The Sunbeam Toaster – Automatic Beyond Belief!

The quality of a toaster can vary greatly. On one hand, you get your student’s average plastic 2-slot, with a sticky slider and just enough space for small slices. One the other, you get something like the Dualit Vario 6-slot toaster – the Rolls Royce Phantom of toasters, clearly intended for drug lords and Russian oligarchs. A good toaster makes better tasting toast, no doubt about it. However, even the splashiest of toasters around today are nothing in comparison to the Sunbeam Radiant Control toaster, and I’m not just talking about the aesthetics.

The Sunbeam toaster is so fascinating it has its own fanbase and a dedicated website.

Originally released in 1949, this toaster entered a market without microchips where manual operation was the norm. You might have noticed the lack of controls on this toaster, this is the interesting part. This toaster is fully automatic, all you have to do is place the bread in the slot, and perhaps adjust the doneness slider. From here the bread will immediately sink into the toaster and, before long, it will slowly reappear as toast. I think this is great design because the mechanism operates by making use of fundamental material properties instead of electronics. In this respect it shares the same level of elegance as the rice cooker. Let me explain.

The ‘radiant shade control’ is the only input on the Sunbeam

It all starts with the heating. When the bread is placed in the toaster, it lands on a lever which activates the heating elements. The heating elements are turned off when the toast reaches the correct temperature. The temperature of the bread is measured by a bimetallic thermometer. This method is better than using a timer because Sunbeam discovered that toast temperature corresponds directly with doneness. This means the toaster will finish at the right time, every time.

Even the design of the thermometer is elegant.

The simple layout of a bimetallic thermometer.

Two different metal strips are attached to each other as shown, so that when heated, they expand at different rates causing the strip to bend. This bending motion is used to complete a circuit. In this toaster the bimetallic thermometer is surrounded on five sides by metal plates, ensuring it measures the temperature of the toast and not the nearby heating elements.

Inside the toaster. Central heating wire shown left, thermometer shown right.

You’ll notice that the central heating element is a single metal nichrome wire wrapped around a frame many times. Believe it or not, this is what powers the movement of the toast.

How? Well, this wire is wrapped so tightly that the frame is being squeezed and elastically deformed. However, as the wire is heated, it expands just a little bit, enough to relax its grip on the frame. The frame returns to an unstrained state. Through a system of levers and linkages, the frame’s movement is transferred to the toast carriage.

A system of levers carries the motion from the bottom to the toast carriage.

Now, the thermal expansion of the wire is on the scale of about 0.1mm, so it must be multiplied using leverage. The two parallel levers in the image above form a third-class lever, with a scaling factor of about 175. This is enough to move the bread all the way down into the toaster. When the toast reaches the right temperature and the heating elements are turned off, the wire cools and slowly contracts, reversing the movement and causing the toast to dramatically rise out of the toaster.

The Sunbeam toaster operates with such a smooth and graceful motion, and with such an elegant design, it makes you wonder why no other toasters are like this. Sure, the reason is probably cost. The absurdly low cost of microelectronics makes it more economical for a manufacturer to throw an entire computer into a toaster than to use simple physical principles, just to reduce assembly costs. I won’t say which approach is better, but I know which toaster I’d pick.