[Aurornis]

Interlocking layers is an interesting idea, but I don't see how this is supposed to work.

You can't use the nozzle to inject that much filament into a large cavity because it will cool and solidify right out of the nozzle. Anyone who has ever cleaned blobs of filament off of a nozzle after a print failure can tell you what happens when you try to pump hot filament into empty space. Filament cools below the melt temperature quickly, especially when it comes into contact with your print.

At least the README admits that it doesn't work:

> What’s NOT yet working: the physical print. On my Ender, same-material plastic injected into freshly-printed cells melts the cell walls before they can seal. The math says this should work; the materials science is the open question.

I like seeing experimentation, but this is a lot of software work dedicated to something that couldn't possibly work. I'm curious about "the math says this should work" combined with the large number of em-dashes and other LLM tells. Was this experiment largely driven by an LLM?

There is some interesting work on the topic of staggered interlocking layers: https://github.com/OrcaSlicer/OrcaSlicer/pull/8181

Reading any of the research on that should make it obvious that you can't "inject" molten plastic into larger cavities, though.

[slabity]

So I'm pretty skeptical about this as well (see my other comment on this), but the particular failure mode you're discussing is not what's happening in reality.

> Anyone who has ever cleaned blobs of filament off of a nozzle after a print failure can tell you what happens when you try to pump hot filament into empty space. Filament cools below the melt temperature quickly, especially when it comes into contact with your print.

That's completely irrelevant because this isn't printing into empty space at all. This is injecting molten plastic into confined channels, with no active cooling, made from material that doesn't conduct heat well. You're saying that the plastic will cool too quickly, but I believe the opposite will be true.

The problem that the author is describing is that the plastic is actually far too hot when injected and causes wall collapse. This is because the author isn't taking into account that FDM walls don't handle the required pressure near/above glass-transition points.

The failure mode you're describing is the complete opposite. If you were correct, it would result in cold plugs or extruder jams. It wouldn't result in wall collapse or layer delamination.

[Aurornis]

> That's completely irrelevant because this isn't printing into empty space at all. This is injecting molten plastic into confined channels, with no active cooling, made from material that doesn't conduct heat well. You're saying that the plastic will cool too quickly, but I believe the opposite will be true.

The filament will cool on contact with the part. Think about it: How are you expecting this filament to stay as hot as the inside of your nozzle while it’s flowing through the part and touching all of those walls? How are you expecting the walls to not melt, but the melted filament to flow through them?

Even filament extruded into free space cools enough to become a solid string barely inches out of the extruder. It will cool even faster if it’s touching something.

The only way this works is by heating the entire part up to a temperature where the filament stays hot enough to flow. So you’d need to heat the chamber and the part to 210C to get PLA to flow through it.

[mgunlogson]

The injection probably happens faster than you think. With a high flow hot-end and 5mm deep channels its reasonable for the injection to complete in less than a second.

> How are you expecting this filament to stay as hot as the inside of your nozzle while it’s flowing through the part and touching all of those walls? How are you expecting the walls to not melt, but the melted filament to flow through them?

Specially formulated injection materials with viscosity near water at injection temps. Dual nozzle setups where PLA is injected near its breakdown temperature into a heat resistant shell like CF-Nylon or Ultem. I need people with more time and hardware to test this. This was a side project for me, out of a dozen I'm working on. And I already spent a bunch of time on it.

For a years there's been talk about doing some kind of 3D injection on the GCODE level, like Z-pinning https://github.com/OrcaSlicer/OrcaSlicer/discussions/4815 . But it was hard to experiment because slicers don't support it. Now there's a codebase with dozens of different knobs to play with.

I added support for dual nozzle printers and using a different material for the injection stage. I just don't have the hardware to test it

[mgunlogson]

> The problem that the author is describing is that the plastic is actually far too hot when injected and causes wall collapse. This is because the author isn't taking into account that FDM walls don't handle the required pressure near/above glass-transition points.

Yes exactly. And it may be a solved problem.

