Fig. 2673.
Shafts at any angle one to another may have motion communicated from one to the other by a similar belt connection, providing that a line at a right angle to the axis of one shaft forms also a right angle with the axis of the other. Thus in [Fig. 2673] the axis of shaft a may be set at any required angle to the plane of rotation of pulley b, provided that the axial line of a be made to lie at a right angle to the imaginary line l, which is at a right angle to the axis of the shaft of b, and that the side of the driving pulley which delivers the belt (as c, [Fig. 2671]) is in line with the centre line of the driven pulley, as denoted by the dotted line c.
Fig. 2674.
But when this provision cannot be carried out, pulleys to guide the direction of motion of the belt must be employed; thus in [Fig. 2674] are an elevation and plan[39] of an arrangement of these guide or mule pulleys; a b is the intersection of the middle planes e e and f f of the pulleys p and p′ to be connected by belt. Select any two points, a and b, on this line and draw tangents a c, b d to the principal pulleys. Then c a c and d b d are suitable directions for the belt. The guide pulleys must be placed with their middle planes coinciding with the planes c a c, d b d, and the belt will then run in either direction.
[39] From Unwin’s “Elements of Machine Design.”