Question about inital sharpening

grelcar

grelcar

Joined
Dec 30, 2007
Messages
268
I have a question about putting a sharpened edge on a new knife. I leave the edge at .040 before heat treat. When doing the initial sharpening I am taking .020 from each side of the edge. Should I also be removing about .20 from the width of the blade edge? I hope my question makes sense.

Greg
 
yes, ideally. I do it by hand with wetted diamond honing blocks rather than on a grinder to avoid the micro heating issue discovered by Roman Landes resulting from dry sharpening in which the steel in immediate contact with a dry abrasive heats up well past tempering heat for a few thousanths of an inch before the heat dissipates into the surrounding metal

-Page
 
The perfect slicing edge is flat sanded to 0.00 thickness at the edge. Then it has a secondary or micro-bevel added at the desired edge angle. The farther this secondary bevel is taken back determines the toughness of the edge. On a slicing kitchen knife or fillet blade, it is just slightly taken back, leaving the edge thickness at the top of the bevel about a few thousandths of and inch. On a camp knife, it is taken back to where the thickness is about .005" to .010" .
 
The reason I asked this is that the knives I have made recently do not seem to hold an edge well until they have had numerous shapenings. Maybe my method of establishing an initial edge is wrong. I start with an extra coarse DMT until I get a burr and then work my way through the coarse, fine and extra fine DMTs. I then finish on a 6000 water stone and add a microbevel with the 6000 waterstone. I end with a shaving sharp edge.

I am using 1084 steel and doing a home heat treat with a two brick forge and canola oil. I temper one hour at 400 two times.

Greg
 
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If you are shooting for an edge that will slice tomatoes it would help you achieve this by continuing to thin the bevels after heat treat. You can put a secondary bevel on a .o40 blade but the blade will not be as sharp as one where the bevels have been ground after heat treat. As Stacy stated, the path to a great slicer is to take the edge to 0.00, then put a micro bevel on it. If you're goal is to use this blade as a chopper or splitting tool then grinding a secondary edge on your already existing 0.400 edge is the ticket.
I will say that choosing an acute or less acute angle for the secondary bevel or micro bevel does not dictate how tough an edge is as much as choosing the correct material thickness at the start of the project. Something else to consider in producing the desired edge is the angle at which the bevels are ground. The correct selection of material, as in thickness, influences the bevel angles as well. So ending up with what you have set out to produce starts with material selection.

Setting secondary bevels on a belt grinder is achieved quickly. Of course dealing with friction and the resulting heat transfer should be considered, but in MHO should not be a deterrent to setting edges on a belt grinder. Just as in grinding bevels after heat treat has to be addressed in the proper manner, so to, setting edges on a moving belt. Its only a matter of doing it correctly.

Good luck with that edge. Let us know how it turns out.

Fred
 
Stacy and Fred, thanks for the responses . I am having a little trouble following what you are saying though.

I am using very basic equipment to make knives. Using some right triangle math I am making my primary bevel before heat treating is about 6* per side. My bevel when I sharpen the blade is about 10* per side to where the sides meet. I then put a micro bevel on the edge. Should I not be sharpening all the way to the edge before putting on a micro bevel? Am I making the edge too weak this way?

I can get the blade very sharp this way but it looses a lot of it's sharpness after cutting up some cardboard boxes to test the knife. It seems to hold a better edge after repeated sharpening at the micro bevel angle. I was thinking that I need to get past the outer edge of the steel after heat treating to get to harder steel.

I hope that this is making some sense and not sounding like I am just babbling.

Greg
 
After H/T you need to remove a layer of decarb from the whole blade,Take the blade down to about .010 at the edge and then do you sharpening.
Stan
 
Applying anti scale compound to your blade before heat treat will help out with carbon loss.

If the edge holds up better after repeated sharpening, sounds like carbon loss.

Fred
 
There are two things that will make an edge not good until several sharpenings;
1) Decarb - If the steel skin has lost a lot of its carbon, it will have poor edge retention until the edge is sharpened back into the harder steel.

2) Edge geometry - If the edge is too thin, it micro-chips away and becomes dull quickly. After several sharpenings, the edge is now thicker, and holds up well. After many years of sharpening, an edge may become too thick, and the bevel will need to be re-ground to make the edge thinner again.
 
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