Alex Gibson alex at alexgibson.net
Sat Nov 23 18:32:26 EST 2019

```I plowed on in the same vein as the previous example, but using TWO
minkowski spheres, one to inflate, and the next to cut.

After 5 HOURS of rendering, I got the intended result:

Here's the slightly tweaked code:

mount_width = 15;

module original_shape()

{

union()

{

//plate

translate([0,0,-5])

cube([200,100,10],center=true);

//mount

hull()

{

translate([0,75/2-mount_width/2,25])

cylinder(50,mount_width/2,mount_width/2,center=true);

translate([0,-75/2+mount_width/2,25])

cylinder(50,mount_width/2,mount_width/2,center=true);

}

}

}

module shape_inflated()

{

minkowski()

{

original_shape();

}

}

difference()

{

shape_inflated();

minkowski()

{

difference()

{

cube([500,500,500],center=true);

shape_inflated();

}

}

}

Doing a minkowski with sphere operation on an already completed minkowski
sphere is super intensive to code, so i will be keen to try any other ways
to achieve the same result.!

Also, I showed the good side above;  here is the other side, with either a
render defect or a hole in the mesh.!

Alex Gibson

edumaker limited

. Project management

. Operations & Process improvement

. 3D Printing

-----Original Message-----
From: Discuss [mailto:discuss-bounces at lists.openscad.org] On Behalf Of
arnholm at arnholm.org
Sent: 23 November 2019 09:57

On 2019-11-22 16:25, Alex Gibson wrote:

> Nice!  I must check out AngelCAD.

>

> So this works well for square-edged items.  I wanted to check how well

> my example would work for  rounded shapes.  Not so well.

>

> In this case the 'mount' is supposed to have rounded ends being the

> union of two cylinders.  But the cubes I used to inflate the original

> piece overpowered the original shape's radii:

I have not tried that, but this technique is equivalent to "machine

away" a layer of material of thickness equal to fillet radius from all

sides, so if the shape is rounded in the first place, that rounding will

be reduced or disappear.

Perhaps the general solution is to first inflate the original rounded

shape using minkowski, using a sphere with the fillet radius. Then apply

the same technique as demonstrated for the square-edge items on the

result.

This could be considered a 3d equivalent to positive followed by

negative offsets in 2d.

Carsten Arnholm

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