Flat Grind Angle

crocogator106

crocogator106

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Nov 16, 2012
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What angle should I grind each side of 3/16 A2 knife? I want to try a full flat grind. The knife blank is about 1 1/2" wide.
 
The exact angle isn't really so important. The angle will be determined by the thickness of the blade and the height of the profile. Don't worry about finding the exact angle from the start. In fact, you should start by marking your center (most people mark a set of parallel lines about 003" apart at the center of the blank). From there, you can start your bevel at a 45 degree angle down to or very close to your marks. This saves your belts as well since you're not trying the start your bevels at an acute angle, thus shearing off a lot of your fresh grit. Once your 45's are established, you start working the bevel up the flat, basically decreasing your angle of grind with subsequent passes until your bevel reaches the height you like. Grinding in this fashion is much more natural than trying to establish the exact angle from the beginning. The exception would be if you were using some sort of jig to assist in your flat grinding.

--nathan
 
I agree with Nathan to a point. I do everything everything Nathan said and free hand grind almost all of my knives however, there are points where I am curious and want to know the angles and details. You should do the trigonometry to find the angle just to know it since you asked.... The final angle when all said and done, after ht and say it was taken down to zero would be

theta = arctan(opposite/adjacent) (important note: this angle that was just solved for is only going to be half of the angle you see when looking at the wedge of the edge when done)

If you need clarification and more help, let me know.
 
The first picture shows a triangle, which is what the cross section of the area would look like if you cut a slice out of your blade.

The second picture shows a jig like piece next to the platen.

AA1E2150-2A56-4F7D-8B8B-60AB2C0FABBF-571-00000032E05844E5_zps00cf734e.jpg


F4975EB0-6B5D-4597-A635-D58E70509E43-571-00000032E79E36D3_zps825c0639.jpg


Theta = arctan(opposite/adjacent)

I believe in giving you just enough information to help you LEARN what you would need, when it comes to this type of stuff, like math etc because you will need to know how to do it in the future no matter what other people tell you.

Solving for theta in the first picture wont give you the exact angle that you will need on the platen, it really depends on the type of jig etc that you are using, so it is hard for me to tell you exactly what is what with that angle.
 
The angle is just whatever it takes to go from the edge to the spine. mark the edge with a .030 center space, and file/grind the bevel so it goes from there to the spine. Stop when just shy of both ends, as some more will come off in sanding.
 
TheWeatherman said:
The first picture shows a triangle, which is what the cross section of the area would look like if you cut a slice out of your blade.

The second picture shows a jig like piece next to the platen.

AA1E2150-2A56-4F7D-8B8B-60AB2C0FABBF-571-00000032E05844E5_zps00cf734e.jpg


F4975EB0-6B5D-4597-A635-D58E70509E43-571-00000032E79E36D3_zps825c0639.jpg


Theta = arctan(opposite/adjacent)

I believe in giving you just enough information to help you LEARN what you would need, when it comes to this type of stuff, like math etc because you will need to know how to do it in the future no matter what other people tell you.

Solving for theta in the first picture wont give you the exact angle that you will need on the platen, it really depends on the type of jig etc that you are using, so it is hard for me to tell you exactly what is what with that angle.
Click to expand...

This does not take account of the edge thickness. In general a knife is ground to a tall trapezoid, not a triangle.
 
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