Daily Archives: February 10, 2006

Diamond Bench Stone, pt. 2

My biggest problem now is with getting the angle right for the bevel. I’m using the basic generic honing guide, the single-roller one you can get just about anywhere. I can just jam the blade in the guide and get any old angle, but the problem is trying to get an angle that I want and, even more important, being able to repeat that angle.

But I think what I remember from high school trig will help out here. We all remember soh-cah-toa, don’t we? The sine of an angle in a right triangle is the length of the opposite side divided by the length of the hypotenuse. From our diagram above, we get sin θ = b / c. And here b is the height that the honing guide holds the blade and c is the length of the blade that sticks out of the guide. And a of course is the sharpening stone. So

sin θ = b / c

Or, for our purposes

c = b / sin θ

Let’s imagine that the height b is 5/8″ and we want a bevel angle of 25˚. So, 5/8 divided by the sine of 25 is 1.47887598947 inches. Let’s call that 1 1/2″ okay? For a 30˚ bevel angle, c would be exactly 1.2500″.

I just need to set up a block or something and scribe some measurements on it to be able to repeat the angles. And measure the height of the honing guide exactly, rather than using 5/8″ as we did in our example.

And there are two different places the guide holds blades, sort of an upper area for plane irons and a lower for chisels. Have to note different c lengths for the two different settings as well.

But better that than the Veritas Mk.II for $48.50, huh? Although the Mk.II does have a better way of making sure the blade is set square to the stone …