Sure. Let's say you have the blade heat treated and ready to finish grind. Depending on the type of knife, the edge should be somewhere in the range of .030-.050 thick. I use the description of a dime's thickness. If it's a hunting knife, I lean toward the thinner edge (thin dime) and for a large knife that will see some chopping, I will make it a little thicker, but not any thicker than a dime's thickness plus a hair.A nickle thickness might be too thick in my opinion. A properly heat treated blade will stand up to a lot of heavy use when this thin.
Note: If you have done your heat treating and the blade is too thick to fit the above description, using fresh belts or a sharp file, bring it on in till your happy with it.
That's where the convex edge comes in. Start by forming a bevel, I would say about a 10-12 degree up from the blade flat. I do this on a fresh 220 or 320 belt so as not to build heat in the blade. Even so, dip it in water as you feel the heat with your bare hands.
Nother note: Remember that by the time it's too hot to hold in your bare hands, the edge has probably gotten so hot that it's tempering has been messed up.
Go till you almost have a cutting edge. Now increase the angle slightly and make a pass on each side, never getting above you final desired sharpening angle. Now you are blending several angles forming a convex cross section of the first 3/16 or so of the edge. All of this should meet at the edge in the form of a sharp edge.
This also called an apple seed grind. Think about the shape of an apple seed and that will be a good guide. No extremes though. There has to be a balance. If it's too blunt, you can drive nails with it, but it wont cut worth shucks. If it's too thin, it will might cut good on very easy tasks.
What you want the blade to do (before you put the handle on it) is to chop wood and not chip or roll the edge, still shave hair, then cut a free hanging piece of rope.
The wood will test the heat treat. If it's not right correct it now at this stage of the game. This will require that you have a good idea of the geometry it will take to perform the test accuratly. Thin Apple seed grind. The reason I say "thin" appleseed grind is, I would like to "know" if it's going to chip or roll and at what level of abuse. Test to failure. Yes, Test to failure! Your not testing the overall knife to failure, just the edge geometry. This will let you know when it's a little too thin in geometry. If it is, you roll it on in some more, shortening the apple seed grind using the above methods. Not much, just a little and re test.
If the blade will chop and hold up, then you are good to go to the rest of the testing and tweak the geometry to suit the intended purpose of the given knife.
The convex edge requires a balance of three or four elements that should be in the makers control. The purpose of the blade, the heat treat, and the edge geometry. They all meet up at the cutting edge.
I have tried to explain my views, but will be glad to clarify anything that I have not made clear. Lin
Topic: Been a Long Road (Read 997 times)
