You've never printed anything with a horizontal hole?

All the time? Low overhang speeds + fan with overhang. Not tricky.

So what? Your average colored PLA has additives in it anyway.

Not remotely the same. Black is carbon black. Basically soot. Tiny amounts. White is titanium dioxide (like in sunscreen - just a mineral). Blues and greens, generally like 1% or so copper phthalocyanines (very stable, sort of like humus, *very* slowly give off copper (an essential micronutrient) as they break down over hundreds of years). Name a colour that you think is bad as "a double digit percentage of the entire volume of the plastic turning into PU / acrylic microplastics". When you have that much persistent additive, you don't want the plastic breaking down - if not recycled, then you want it incinerated.

It reduces it, it doesn't eliminate it. Try actually printing some PLA+.

Yes, I've totally never printed PLA+ before *eyeroll*.

Bambu PETG Basic vs. Bambu PLA Tough:

Max overhang angle: 70C vs. 55C (PETG wins)
Max bridging length: 30mm vs. 30mm (Tie)
Melting point: 225C vs. 151C (PETG wins)
Glass transition temperature: 68C vs. 61C (PETG wins)
Heat deflection temperature 1.8MPa: 65C vs. 58C (PETG wins)
Heat deflection temperature 0.4MPa: 69C vs. 61C (PETG wins)
Young's Modulus (XY): 1460MPa vs. 1860MPa (depends on whether you want high or low, as per the application; the Tough PLA is somewhat stiffer than PETG, though not as much as regular PLA)
Young's Modulus (Z): 1120MPa vs. 1920 MPa (same story)
Tensile strength (XY): 48MPa vs. 34.9 MPa (PETG wins solidly)
Tensile strength (Z): 39MPa vs. 20.9 MPa (PETG wins even more because PLA has *worse* layer adhesion)
(Skip bending modulus and bending strength, as they're derived parameters)
Impact strength (XY): 52.7 kJ/m2 vs. 80.6 kJ/m2 (Finally, something the PLA wins on!)
Impact strength (Z): 13.6 kJ/m2 vs. 25.9 kJ/m2 (Same)
Flammability: Flammable and self-extinguishing vs. just flammable (PETG wins)
Cost: Depends on the store, but Bambu's base price is cheaper (and I buy filament wholesale, and there's a pretty stark difference in price, with PETG at the factory door in China being under $4/kg, and even plain PLA being over 5$/kg)

So I have no idea why so many people are stuck on PLA.

I can understand arguments against ABS, ASA, PC, PA, etc. They're more difficult to print, need enclosed chambers, etc. But that doesn't apply to PETG; it's super-easy to print (IMHO, easier than PLA). And basically any modern printer can handle it. And it's cheaper. So I simply do not understand the people still sticking with PLA so much (beyond a desire to be more environmentally conscious, or wanting a very specific product that doesn't have a PETG equivalent).

I've never experienced any sort of "sagging" with PETG, and honestly don't even know what you mean by that (and I generally print very hot). Do you mean printing overhangs without support? That's not great with anything. Do you mean elephant foot? Never experienced it. I make primarily functional parts, not decor, so dimensional accuracy is key; zero problems. And concerning sagging, let me tell you, PLA *really* sags if it sits in the hot sun long enough...

To get PLA to be "tough" (impact resistant) on the order of PETG you have to load it up with PU microplastics, which makes it worse for the environment than PETG so you lose that advantage. And it gets rid of its stiffness, which is the main thing PLA had mechanically on PETG. You basically make PLA be "not as crap" by making it... have increasingly low fractions of PLA, and higher fractions of "other stuff".

The criticism that many people still use PLA even when there's far better options available is an argument not exactly responded to with "X community overwhelmingly uses it". Yes, and for them too there are far better options available. Unless you like your guns melting in a hot car, being brittle (or being loaded with PU), not entirely water stable, etc etc.

And if we're doing the "X community overwhelmingly uses" argument, let me point to where things are made for critical function, not for fun: the war in Ukraine. Both Ukraine and Russia extensively use 3d printed parts. And almost none of them are PLA - it's overwhelmingly PETG.

It's just a hobby (and content for his channel). Everyone has their own :) Right now I'm working on a CO2 capture system to take atmospheric CO2 and pump it into my greenhouse.

I imagine a standard thickness is probably something like 9.5mm.

