THRESHER DESIGN ADOPTED
It was decided to produce a 4-pedaller / 2-feeder thresher without concave, and with plain wooden beaters. The design includes a grain milling device although the unit produced did not have that feature.
For the thresher unit itself, 6 plain wooden beaters, each 1000 mm long x 75 mm wide x 25 mm thick spin at about 36 radians /second (344 rev/minute) at a radius of 320 mm, giving a beater velocity of 11.5 metre/second. Heads of sorghum or millet are fed by hand into the gap of approximately 10 mm between the beaters and the wooden stator board, which is adjustable after loosening the 2 clamping nuts. The heads, now with no grain, may be pulled back by hand from the threshing interface, or may be released from the feeder's grasp to pass through the machine with the threshed grain and chaff. The complete drum unit is covered in 0.45 mm thick galvanised steel sheet, which is pop rivetted or fastened by self-tapping screws to the machine frame. This cover stops grain flying all over the place and is also a safety device in the event of a beater breaking. There is only a small gap visible to the feeders. The output from the thresher is collected in a sheet metal collecting tray, on a tarpaulin, on a heavy duty polythene sheet, on sacks, or on a concrete floor at the drum exit. Separation and winnowing are NOT performed by the machine. The threshing technique requires, for the feeders' safety and convenience, that around 100mm of stalk be retained with the heads of grain during the harvesting operation.
The beaters are bolted to the 2 sets of 6 spokes, welded to 2 spoke hubs, which in turn are welded to the 25mm mild steel shaft. 2 alternative designs of spoke hubs are shown in the drawings for this report, depending on the sophistication of facilities available (e.g. indexing vice and pillar drill). The less sophisticated design requires slightly more skill during production, assembly and assembly welding, but both are OK. The shaft runs in 2 20mm bore double-metal-sealed ball bearings, which are located in locally-manufactured mild steel bearing housings, bolted to the thresher frame, which is welded up from lengths of mild steel rectangular hollow section. These sections provide lightness, strength, and ease of welding.
Drive comes to the drum from a bicycle chain powering an 18 tooth sprocket welded to a hub, which is located on the thresher shaft by a keyway and nut. The keyway can be produced by a chisel by a skilled operator and does not need a milling machine or lathe with milling attachment.
The threshing drum is statically balanced on assembly by sawing or planing overweight beaters. Spacing washers are used if necessary to ensure that all beaters produce the same gap (about 10mm ) with the stator board.