Two Quarters?

J

Jmurman

Joined
Dec 16, 2006
Messages
53
I was reading my American Handgunner magazine this afternoon and ran across and ad from DMT sharpeners. They are selling a DVD on "How to get a magnificent edge on your knife using two quarters"...and of course the DMT sharpeners.

I have two of the DMT full size sharpeners, a coarse and a extra fine, and I really like them both.

Can anyone tell me what the "two quarters" is all about? I am assuming they are talking about blade angle, but how would two quarters figure into that?

Thanks
 
The problem is that the angles are off by more than a factor of two. A seventeen degree included angle is in the right ballpark for a rather dull razor, but this calculator is setting the bevel angle for each side. The included angle is 2x the bevel angle so the 17-degree bevels give you a 34-degree included angle. That is more what I want for a coarse axe, not a razor. It is almost as bad as a crummy factory knife edge. You know that it has to be wrong if you think about how a straight razor is sharpened. I just looked at an old straight razor and it is about .18-inch thick and .75-inch wide. The calculator indicates that I need a .129-inch (over 1/8-inch) spacer between the spine of razor and the hone when sharpening. In reality you sharpen a razor by laying it flat on the hone. The razor is designed to be honed at about 5-degrees per side while this calculator would say to hone at 17-degrees per side!

The general formula is:
spacer = width x sin (honing_angle) - .5 x blade_thickness

For a sharp knife (17-degree included angle = 8.5-degree honing_angle) and a 1-inch-wide blade that is 1/8-inch thick you get:
width = 1
honing_angle = 8.5---> sin(8.5-degrees)=.147
blade_thickness = .125--->.5 x blade_thickness = .063

spacer = 1 x .147 - .063 = .084

This is only a little thicker than a single nickel. It is the thickness of a old half-dollar if you can find one.

The calculator on the website works, but it is for honing_angle not edge angle. Unless you have a two-inch-wide blade you only need a couple pennies rather than a couple of quarters for your spacers.
 
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