We’re off and running. I built the first trial cardboard mold for the Biscotto di Sorrento Cupola cast in place pizza oven kit a few weeks ago, and I’m going to analyze what I did right, and wrong, and put a plan in place to significantly improve Beta 2. If you are reading about our upcoming pizza oven kit for the first time, the Cupola is a complete kit for building a high-end pizza oven, including the mold and castable refractory material to cast a durable, well-shaped, high quality oven dome—along with the insulation, floor, chimney and door.

The key is that sentence is the word “mold”. A perfectly shaped mold is the element that makes the concept of a cast in place oven kit work. Mixing and hand casting the oven dome is not time consuming or difficult, so once we have the mold just right (and some excellent instructions), everyone is going to be able to do it. But what is a “perfect” mold?

First, the mold needs to have the right proportions for (1) dome height to oven floor diameter, (2) the oven opening height to dome height and (3) the oven opening height to opening width. The mold needs to have the right combination rigid and flexible cardboard that can hold up to the weight of the castable material without bowing or losing its shape, and it need to be easily assembled by the user. Finally, the mold needs to be knocked down for easy to shipment, and the tape that holds the joints together needs to be strong enough to stand up to the weight and moisture of the castable material.

Using these standards as a guideline, as you can see, the Beta 1 mold leave a lot to be desired. Basically, it gets just about everything wrong. As you can see, I made it using old cardboard shipping boxes that had been used two or three times. We were recently living in Europe, splitting our time between Brussels and Beaune, France, and in order to move back to our house in Alexandria, VA, we need to ship quite a few household items from Belgium to France, and then on to the US. So these boxes were pretty well-used.

Equally important, although I had already produced the drawings for the mold in a 2D CAD program, seeing how the various design trade-offs looked in the physical world was very instructive. The mold is for a 32″ oven. Right off the bat, I think you can see that the dome is a little (not very much) too low, and the flat disk in the center of the oven is 8″, which is too small. Next, although it is difficult to see on the photo, the original design had the dome shaped with straight lines and three inward angles. I think the design would have worked well with a steel mold, but putting straight bends in cardboard (without the aid of a stamp) is very difficult. So going forward, the mold will have a curved, rather than angle-linear shape.

Of course the inexpensive yellow masking tape and clear plastic box tape aren’t up to the task of holding concrete. The inner supports were cut as single, 32″ pieces, with notches for them to slide into each other, but the notches were difficult to cut and the 32″ pieces are unwieldy and difficult to ship. I’ve come up with a method the assembling the mold with diameter length supports — 16″ for a 32″ oven, 18″ for a 36″ oven, etc.

I’ve also come up with a method for locking the cross supports to the outer dome shell pieces. And a strategy for tape. More to come on that.

And finally, I am working on a method the form the doorstop inside the vent landing area, so there is a positive “stop” for the oven door to control, and cut off the air into the oven. More to come on that.

The second beta for the mold will try to take all of these factors into consideration and I will be drawing, cutting and building it shortly, and I will keep you up to date on my progress.

One last note. The first molds will be drawn and cut by hand. We will “dry” assemble them to make sure they fit nicely, and then disassemble them. Over time, we will start using the 2D CAD drawings for the oven molds to cut the mold pieces with a CNC laser cutter. But that’s for later. Right now, it’s time to get the design right, and for me to cast my own oven at my own house. And to take lots of photos.