Calculating Edge Angle.

JTknives

JTknives

Joined
Jun 11, 2006
Messages
8,651
This is how i calculate edge angle is it correct.

Tan-1(A/(2xB))=C

A= steel thickness.
B= is the angle you want per side.
C= is how high you need to take the grind line.
Tan-1 is the negative Tan function on the calculater.

does it look good.
 
I think you have entirely too much time on your hands. There is no one exact angle for every purpose, or every blade.
 
Negative Tan - that's what happens to our skin up north in the winter !
 
Mete - tell me about it, I work in a windowless basement all day.

JT - practically speaking it'll work just fine, although you'll run about 1° shallower than you intend to (ie. 19° instead of 20° for 1/4" stock). C=0.5A(Sin (90-B))/(Sin B) is slightly more exact, but you can decide if you really care. :-)
BTW, nice knife you made for the Christmas exchange.
 
I don't think you're relationship is correct. Also, there are easier ways than using the inverse tangent function.

Which angle are you using?

- the complete angle from beveled edge to beveled edge?
- Or, 1/2 the angle from beveled edge to beveled edge?

......./|\
....../ | \
...../..|..\
..../__|__\

....---A---


There's two ways to look at this:

1) Calculate the top angle (vertex angle) of an Iscoceles triangle
2) Break it up into two right triangles and use the law of sines.

The second method is much easier.

If you use the law of sines, blah blah blah, you get the following relationship:

Let's assign a few variables first.

B = the overall angle from beveled edge to beveled edge.
A = thickness of blade
C = length of bevel grinds

C can be found as follows:

Sin(90)/C = Sin(1/2*B)/(1/2*A)...................(1)

Which cleans up to:

C = A/(2*Sin(1/2*B)).................................(2)

Thus, if you know the desired angle and thickness of your steel, simply plug them in to the above equation (2), and the output will tell you how long your grind lines should measure.

Hope this helps.

Take care,
Brook


JTknives said:
This is how i calculate edge angle is it correct.

Tan-1(A/(2xB))=C

A= steel thickness.
B= is the angle you want per side.
C= is how high you need to take the grind line.
Tan-1 is the negative Tan function on the calculater.

does it look good.
Click to expand...
 
hu that does make a diffrince. using my formula wanting 5º per side on .088 thick stock i got .50419 and when i used yours i get .502922 thanks. when trying to get 5º it makes a difrince
 
Took another look at your equation. I think what you were looking for, using tanget, might be:

C = A/(2tanB)

I think you might have had B and C switched in your eq, which forced you to do the inverse tan of C. I'm probably wrong, though, without seeing how you set your relationships.

My wife just told me that my geekness is glowing today... :)
 
Angle-1.jpg


This is the way I see it.

B - is the angle on one side
1/2 b - half the thickness of the steel (Therefore, b would be the thickness of the steel)
c - how high to make the grind line

In this case, the formula would be: c = 1/2 b
....................................................Tan B

Give this a try. Hopefully I am talking about the same thing you are.

PS. I am currently in high school, so trigonometry is fresh in my head.
 
what im trying to find is the sharpening angle per side. if i know how thick the steel is and the angle i want i should beable to get the hight of the grind line.
 
ok i have got it.

(thicknes/2)/Tan(angle) = grind height.

thanks everyone. teachers allways told me this stuff was important to learn but who would have known :D
 
Let's see if I got this right....you're looking to solve for "b"?
 
Then my guess is b= a Tan x, where x=90*-desired angle :)

And that's just a guess.... which isn't too bad, because it's the same thing you said but yours is more elegant, lacking the subtraction. Been awhile since I thought any trig. Thanks for the fun.
 
Ok, so what's my prize for winning this competition?:D Just kiddin. Just glad I could help. It also shows how useful trig is in life.
 
rpbali, your earlier comment about "fresh in my mind" has relevance to me in how I could come up with my own solution but not see it's equivalence to the other, earlier solutions near as readily as I once did.

+1 for "fresh knowledge" versus dormant. :)
 
rpbali said:
Angle-1.jpg


This is the way I see it.

B - is the angle on one side
1/2 b - half the thickness of the steel (Therefore, b would be the thickness of the steel)
c - how high to make the grind line

In this case, the formula would be: c = 1/2 b
....................................................Tan B

Give this a try. Hopefully I am talking about the same thing you are.

PS. I am currently in high school, so trigonometry is fresh in my head.
Click to expand...

This is the same as what I came up with the second time.

C = A/(2tanB)


Also, there may be a domain error when using the sine function. I didn't put any numbers into the forumula, so that may be the issue. With the first one I listed.
 
Surely this fomulae is only going to be accurate if everything else is equal, but what happens when you have a distal taper ......will it still work?
 
bjalongi said:
This is the same as what I came up with the second time.

C = A/(2tanB)


Also, there may be a domain error when using the sine function. I didn't put any numbers into the forumula, so that may be the issue. With the first one I listed.
Click to expand...

So it is... Guess you beat me to it!
 
Sharpen it at the angle that works for the job intended. It is more of a feel thing for me and it works great. If I had to sit down and calculate the angle each time i sharpened a knife I would go insane.
 
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