456 STEPHENSON'S PATENT 



the axle and nave ; figs. 34 and 35, being similar sections of one of the driving wheels. 

 ^4 ^4 is the axle of each wheel, the large one is 5^ inches diameter inside the 

 wheel, and the small one is enlarged to 4 inches ; the outside bearing, B, of both, 

 are of the same size. C C are the naves of the wheels, made of cast iron ; the large 

 one is 18 inches diameter and the small one 13 inches ; the length of both in 

 the centre where they are fixed to the axle is 7-g inches, and they are fixed 

 by four keys, E E, each, driven into grooves cut in the axles and inside the 

 naves. The wheels are entirely supported and held by these keys, as the naves do 

 not touch the axle; and by this means a firm and uniform bearing can be obtained, 

 and the wheels can also be fixed truly at right angles to the axle and at the proper 

 distance from each other. Hollows, E E, are cast in the naves between each of the 

 keys to diminish the metal. 



The rims of the wheels, F F, are of cast iron, four inches and a half wide and two 

 inches and a half deep ; they are cast with a groove round them on the outer side to 

 diminish the weight; bosses, G G, are cast on the inner side, where the spokes are in- 

 serted. The spokes, H H, are wrought iron tubes one quarter of an inch thick and 

 tapering from two inches and a quarter to two inches in diameter, and they are cast in 

 the nave and rim. The spokes are inclined to the plane of the wheel, so as to come 

 nearly to one face of the nave and the opposite face of the rim ; and they are inclined 

 alternately in opposite directions, as shewn in the figure, for the purpose of increasing 

 the lateral strength of the wheels, and preventing their bending and getting out of the 

 vertical position with the great strains to which they are subjected. The spokes are 

 laid in the moulds in which the wheels are cast, and the metal cast round them, the 

 ends of the spokes being first plugged up ; and the spokes are covered at the ends with 

 a composition of borax, which causes them to partially melt when the metal is poured 

 in, forming so close and firm a joint that they never get loose. The rims of the 

 wheels are cast first, and allowed to remain for about three quarters of an hour 

 before the naves are cast, because they contract much more in cooling than the 

 naves, being of a much larger diameter, tending to force the spokes nearer to the 

 centre ; and if the naves were cast at the same time, the spokes would be prevented 

 from approaching the centre, and there would consequently be a very great 

 strain upon them, and the metal in the rims would not set firm from cooling in a 

 state of tension, and would be liable to break with any blow ; but by allowing the 

 rims to set before the naves are cast, this action is prevented. 



/ / are the tires of the wheels ; they are made of wrought iron rolled into the 

 required shape, with the ends welded together ; the plain one for the driving wheels 

 is 5| inches wide, and the flanch tire for the small wheels 4^ inches wide. Sections 



