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convex grind advice
- Thread starter cjd1980
- Start date
- Joined
- Feb 4, 2005
- Messages
- 834
There are two kinds of convex grinds. One is done on a slack belt, one is flat ground on a platen with the near-edge area convexed. Seems like the slack belt grind is used more on large blades. Either type will produce more metal behind the edge for support... the slack belt type produces more metal all the way to the spine.
In convexing near the edge, I flat grind to a minimum edge, leaving some to avoid decarb at the edge and maybe avoid warping at the edge. Then, after HT, use stones to build the convex shape before finishing the entire blade.
Kevin Cashen said rececently, historical knives/swords have convex edge geometry... that is, do not have a secondary sharpening bevel. Wayne Goddard builds convex edges with a minor secondary bevel to facilitate resharpening by customers... a convex edge is harder for most folks to sharpen well, was my read on Wayne's statement.
Mike
In convexing near the edge, I flat grind to a minimum edge, leaving some to avoid decarb at the edge and maybe avoid warping at the edge. Then, after HT, use stones to build the convex shape before finishing the entire blade.
Kevin Cashen said rececently, historical knives/swords have convex edge geometry... that is, do not have a secondary sharpening bevel. Wayne Goddard builds convex edges with a minor secondary bevel to facilitate resharpening by customers... a convex edge is harder for most folks to sharpen well, was my read on Wayne's statement.
Mike
jdm61
itinerant metal pounder
- Joined
- Aug 12, 2005
- Messages
- 47,357
Bill Moran said that a slack belt can leave a blade TOO convex. I use the KMG rotary platen for convexing after I heat treat. But I still grind the knives using a flat grind before I heat treat. Bill used to do his free hand in a big emery wheel and horizontally on a contact wheel. For us mere mortals, the rotary platen works very well.
- Joined
- Oct 23, 2006
- Messages
- 1,461
Chris,
I grind free hand, I'm not sure it's the "correct" way but it works for me.
I start on a bench grinder, rough grinding a full convex geometry. I grind edge up so I can see my scribe lines.
Then I move to the belt grinder, put on a 36 grit belt and refine the convex on the flat platen. Then I put on a 60 grit and work exclusively on a slack belt from here on out. I work up to 120 grit before heat treat. After heat treat I grind the scale off on a slack belt and finish up to a 400 grit with a light buff.
My blades definitely aren't perfect but I'm getting better with each blade. I notice a huge difference from a year ago.
The key for me is to hog out about 80% of the material on the bench grinder. Just make sure to keep your grinds the same depth, otherwise you have deep gouges to grind out on the belt grinder.
As a side note, to get the rough convex grind started, I use an up and down sort of rocking motion.
Hope this helps some,
Israel
I grind free hand, I'm not sure it's the "correct" way but it works for me.
I start on a bench grinder, rough grinding a full convex geometry. I grind edge up so I can see my scribe lines.
Then I move to the belt grinder, put on a 36 grit belt and refine the convex on the flat platen. Then I put on a 60 grit and work exclusively on a slack belt from here on out. I work up to 120 grit before heat treat. After heat treat I grind the scale off on a slack belt and finish up to a 400 grit with a light buff.
My blades definitely aren't perfect but I'm getting better with each blade. I notice a huge difference from a year ago.
The key for me is to hog out about 80% of the material on the bench grinder. Just make sure to keep your grinds the same depth, otherwise you have deep gouges to grind out on the belt grinder.
As a side note, to get the rough convex grind started, I use an up and down sort of rocking motion.
Hope this helps some,
Israel