the square of the diameter of the cylinder in
inches, multiplied by the pressure on the piston in lbs. per square inch;
extract the square root of the sum, which multiply by the diameter of the
cylinder squared in inches, and by the pressure on the piston in lbs. per
square inch; divide the product by 9,000, and extract the cube root of the
quotient, which will be the proper thickness of the web of the crank when
of malleable iron, supposing the web to be continued to the centre of the
shaft. The thickness of the web at the crank pin centre, supposing it to be
continued thither, would be 0.022 times the square root of the pressure on
the piston in lbs. per square inch, multiplied by the diameter of the
cylinder. The breadth of the web of the crank at the shaft centre should be
twice the thickness, and at the pin centre 1-1/2 times the thickness of the
web; the length of the large eye of the crank would be equal to the
diameter of the shaft, and of the small eye 0.0375 times the square root of
the pressure on the piston in lbs. per square inch, multiplied by the
diameter of the cylinder.

363. _Q._--Will you apply the same method of computation to find the
dimensions of a malleable iron paddle shaft?

_A._--The method of computation will be as follows:--to find the dimensions
of a malleable iron paddle shaft, so that the strain shall not exceed
5/6ths of the elastic force, or 5/6ths of the force iron is capable of
withstanding without permanent derangement of structure, which in tensile
strains is taken at 17,800 lbs. per square inch: multiply the pressure in
lbs. per square inch on the piston by the square of the diameter of the
cylinder in inches, and the length of the crank in inches, and extract the
cube root of the product, which, multiplied by 0.08264, will be the
diameter of the paddle shaft journal in inches when of malleable iron,
whatever the pressure of the steam may be. The length of the paddle shaft
journal should be 1-1/4 times the diameter; and the diameter of the part
where the crank is put on is often made equal to the diameter over the
collars of the journal or bearing.

364. _Q._--How do you find the diameter of the crank pin?

_A._--The diameter of the crank pin in inches may be found by multiplying
0.02836 times the square root of the pressure on the piston in lbs. per
square inch, by the diameter of the cylinder in inches. The length of the
pin is usually about 9/8th times its diameter, and the s