The post-harvest unit operations of onion umbels are being carried out manually. To mechanize this process, the present study was carried out to develop an onion umbels thresher. The developed machine works on the principle of abrasive and impact actions from rasp bars. Thresher performance was evaluated at different numbers of rasp bars (2, 3, 4, and 8 numbers), feed rates (25 ± 1, 30 ± 1, and 35 ± 1 kg/h), concave clearance (6.5 and 7.5 mm), and peripheral speeds (2.5 and 3.3 m/ s). At 35 ± 1 kg/h feed rate, 2 numbers of rasp bars, 7.5 mm concave clearance, and 2.5 m/s peripheral speed recorded higher threshing efficiency (97.82%) and lower seed damage (2.08%). The parameters such as the number of rasp bars on the threshing cylinder, peripheral speeds, concave clearances, and feed rates recorded significant effect (p < 0.01) on threshing efficiency and seed damage.

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