Hand Tools Archive

Subject:
Response To:

John Aniano in Central NJ
Hi Patrick,

I thought I'd give some actual numbers to the blade camber radiuses you/we are talking about here. I was curious...

Used the formula for a circle's sagitta "x" which is the perpendicular height above a chord of a length "y". See the Wikipedia link below for the drawing. It's a bit down in the Wikipedia entry under "Properties" of a circle.

r= (y^2/8x) + x/2

Let's assume a 2" wide plane blade that when radiused, will just barely cut at the edges. Patrick, if I understood you correctly, you suggested that it was difficult to push your #6 jack plane with the blade and chip breaker projecting 0.005" (5 mils) from the sole of the plane. Plugging in the values of 0.005" for x and 2.000" for y one gets a blade camber radius of 100" or about 8 feet. Pretty large!

Of course, you can make a smaller radius and more blade would be projecting out at the center, but, it would be harder to push the plane. Conversely, you could make the radius smaller, but not have the blade cut at its edges.

Food for continued thought!

John