This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The ordinary form of jig-saw blade has a tendency to pull the fiber of the wood in one direction, thereby producing a jagged cut. To overcome this I made several blades with teeth as shown in the sketch. After the down-stroke is completed, the teeth A will cut on the upstroke, the teeth B cutting on the downstroke, etc. The upstroke teeth should be a trifle longer than the others and from 4 to 6 in number. - Contributed by Phillip Caf-lish, Buffalo, N. Y.
Ill: Teeth Cut in Opposite Direction