> One part that confused me is how I needed to use let() to define startColumn and startRow inside the loop. I don’t understand this…

That's because you wrote a for-loop without braces, so it can only contain a single statement, and that single statement is your let().

Here is an equivalent way to write that section of code (and I did test it):

    for (r = [ 1 : numRows ]) {
        startColumn = ((c * thicknessWall) + ((c - 1) * batteryType));
        startRow = ((r * thicknessWall) + ((r - 1) * batteryType));
        translate([startColumn, startRow, thicknessWall])
            cube([batteryType, batteryType, heightCompartment + 1]);
    }

Side note, related to declaring variables but not an issue that you encountered: OpenSCAD does not allow setting the value of a variable more than once. So this code is illegal:

    x = 1;
    echo(x);
    x = 2;
    echo(x);

Second note is that whenever you introduce a construct such as {union(), difference(), if(), for()}, variables declared within the braces are scoped, so they don't exist between iterations or after the scope ends.

    if (true) { y = -1; }
    echo(y);  // Illegal

However, just introducing braces without a construct does not restrict the variable to the scope:

    { z = 5; }
    echo(z);  // Legal

That let() {} expression seems pretty similar to the LISP let()() form: https://lisp-lang.org/learn/variables

I find myself using OpenSCAD regularly to 3D print little things for the house. (Most recently: hooks to attach Christmas lights to our roof deck's glass walls)

And when something gets too trick, ChatGPT is amazing at writing in it. Often it nails the whole design in the first try, like https://bsky.app/profile/bradfitz.com/post/3maelwomyw22n to mask off certain Raspberry Pi pins to make reassembly of projects easier later.

Tip (a lot of people don't know this): you can set the resolution by setting the $fn variable. This can be useful when you want to export smooth objects.

  $fn = $preview ? 32 : 64;

Oh I had no idea that OpenSCAD was a programmatic toolkit. I recently bought a 3D printer and I don't model so much as describe to Claude Code how to write a Python script that will generate the required STL that I then rescale or whatever in Bambu Studio. LLMs are great at code-oriented stuff so I've stayed away from traditional modeling tools because I assumed you'd have to point and click and so on and I don't really want to learn the ins and outs of their interface. I just need the right mesh made.

The chatbots kept recommending I try using OpenSCAD but I resisted without even giving it a look. The results I had with just the Python script are quite adequate for the tasks I had. You can just ask the LLM to add a fillet to a vertical pin on a plane or to chamfer some edge and it is pretty good at doing it.

https://wiki.roshangeorge.dev/w/Blog/2025-12-01/Grounding_Yo... if you want to roughly see the workflow.

I'm going to try using OpenSCAD for things in the future. Does anyone else use exclusively an LLM with OpenSCAD (I used Claude Code and Codex) and if you do what did you do to make it more effective? The Python script wouldn't always generate printable meshes so I had to give it a check script to operate on.

I really wish OpenSCAD had objects, so you could use something like box1.width rather than having to declare variables for such things.

I tried using Build123d, a Python library that lets you use all of the features of Python. And it's supposed to allow specifically things like box1.width, but it's always 0. Lots of other issues/bugs too, and severely lacking in ddocumentation.Maybe it'll get there some day.

A long time ago I read that CadQuery has a fundamentally more powerful geometry kernel than OpenSCAD, so I dropped any attempt to try OpenSCAD.

Years later, I never actually got the hang of CadQuery, and I'm wondering if it was a mistake to write off OpenSCAD.

I am pretty new to CAD, so I don't actually know when I would run into OpenSCAD's limitations.

Neat-ish.

I don't really see why that code is better, more logical, more readable or more robust than the equivalent quite trivial parametrics in more or less any GUI CAD program, and I think the geek discourse is really harmed by people who don't understand the value of the things that OpenSCAD can't ever offer.

worth also looking at cadquery, build123d and similar

https://github.com/gumyr/build123d

OpenSCAD has become my go to with my 3-D printer for dumb little things. And the best part is LLMs are getting decent / pretty good with it!

My favorite thing I’ve printed is a little downsize coupler for the cool shirt system I built for my spec miata. It’s realllly silly & small thing, but it saved me!