Vermont Rapid Prototyping

Providing rapid prototyping services to inventors and businesses.

Casting the Enigma Lock

I was recently asked to produce 3D printed and then cast reproductions of the lock mechanisms for Enigma cipher machines. This describes my first cut at the casting.

My experience has been that two part molds do not release well from the casts, so this time I went crazy (in OpenSCAD) and produced an 8 part mold: 4 parts for the top, 4 for the bottom. The good news is that all of the mold pieces came off of the casting relatively easily. The bad news is that the registration between the pieces needs to be improved.

Here are the mold pieces just after printing:

This is what they looked like after I assembled the top and bottom halves, using rubber bands:

I used olive oil as a mold release:

This is the mold assembled and ready for the pour. Notice that B1 needs to be pushed slightly to the right to perfect the circular pour hole:

After the pour. I should have scraped off the excess. I had to melt it off later. I used a pot metal that melts at about 160 F; the mold was made of PLA.

The top parts of the mold came off easily. The bottom parts needed some teasing. The parts of the mold that attempted to create details in the lock mechanism were lost during the casting, so the mold cannot be reused.

The detail in the top was not sufficient. The counterbore for the lock is visible, but the key slot vanished entirely.

From the side

From the bottom. The cylinder you see here is what is left of the pour sprue after I melted most of it off in the pot.