[FarmerPotato]

I know, right? Exceptions:

1. The texture on the top slope of roof bricks is a standard mold finishing (acid etch?) that works fine with mold release.

2. Headlight grille bricks in the 70s used to have texture, along with printing. I'm not in the know but I suspect the texture could be a byproduct of the printing machine that was used then. (I've only seen 2000s era trade machines that used inkjet printing post-moulding.)

3. The 1x2 brick with vertical grooves on one face, horizontal grooves on opposite face... this has been common since the 80s! 1979's Galaxy Explorer had two of them (I think). "Corrugated Steel" or spaceship "greebling" texture.

Trying to puzzle out that mold, I imagine you need a moving insert textured with the horizontal grooves.

Some sets have had dozens or hundreds of that brick (Star Wars), without a noticeable impact on price/piece?

[voidUpdate]

1 - No problem, you can just make the texture not have any overhangs when viewed from the top

2 - I'm not sure what piece you mean :/

3 - That's a very good point that I hadn't thought of. That's piece 2877, and I'm not sure how that would be manufactured... You could potentially have one part on the "bottom" of the mould extend out with the horizontal grooves, and have the vertical grooves on the "top" half of the mould. When the mould separates, the horizontal grooves are locked into the bottom half of the mould, but the vertical ones slide out. Then, when the moulds are fully separated, the part can fall off the bottom half sideways. I hope that makes sense, I don't know how better to describe it. However, that only works if you can cleanly separate the moulds and then have the piece fall off, if the texture was on all sides then you wouldn't be able to separate the mould halves or extract the piece without a complex separating assembly

[FarmerPotato]

Yeah 1) is a very old technique. I forget whether the texture makes the part release more easily, or not. 2) This is what they look like now (90s or later) https://img.brickowl.com/files/image_cache/larger/lego-red-b... 3) I see on 2877 that the runner is on a top stud, just like other bricks. I don't know where I'd put the mold parting line, but I think it's usually in the plane of the brick. Stunning how Lego parts never have flash!

[FarmerPotato]

You think this one is tough, imagine how they make screw tops for plastic soda bottles!

I've seen a machine that makes 64 of them in one go. Inside the cap is a collapsible core, because the molded screw is all undercuts... the mold opens (horizontally), the cores collapse, and 64 caps fall into the bin. On top of that, it's two materials, over-molded!