Proper edge geometry?

Wade Jones

Wade Jones

Joined
Nov 1, 2009
Messages
183
I started draw filing my first edge today, then stopped 'cause I realized I don't know what the hell I'm doing. :D

I looked and couldn't find a whole lot on proper edge geometry. What I did see, seemed to be guys doing about a 22° angle (11ish° on each side).
Is this pretty standard?

Then, I guess you'd draw down to about dime's thickness, HT and temper, then the secondary edge will be about 45°? Am I thinking this through correctly?

Blade is going to be pretty thick and heavy, to facilitate heavy work like chopping through brush and whatnot.

Any tips would be appreciated!
 
a 22 degree angle is traditional for single bevel scandi knives. Probably not what you're going for.

If your draw filing with a jig then it's time to bust out that old trigonometry thing. Find out how far it is to file it down to a dime thickness, if thats what you want. Then decide how far back you want the grind to go. Then figure out the angle you need to be at. It will probably end up being around 2-5 degrees.
 
Yep between 2-5 deg. on your primary bevels and the 22 deg on your secondary bevels for your edge.
Stan
 
I'd go to an edge thickness of less than half the thickness of a dime - a dime is about 0.048" thick, give or take a bit -- go to about 0.020" since you're working by hand, and you want a minimum to get rid of after heat treatment.

Assuming you have steel 0.125" thick and 1" wide and you want to give it a full height primary bevel with 0.020" edge thickness, then you need a 3 degree primary bevel per side.
 
And to clearify Sbuzek, he meant 22 degrees per side. not 22 degrees inclusive, that would just fold on you. It's fine for scandi knives, because they're so thick and have lots of suport, but for a flat grind it would be toast on everything except maybe a fine kitchen knife. keep primary edges between 15-25 per side.
 
He can speak for himself, but I'm pretty sure Stan meant 22 degrees inclusive. Virtually every knife I have is well under 30 degrees inclusive, regardless of use. Kitchen knives are normally under 20 degrees inclusive. This is pretty typical working edge geometry for knives with good steel and proper tempering -- heck, I don't even own an axe with more than 40 degrees inclusive edge. If an edge should need a bit more support, I'll do the microbevel thing.
 
Just took a look at the DMT site

http://www.dmtsharp.com/general/basicsharp.htm#knifesharp

They recommend a 20 degree per side edge for most knives.

The spyderco sharpmaker

http://www.thespydercostore.com/Spyderco-Tri-Angle-Sharpmaker-Sharpening-Set-p/204mf.htm

uses either 15 or 20 degrees per side.

I can't imagine after all their research, that they chose these angles so people would get poor results with their products. Years ago, I was taught 20 degrees per side for normal use and 15 per side for a very sharp but delicate edge.

Maybe we can put this discussion to bed by all switching to convex edges. Trying to quantify the arc would make most of us crazy. :D

Rob!
 
When I grind, take the edge to about 1/16" (0.0625") before heat treat. I leave things a little thicker to avoid issues with warpage in the quench. If you don't have a grinder, this is probably not the best for you as you can't draw-file a hardened blade. I would rather grind a hardened blade than try to deal with a warped edge. What I do after HT depends largely on what the blade will be used for:

-on kitchen knives I take the edge down to 0.010-0.025" before sharpening (thin for veggie or paring knives, thicker for knives that will be used for meat prep or chopping).

-on hunters and skinners, I will usually leave it at about 0.020-0.030" (again, this depends on the customer's intended usage).

-on bush blades and heavy choppers I usually leave it at about 0.045"-1/16" (allowing for cleanup after HT)

The proper edge geometry for any blade is the one that fits the purpose of the knife. The edge geometry on my knives is anywhere between 10-25 degrees per side depending on what type of knife it is. If it is a small paring knife meant for making small, delicate cuts in soft material (vegetables and fruit) - then it will be sharpened with a much finer edge to suit that purpose. If it is a bush chopper, then the edge will be set at a higher angle to give it slightly more strength to stand up to impact.

Hope it helps, have a good one,
Nathan
 
45 degree total (22 1/2 degrees per side) at the edge bevel is ok for a machete with poor heat treat where you have to worry about rolling and chipping, or steel with large chunky carbides that tend to break and fall out. If you are using a steel with smallish carbides, or a plain carbon steel that is properly heat treated you should be fine with a 36 degree total edge bevel (18 degrees per side) for a chopper and 24 degrees total for fine cutting (12 degrees per side)

-Page
 
Not sure how well the bubble jig would work for draw filing.

This has been an enlightening discussion. Really gives me something to think about...
 
Last edited:
My edges are a mix of three geometries... Flat, Convex and V-grind... If that makes sense.

