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Ed Caffrey's Workshop Talk to Ed Caffrey ... The Montana Bladesmith! Tips, tricks and more from an ABS Mastersmith.

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Old 02-24-2013, 05:09 PM
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Question gringing a concave

Dear Ed, I have some orders for knives with a concave shape blade (like a Krambit) I normally grind my blades edge up, and have had good luck with straight or convex (up-swept) blades. When I try to do a concave blade this way, I get 2 or 3 straight or "flat spots" in the curve. I start out with a curve blade, and end up with a real mess! I'm grinding against a flat hard platen, is this the problem? Do I need to make some kind of rounded or curved platen to allow the belt to curve? This is "way out there" for me! How do you do it? Thanks! Jon


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Old 02-24-2013, 08:42 PM
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Jon, are you talking about a hollow grind?
Done with a wheel?


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Old 02-24-2013, 10:00 PM
Doug Lester Doug Lester is offline
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No, I think that he means a blade that curves toward the edge, at least from the way that I read his post. I think that he's having problems with flat spots in the curve of the blade as he grinds the bevels into the downward curve of the blade. No sage advice from this quarter as I still have a little problem at that with a trailing point blade.

Doug


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Old 02-25-2013, 08:11 AM
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There are a variety of solutions that folks use. Personally, an easy solution that I stumbled upon by accident was to grind as you normally would with the flat platen, paying special attention to the "recurve" area of the blade.....keeping those "flats" to a minimum.....then using a very tight slack belt, cleanup/blend those "flat spots" near the end of my finish grinding.
It takes some practice, and time, and you will end up with a gently covex......but that's what I prefer anyway.
It's just like any other issue we run into when we're doing something new/different from what we're used to.......take it slow, keep a clear mind, and THINK twice as much as you grind......in the end your solution may not be the same as mine, but you'll find a solution that works FOR YOU.


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Old 02-25-2013, 07:26 PM
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Cool concave blade shape-- like a Krambit

Yes Doug, you are right- I was talking about a blade shape, not the actual grinding of the edge to a "convex" shape. Through this process I have gained a new respect for those who can grind edges on a blade that curves forward-- as in a "Krambit" style fighting knife. My first attempt, I started with a forged blade about 1-1/4" wide (from spine to edge) and finished up with the blade about 7/8" wide!!! (with some very ugly flat spots) I didn't even want to put handle's on it, but the customer saw it and still wanted it finished, and paid for it!!! Then to make things worse, he wants another!!! He raves about the curved blade's cutting ability, so I guess as long as he's happy! Anybody else have advise, please jump in here! Thanks ED!!! Jon


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Last edited by jonwelder; 02-25-2013 at 07:30 PM.
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