I've been goofing around and made a knife I call the "Chungus" (my 10-year-old son thinks that's hilarious). For the heck of it I made the thing pretty thin behind the edge - .008-.010 measured with my calipers - and the angle according to the DMT chart I have is supposedly about 16 degrees inclusive (I had to interpolate). I know that's not an exact angle measurement, but it's pretty acute. The steel is AEB-L. I took a Douglas Fir 2x4, made some feather sticks, did some twist cuts and some notches. When I went to chop with it it performed well until I decided to chop and twist out a knot. I got some minor rolling on the edge in one small area that was pretty easy to remove, and other than that I was still able to shave hair and cut notebook paper on the undamaged portions of the knife. So overall I'm pleased, but because I would like to regularly use this knife about as hard as I did during the test, I'd like to know what angle to select and how thin behind the edge I should go. I know there are a lot of factors, but assume a decent heat treatment.
Nice looking blade.
Woods blades can definitely be made too thin. If your primary use is cutting meat, hide, and food, a very thin edge with an obtuse 30+total angle edge will work fine. If you cut and carve wood, a lower edge angle with a taller bevel with the attendant thicker edge will often work better.
I have had some chopping blades with what was probably a high 30 to low 40 degree total included edge, and they were far too ready to glance off wood when I was trying to do controlled crafting work.
The majority of what I have made would be classed as woods-knives, mostly in the 3.5 - 5" range. When I started I didn't have a grinder and pre-HT edge thickness (home heat treated carbon tool steel) tended to be 0.75mm. Sharpening/grinding on a 220grit water stone by hand created a convex bevel that had a total included angle in the mid-20 degrees, but was quite tall before transitioning to the primary grind. This grind actually worked rather well in the woods and for related tasks. It wasn't used much for game prep, but did a lot of wood work and a reasonable amount of food prep.
Measuring such a knife I have here shows a 2mm (0.079") tall bevel going to 0.67mm (0.0264") at the transition. This is a mild convex, so a little more at the edge than the 20deg total included you would get with a flat bevel. It carves/feathers wood great.
Following much reading on this forum, particularly the posts that Stacey has made about edge thickness, I made an AEBL blade with 0.45mm (0.0177") at 2mm tall. This is sharpened at my customary angle with a convex edge. Cuts meat very well, great in the kitchen, sharp as hell....but rather disappointing for a woods knife. It really doesn't run long shavings well at all. A tall bevel contributes to control when trying to run a long shaving, as in making feather sticks, or trying to craft something, be it a spoon or a canoe paddle. This otherwise beautiful AEBL blade just lacks stability in a long cut.
On a wood chopping blade, you don't want the blade to over penetrate and bind in a cut, so again, a bit of thickness not too far back from the edge can be helpful. I would probably keep the same angle, but make the bevel a little taller before starting the primary grind. This isn't so much about steel strength, but about blade height and length increasing instability and trying to offset this with a taller bevel.
All the best
Chris
