Knife Bevel Rule of Thumb

B

Barehunter

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Feb 6, 2009
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I'm a knife making newbie and probably like most of us the most difficult part of knife making is learning to grind the bevel. Am trying several methods and getting better with practice.

Anyway, here's my question: Take for example a standard "hunting" style knife that has a 1 1/4" wide blade .125" thick with a flat bevel grind. How far from the cutting edge should the bevel extend. Another way to ask it would be what should the angle of the grind be. (not referring to the cutting edge but the overall bevel).

I realize that there is some personal preference here but just looking for a range and/or suggestions as to what is best as far as cutting ability and durability etc.
 
Id like to know this also. I'm trying to remember the formula to determine the angle of an isosceles triangle by the length of it's base and height.

An isosceles triangle split in half perpendicularly creates 2 right triangles. So, one of the angles is 90 degrees. I don't know; it's been a long time since I even thought about any of this crazy math stuff.:rolleyes:
 
I take mine to the top on drop points, for a hunter or other non-drop point (ie the spine is flat) typically you would go at least about 1/2 up toward the spine. Dont over grind at the top, just get really close and stop, you dont want the blade to be thinner than the handle at the very top. The main point is what are you looking for in the knife, I go to the top to reduce the angel which makes the blade more of a slicer, however, this will get thin toward the tip which is not good from heavy use.

As a newby I would suggest draw a line in the middle of the blade, draw another 1/4" below that one. Do your initial grind to the lower line, then finish the grind to the upper. This way if you mess up you will still have a nice blade, it just gives you a target.

HPIM3466.jpg
 
My suggestion is forget the math unless you are going to make a jig to hold the knife. I dont think you can hold the blade accurately enough by hand to get a proper grind while looking at some sort of angle.

The trick to flat grinding is to get a 45 at the edge on both sides and then grind the bevel of the 45 (not the edge). If you keep the edge off the belt you can move the grind toward the spine.
 
Patrickknives said:
I take mine to the top on drop points, for a hunter or other non-drop point (ie the spine is flat) typically you would go at least about 1/2 up toward the spine. Dont over grind at the top, just get really close and stop, you dont want the blade to be thinner than the handle at the very top. The main point is what are you looking for in the knife, I go to the top to reduce the angel which makes the blade more of a slicer, however, this will get thin toward the tip which is not good from heavy use.
Click to expand...

Appreciate the input. I can definitely see your point about not grinding to the top. I just "finished" my 5th knife. Put a lot of work into it. D2 steel, stabilized lacewood scales....sent it to Texas Knife Supply for heat treat etc but after completion and final sharpening I realize that I made a stupid newbie mistake and did not grind the bevel back nearly enough and the blade is too thick just behind the cutting edge. Oh well. Lesson well learned. Can't decide whether to attempt to regrind or just keep it as is for a reminder of my mistake!
 
Patrickknives said:
My suggestion is forget the math unless you are going to make a jig to hold the knife. I dont think you can hold the blade accurately enough by hand to get a proper grind while looking at some sort of angle.

The trick to flat grinding is to get a 45 at the edge on both sides and then grind the bevel of the 45 (not the edge). If you keep the edge off the belt you can move the grind toward the spine.
Click to expand...

Interesting approach....I'll give that a try. Assume you are grinding edge up?
 
Ditto on the 45 degree bevel (though it doesn't have to be exactly 45). You'll want to scribe lines down the center of where the edge will be and then grind to them. You're probably doing that anyway. Then it's easy to grind toward the spine (yes, edge up) without making the edge too thin for HT. I'm still working on consistent bevels myself, and ate into the spine on my first 5. I don't like to leave much flat at the top of the bevel below the spine unless it's a really big knife, because I feel like i'm giving up cutting performance by not making the grind angle more acute. And i think it looks cooler too.
 
wordsmith said:
Ditto on the 45 degree bevel (though it doesn't have to be exactly 45). You'll want to scribe lines down the center of where the edge will be and then grind to them. You're probably doing that anyway. Then it's easy to grind toward the spine (yes, edge up) without making the edge too thin for HT. I'm still working on consistent bevels myself, and ate into the spine on my first 5. I don't like to leave much flat at the top of the bevel below the spine unless it's a really big knife, because I feel like i'm giving up cutting performance by not making the grind angle more acute. And i think it looks cooler too.
Click to expand...

