164 



WINTER SHOEING. 



may be compeDsated by the use of thoroughly good material. 

 The improved foothold is of course a great advantage. 



In inserting and removing screws a key is employed, one of 

 the simplest and most effective forms being that shown in fig. 

 133, which fits all forms of screws ; the head is hardened. 



4. Cogs. 



Shoes destined to receive cogs differ in no important 

 respect from ordinary shoes. To prevent the cogs being 

 lost they should be conical in form and exhibit a taper 

 of about one in ten, while the holes for their reception must 

 correspond exactly in size with tlie thickness of the centre of 

 the shank. 



(a) Bound cogs were invented in 1869 by Judson. The 

 holes to receive coq;S can be made in the heated or unheated 

 shoe. In the first case the hole is formed with a round punch 

 rather smaller than the shank of the cog and finished, after 

 fitting the shoe, by means of a conical slightly oiled steel drift 



tanerinii; from either end 

 about one in ten. The 

 holes can also be bored and 

 countersunk in the cold 

 shoe. For this purpose a 

 drill (the best form is the 

 American twist drill) is 

 necessary, the diameter of 

 which exactly corresponds 

 to the thickness of the 

 upper end of the cog (figs. 

 134 and 135, c). After the 

 shoe is fitted to the foot the 

 holes are widened by means of the counter-sink shown in 

 fig. 136, which is introduced from the ground surface. As the 

 shank of the counter-sink corresponds in. thickness to that of 

 the cog, the latter should then fit firmly. Any little rough- 

 ness of the margin of the hole is removed with a file and the 

 border once more smoothed ofi' by introducing the counter-sink. 

 The cogs are made of rolled cast steel of round section, and 

 may be the same diameter as the hole or about J>- inch thicker. 



Fig. 134. Fig. 135. Fig. 136. 



Fig. 134. -Sharp cog. 



Fig. 135. — Blunt cog. a, head ; b, shank. 



Fig. 1.36. — Counter-sink fur enlarging holes iu shoe. 