I need someone with a dual nozzle printer to try injecting something like PLA in a CF-Nylon part. I anticipated this and added support for dual nozzle and multi-material with a different material selectible for the injected channels. But be warned, it hasn't been tested it at all.

[mgunlogson]

The filament is injected into tiny triangular U shaped channels, about twice as wide as the filament diameter. The depth of the channels is configurable and you can go as shallow as ~4mm. If you inject at a high rate that's not nearly enough time for the filament to cool off.

I actually had the opposite problem in testing. Plastic has bad thermal conductivity and the large volume of plastic in the channel was melting the top of the cell. That's why I asked for testers with dual nozzle printers. So they could try injecting a low melting point material into the channel while printing the rest of the part with something like Polycarbonate or CF-Nylon.

Some of the docs were written by LLM because writing docs is boring. Did you look at the code or try the binaries?

> Reading any of the research on that should make it obvious that you can't "inject" molten plastic into larger cavities, though.

There is quite a bit of research on injection molding. The pressure at the tip of a regular 3DP nozzle is around 200psi. That's actually high enough to inject a reasonably large cavity.

[smrq]

Everything about that readme quote screams LLM. All it's missing is the user responding, "that doesn't make any sense, this won't work at all", and Claude responding back, "you're absolutely right".

[mgunlogson]

The post was from a week ago. Must have been refreshed by the algo (or admins) for more visibility. Originally never got any comments.

Have you looked at the code or tried the binaries? I can assure you it very much exists as described.

Maybe I should have spent more time on the docs. I had LLM write some of the settings pages and other boring stuff.

[Toutouxc]

It doesn’t have to be a large cavity in order to be useful. Imagine being able to reliably fill a hole that’s 5mm deep. Not amazing, but that could mean 25 layers. That’s 24 layers more than what we can fuse together now.

[mgunlogson]

It's more than that.

I added a SAT solver to refine the tube endpoints so that nearby tubes don't start or end on the same layers. Even the default greedy solver (CP-SAT is SLOW) does a pretty good job at "staggering" the tube ends.

The part is "knitted" together in 3D at different Z layers.

Try the binaries. They've only been tested in Linux but they build fine for all platforms.

Slice something with MAGMA infill turned on and flip off the visibility of everything but injection lines. You'll see how the U shaped tubes knit the part together

[Aurornis]

> Imagine being able to reliably fill a hole that’s 5mm deep

You can’t inject filament into a hole without it cooling and solidifying at the top. That’s the problem with this whole idea.

[mgunlogson]

I did some basic calculations on isotropic heat loss in a circular tube. I don't have the knowledge to model it in detail but I don't think this is correct.

You can set tube height to something tiny like 5mm. It takes a fraction of a second to fill that.

As someone who's printed a lot, on fast printers you have to set a minimum layer time because it takes up to 20 seconds for the layer below to solidify, cool to below the glass transition. Plastic is a bad conductor so heat loss through the walls probably isn't as bad as you'd think

[Toutouxc]

I own a 3D pen and I use it to repair and tweak prints. Sometimes I use it to fill small cavities with material. The surrounding area usually doesn’t enjoy the heat, but PLA definitely can be injected to a degree. Maybe not to fill thin channels in the infill, but to fill a few strategically placed and shaped voids, yes.

[stirfish]

There's a YouTube video out there of someone doing this with a long (airbrush?) nozzle that is inserted into those empty spaces.

[stirfish]

I found the video: https://www.youtube.com/watch?v=H7nrJRBAMOA

[warumdarum]

Secondary epoxxy nuzzle?

[xnyan]

It's always a balance of tradeoffs and benefit. That might work, but there are already alternatives. If possible, change the design so that the anticipated load is acting on the x and y axis of the print. If that's not possible, another common tactic is to do something like partial print > insert metal rod in printed channel along y axis > resume print.

[mgunlogson]

Resin would be very interesting. The tube design seals them everywhere below the top layer. And the two ends of the tube tops are always at the same Z.

You could technically inject anything liquid enough into the tubes. Grout, resin, glue, silicone.