explain the construction of locomotive wheels?

_A._--The wheels of a locomotive are always made of malleable iron. The
driving wheels are made larger to increase the speed; the bearing wheels
also are easier on the road when large. In the goods engines the driving
wheels are smaller than in the passenger engines, and are generally coupled
together. Wheels are made with much variety in their constructive details:
sometimes they are made with cast iron naves, with the spokes and rim of
wrought iron; but in the best modern wheels the nave is formed of the ends
of the spokes welded together at the centre. When cast iron naves are
adopted, the spokes are forged out of flat bars with T-formed heads, and
are arranged radially in the founder's mould, the cast iron, when fluid,
being poured among them. The ends of the T heads are then welded together
to constitute the periphery of the wheel or inner tire; and little
wedge-form pieces are inserted where there is any deficiency of iron. In
some cases the arms are hollow, though of wrought iron; the tire of wrought
iron, and the nave of cast iron; and the spokes are turned where they are
fitted into the nave, and are secured in their sockets by means of cutters.
Hawthorn makes his wheels with cast iron naves and wrought iron rims and
arms; but instead of welding the arms together, he makes palms on their
outer end, which are attached by rivets to the rim. These rivets, however,
unless very carefully formed, are apt to work loose; and it would probably
be found an improvement if the palms were to be slightly indented into the
rim, in cases in which the palms do not meet each other at the ends. When
the rim is turned it is ready for the tire, which is now made of steel.

528. _Q._--How do you find the length of bar necessary for forming a tire?

_A._--To find the proper length of bar requisite for the formation of a
hoop of any given diameter, add the thickness of the bar to the required
diameter, and the corresponding circumference in the table of
circumferences of circles is the length of the bar. If the iron be bent
edgewise the breadth of the bar must be added to the diameter, for it is
the thickness of the bar measured radially that is to be taken into
consideration. In the tires of railway wheels, which have a flange on one
edge, it is necessary to add not only the thickness of the tire, but also
two thirds of the depth of the flange; generally, however, the tire bars
are sent