Letter: Thicknessing Router Article in AL#101 - Surfacing Bit

by John Park

Originally published in American Lutherie #102, 2010



Tim,

Since the thicknessing router article (AL#101, p. 58) was written, a friend has tried using a 1" surfacing bit. It has blades on the bottom, much like an auger, which seems to have the trait of lifting the wood. I think it has a propeller action that creates a suction problem. In my opinion, using a cutter like that defeats the purpose. A straight bit cuts the end grain and so can disregard runout and figure.

There will always be a slight suction due to the velocity of the air over the top surface being higher than the air under the wood. This is Bernoulli’s Principle which is what gives wings lift. I use a 3/4" straight bit and I’ve yet to encounter enough lift to make a significant error at a dimension of about 2MM or .080". Using this device to give less thickness than that could cause problems because the span from the hold-down remains fixed while the stiffness drops as the cube of the thickness. In other words, making veneer would not be practical.