Wandering Minstrel's description is a good one.

Any carpenters saw with a blade length of more than 16 inches works perfectly.

It s important to bend the blade into an "S" shape with the curve nearest your hand holding the blade in a downward curve, and the curve nearest your torso going upwards.

Draw the bow ( I use an inexpensive fiddle bow) against the blade at the point where the upward curve begins.

Raise the pitch by making the S curve more pronounced. Lower the pitch by relaxing the cuve.

Good luck