Ripleys Bevel It Or Not .

K

Kevin the grey

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Aug 26, 2005
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How many of you guys put a secondary bevel on your knives and exactly what does it accomplish ? Does the blade stay sharper longer ? Does anyone put an equivalent of a secondary bevel on a convex edge by changing the curve of the radius ? (Or is that the radius of the curve ? )
 
I ususally touch up with crock sticks that have 2 angle settings. That gives a small secondary bevel. For more intense sharpening I usually (unless I'm feeling "retro" that day) go to my belt grinder with a slack belt, which gives me a convex edge. The geometry of a convex edge or a secondary bevel provides more support to the blade edge, and makes it less likely to ge pushed out of allignment. It does, in general, stay sharper longer. Of course, many other factors also influence edge holding.

The convex edge as it is, is essentially an infinite number of secondary, tertiary, etc. bevels. I don't see any point in trying to make it into a discrete number of curves with different radii. When pushing down on a slack belt I doubt you are getting a perfect segment of a circle for a profile anyway.

Why would you want to do this?
 
Don,t get tertiary with me ! L:O:L

Just trying to learn a bit more . One of these days I will have to get me one of those belt grinders .

What I think I will do is use a knife for various tasks with a simple edge and then duplicate the tasks utilising a secondary bevel .
 
Kevin the grey said:
How many of you guys put a secondary bevel on your knives and exactly what does it accomplish ? Does the blade stay sharper longer ? Does anyone put an equivalent of a secondary bevel on a convex edge by changing the curve of the radius ? (Or is that the radius of the curve ? )
Click to expand...

You may have to put some type of secondary bevel on a fat blade that you dont't necessarily want a "flat" grind on. However, installing more than one bevel on a blade is probably more a matter of time savings. Most woodworkers have told me they will put a sceondary bevel on their plane irons or chisels to touch them up during a project rather than take the whole bevel down. It is not a preferable situation though.

IIRC, the Japanese change the curves of their radii (sp?) according to the target material. For cutting through armor, more radius (nikko) is applied toward the edge - for unarmored targets less radius, etc.
 
cliff355 said:
... Most woodworkers have told me they will put a sceondary bevel on their plane irons or chisels to touch them up during a project rather than take the whole bevel down. It is not a preferable situation though.

IIRC, the Japanese change the curves of their radii (sp?) according to the target material. For cutting through armor, more radius (nikko) is applied toward the edge - for unarmored targets less radius, etc.
Click to expand...

Which illustrates an important point. You should choose the appropriate edge geometry for the task at hand. For something that needs to be "shaving sharp" like a straight razor or a blade for a wood plane, you want a very acute angle on the blade, and you don't want to push the material further apart than you have to. A convex edge or a secondary bevel is not ideal in such situations. Of course, the tradeoff is that the edge is less supported and more fragile. It will require more frequent touch-ups than an edge with a more robust geometry. For critical applications, like shaving a face or planeing a handcrafted piece of furniture, the extra maintenance is worth the trouble.

A working axe often has a pronounced convex edge (small radius) maintained by hand with a file. This not only provides a well-supported edge, but also helps pop chips of wood out by causing greater seperation of the material being cut. A hunting knife may have a convex edge of much larger radius because of the different types of tasks it is commonly used for.

I'm using the word radius for simplicity, knowing that the profiles are almost certainly not perfect arcs of circles.
 
I don't sweat the details, just sharpen the thing and go cut. Any old knife takes on a convex edge after enough times being sharpened free hand. Good point on the woodworking tools though (and I consider my puukkos to be such), they have clearly defined bevels for a purpose, and it behooves one to maintain those bevels as best as possible. A properly honed spokeshave makes a pleasing hiss as it cuts a smooth, thin, shaving from a hickory bow stave. One sharpened wrong will chatter infuriatingly as it dips and skips, ruining your work. Right edge for the task at hand? I'll drink to that.

Sarge
 
One sharpened wrong will chatter infuriatingly as it dips and skips, ruining your work. Right edge for the task at hand? I'll drink to that.

Sarge[/QUOTE]
I don,t mind chatter in the workshop as long as the tools are put away and it is my teeth chattering from an ice cold Milwaukees best dry .

I think my main isue is I am used to thinking that 15 degrees is right for anything and really it is just a compensation edge a kind of jack of all trades edge . I have never even sharpened a chisel yet . I am just starting to sharpen the convex edge on my drawknife . Its lots of fun .
 
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