colin

@vogon

the evil "Website Boy"

he/him
gameboat.org/

member of @staff, lapsed linguist and drummer, electronics hobbyist

zip's bf

no supervisor but ludd means the threads any good

mastodon

mastodon.social/@vogon

twitter (inactive)

twitter.com/vogon

bluesky

if bluesky has a million haters I am one of them, if bluesky has one hater that's me, if bluesky has no haters then I am no more on the earth (more details: https://cohost.org/vogon/post/1845751-bonus-pure-speculati)

irl

seattle, WA

colin @vogon8/12/2023, 7:09 PM

@hillexed

@hillexed8/12/2023, 7:02 PM

Which 3D model takes less material to print?

turns out it's...

click to reveal

the first one?? 3D printers fill the inside of objects with really lightweight infill, and it's so light compared to 100% filled walls that it takes both less time and ends up being less weight than the fancy truss on the right. Which sucks because I spent such a long time designing that fancy truss only to be outdone by a brick.

#astronomy

colin @vogon8/12/2023, 7:09 PM

this is one of the process properties of 3D printing I have the hardest time coming to grips with, solid objects were not meant to have internal structure

You must log in to comment.

in reply to @hillexed's post:

@Janet8/12/2023, 7:09 PM

The trussed version is probably structurally a bit weaker too but if you were to use it to make a mold, the resulting part might be stronger than the infilled one

Maybe 😁 idk rly

Trashcanned Man @BeasMeeply8/12/2023, 7:10 PM

Any chance the truss would be more rigid? Or potential issues with bonding between the infill and exterior material? I don't have any objective predictions here, just a general distrust of simple solutions.

colin @vogon8/12/2023, 7:44 PM

not sure about rigidity; there definitely can be issues with bonding between the infill and perimeters, but some 3D printing folks have done experiments and discovered that most of the strain gets borne by the surface of the part anyway and the infill mostly serves as a scaffold on which to extrude it. my mostly uneducated guess is that, lightly loaded, you're better with whatever's lightest, but if a reasonably light hollow part would buckle under the load, you should build a truss.

Trashcanned Man @BeasMeeply8/12/2023, 9:19 PM

Interesting! I haven't kept up with any 3d printing stuff since maybe 2009, so I'm absolutely in the dark on it. The specific concern with the pivot point on a telescope mount (especially a top-heavy one as I think @hillexed has) is that the weakest/most flexile component determines how steady the view is ultimately going to be. As a result the conventional wisdom is to overbuild things to an absurd degree. This kind of work in 3d printing has the potential to remove some truly egregious barriers to entry.

Lichenthrope @SkeletonsDotCom8/12/2023, 8:22 PM

It’s definitely less rigid. Infilled with no trussing is gonna be essentially a box, the only way to make that more rigid is to make the walls thicker or increase infill density. That said, it’s probably not much less rigid, or too much weaker.

Trashcanned Man @BeasMeeply8/12/2023, 9:06 PM

It's cool to see the new experimentation 3d printing is bringing to telescope making. For a long time there was a huge amount of orthodoxy, from what was the one correct plywood to use to the right production run of the correct counter formica that makes the only acceptably smooth bearing surface.

@hillexed8/12/2023, 9:39 PM

If I understand stiffness correctly, which I might not, it depends on the second moment of inertia. I think that means the edges of the box carry the most stress and the center carries the least, proportional to (distance from center of gravity)^2 I think since the truss places a second full inner wall with a lot of mass far away from the center of mass, vs just one for the box, it might be stiffer.

Lichenthrope @SkeletonsDotCom8/12/2023, 11:15 PM

I think your understanding is correct, and since the trussed design requires more material then it might actually be more stiff overall. But for a similar amount of material a box is better because it means a higher ratio of the total material is farther from the center of gravity. A lot of that truss is much closer to the center of that section there and creates an open section, so it’s more susceptible to torsion and probably to bending in one direction but more resistant to bending in another if that makes sense.

Either way thanks for sharing and keep experimenting!

Chamomile🐑@chamomile8/12/2023, 8:16 PM

This feels a lot like the phenomenon where compilers are better at optimizing low-level code than most programmers.

@hillexed8/12/2023, 9:45 PM

Huh, yeah.

in reply to @vogon's post:

nys @nys8/12/2023, 7:22 PM

something i’ve rarely hard to think about before because all the engineering i did previously wasn’t on layered materials is that certain infills help link those layers together better and how choosing infill based on usage is this extra layer of complexity.

colin @vogon8/12/2023, 7:26 PM

yep! CNC Kitchen on youtube has done a bunch of experiments on compressive and shear strength of various infill patterns and I mostly just use the non-intersecting patterns he found to be strongest for their weight (line, gyroid) but I imagine if you were using printed parts for a really demanding application you would want to print test articles with different infills and load them under real-world conditions

Pim de Groot @mifune8/12/2023, 8:05 PM

As soon as you put a bit of bending on a structure, a box girder becomes more efficient than a piece of solid material. The outer bit of material does most of the work, so you can just leave the middle empty. Or more accurately use the same amount of material, but make it bigger and stiffer.

The best example of this in one axis is the H beam. The top and bottom flange take up the bending stresses, and the middle web is only there to transfer shear and keep the flanges distanced.

forivall/emk on cohost! Today!@forivall8/12/2023, 11:30 PM

Would the truss one at least be faster to print?, since, in my experience, infill can sometimes be rather slow to print.

Pinned Tags