If you use a jig of some type to flat grind, it helps to know the angle that you need to set up at to get the bevel that you want.
Here is a formula given to me by Dwight Huges. It will allow you to figure in any thickness of steel, width of bevel, edge thickness. to get the angle in degrees per side.
A = arctan((S - E)/(2*G))
Where:
A = angle of flat grind per side
S = stock thickness
E = edge thickness
G = grind depth desired (maybe I should call this grind width
instead -- it's how wide the grind will be when done)
Note that A is the angle *per side* that you are looking for
(naturally enough); but S is the *total* stock thickness, and
E is the *total* final edge thickness desired after the grind.
arctan is the same as an "inverse tangent" or sometimes you'll
see it as written as atan
Let's say you have a blade that is 1/4" thick, and you want a grind
1 1/2" wide on a 2" wide blade (note the formula doesn't care about
how wide the blade is total -- only the actual desired grind width), and a final edge thickness of 0.040":
So
S = 0.25"
E = 0.040"
G = 1.5"
so the angle we want is:
A = arctan ((0.25 - 0.040) / (2*1.5))
which is
A = arctan (0.21 / 3) = arctan (0.07) = 4 degrees
If you're using the calculator in Windows, you need to click on the
"Inv" box then hit the "tan" button to do the arctan. Also, make sure the box under the number display has "Degrees" selected.
This formula works, it took me a little bit of playing and some help from Dwight to figure out how to use it, if you put it all in the calculator just as it appears it works. Hope this can be of help.
Dale
Here is a formula given to me by Dwight Huges. It will allow you to figure in any thickness of steel, width of bevel, edge thickness. to get the angle in degrees per side.
A = arctan((S - E)/(2*G))
Where:
A = angle of flat grind per side
S = stock thickness
E = edge thickness
G = grind depth desired (maybe I should call this grind width
instead -- it's how wide the grind will be when done)
Note that A is the angle *per side* that you are looking for
(naturally enough); but S is the *total* stock thickness, and
E is the *total* final edge thickness desired after the grind.
arctan is the same as an "inverse tangent" or sometimes you'll
see it as written as atan
Let's say you have a blade that is 1/4" thick, and you want a grind
1 1/2" wide on a 2" wide blade (note the formula doesn't care about
how wide the blade is total -- only the actual desired grind width), and a final edge thickness of 0.040":
So
S = 0.25"
E = 0.040"
G = 1.5"
so the angle we want is:
A = arctan ((0.25 - 0.040) / (2*1.5))
which is
A = arctan (0.21 / 3) = arctan (0.07) = 4 degrees
If you're using the calculator in Windows, you need to click on the
"Inv" box then hit the "tan" button to do the arctan. Also, make sure the box under the number display has "Degrees" selected.
This formula works, it took me a little bit of playing and some help from Dwight to figure out how to use it, if you put it all in the calculator just as it appears it works. Hope this can be of help.
Dale
