32 



COLLINGE AXLE 



CH. Ill 



so as to fit with accuracy.* This box is closed at 

 its outer end, and there are neither nuts nor linch- 

 pin. Behind the collar of the axle there is a loose 

 circular plate, called the moon plate, which has been 

 put on before the axle is welded together in the 

 middle. Around the edge of this plate there are 

 three holes ; three bolts run entirely through the 

 hub from the front and pass through the holes in the 

 moon plate, terminating in threaded ends, on which 

 there are nuts. As will be seen in Fig. 13, these 

 bolts hold the wheel, by drawing the moon plate 

 toward the back of the hub, the collar of the axle 

 being between them, so that the wheel cannot come 

 off unless all three bolts break, and even if the axle 

 breaks, the wheel will not be released unless the 

 fracture takes place behind the collar. For this 

 reason the mail axle is the safest axle in use. 



The Collinge axle (Fig. 14), so named from its in- 

 ventor, was intro- 

 duced in 1792.-J- 

 Its arm is also 

 cylindrical and 

 fits accurately to 

 its box. The arm 

 extends through the box and has on its end two 

 nuts having threads running different ways, so that 



* A journal which is an absolute fit will not run so easily as one 

 that has a little play both in its diameter and endwise. — Thurston, 

 Frictio)i and Lost Work in Machinery, p. 44. 



I It is interesting to note that this axle, first made at a date when 



