Sometimes parts are assembled in a cylindrical or slightly tapered form, and fitted under pressure. The method is called a forced fitting. An allowance of .001 or .002 is made for each inch in diameter.
To illustrate: What pressure would be required for forcing a 9 in. diameter crank pin into a cast steel center? The pressure required is expressed by the following formula, where P is pressure and D diameter of pin.
P = 15 D + 15 , :.P = 15 X9 + 15 = 150 tons