Yes...I recently learned to mark the center or rather a line on each side of center. This certainly helped with consistency on the edge side. I definitely gave up cutting performance on the last one.

A related question: What are some methods that are used to assure that you don't overgrind toward the handle. I made a device from two pieces of flat metal that clamps to the blade with wingnuts. Other suggestions?
 
Words got it, on a 1/8 thick blade I mark 0.040" on each side leaving a 0.045 strip in the middle. Grind the 45, or any big angle to the lines leaving the edge. Now stay away from the edge, grind the corner where the 45 meets the surface of the blade. Take a look.. if you getting too close to the edge move the back of the blade toward the belt (moving the edge away) if you are going too quickly toward the spine..move the angel more to the edge, just a little dont grind you edge. I do grind edge up.

I have made some hardend steel devices like you described to keep the bevels even. Since it butts against the platten they dont see much wear, so any steel can be use for a while.

Once heat treaded I will regrind to about 0.030 so you can regrind if your edge is too thick, sharp belts and lots of water. Prior to HT I leave about 1/2" at the spine and a little edge of the 45 bevel, that way I can grind a little more and it will follow the orginal grind which should be pretty good. Since your grind is finished I would carefullytouch the edge to the belt (120) at 30 degrees to make a small bevel (this will prevent loosing your edge) and then grind very carefully up the spine, with a sharp belt and light touch you can fix anything.


Full flat grind to top


BowieHunter015.jpg
 
Dang....I'm taking my big knives down to .020 and then convexing.:D
 
At 0.020 that must be a real slicer, I have only gone that thin a couple of times by request. I do convexing as well. I am ordering the paper wheels, will be interesting because I get them pretty sharp already.
 
barehunter, thanks for atarting this thread and thanks to everyone else for thier inputs. It was a question I had thought about as well.
 
Barehunter,

May I recommend reading the following "Blade Geometry by Joe Talamadge".
http://www.worldknives.com/info/blade-geometry-by-joe-talamadge-25.html

It provides a good discussion on the various blades styles and grinds. Form follows function.

Next, this link, Edge Angles, found at: http://www.knives.com/angle.html provides the angles of various cutting edges. Scroll to the bottom of that document and you will find a 'rough guide', i.e. a 'rule of thumb' if you will. It can serve two purposes: determining/establishing the angle of the primary bevel and the angle of the secondary, i.e., cutting edge, bevel. It is easy to establish the measurements of the primary bevel and is a little more difficult on the secondary bevel when the measuring in thousandths of an inch.

Enjoy the read.

Randy
 
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jorasco312 said:
Barehunter,

May I recommend reading the following "Blade Geometry by Joe Talamadge".
http://www.worldknives.com/info/blade-geometry-by-joe-talamadge-25.html

It provides a good discussion on the various blades styles and grinds. Form follows function.

Next, this link, Edge Angles, found at: http://www.knives.com/angle.html provides the angles of various cutting edges. Scroll to the bottom of that document and you will find a 'rough guide', i.e. a 'rule of thumb' if you will. It can serve two purposes: determining/establishing the angle of the primary bevel and the angle of the secondary, i.e., cutting edge, bevel. It is easy to establish the measurements of the primary bevel and is a little more difficult on the secondary bevel when the measuring in thousandths of an inch.

Enjoy the read.

Randy
Click to expand...

Great stuff Randy....many thanks!
 
I made a small fence for my platen so I can regulate the grind height by moving the platen in and out.
Richard
MVC-012F.jpg


MVC-013F.jpg
 
I realize this is a very old thread. But I would like to read the embedded links on angle rule of thumb.
Would someone let me know how to open or any other suggestions?

Thank you
 
Welcome to Shop Talk.

I assume you're wanting to read the links in jorasco312's post above? The Wayback Machine (internet archive) is your friend for that type of thing. It won't always have what you're after, but in this case, it appears that it does.

Here's the first one:
https://web.archive.org/web/2012050.../info/blade-geometry-by-joe-talamadge-25.html

Here's the second:
https://web.archive.org/web/20090826024450/http://www.knives.com/angle.html

FYI, resurrecting 10+ year old threads is generally frowned upon. In the future, I'd recommend starting a new thread and linking to the old one.
 
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