To tell you the truth, I pay little attention to the primary bevel angles on my knives. I hammer them full flat from spine to edge. I leave them at about .060-.080". The I clean them up to .040" or so before heat treat. After heat treat, I take the flats down to around .030". Then I grind the edge to a very shallow convex... actually TOO THIN to retain sharpness in use. My final process is putting a micro-bevel on with a stone (up to 8000grt) then I do a final strop with wet newspaper laid across the stone.

Crappy picture to illustrate the final geometry...
SharpeningWT-1.jpg


Rick
 
You could clamp your bar down flat. Set your angle on the bubble and then stick it right to your file and go to work. I think it would work fine. -Burton
 
blade geometry is hard to get right with a file, my fist knives I used a file on were ground like axes, when I got a belt grinder I went back and ground it like a knife it cuts now :)
 
KnifeMaker.ca said:
Just took a look at the DMT site
....
The spyderco sharpmaker
....
uses either 15 or 20 degrees per side.

I can't imagine after all their research, that they chose these angles so people would get poor results with their products. Years ago, I was taught 20 degrees per side for normal use and 15 per side for a very sharp but delicate edge.

Maybe we can put this discussion to bed by all switching to convex edges. Trying to quantify the arc would make most of us crazy. :D

Rob!
Click to expand...

Rob, you have to remember that both DMT and Spyderco are *selling sharpeners* -- they are thus selling most of their sharpeners for the lowest common denominator in modern knives - the typical mass marketed knives (even some rather expensive ones) with steels that are chosen with the primary considerations of (in descending order of importance): 1) to be (very) stainless; 2) to be cheap; 3) to be easily blanked (ie: easy on their equipment); and finally, if they think about it, 4) hold an edge? oh, yeah, maybe we should think about heat treating those blades.... And yes, knowing this, 40 degrees included is about all most of these "knives" can stand (maybe). But with real knives with proper steels and heat treatments, you can do much better. And isn't that what we are all here for?

-- Dwight
 
Wade Jones said:
I started draw filing my first edge today, then stopped 'cause I realized I don't know what the hell I'm doing. :D

I looked and couldn't find a whole lot on proper edge geometry. What I did see, seemed to be guys doing about a 22° angle (11ish° on each side).
Is this pretty standard?

Then, I guess you'd draw down to about dime's thickness, HT and temper, then the secondary edge will be about 45°? Am I thinking this through correctly?

Blade is going to be pretty thick and heavy, to facilitate heavy work like chopping through brush and whatnot.

Any tips would be appreciated!
Click to expand...
If you are grinding at 11 to 1 5 degrees, angle of approach, you no doubt want a knife with a "scandi" grind.
If you grind, with an angle of approach of 3 degrees per side, you are looking to produce a blade with a flat grind.
Assuming the blade is one inch wide; as stated below. Three degrees will give the blade a flat grind from spine to edge.

The Secondary or the working edge as it is usually refereed to can run from 10 degrees per side for thinner fillet knives to 15 degrees per side for an axe. Under 10 degrees is too thin for most working knives where above 15 degrees is unnecessary.

The common compound grind, twenty years ago was 35 degrees for most knives.

We have learned a great deal about edge geometry, in twenty years.

The jig I make will work in most situations, where you want to produce matching surfaces. Whether you remove the steel with files or belts makes little difference. If you follow the basic set up that Burton suggest below, you will be able to file evenly across the flats using the jig I make.

You can use the same set up to file machined looking lawn mower blades.:D

Happy grinding, Fred
 
Hey Fred, hopefully I'll get to heat treating soon so I can post pics of my bubble jig knives.

I've had problems using such low degrees of an angle on 1/4"X 1 1/2". Starting with the 5 degree, it's already not enough angle. I am cutting into the spine before I get the edge down to my scribed lines.

I read an early post you wrote about starting with an 11 and working the grind up through an 8 to get to the spine. This seems like it would work for thick but under 2" wide blades.

Does this make sense, or has third shift ate my brain? It does feel like it sometimes.

Thanks Fred,
Jason
 
wingchun74 said:
Hey Fred, hopefully I'll get to heat treating soon so I can post pics of my bubble jig knives.

I've had problems using such low degrees of an angle on 1/4"X 1 1/2". Starting with the 5 degree, it's already not enough angle. I am cutting into the spine before I get the edge down to my scribed lines.

I read an early post you wrote about starting with an 11 and working the grind up through an 8 to get to the spine. This seems like it would work for thick but under 2" wide blades.

Does this make sense, or has third shift ate my brain? It does feel like it sometimes.

Thanks Fred,
Jason
Click to expand...

Hi Jason,

How are you setting the bubble? A five degree set should not cut the spine of the blade, especially if you are grinding 1/4 x 1 1/ 2 inch stock.

Fred
 
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