Before we continue with the printers let's have a look at how to construct a radius on the edges of your product.

Observations

I like to study real life objects to figure out how things work. In this video I have used a clear plastic case with a big radius on the corners.

Note that the radius is actually 1/4 of a full circle.

The theory of the slow and the fast turn

When we divide a circle into 4 equal parts in perspective we can see that the curvature of each segment is very different.

When the two edges of the box form an angle that is bigger than 90° you get a 'slow turn'. When the two edges form an angle that is smaller than 90° you get a 'fast turn'.

These fast and slow turns can also be applied to the corners of any rectangular surface in perspective.

When projected to the other side of the object the two curves form a radius.

Tip: connect the two curves with thin straight lines through the start and endpoints to make the radius more visible.