Hatchet edge geometry

S.Alexander

S.Alexander

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Jul 7, 2013
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I am doing a small run of full tang hatchets, and I needed some guidance for the edge geometry. I will do some testing once they are heat treated, but I was looking for a starting point.

They are 1/4" 1075 steel. I will be aiming for 57-58 rockwell. They will be flat ground, with a convex secondary bevel

I would like to know what edge thickness I should use before sharpening? Does .04" sound right? With a 25 dps secondary bevel?
 
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Depending on what the hatchets will be used on, that would be POK, but I would go down thinner. The convex grind at the edge will make for a stronger edge anyway. Try one at .020".
 
What is the intended use? I agree with Stacy, I think you can go thinner with the convex assuming they are for general wood use. I just made one with a bit more than that behind the edge, it's leaning towards carving over chopping though at that thickness. I also didn't convex the secondary and they are more like 20 DPS.

I just reread your post and saw that you are talking about .04" before sharpening. At that thickness I doubt you will be happy with the performance, testing will likely necessitate thinning down. Of course, chopping and cutting performance with a hatchet will also be hugely dependent on the primary bevel angles, since you're forcing a wedge shape into wood with much less actual slicing being done.
 
The general use will be chopping wood and delimbing branches. I will take it down to .02 before sharpening as you guys suggested, and see how it does. Thanks
 
"DPS" degrees per side.
Fwiw, Unless there is a reason to have different degrees per sides, I never express that way. Just the total.

That .02" refers to thickness of unsharpened 'apex' of edge left on the tool before heat treating.
After heat treating, then final grinding & sharpening takes place.
Leaving that much thickness reduces the edge warping during heat treat. Also during heat treating a very thin layer on the entire surface decarburises. This 'decarb layer should be ground away to expose fresh & fully hardened steel.
The old saying "Forge it thick, then grind it thin" is based on this.
 
Lieblad said:
"DPS" degrees per side.
Fwiw, Unless there is a reason to have different degrees per sides, I never express that way. Just the total.

That .02" refers to thickness of unsharpened 'apex' of edge left on the tool before heat treating.
After heat treating, then final grinding & sharpening takes place.
Leaving that much thickness reduces the edge warping during heat treat. Also during heat treating a very thin layer on the entire surface decarburises. This 'decarb layer should be ground away to expose fresh & fully hardened steel.
The old saying "Forge it thick, then grind it thin" is based on this.
Click to expand...

Thank you for clarifying. Makes full sense now. That's what I've been doing, but the DPS through me off.
 
Lieblad said:
"DPS" degrees per side.
Fwiw, Unless there is a reason to have different degrees per sides, I never express that way. Just the total.

That .02" refers to thickness of unsharpened 'apex' of edge left on the tool before heat treating.
After heat treating, then final grinding & sharpening takes place.
Leaving that much thickness reduces the edge warping during heat treat. Also during heat treating a very thin layer on the entire surface decarburises. This 'decarb layer should be ground away to expose fresh & fully hardened steel.
The old saying "Forge it thick, then grind it thin" is based on this.
Click to expand...

Just a minor clarification - the .020" is the thickness at the edge after HT and finishing, but before sharpening. I would leave the edge at .040" before HT. After HT and sanding the bevels, the edge is left at .020", then the convex edge is sharpened on the belt grinder with a 400 grit belt..
 
I thinned down the edge to .02 and sharpened on a slack belt, to get a slightly convexed edge.

I chopped with it a little bit, and it seemed to hold up well. I will have time to test it more tomorrow.
 
Thanks for the input guys. Here is what I ended up with on the first hatchet. Bevels were ground at 20 degrees inclusive, with the edge convexed at 25 dps. The handle was somewhat skeletonized, but I am sure I could have removed more material.



 
S.Alexander said:
Thanks for the input guys. Here is what I ended up with on the first hatchet. Bevels were ground at 20 degrees inclusive, with the edge convexed at 25 dps. The handle was somewhat skeletonized, but I am sure I could have removed more material.
Click to expand...


I'm obviously late to this party, but I have spent way, way too much time thinking about axe edge geometry. The best resource on the web used to be the Blue and White Crew forestry sharpening page. Unfortunately, it has since been taken down, but I downloaded and saved a copy. Here's a quote:

"
The primary bevel angle on new felling axes ranges from 7.5° to 15° per side and can be as narrow as 1/2" or as wide as the full cheek of the axe; secondary bevel angles of 15° to 22.5° per side are typical, with widths ranging from 1/4" down to 1/64" or less……

.. a primary bevel angle of 10° to 12° per side and a 1/16" wide secondary bevel of 17.5° per side are safe starting points….[and] will hold up in the species of wood found in the PATC territory, even chestnut oak, shagbark hickory, and black locust.
"
 
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