Best Way to Grind Small Blade With Concave Cutting Edge?

T

The Mighty Ginsu

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Aug 11, 2016
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I have decided to try my hand at making a knife. I ordered the parts already. I thought the smartest thing was to make something small and simple, so I drew a design for a birds beak paring knife, which I hope to use for boning poultry. The steel I ordered is 1/8" thick. I plan to leave the steel thick on the upper (non-cutting) side and thin it toward the edge. Obviously, I guess.

I think I understand most of the process, but one part concerns me. The knife will have a blade about 2.5" long, and it will be curved inward toward the point. That means the cutting edge will be concave. I can't just hold the bar up to a belt grinder to hollow it out, because the belt would only make contact with the knife at the belt's edges.

What's the best answer? I'm thinking maybe round files.
 
Put up a drawing of what you have in mind.

What do you plan to grind the bevels with?
 
Managed to locate my Photobucket login. Here is a sketch.

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AVigil said:
What do you plan to grind the bevels with?
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The Mighty Ginsu said:
What to grind the bevels with was actually the problem that drove me to post a question.
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I believe Adam was wondering what type of equipment you have to work with. Do you have a 2x72 belt grinder or a cheap 1x30 belt sander or etc.?

Also, as suggested above many makers use the edge of the belt to grind in the bevels on recurved blades. Basically this makes it so you're using less of the belt so there is much less surface area than using the whole width of the 2" belt, which will cause the problems you already mentioned above.

I'm some cases you can also grind the bevels using a contact wheel or one of the flat platen idler wheels (wheel size depends on how large the blade is) while holding the knife vertically (tip down) and moving the blade up and down to grind the bevel the entire length of the blade.


~Paul
My YT Channel Lsubslimed
... (It's been a few years since my last upload)
 
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I've wondered if anyone has ever contoured a contact wheel so the profile of the wheel was convex, I'm thinking with enough belt tension the belt would form over a convex wheel and allow grinding of recurves.

Either way it's a pretty ambitious first blade.
 
kuraki said:
Either way it's a pretty ambitious first blade.
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I was trying to come up with something really easy! Maybe I need to start over.

I appreciate the tip about using the edge of the belt.

Right now the only belt grinder I have (other than an oscillating job) is a 1x42 Rockwell with a 1 HP treadmill motor. I also have a bunch of files and a drill press with a special chuck that allows it to be used for sanding with drums.

I guess I could grab a piece of scrap and see how hard it is to put that kind of bevel on it.
 
I may be right or wrong but here's my take on blade geometry and difficulty in producing. The first one, what I call a sheepshead, is the easiest. It's straight from ricasso to point, there is no distal taper other than what is produced by the bevel angle. The middle one adds some complexity with the swept point, whether it's a clip point or other variation, but the sweep is the only additional geometry change. There is still very little distal taper unless you choose to add it. The last is a little tougher, you have the straight to swept bevel, and a distal taper that thins the blade thickness towards the end. Just my opinion, these three blade types are what a beginner should work on because they're A) useful blade designs and B) low complexity but teach you fundamentals that you'll use in more complicated designs.

Recurves and tanto edges and false edges etc etc are more advanced skills that require some base knowledge/ability to produce.

Just my opinion.

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Well this might help. Perhaps take one of those 1" by belts and slit it in half or less. Or, drift the belt far over to one side of the platen so it is running over the edge. With a wheel I simply build it up in the center with layers of masking tape and run a belt about the same width.
Frank
 
If grinding a blade on a grinder with a contact wheel, just raise/lower the tip and the edge will grind at an angle from the horizontal. In other words, angle the blade, and it will be contacting a curved surface. It takes a little practice, but you can even hollow the urasuki on a Japanese blade this way. The amount of hollow will be related to the wheel size and the angle you hold the blade at. If the blade is held vertical, the curve will match the wheel curvature.
 
Thanks.

I'm thinking I may just change the design and try to make a short knife with a straight edge. Sort of a miniature chef knife.
 
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