Word of the day: Frustum-a portion of a solid that lies between two parallel planes cutting the solid.

Our inverted lampshade-like pot skirt is a frustum of a cone, or so we discovered when we tried to construct it from sheet metal. It’s not as easy as it seems; you can make a cylinder from a rectangle or a cone from a semi-circle, but a frustrum is constructed from a “rainbow”-shaped template whose dimensions determine the height and diameters of the part’s top and bottom surfaces.

Because we didn’t know that our pot skirt was formally called a frustum, figuring out how to build it was an adventure. Matt (a former teammate) and I had a friendly competition: he tried looking for the equation on the Internet while I made a barebones paper frame of the shape we wanted and then unfolded it to get a rough outline of the template. I like to say I figured it out first, but he found a neat little frustum dimension calculator that proved very useful for trying different pot skirt heights and widths!

I mentioned in my last entry “Skirting the Issue” that most pot skirts are actually cylindrical. So why in the world did we go through all this trouble to make such a tricky shape? There is an ideal gap for efficient air flow (about ¾”) between the pot and the pot skirt. When the team was in Myanmar, we saw that the women there cooked with an astounding range of pot sizes , with the smallest one having about a 5″ diameter, to the biggest one about 16″. To make matters more complicated, women often cooked on a wok as well. Thus, our pot skirt had to be designed to create the same ideal gap for multiple pot sizes. The “inverted lampshade” shape allows smaller pots to sit lower and bigger pots to sit higher on the skirt, creating a reasonable gap for air to pass through.

However, one of the difficulties with this design is that women have to reach further inside the pot skirt to take a small pot out. Since the air between the pot and the skirt is VERY hot, this poses a significant burning hazard for women. This safety issue is one reason why we are still hard at work at improving our initial concept!

Tags: frustum, pot skirt, prototyping, safety

This entry was posted on Thursday, May 21st, 2009 at 10:00 am and is filed under Stove Design. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.