printable

name	printable
description	Use when the user wants to create, design, or build a 3D model for 3D printing using OpenSCAD. Triggers on mentions of 3D printing, OpenSCAD, STL export, printable parts, or physical object design.

Printable 3D Model with OpenSCAD

Overview

Guide the user from idea to validated, print-ready STL. Workflow: Interview → Design → Code → Validate → Export.

All models are parametric OpenSCAD scripts. All dimensions in mm. Every model must pass validate-model.sh before delivery.

Workflow

digraph workflow {
  "User request" -> "Interview";
  "Interview" -> "Research dimensions (web)";
  "Research dimensions (web)" -> "Design & code .scad";
  "Design & code .scad" -> "Run validate-model.sh";
  "Run validate-model.sh" -> "Pass?" [label=""];
  "Pass?" -> "Export STL to ~/Downloads" [label="yes"];
  "Pass?" -> "Fix issues" [label="no"];
  "Fix issues" -> "Run validate-model.sh";
}

Interview Checklist

Ask these BEFORE writing any code. Use AskUserQuestion for structured input.

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

Material	Best for	Snug tol.	Loose tol.	Press-fit	Nozzle °C	Bed °C	Shrinkage	Heat limit
PLA	Prototypes, displays, low-stress	0.3-0.4mm	0.5mm	0.1mm	190-220	50-60	Low	60°C
PETG	Functional parts, outdoor	0.3mm	0.5mm	0.15mm	220-250	70-80	Low-Med	80°C
ABS	Mechanical, heat-resistant	0.4mm	0.6mm	0.2mm	230-250	90-110	Med-High	105°C
TPU	Flexible, impact-absorbing	0.5mm	0.7mm	N/A	210-230	60	Low	80°C

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.

Rule	Value	Why
Min wall thickness	1.2mm	3 perimeters × 0.4mm nozzle
Max overhang	45° from vertical	Beyond this needs supports
Max bridge span	10mm	Longer spans sag
Min hole diameter	2mm	Smaller holes close up
Diameter jump transition	45° cone if jump > 10mm	Prevents floating layers in slicer
Flat base surface	Required	Bed adhesion
Bottom edge fillets	1-2mm radius	Bed adhesion + stress reduction
All exposed edge fillets	1mm radius	Comfort + print quality
Vertical dims	Multiples of 0.2mm (layer height)	Dimensional accuracy
Min standalone feature	2mm width	Thin walls break
Boolean overlaps	≥0.5mm	Prevents coincident surface artifacts

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)

Mistake	Symptom	Fix
Pre-hollowed parts in union	Cavity filled by other solid	Cut cavities at assembly level
Coincident surfaces in union	Non-manifold edges, slicer warnings	Overlap shapes by ≥0.5mm
Separate gusset hull + stem	4+ faces per edge at tangent line	Build taper into the stem itself
Axis-aligned cut on curved wall	Slanted hole, connector won't fit	Radial cut with rotate([0,0,asin(...)])
Variable used before defined	WARNING: unknown variable	OpenSCAD top-level evaluates in order — define dependencies first
ASCII STL export	Slicer parsing issues	Always --export-format binstl
Stem-to-cup diameter jump	Slicer "floating regions"	Add 45° transition cone
Cable channel groove on stem	Weakened wall, visible artifact	Route cables externally instead
Tolerance too tight (0.2mm PLA)	Parts need force to fit	Use 0.3-0.4mm for PLA snug fit
Ring height < component thickness	Component sticks out, holes misaligned	Measure actual component, add ledge + clearance

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