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Why
Good quality concrete asks for the right mix of small and larger stones. To sift the right grade out of gravel as found in a riverbed takes at least three sieves with up-going mesh size. Such sieves should be sturdy to stand up against rough handling at a building site. The size of the sieve should accomodate the job at hand. A small batch can be sifted by hand as illustrated. For larger quantities larger frames are needed, for a different method of sifting.
How
The frame of the sieve is made of round wood, split lenghtwise, as shown in the sketch. A narrow metal strip is nailed to each menber of this frame. From this strip hooks are bent up set apart with the size of the desired mesh. The mesh can be woven by bending steel wire around these hooks,. These hooks are made by short incisions cut cross wise in a long sheet metal strip. Every second lip is bent up and over, leaving just enoung space for the wire.
The mesh is woven from steel wire as can be cut out of a car tire. Mesh can be woven with a size up from 5 mm. up to 25 mm. Smaller than a mesh size of 5 mm is difficult with hard wire coming from a car tire. Mesh with a size over 25 mm is not stable anymore. During use wires may move sideways, making some holes larger, other smaller.
To sift larger quantities by hand works best with a long narrow sieve, width 40 cm, length 150 cm. Place this sieve in a sloping position. Throw with a shovel batches gravel on the top part of the sieve. Stones to big roll down, stones of the right size fall through and collect under the sieve.
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