The haJf-lap coupling, first introduced by Sir "William FairbairPf ■*
shown in Figs. 257 and 258. The lap-joint slopes slightly, so as *"
prevent the shafts being separated so long as the box covers the i^P-
The box is kept in position by means of a saddle-key. The portion of
the shaft within the box should he enlarged so as to make up for w
loss of strength due to the cutting away of the material to form the lap
joint If D is the diameter of the shaft, and Dj the diameter of tha
enlarged part, then Dj -^ D ^2 very nearly, or Dj = 1 '26 D.
SHAFTING AND SHAFT COUPLINGS.
The half-lap coupling is expensive when properly made, and it is
Beldom need.
Dimensions of Solid Box Couplingg,

D = diameter of shaft,

D, = diameter of shaft at lap.
I = length of lap.
T = thickness of metal in box.
L = length of box for butt coupling.
L^ = ler^th of box for lap coupling.
D.
li


3


9i


3


J»


•


*s.
a


s


D,


2^


3


3|t


^


5,".
