An axial flow thresher was modified to maintain the seed quality in terms of broken grains. The machine got fabricated from local market and its performance was studied on paddy PR-118 to ascertain the effect of cylinder speed, louver angles and feed rate on threshing efficiency, cleaning efficiency, broken grains, grain output, rate of crop flow, non collectable loss and power requirement. The louver angles, cylinder speed and feed rate had a significant effect on grain damage during the paddy threshing. The broken grains varied from 0.11 to 2.48%. The broken grains were decreased with increase in louver angles from 10o to 15o but further increase in louver angles from 15o to 20o, the broken grain was increased. The similar trend was obtained for threshing efficiency. The rate of crop flow increased with increase in louver angle. Grain output was found to be in the range of 319 to 555 kg/h for the feed rate of 1.5 to 2.5 t/h. The power requirement decreased with increase in louver angles. Similarly non collectable loss decreased with increase in louver angles. The optimum values for broken grains, threshing efficiency, cleaning efficiency, Retention time, power requirement, grain output, rate of crop flow and non collectable loss was 0.11%, 98.6%, 97.27%, 5.09 seconds, 12.86 kW, 543.13 kg/h, 5.24 q/h and 0.01% respectively

Keywords: Axial flow, paddy, threshing, louver angles, CAD, solid modeling, IRRI