Flat Belts
Make your own belt dressing.
2 lbs. gum damar
4 lbs. castor oil
Mix well, then heat carefully. When cooling, remove the scum. Apply sparingly.
The pull of the belt should be on the bottom, because then the slack part of the belt will 'sag' on top giving more gripping surface.
Diameter and speed of pulleys are found by proportions. In most cases, however, it is advisable to make sketches to prevent errors.
Let R = revolutions of driving pulley. Let r = revolutions of driven pulley.
Let D = diameter of driving pulley. Let d = diameter of driven pulley.
To find the diameter of a pulley to be driven at 150rpm off a shaft doing 50rpm with a driving pulley 18 inches in diameter:-
For speed reduction:-
To find the diameter of the driving pulley, the following is used:-
Diameters of pulleys 'D' and 'd' are found by dividing the revolutions of the shaft to be driven, by the revolutions of the driving shaft; the result will be the ratio of the pulleys.
For instance:- Driving shaft (R) revolves 80 times per minute, and the driven shaft (r) is to make 200 revolutions per minute, then 200 divided 80 = 2.5.
Therefore the driving pulley (D) must be 2.5 times larger in diameter than the driven pulley (d).
