruding more slowly anyway). I know the latest version of Simplify3D does use variable line width in certain circumstances, but I'm not sure if it'd fully take advantage of an elastic nozzle.

Regarding the nozzle flexibility, I'm not envisioning a big old pointy rubber nozzle that would deflect horizontally as you print - I'm thinking more of a rubber orifice area backed up by a metal cone. I haven't fully worked out what this would look like yet, if anyone has any ideas.

Here is what I was picturing when you mentioned this.

Inside the nozzle is a cone. This cone is there to keep the tip of the nozzle from bulging out, it's thicker then the rest.
The area around the cone is air, to give space for the cone to expand into.

The bottom is corrugated. This may or may not be needed, but could make it easier to expand without pushing the silicone downward.

The yellow paint represents the solid casing used to attach it to a standard hot end.

Quote
Number_5
Here is what I was picturing when you mentioned this.

Inside the nozzle is a cone. This cone is there to keep the tip of the nozzle from bulging out, it's thicker then the rest.
The area around the cone is air, to give space for the cone to expand into.

The bottom is corrugated. This may or may not be needed, but could make it easier to expand without pushing the silicone downward.

The yellow paint represents the solid casing used to attach it to a standard hot end.

Yeah, something like that. All I have to do is figure out how to make it. 3D printed RTV?

corrugated, I think you mean puckered annulus

Edited 2 time(s). Last edit at 11/20/2018 04:49AM by MechaBits.

Biggest problem I see is nozzle wear. Brass already wears down quickly, how will silicone fair?

Why not a silicone sock placed over a brass nozzle secured in place by a metal zip tie?

Edited 1 time(s). Last edit at 11/19/2018 08:49PM by Origamib.

Quote
Origamib
Biggest problem I see is nozzle wear. Brass already wears down quickly, how will silicone fair?

Why not a silicone sock placed over a brass nozzle secured in place by a metal zip tie?

I really like the silicone sock idea. I wonder if you overmolded silicone on to a brass nozzle if it would adhere we
ll enough to not separate at the tip from the extrusion pressure.

Interesting debate, yet a bit futile as it assumes this nozzle is made and behave as expected.

So not much to add, just wait for a prototype and a demo.

Edited 1 time(s). Last edit at 11/20/2018 02:35AM by MKSA.

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Quote
MechaBits
corrugated I thing you mean puckered annulus

Funny, I read a bit quickly and coudn't stop a smile. (OK, I learned Latin in high school, not much left though)

Edited 1 time(s). Last edit at 11/20/2018 02:34AM by MKSA.

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Never learned Latin, bloody French...what use is that when you had german pen friends, & specially now we are sailing away, avec un baguette, but I do like a good double entendre, & a little en passant, Latin is mostly greek to me??? but I know which words are & aren't or derivatives,
though by the looks of things I can't even spell thunk...
So if you fill a balloon with water & let go of the annulus which way does the water go...

I wonder if this has any relevance
[www.bbc.co.uk]

"So if you fill a balloon with water & let go of the annulus which way does the water go..."

Out

but yes, at what ever direction it feels like.


Things people seem to be forgetting..

silicone doesn't stick to anything but silicone... (more or less) So it not going to adhere to a nozzle, not without some cleaver mechanical fastening system

Temperature, although i'm sure there are a bunch of variants of Silicone rubber, its doesn't like higher extrusion temperatures...
"Silicone rubber can be used indefinitely at 150°C with almost no change in its properties. It withstands use even at 200°C for 10,000 hours or more, and some products can withstand heat of 350°C for short periods."

Quote
Dust
silicone doesn't stick to anything but silicone... (more or less) So it not going to adhere to a nozzle, not without some cleaver mechanical fastening system

From what I understand, silicone overmolding with proper primers you can get very good adhesion to most metals. Acquiring non-industrial quantities of the proper primers and molding compound may be a bit of a challenge...

It's probably not worth trying to bind it to metal due to cost and also the dispensable nature of nozzles in general. It could be clamped to the hotend in various ways.

Quote
Number_5
It's probably not worth trying to bind it to metal due to cost and also the dispensable nature of nozzles in general. It could be clamped to the hotend in various ways.

Yeah, I think that's what I'm leaning towards - a small silicone disc (maybe 3mm dia, <1mm thick) clamped to a nozzle tip (drilled out to maybe 0.6mm) with a metal sleeve. And then poke a tiny hole in the silicone.

I suspect the issue will be that the pressure changes during normal printing. Using that same pressure to change the size of the orifice may not be practical.

Perhaps what is needed is a tiny silicone tire as a nozzle, having its own independent pressure system to adjust the orifice size. (probably liquid filled, as it doesn't compress)

Edited 2 time(s). Last edit at 11/22/2018 01:29AM by Dust.

Quote
Dust
I suspect the issue will be that the pressure changes during normal printing. Using that same pressure to change the size of the orifice may not be practical.

Perhaps what is needed is a tiny silicone tire as a nozzle, having its own independent pressure system to adjust the orifice size. (probably liquid filled, as it doesn't compress)

I agree, what actual nozzle diameter you get is a squirrely proposition. I like the idea of a controlled orifice diameter. The hard part I see, though, is that the tip needs a pretty sharp edge to make sure the filament goes where it is directed. I think having any sort of radius where the orifice pierces the tip would defeat the purpose of having a small nozzle. I'm having a hard time envisioning a little tire that maintains a sharp edge as it grows or shrinks.