Wheel centers arranged in this manner would have the following
number of spokes:
TABLE XII
Spoke Data - General
| Diameter of Centers |
Number of Spokes |
Diameter of Centers |
Number of Spokes |
| 38 |
10 |
72 |
18 |
| 44 |
11 |
74 |
19 |
| 50 |
13 |
76 |
19 |
| 56 |
14 |
78 |
19 |
| 62 |
16 |
80 |
20 |
| 66 |
17 |
|
|
Among pattern makers and foundry men, there is an impression
that an uneven number of spokes should be used so as to avoid getting
two spokes directly opposite each other in a straight line. The
following table has been made up on this basis:
TABLE XIII
Spoke Data - Foundry Rule
| Diameter of Center |
Number of Spokes |
Pitch |
| 44 |
11 |
12.5 |
| 48 |
11 |
13.6 |
| 50 |
13 |
12.6 |
| 54 |
13 |
13.0 |
| 56 |
13 |
13.5 |
| 60 |
15 |
12.6 |
| 62 |
15 |
13.0 |
| 66 |
15 |
13.8 |
| 68 |
17 |
12.5 |
| 70 |
17 |
12.9 |
| 72 |
17 |
13.3 |
| 74 |
17 |
13.6 |
| 76 |
19 |
12.6 |
| 78 |
19 |
12.9 |
The spokes at the crank hub should be located so that the hub
will lie between two of the spokes and thus avoid a short spoke
directly in line with the crank pin hub.
Cast steel driving wheel centers should be preferably cast with the
rims and uncut shrunk slots omitted whenever steel foundries will
guarantee satisfactory castings. For wheel centers 60 inches in
diameter and when the total weight of the engine will permit, the rims
should preferably be cast solid without cores so as to obtain the
maximum section and have full bearing surface for the tires.
It is difficult to get sufficient counterbalance in centers smaller
than 60 inches in diameter so that it will be found very desirable to
core out the rims to obtain the maximum lightness on the side next
to the crank pin and in some cases on the counterbalance side in order
to fill in with lead where necessary.
The American Master Mechanics' Association recommends
a rim section as shown in Fig. 73 for wheel centers without retaining
rings. The tire is secured from having the center forced through
it by a lip on the outside 3/8 inch in width and about 1/8 inch in height,
the tire being left rough at this point. The height of the lip, therefore,
depends upon the amount of finishing left on the interior of the tire.
Accurate measurements of tires after they have been in service for
some time, especially when less than 2-1/2 inches in thickness, show that
a rolling out or stretching of the tire occurs, and for reasonably heavy
centers, these figures will account more for loose tires than any
permanent set in the driving wheel center.
Counterbalance. A study of the construction of the driving
wheel brings up the question of counterbalance since it is made a part
of the wheel center. The counterbalance, Fig. 72, is the weight or
mass of metal placed in the driving wheel opposite the crank to
balance the revolving and reciprocating weights.
The revolving weights to be balanced are the crank pin complete,
the back end of the main rod or connecting rod, and each end of
each side rod complete. The sum of the weights so found which are
attached to each crank pin is the revolving weight for that pin.
The reciprocating weights to be balanced consist of the weight of the
piston complete with packing rings, piston rod, crosshead complete,
and the front end of the main rod complete. The weight of the rod
should be obtained by weighing in a horizontal position after having
been placed on centers.
The revolving weights can be counterbalanced by weights attached
to the wheel to which they belong, while the reciprocating
weights can only be balanced in one direction by adding weights
to the driving wheels as all weights added after the revolving parts are balanced overbalance the wheel
vertically exactly to the same extent that they tend to balance the
reciprocating parts horizontally. This overbalance exerts a sudden
pressure or hammer blow upon the rail directly proportional to its
weight and to the square of its velocity. At high speeds, this
pressure, which is added to the weight of the driver on the rail,
may become great enough to injure the track and bridges.
The best form of counterbalance is that of a crescent shape
which has its center of gravity the farthest distance possible from the
center of the axle. The counterbalance should be placed opposite
the crank pin as close to the rods as proper clearance will allow.
The clearance should be not less than 3/4 inch. No deficiency of
weight in any wheel should be transferred to another. All counter
balance blocks should be cast solid. When it is impossible to obtain
a correct balance for solid blocks, they may be cored out and filled
with lead, which will increase their weight. In all such cases the
cavities must be as smooth as possible. Holes should be drilled
through the inside face of the wheel to facilitate the removal of the
core sand.
In counterbalancing a locomotive, the following fundamental
principles should be kept in mind:
- The weight of the reciprocating parts, which is left unbalanced,
should be as great as possible, consistent with a good riding and smooth working engine.
- The unbalanced weight of the reciprocating parts of all engines for
similar service should be. proportional to the total weight of the engine in
working order.
- The total pressure of the wheel upon the rail at maximum speed
when the counterbalance is down, should not exceed an amount dependent
upon the construction of bridges, weight of rail, etc.
- When the counterbalance is on the upper part of the wheel, the
centrifugal force should never be sufficient to lift the wheel from the rail.
The following rules have been generally accepted for the counterbalancing of locomotive drive
wheels:
- Divide the total weight of the engine by 400, subtract the quotient
from the weight of the reciprocating parts on one side including the front
end of the main rod.
- Distribute the remainder equally among all driving wheels on one
side, adding to it the sum of the weights of the revolving parts for each wheel
on that side. The sum for each wheel if placed at a distance from the driving
wheel center, equal to the length of the crank, or at a proportionately less
weight if at a greater distance, will be the counterbalance weight required.
The method of adjusting the counterbalance in the shop is as
follows: After the wheels have been mounted on the axle and the
crank pins put in place, the wheels are placed upon trestles as
illustrated in Fig. 74. These trestles are provided with perfectly level
straight edges upon which the journals rest. A weight pan is
suspended from the crank pin as shown. In this pan is placed weight
enough to just balance the wheels in such a position that a horizontal
line will pass through the center of the axle and crank pin and
counterbalance on one wheel, and a vertical line will pass through the axle
and crank pin centers of the other side, the crank being above. The
amount of weight thus applied, including the pan and the wire by
which it is suspended, gives the equivalent counterbalance at crank
radius available for balancing the parts. This weight found must
not exceed that found to be necessary by the formula. Should the
counterbalance be left with extra thickness, the extra weight can be
turned off with little trouble after the trial described has been
completed. This process should be repeated for the opposite side.
The weight of the reciprocating parts should be kept as low as
possible, consistent with good design. Locomotives with rods
disconnected and removed should not be handled in trains running at
high rates of speed because of the danger arising from damage to the
track and bridges, due to the hammer blow.
