Printable

1. What is the object? Physical description, purpose, how it will be used
2. Dimensions — all critical measurements. If unknown, WebSearch for product specs (check printables.com, dimensions.com, manufacturer sites)
3. Fit requirements — what fits into what? Snug, loose, or press-fit?
4. Material — PLA, PETG, ABS, TPU? (suggest based on use case, see table below)
5. Printer specs — nozzle diameter (default 0.4mm), bed size, layer height (default 0.2mm)
6. Print orientation — which face on the bed? (suggest largest flat surface)
7. Supports — design to avoid if possible; ask if user accepts supports
8. Cutouts/holes — cable passages, mounting holes, ventilation?

Material Guide

Suggest PLA unless: part sees heat (→PETG/ABS), needs flexibility (→TPU), or is mechanical/outdoor (→PETG).

For materials not listed, WebSearch: "[material] 3D printing tolerance temperature settings"

Design Rules (Hard Requirements)

Every model MUST follow these. Violations cause print failures.

OpenSCAD Code Patterns

File Template

// === [Model Name] ===
// All dimensions in mm
// Material: [PLA/PETG/ABS]
// Print orientation: [description]

$fn = $preview ? 32 : 64;

// --- Tolerances ---
tolerance = 0.4;  // per side — adjust per material table

// --- [Component] dimensions ---
// group related params with comments noting source measurements

// --- Derived ---
// computed values from above params

// === Modules ===

// === Assembly ===
module assembly() {
    difference() {
        union() {
            // ALL solid geometry here
        }
        // ALL cavities/holes here (cut from full assembly)
        // Flatten base
        translate([0, 0, -500]) cube([1000, 1000, 1000], center = true);
    }
}

assembly();

Critical: Assembly-Level Cavity Cuts

NEVER pre-hollow parts before union. When you union a hollowed ring with a solid stem, the stem fills the cavity back in.

// ❌ WRONG: cavity gets filled by stem union
module ring() {
    difference() {
        cylinder(h = 10, d = 100);
        cylinder(h = 11, d = 94);  // hollow
    }
}
union() { ring(); stem(); }  // stem fills cavity!

// ✅ CORRECT: hollow at assembly level
difference() {
    union() {
        cylinder(h = 10, d = 100);  // solid ring
        stem();
    }
    cylinder(h = 11, d = 94);  // cavity cut AFTER union
}

Fillet Helpers

fillet_r = 1.0;

// Round outer convex edge of cylinder (subtract from model)
module outer_fillet(d, z, r) {
    translate([0, 0, z - r])
        rotate_extrude()
            translate([d / 2 - r, 0])
                difference() {
                    square(r + 0.01);
                    circle(r = r);
                }
}

// Round inner lip edge of cylinder (subtract from model)
module inner_fillet(d, z, r) {
    translate([0, 0, z - r])
        rotate_extrude()
            translate([d / 2, 0])
                difference() {
                    square([r + 0.01, r + 0.01]);
                    translate([r, 0]) circle(r = r);
                }
}

// Fill concave inner corner (add to model via union)
module concave_fillet(d, z, r) {
    translate([0, 0, z - r])
        rotate_extrude()
            translate([d / 2, 0])
                difference() {
                    square(r);
                    translate([r, r]) circle(r = r);
                }
}

// Rounded rectangular through-hole
module rounded_hole(w, h, d, r) {
    hull() {
        for (x = [r, w - r])
            for (z = [r, h - r])
                translate([x, 0, z])
                    rotate([-90, 0, 0])
                        cylinder(h = d, r = r);
    }
}

Radial Hole Through Curved Wall

Axis-aligned cubes create slanted cuts through curved walls. Use radial rotation:

hole_angle = asin(hole_x_offset / (outer_dia / 2));
rotate([0, 0, hole_angle])
    translate([-hole_w / 2, -(outer_dia / 2 + 1), 0])
        rounded_hole(hole_w, hole_h, wall + 4, fillet_r);

Undersized Hole Compensation

OpenSCAD inscribes polygons in circles, making holes smaller than specified:

// Compensated radius for accurate holes
comp_r = desired_r / cos(180 / $fn);

At $fn=64, the error is ~0.04% (negligible). At $fn=32, it's ~0.15%. Apply compensation only when tight tolerances matter.

Z=0 Base Cut

When tilting geometry, parts extend below z=0. Cut flush:

// ✅ CORRECT: cube top face at exactly z=0
translate([0, 0, -500]) cube([1000, 1000, 1000], center = true);

// ❌ WRONG: leaves 1mm gap (cube goes to z=-1, not z=0)
translate([0, 0, -501]) cube([1000, 1000, 1000], center = true);

Pitfalls (Learned from Real Prints)

Validation & Export

After writing the .scad file, ALWAYS validate before delivering:

# Run the validation script (must be executable)
${CLAUDE_PLUGIN_ROOT}/skills/printable/scripts/validate-model.sh model.scad

# Or manually:
openscad -o model.stl --export-format binstl model.scad 2>&1  # check for warnings
admesh model.stl  # check: parts=1, disconnected=0, degenerate=0

If admesh is not installed: brew install admesh (macOS) or apt install admesh (Linux).

Copy validated STL to ~/Downloads for user access.

Web Resources

Query these when you need more information:

Product dimensions (when user doesn't have measurements):

• WebSearch: "[product name] dimensions mm" or check dimensions.com, printables.com
• Check manufacturer spec sheets

OpenSCAD syntax (beyond the inline reference):

• https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/The_OpenSCAD_Language
• https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids
• https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Transformations
• https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem
• See openscad-reference.md in this skill directory for full offline reference

Material properties (for materials not in the table):

• https://www.simplify3d.com/resources/materials-guide/properties-table/
• https://www.matterhackers.com/3d-printer-filament-compare
• https://ultimaker.com/learn/petg-vs-pla-vs-abs-3d-printing-strength-comparison/

Design rules & tolerances:

• https://www.hydraresearch3d.com/design-rules
• https://hackaday.com/2025/08/04/how-to-design-3d-printed-parts-with-tolerance-in-mind/
• https://jlc3dp.com/help/article/3D-Printing-Design-Guideline

Community models (for reference designs):

• https://www.printables.com — Search for similar designs with known dimensions
• https://www.thingiverse.com — Community 3D models