parametric-design

Parametric Design Workflow

A structured approach to creating parametric 3D models with OpenSCAD and the model viewer.

Design Process

1. Understand the Requirements

Before writing any code, clarify:

• Overall dimensions (or constraints)
• Mounting/interface requirements (screw holes, snap fits, mating surfaces)
• Manufacturing method (3D printing, CNC, laser cut)
• Material and minimum wall thickness
• Tolerances for mating parts

2. Set Up the File

// [Part Name] - [brief description]
// Units: mm

// === Parameters ===
width = 50;
depth = 30;
height = 20;
wall = 2;
corner_r = 2;

// === Derived ===
inner_w = width - 2 * wall;
inner_d = depth - 2 * wall;
inner_h = height - wall;

// === Quality ===
$fn = 32;

// === Assembly ===
main_body();

3. Build Incrementally

1. Start with the outer shell / bounding volume
2. Open the file: openscad-viewer:open { "file": "part.scad" }
3. Verify dimensions with view from front and top
4. Add internal features (cavities, channels, ribs)
5. Verify with isometric and section views
6. Add mounting features (holes, bosses, snap fits)
7. Verify from all relevant angles

4. Edit-View-Verify Cycle

After each significant change:

1. Save the .scad file (viewer auto-recompiles)
2. Check bounding box in open result for dimension sanity
3. View from the angle most relevant to the change:
   • Added a hole? View from the axis the hole runs along
   • Changed width? View from front (azimuth=0, elevation=0)
   • Added features on top? View from above (elevation=90)

Common Design Tasks

Enclosure / Box

module enclosure(size, wall, lip_h) {
    difference() {
        cube(size, center = true);
        translate([0, 0, wall])
            cube([size.x - 2*wall, size.y - 2*wall, size.z], center = true);
    }
}

module lid(size, wall, lip_h) {
    // Outer lid
    cube([size.x, size.y, wall], center = true);
    // Inner lip
    translate([0, 0, -lip_h/2])
        difference() {
            cube([size.x - 2*wall + 0.2, size.y - 2*wall + 0.2, lip_h], center = true);
            cube([size.x - 4*wall, size.y - 4*wall, lip_h + 0.1], center = true);
        }
}

L-Bracket

module l_bracket(w, h, d, t, hole_d) {
    difference() {
        union() {
            cube([w, t, h]);           // vertical
            cube([w, d, t]);           // horizontal
        }
        // mounting holes
        for (x = [w*0.25, w*0.75]) {
            translate([x, d/2, -1])
                cylinder(h = t+2, d = hole_d);
            translate([x, -1, h/2])
                rotate([-90, 0, 0])
                    cylinder(h = t+2, d = hole_d);
        }
    }
}

Threaded Insert Boss

module insert_boss(outer_d, inner_d, height) {
    difference() {
        cylinder(h = height, d = outer_d);
        cylinder(h = height + 0.1, d = inner_d);
    }
}

3D Printing Considerations

Constraint	Guideline
Min wall thickness	1.2mm (2-3 perimeters at 0.4mm nozzle)
Hole tolerances	Add 0.2-0.4mm to nominal diameter for FDM
Overhangs	Keep under 45 degrees or add supports
Bridge length	Under 10mm unsupported
Layer orientation	Strongest perpendicular to layer lines
Mating clearance	0.3-0.5mm gap for FDM
Min feature size	0.8mm for FDM

Multi-Part Assemblies

When designing parts that fit together:

1. Define shared dimensions in a config.scad file
2. include <config.scad> in each part file
3. Use openscad-viewer:open to switch between parts during design
4. Test mating dimensions from appropriate angles

Tips

• Start with $fn = 16 for fast iteration, increase to 64+ for final
• Use # prefix to highlight a shape in debug: #cylinder(h=5, r=2);
• Use % prefix for transparent preview: %cube(20);
• Use ! prefix to show only one shape: !cylinder(h=5, r=2);
• Use echo() to print computed dimensions to the console for debugging
• Add 0.1mm to difference() cutters to avoid coincident faces