In my exploration of openSCAD, the Minkowski sum looks interesting. The example given in the Wikibook is of rolling the z-axis edges of a cube:

minkowski() { cube(12,center=true); cylinder(r=4, h=1); }

although for this task, it's faster to do the minkowski operation in 2-D and then extrude:

linear_extrude(height=20) minkowski() { square(12,center=true); circle(r=4); }

In both cases, the result is a cube of size 20 - the inner cube of size 12 + 2 * 4, the radius of the circle or cylinder

If we want to roll all edges:

minkowski() { cube(12,center=true); cylinder(r=4, h=1); rotate([90,0,0]) cylinder(r=2, h=1); rotate([0,90,0]) cylinder(r=2, h=1); }

but this takes a minute on my basic laptop to run.

More simply, we can roll all edges by summing with a sphere instead of a cylinder although this takes longer to run:

minkowski() { cube(12,center=true); sphere(r=4); }

$fn=6; minkowski() { cube(12,center=true); sphere(r=4); }

but this is not accurate. A precise approach uses a rotated cube. Here I've defined a module to parameterize the dimensions:

module chamfered_cube(s,c) { minkowski() { cube(s,center=true); rotate([45,0,0]) cube(c); rotate([0,45,0]) cube(c); rotate([0,0,45]) cube(c); } } chamfered_cube(20,4);

The main use I've seen so far for minkoski operator is to create a cookie cutter. Here the operator is used to add a constant width boundary around an arbitrary curve. One of my projects was to make a heart-shaped box, but my first attempts to remove the box inside with a scaled version of the outside yielded odd wall thicknesses. Minkowski is the way to go for irregular shapes.

module heart_shape(size) { union() { square(size,size); translate([size/2,size,0]) circle(size/2); translate([size,size/2,0]) circle(size/2); } } module heart(size,thickness,height) { linear_extrude(height=height) minkowski() { heart_shape(size); circle(thickness+0.1); //because 0 would produce an empty object } } module heart_box(size,height,thickness) { difference() { heart(size,thickness,height); translate([0,0,thickness]) heart(size,0,height); } } heart_box(20,10,3);

The Minkowski sum is used to add a thickness of 3 mm either side of the heart-shaped boundary, giving a wall thickness of 2 * 3. The heart-shape is offset by the thickness for the outside and by zero for the inside of the box, leaving a constant wall thickness of 3.

Making a box and lid, with clearance between box and lid proved a bit trickier. I found the most accurate approach was to start with a heart shape sized to the inside of the lid, requiring 4 shapes with different boundary thicknesses:

- inside lid : 0
- outside lid : thickness + clearance
- inside box : clearance
- outside box : thickness + clearance

I had this printed on a Makerbot and it looks rather good. The lid is a little sloppy and the depth of the inset is too shallow, so some adjustment is needed.