29-5



For the crank pin, Z, M, = 1913 x -*'' - =* 28216 inch-lbs.
Cross-section = area of 3*14 = 7*74
28216



774'



= 3644 inch-lbs. per square inch.
(b.) Double Crank Shafts.
Also here the first point to be determined is the pressure on the
bearings ; for simple calculation the pressure on the two pistons
may be taken as equal.
Fig. 195.
4








Fig. 196.
Fig. 198.
. (12)



In figs. 195, 196,
A __ P(t + P (g + ft) + GZ _ p . p I

In figs. 197, 198,
A. = Pa-fP(a+^LJLQJLji.Q^p + G + G^ . (13)

The twisting and bending moments for the cheeks, S, crank pin,
Z^,aud bearing, A,, can be determined by i\^ same method as above



a DETAILS OF STEAU EXQIKES.
A useful furmula fi>r calculating the diameter of a crank shaft is

as follows : d — A / -^- X 1^- ^^lel■e N = numlier of revolutions

per minute, c = a constant l>ased on practice. When aaing the
somewhat vague term of " nominal " horse-power, the constant may

be taken as 500 ; d = A/ -5, - x 560. When using indicatetl

hoi-se-power, the constant may be takeu as 190 ; d = a/ -^^ x 1£K),
this will give ample strength for mild steel ehnfts.
Ucthoda of oiling Crank Tins of Sent find Slotted-ont
Cranks. — The usual method is based on that shown on pt^ 57,
flg. 185, where the crank pin is oiled tlirough the connecting rod end.