It's not all resin printing, he only used resin printing for one part in the video. Most was FDM printing. Though I did find it strange that he was using PLA. If it's parts facing repeated impact, you think he'd at least go with PETG, if not something like ABS/ASA or a nylon. I really don't get why so many people are so averse to non-PLA polymers. I guess PLA is more "eco-friendly"**, and yeah, there's a ton of PLA options out there, but that's mainly just because people are buying so much PLA.

** I'm actually thinking about switching some of my prototyping back to PLA, even though it costs more than PETG, because I can break down my PLA waste in sodium hydroxide at home. But I almost never make production parts in PLA unless that's the only practical option (for example, a given type of material only being available in PLA). Who wants parts that break if you look at them wrong, or melt in a hot car?

By "quite a large scale" you mean 1.3m long. He certainly could have made it longer than that. Honestly, I mainly think he just wanted an excuse to do more 3d printing and electronics work ;)

As per the principle in this article, that would make it worse if applied to the Reynolds regime in question. This is not about "general roughness", but specifically shaped roughness. In particular, a very sparse roughness on an otherwise smooth surface.

Sanding a hull is dealing with entirely different things. Sanding in general first off gets rid of microprotrusions and broader undulations. There is no question that this helps. The question to whether to polish to a matte or smooth surface is less obvious. Matte probably is better in general, as it helps make the surface more hydrophilic (there is also argued to be some potential to be making something like "riblets", although in practice you're unlikely to get the geometry right (true riblets are extremely thin walled).

This comment section is jam packed full of people mentioning the same misconceived and inapplicable thing, over and over. A thing that was actually discussed in the article, which they did not read.

How deep are the grooves?

A phrase to be heard either uttered on Slashdot in 2026, or at Woodstock ;)

But to be clear, the answer (assuming you're talking about sharkskin / riblets): a few dozen microns tall and a few dozen microns apart, with the individual riblets being very narrow, just a couple microns.

Hi, someone who regularly does CFD simulations in OpenFOAM here. It is a fundamental principle. I hope that helps.

This has nothing at all to do with how dimples help golf balls (just the opposite, actually)

This actually effectively "is" the paint. The only questions are about how durable it will be in flight conditions (two types are discussed, protrusions and dimples). Basically, paint with bumps vs. paint with nicks in it.

The dimples on golf balls are actually to create turbulent flow. TL/DR, a sphere isn't a very aerodynamic shape; its rear taper is too sharp, so flow detaches and there's a big low pressure wake in the back. High pressure in the front and low pressure in the rear = pressure differential, and a large area times the pressure differential = large drag force.

While it's best to not have flow separation, or at least delay it as long as possible, if you're going to have flow separation, you commonly want to generate vortices at the point of flow separation. That's why cars commonly abruptly truncate (kammback) where they'd become too steep in the rear rather than continuing to curve, and often have various vortex generating surfaces (lips, radial protrusions, etc) at the termination; it causes air to "pull down" and help fill in the wake. This is what the dimples on golf balls do.

Now, most of the dimples on a golf ball at any time are actually doing harm, or at least not helping. You really only want the dimples right around the point of flow separation. Unfortunately, golf balls don't have a specific flight orientation, so it's all or nothing - and "all" happens to be the better choice.

But as mentioned, this is entirely different than what is being talked about here, which is about the laminar-turbulent flow transition.

I think the only reading comprehension difficulty here is on your side. The impacts of "roughness" as a general term is a fundamental aspect of aerodynamic engineering. There has been evidence steadily emerging over time that this isn't exactly correct, that the distribution of roughness matters greatly, and the right distribution can even surpass a smooth surface. The confirmation in this paper helps close the chapter on this.

And honestly, their two approaches doesn't sound that difficult to manufacture at all. Certainly much easier than riblets. And the side effect of the first one - surface glass beads - would actually be beneficial for RAM. One of the principles for radar absorption is that you want a steady transition of the impedence (and by relation, dielectric constant) from the surface (which you want to be as much like air as possible) to the deeper layers. The outermost layer of RAM is commonly something like PTFE full of hollow glass beads. Under that you may have pure PTFE, and under a polymer with like 5% chopped carbon fibre fill, and so on. Well, here it turns out that having tiny glass beads on the surface can improve your drag coefficient as well.