DRAFT OF PLOWS 209 



control of the operator so vitally affects the resistance of the 

 plow as the one just reviewed, and success demands careful 

 observance of the principles governing the lines of draft and 

 resistance. 



According to Sanborn, the plow shows the lightest draft 

 when set to cut the widest furrow of which it is normally capa- 

 ble. This is probably accounted for by the remarkable results 

 of an experiment at^ the Utica trials which showed that 55 per 

 cent, of the draft of the plow was causeoTby the cutting of the 

 furrow slice, 35 per cent, by the friction of the soTeTjinaomy 

 10 per~cent. by the work of lifting and turning the furrow. 

 The average draft of a number of plows running in the empty 

 furrow was 168 Ibs. The whole draft was 476 Ibs., and that 

 with the moldboard removed 434 Ibs. The difference between 

 168 Ibs. and 434 Ibs. was taken to be the draft required for 

 cutting the furrow slice. Sanborn states later that 42 per cent, 

 of the draft is used by the share and landside, and another 

 writer puts the moldboard friction at only 2 per cent. These 

 figures will not hold for all conditions, but even an approximate 

 idea of the division of draft explains many frequently observed 

 facts. 



In relation to the size of furrow, the cutting edge should be 

 as small as possible. A furrow 4 x 12 niches has a line 16 inches 

 long which must be cut, and an area of cross section of 48 square 

 inches, a proportion of 1 to 3. One 6 x 14 inches has a cut 

 surface of 20 inches and an area of 84 square inches, a ratio of 

 1 to 4.2. The larger the furrow cut, therefore, the less the 

 influence of the cutting edges on each square inch of cross sec- 

 tion, which is the commonly accepted unit of comparison. 

 Sanborn found a constant decrease in draft per square inch as 

 the furrow was deepened or widened up to the normal capacity 

 of the plow. When made to cut wider, narrower, shallower, or 

 deeper than the adjustments of the plow ordinarily permitted 

 there was an increase in draft of 15 to 20 per cent., much harder 

 work for the plowman and a poorer quality of plowing. 



