For my Metals 2 class in Industrial Design I made these coins using cold rolled steel, extruded brass, and extruded acrylic. We were asked to design an object that had two different materials interacting with each other.
I started my design process by reflecting on what we learned earlier that year. I chose press fitting as my method of interaction between materials, typically used exclusively with round stock material. This is because press fitting uses friction to keep things in place, with the difference in circumference of the hole to the peg being .001 micrometers. I decided that the challenge I wanted to face was making a square hole.
I took the opportunity to consider the limitations of my equipment. I was using round cutting heads on Bridgeport milling machines, and in exercises prior I remembered that in order to make a square edge the cutting head always moved farther beyond the limit of the desired square.
With this in mind, my design took the shape of a #.
I figured that as long as the four sides of the square were supported, I could play with the corners and even the coordinates of the square.
I used 2in. diameter extruded cold rolled steel for the bulk of my coins, and 1in extruded brass and acrylic for the accent squares. After carving the channels with the proper coordinates, I used a metal bandsaw to rough cut the coin, releasing the steel square in the center, and press-fit the brass and acrylic squares.
To get to the final thickness, I faced each coin on the lathe, and finished them with spray sealant.