Creating a Rounded Box in OpenSCAD

Make a box with rounded corners using the offset() technique.

Step 1: Define the rounded rectangle

Create a 2D shape with rounded corners using a two-pass offset technique.

w = 60;
l = 40;
h = 20;
rad = 3;

module rounded_rect() {
  offset(r=rad)
  offset(delta=-rad)
  square([w, l]);
}
rounded_rect();

This offset technique expands then contracts the base shape to create rounded corners.

Step 2: Extrude to 3D

Use linear_extrude() to give the shape depth.

linear_extrude(height=20)
rounded_rect();

Final code

$fn = 100;
w = 60; l = 40; h = 20;
wall_thickness = 2;
lid_thickness = 4;
lid_clearance = 0;
rad = 2;

module outer_rec() {
  linear_extrude(height = h)
  offset(r=rad) offset(delta = -1*rad) square([w, l]);
}

module inner_rec() {
  linear_extrude(height = h)
  offset(r=rad) offset(delta = -1*rad)
  square([w - (wall_thickness*2), l - (wall_thickness*2)]);
}

difference() {
  outer_rec();
  translate([wall_thickness, wall_thickness, wall_thickness])
  inner_rec();
}

Tip: The offset() method is lightweight and efficient — perfect for clean rounded edges without the complexity of minkowski().