Cracking nuts

Taking a sledgehammer to crack a nut may be a metaphorical expression – but there are some nuts, such as macadamias, requiring that amount of effort to break them

On the other hand, while African peanuts are relatively easy to shell, most people can only manage about 1kg per hour – so the effort required to hand shell enough each day to feed the average African family is still excessive. This sometimes puts African villagers off planting them as a crop, which is unfortunate, since the nuts are nutritious, and the plants they come from fix nitrogen in the soil, improving its fertility. In developed countries, most nuts are shelled in dehulling machines. These are fairly massively constructed, precision-made, power-operated pieces of equipment. Many are now made in China, but still beyond the budgets of African villagers – even when electrical power is available to run them. The Challenge Our challenge is to come up with a hand- or possibly foot-operated nut shelling machine, capable of handling sufficient quantities of peanuts to feed a large African family. It should not be unnecessarily taxing on the operator – likely to be the mother, who will have a host of other tasks to perform. The machine should be constructed from locally available materials, and simple enough in design that relatively unskilled persons can manufacture them without too much trouble. Large hammers usually smash the kernels as well as the shells. The machine needs to work fairly precisely, without having to be made too precisely. Maintenance in service is likely to be minimal, if any. It should also be capable, with only minor modification, of being able to dehull other kinds of nuts. The solution offered below solves the problem simply, at very low cost. We consider it ingenious in terms of both its design and manufacturing. For those without access to the web, the solution will be described fully in our October edition. See if you can come up with anything as good or better. Solution The solution to this month's challenge is the brainchild of Canadian sound and light engineer, Jock Brandis, and is being promoted by the Full Belly Project based in Wilmington, North Carolina. The technology of the "Universal Peanut Sheller" depends on two inverted, cast concrete flowerpot shapes. The inner rotor is rotated within the outer stator. The peanuts enter the top and full under the action of gravity as they spin at about 300 rpm across the stator. With each rotation, the shells come into contact with a rough concrete surface as they fall further down the space between the rotor and stator as it tapers, ensuring that only the kernels are able to drop through the space at the bottom without their shells. Screw adjustment of the shaft used to turn the rotor controls the size of the exit aperture, according to the sizes of the nuts going through. As well as peanuts, the machine has been used to shell wing beans, pine nuts, neem nuts, shea nuts, and pecans. It is said to be possible to use it to process 50kg per hour. Manufacture requires two glass fibre reinforced plastic moulds, some widely available metal parts, cement and sand. The cost, not including shipping of one set of moulds and enough parts to make five machines is $600.