SMALL SAWMILLS, THEIR EQUIPMENT, ETC. 23 
are also used in emergencies. Special endless belts with a diagonal 
splice are supplied by some manufacturers. 
A belt should be capable of transmitting from 5 to 25 per cent more 
power than is actually needed, the excess capacity being governed 
by the type of drive, the smaller excess for heavy main drives, and the 
greatest for machine belts. Never use belts the full width of' the 
pulley face, as a slight lack of alingment may cause part of the belt 
to run beyond the edge of the pulley and perhaps against a shifting 
linger or pulley flange. This is sure to result in loss of power and 
perhaps in a badly damaged belt. On the other hand, a belt too 
narrow necessitates high tension to transmit the required power, thus 
causing excessive journal friction and the early destruction of the 
belt. 
Generally speaking, single belts, if heavy enough to carry the load, 
should be used on small pulleys. A single belt should never be wider 
than 1J times the diameter of the smallest pulley. Where small 
diameter pulleys and the load would require an unusually wide single 
belt, it is advisable to substitute narrower pulleys and a narrow 
double belt. Thin wide belts give the best service; working verti- 
calty, a thick narrow vertical belt will not r grip the pulley well. 
Double belts of medium or heavy weight should never be used on 
pulleys less than 12 inches in diameter, or, even better, on pulleys 
less than 20 inches in diameter. 
Belts too heavy for the load weave back and forth on the pulleys. 
This is best illustrated by a belt working under intermittent loads, 
which runs straight while carrying the maximum or proper load 
but shows a tendency to weave when the load is reduced. 
The tightness with which belts are adjusted to the pulleys is of 
prime importance. If they are put on too tightly, there is a large 
unnecessary loss of power from excessive friction at the bearings, to 
say nothing of the overstrain and injury to the belt itself. If, on the 
other hand, the belt is too loose, it is likely to flop around and jump 
from the pulleys, particularly when a load is suddenly thrown on 
or off. The slacker a belt can be run up to a certain point while 
doing its work satisfactorily, the greater the economy. In installing 
belting and taking it up, it should be remembered that certain kinds 
of belting are affected by weather conditions, lengthening and 
shortening according to the amount of moisture in the air. Instances 
have been known where the babbitt was melted out of the boxes and 
even shafting pulled out of alignment as a result of belting being put 
on too tight. 
Be sure to note carefully whether your shafting is properly in 
line. More belting is ruined by improperly lined shafting and pul- 
leys than in any other way. The belts under this condition are 
