The finished foam phone

To get acquainted with prototyping with 2" blue insulating foam, I decided to build a large-scale model of a classic phone-booth telephone handset.

The process was relatively simple.

Each step is documented below.

First, I cut two pieces of 2" thick foam down to the approximate size of the handset, and then joined the pieces using transfer tape.

Joining the pieces

Next, I sketched the basic outline of a two-dimensional version of the phone, and did a rough cut on the band saw.

Cutting plan, including relief cutsFirst two dimensions of cuts

With a basic two-dimensional version of the phone in hand, I sketched out the third dimension and made the corresponding cuts on the band saw.

Planned cuts on the next planeFinished cuts in three dimensions

And finally, the ear and microphone cups were sketched and cut. I removed a wedge of foam from each disk on the belt sander to make sure they would mate to the handset at a slight angle. A drill press took care of the holes in each disk.

Preparing the ear cupsEar cups ready for attachment

I used another round of transfer tape to attach the disks to the handset. About 20 minutes of sanding and finishing work leaves the finished phone:

The final foam phone

I learned a few things about the material that will guide any future use:

  • Higher speed tools do cleaner, more consistent work — the belt sander and band saw avoid tearing / chunking the foam the way hand tools do.

  • Extra-wide transfer tape is worth the up-front expense for larger projects.

  • The foam seems to have a grain. Sanding in certain directions minimizes chunking. I haven’t figured out how to identify the grain.

  • Relief cuts make shorter work of tight curves.