apparent that as striking surface 65 of tool 31 penetrates surface 22 the distance from node 72 to the point at which striking surface 65 contacts surface 22 as represented by line 73 39 increases as a result u03b8 39 the angle of motion of point 34 b 34 is greater than u03b8 the object of the present invention is to maintain u03b1 constant and since u03b8 decreases as the point of impact moves outwardly along the tool u03b3 the angle of a tangent to the striking surface of the tool decreases by the same amount referring to fig3 coordinates x and y are located at the theoretical base of the tool determined by the point at which striking surfaces 65 66 would meet if they were not truncated by flat surface 68 in the embodiment shown the theoretical base of the tool is located 25 inches forward of and 281 4 inches below forward node position 72 the shape of striking surface 65 and mirror image surface 66 is determined by the following table ______________________________________x y x y______________________________________0 0 8 5 5 161 2 7 32 81 2 53 41 15 32 9 6 3 1611 2 23 32 91 2 65 82 1 10 71 821 2 1 5 16 101 2 75 83 15 8 11 81 831 2 1 29 32 111 2 8 23 324 21 4 12 91 441 2 2 9 16 121 2 9 25 325 27 8 13 103 851 2 3 9 32 131 2 11 1 326 3 21 3261 2 4 1 167 4 15 3271 2 47 8______________________________________ in operation tool 31.