A tool for LLMs (specifically Claude on claude.ai) to design 3D printable models using OpenSCAD with a visual feedback loop. The key insight: LLMs can't do spatial reasoning blind. They need to render → see → fix → repeat.

This is the core workflow that makes LLM-driven CAD actually work. Without it, you're guessing and will get geometry wrong every time.

These tools are available in Claude's container environment:

# Install OpenSCAD (may already be installed)
apt-get update && apt-get install -y openscad xvfb

# Verify
xvfb-run -a openscad --version

1. WRITE → Create/edit a .scad file
2. RENDER → xvfb-run -a openscad -o render.png --imgsize=800,600 \
              --camera=200,200,150,0,0,40 model.scad
3. VIEW → Use the `view` tool on render.png — YOU CAN SEE THE IMAGE
4. ASSESS → What's wrong? Too flat? Wrong orientation? Missing features?
5. FIX → Edit the .scad file
6. GOTO 2

The --camera flag takes: eyeX,eyeY,eyeZ,centerX,centerY,centerZ

# Isometric (best for first look)
--camera=200,200,150,0,0,40

# Front view
--camera=0,250,40,0,0,40

# Top down  
--camera=0,1,300,0,0,30

# Bottom up (to see underside)
--camera=0,1,-300,0,0,20

# Orthographic projection (engineering drawings)
--camera=100,0,40,0,0,40 --projection=o

If the model is too big/small in frame, adjust the eye distance (first 3 numbers).

To see internal geometry (cavities, bores, channels), cut the model in half:

difference() {
    // Your full model here
    my_model();
    
    // Cut away half (adjust plane as needed)
    translate([0, -200, -10]) cube([400, 400, 200]);  // removes Y > 0
}

Then render from the cut side to see inside.

Always render at least 3 views:

• Isometric — overall shape check
• Front/Side — proportions, symmetry
• Cross-section — internal geometry verification

xvfb-run -a openscad -o iso.png --imgsize=800,600 --camera=200,200,150,0,0,40 model.scad
xvfb-run -a openscad -o front.png --imgsize=800,600 --camera=0,250,40,0,0,40 model.scad
xvfb-run -a openscad -o section.png --imgsize=800,600 --camera=200,0,40,0,0,40 section.scad

• CLI rendering: openscad -o file.png works headless with xvfb. JSCAD has no CLI renderer.
• Visual feedback: The whole point is render → view → fix. JSCAD can only output geometry data, not images.
• Simpler syntax: OpenSCAD's declarative style is easier for LLMs than JSCAD's imperative JS.
• Cross-sections: OpenSCAD's difference() with a cutting plane lets you see inside models.
• Well-documented: OpenSCAD has extensive docs and examples the LLM already knows.

// Primitives
cube([x, y, z]);                    // box
cube([x, y, z], center=true);       // centered box
cylinder(r=10, h=20);               // cylinder
cylinder(r1=10, r2=5, h=20);        // cone/taper
sphere(r=10);                       // sphere

// Transforms
translate([x, y, z]) child();
rotate([rx, ry, rz]) child();
scale([sx, sy, sz]) child();

// Booleans (THE KEY OPERATIONS)
union() { a(); b(); }               // combine
difference() { a(); b(); }          // a minus b
intersection() { a(); b(); }        // overlap only

// Hull (convex hull — great for organic shapes)
hull() { a(); b(); }

// Loops
for (i = [0:4]) translate([i*10, 0, 0]) cube(5);

// Modules (reusable parts)
module my_part(size=10) {
    difference() {
        cube(size);
        sphere(r=size*0.6);
    }
}

// Resolution
$fn = 64;  // smooth curves (put at top of file)

1. Threads on the outside: When making internal threads (female), you SUBTRACT rings slightly larger than the bore. The grooves go INTO the wall, not out.

2. Orientation confusion: Always define your Z-axis convention upfront. For 3D printing: Z = up, build plate is Z=0.

3. Forgetting to look: ALWAYS render and view before declaring something done. You WILL get geometry wrong on the first try.

4. Camera too close: Start with eye distances of 200+. If you see a wall of color, zoom out.

5. Flat chambers: If you want a cone/pyramid shape, make sure height > base radius. Otherwise it looks like a disc.

6. Overcomplicating: Start with the simplest possible shape. A manifold is just cylinders entering a hollow cone. Don't add channels, hulls, and complex merging unless actually needed.

main.ts          — HTTP server: viewer page + design API
designs/         — OpenSCAD design files  
  bottleSplitter.scad — 3-way bottle manifold
README.md        — This file (YOU ARE HERE)

GET  /                    → viewer page (Three.js + OpenSCAD WASM)
GET  /api/designs         → list all designs
GET  /api/designs/:id     → get design SCAD code  
POST /api/designs/:id     → save design { name, scad }

This approach is based on CADCodeVerify (ICLR 2025) which showed that LLMs need visual feedback loops for CAD:

• Render the model
• Vision model inspects the render
• Provides corrective feedback
• Iterate until correct

Our implementation uses OpenSCAD CLI + xvfb for rendering and Claude's view tool for visual inspection. It's the same principle, just using tools already available in the environment.

If you're picking this up:

1. Install first: apt-get install -y openscad xvfb (may already be there)
2. Test the loop: Write a cube.scad, render it, view it. Make sure you can see images.
3. Read the designs/: See what exists already
4. Iterate visually: Never commit a design you haven't rendered and viewed from multiple angles
5. Cross-section complex parts: If there's internal geometry, cut it open and look inside
6. Keep it simple: Most printable objects are just cylinders, cubes, and cones with boolean operations