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DH Worm gear ratio = 60:1No rapid indexing plate availableDivisions of workpiece = 21Ratio/Divisions = 60/21 = 2.85714285714286Turns required = 20/7 = 2 & 6/72 full turns of crankand 36 holes on 42 hole plateor 42 holes on 49 hole plateor 66 holes on 77 hole plateor 78 holes on 91 hole plate
1 full turns of crankand 30 holes on 42 hole plateor 35 holes on 49 hole plateor 55 holes on 77 hole plateor 65 holes on 91 hole plate