402 APPLIED MECHANICS 
as it cuts out the acting surface. The developments of the edges of the 
correct cam surface will not be exactly the same’as the shaded lines on 
the developments to the right and left of Fig. 649, but when the roller 
Fig. 649. 
is small compared with the diameter of the cam, the differences may 
generally be neglected. 
The cam may be made to drive the follower positively in both direc- 
tions by having two acting surfaces on opposite sides of the pin or roller. 
These acting surfaces will then form the opposite sides of a groove on the 
cylinder. . 
338. Form of Roller for Cylindrical Cam.—It is obvious that a 
cylindrical roller will not work correctly on a cylindrical cam, that is, it 
LL 
a MLE 
MOLIF/ 7 
Fig. 650. 
will not roll without slipping, since the path upon which the roller has to 
travel is longer for the outer than for the inner end of the roller. It is 
also obvious that on that part of the cam which is in contact with the 
roller when the follower is at rest a conical roller will work correctly if the 
