||10-1/2| 41.3 ||15-1/2| 27.4 |
|2 | 240 ||4-1/2| 101 ||7 | 64 ||11 | 39.3 ||16 | 26.5 |
|2-1/4| 212 ||4-3/4| 96 ||7-1/4| 61 ||11-1/2| 37.5 ||16-1/2| 25.6 |
|2-1/2| 189 ||5 | 91 ||7-1/2| 59 ||12 | 35.9 ||17 | 24.8 |
|2-3/4| 171 ||5-1/4| 86 ||7-3/4| 57 ||12-1/2| 34.4 ||17-1/2| 24.1 |
|3 | 156 ||5-1/2| 82 ||8 | 55 ||13 | 33.0 ||18 | 23.4 |
|3-1/4| 143 ||5-3/4| 78 ||8-1/2| 52 ||13-1/2| 31.7 ||.... | .... |
+-----+-----++-----+-----++-----+-----++------+------++------+------+

Assuming that _A_ = area of fitted surface; _a_ = total allowance in
inches; _P_ = ultimate pressure required, in tons; _F_ = pressure factor
based upon assumption that the diameter of the hub is twice the
diameter of the bore, that the shaft is of machine steel, and the hub of
cast iron, then,

_A_ x _a_ x _F_
_P_ = ---------------
2

_Example:_--What will be the approximate pressure required for forcing a
4-inch machine steel shaft having an allowance of 0.0085 inch into a
cast-iron hub 6 inches long?

_A_ = 4 x 3.1416 x 6 = 75.39 square inches;

_F_, for a diameter of 4 inches, = 115 (see table of "Pressure
Factors"). Then,

_P_ = (75.39 x 0.0085 x 115)/2 = 37 tons, approximately.

=Allowance for Given Pressure.=--By transposing the preceding formula,
the approximate allowance for a required ultimate tonnage can be
determined. Thus, _a_ = 2_P_ / _AF_. The average ultimate pressure in
tons commonly used ranges from 7 to 10 times the diameter in inches.
Assuming that the diameter of a machine steel shaft is 4 inches and an
ultimate pressure of about 30 tons is desired for forcing it into a
cast-iron hub having a length of 5-1/2 inches, what should be the
allowance?

_A_ = 4 x 3.1416 x 5-1/2 = 69 square inches,

_F_, for a diameter of 4 inches, = 115. Then,

2 x 30
_a_ = -------- = 0.0075 inch.
69 x 115

=Shrinkage Fits.=--When heat is applied to a piece of metal, such as
iron or steel, as is commonly known, a certain amount of expansion takes
place which increases as the temperature is increased, and also varies
somewhat with different kinds of metal, copper and brass expanding more
for a given increase in temperature than iron and steel. When any part
which has been expanded by the application of heat is cooled, it
contracts and resumes its original size. This expansive property of
metals has been taken advantage of by mechani