openscad-design

name	openscad-design
description	OpenSCAD parametric 3D modeling best practices, common patterns, and printability guidelines for designing 3D-printable parts.

OpenSCAD Design Skill

When designing 3D-printable parts in OpenSCAD, follow these guidelines.

Parametric Design Principles

• Always parameterize dimensions. Define all measurements as variables at the top of the file so the user can easily adjust them.
• Use named modules for reusable components. A part should be composed of well-named modules, not a single monolithic block.
• Group related parameters with comments explaining their purpose and valid ranges.

// --- Parameters ---
wall_thickness = 2;       // mm, minimum 1.2 for FDM
inner_diameter = 20;      // mm
height = 30;              // mm
corner_radius = 2;        // mm, 0 for sharp corners
$fn = 60;                 // mesh resolution

// --- Derived ---
outer_diameter = inner_diameter + 2 * wall_thickness;

Common Primitives & Patterns

Rounded box

module rounded_box(size, radius) {
    minkowski() {
        cube([size.x - 2*radius, size.y - 2*radius, size.z/2]);
        cylinder(r=radius, h=size.z/2);
    }
}

Hollow cylinder (tube)

module tube(od, id, h) {
    difference() {
        cylinder(d=od, h=h);
        translate([0, 0, -0.01])
            cylinder(d=id, h=h+0.02);
    }
}

Screw hole with countersink

module countersunk_hole(d_hole, d_head, h_head, depth) {
    union() {
        cylinder(d=d_hole, h=depth);
        translate([0, 0, depth - h_head])
            cylinder(d1=d_hole, d2=d_head, h=h_head);
    }
}

Snap-fit clip

module snap_hook(width, length, hook_height, thickness) {
    // Cantilever beam with hook
    cube([width, length, thickness]);
    translate([0, length, 0])
        cube([width, thickness, hook_height]);
}

Linear and circular patterns

// Linear pattern
for (i = [0 : count-1])
    translate([i * spacing, 0, 0])
        child_module();

// Circular pattern
for (i = [0 : count-1])
    rotate([0, 0, i * 360/count])
        translate([radius, 0, 0])
            child_module();

Printability Guidelines

Wall Thickness

• Minimum wall thickness: 1.2mm (3 perimeters at 0.4mm nozzle)
• Recommended: 1.6–2.0mm for structural parts
• Thin vertical features (< 0.8mm) will likely fail

Overhangs & Supports

• Overhangs up to 45° print without supports on most printers
• Design chamfers or fillets at 45° to avoid supports where possible
• Use rotate([0, angle, 0]) to tilt features within the printable range

Bridging

• FDM printers can bridge gaps up to ~10mm reliably
• For longer spans, add intermediate support geometry in the design

Tolerances & Fit

• Press fit: subtract 0.1–0.2mm from the mating dimension
• Sliding fit: add 0.2–0.3mm clearance
• Loose fit: add 0.4–0.5mm clearance
• Holes print smaller than designed — oversize by 0.2mm

Elephant's Foot

• The first layer squishes slightly, expanding the base by ~0.2mm
• Add a small chamfer (0.4mm at 45°) to the bottom edge for precise base dimensions

Orientation Considerations

• Strongest axis: layers are weakest in Z (layer adhesion). Orient the part so stress is along X/Y.
• Surface quality: downward-facing surfaces against supports will be rough. Orient the best surface upward.
• Minimize supports: rotate the part so overhangs stay under 45°.

Mesh Resolution

• Use $fn for circles and spheres. Values:
  • Preview: $fn = 30 (fast)
  • Render/Export: $fn = 60–120 (smooth)
• For small features (< 5mm), lower $fn is fine: $fn = 24
• Avoid $fn > 200 — it dramatically increases render time with negligible visual improvement

Boolean Operation Tips

• When using difference(), extend the cutting tool 0.01mm beyond the surface to avoid zero-thickness faces:

  difference() {
      cube([10, 10, 10]);
      translate([-0.01, 2, 2])
          cube([10.02, 6, 6]);  // extends 0.01 past both sides
  }
  

• Order matters in difference(): the first child is the base, all subsequent children are subtracted.
• Use intersection() for complex shapes that are easier to define by overlap than subtraction.

File Organization

project/
├── main.scad          # Top-level assembly, parameters
├── parts/
│   ├── base.scad      # Base module
│   └── lid.scad       # Lid module
└── lib/
    ├── fasteners.scad # Reusable screw holes, standoffs
    └── utils.scad     # Helper modules (rounded_box, etc.)

Use include <path> for files that define geometry directly, use <path> for files that only define modules/functions.