convex grinds

jgcustoms

jgcustoms

Joined
Jul 14, 2008
Messages
106
how do you get that high defined grind line on a convex grind that ends half way up the blade? I am doing an order and i want the line to be defined like the flat grinds on the top. Can someone help me? I just dont know if theres a technique that make this a little easier for me to acomplish what im looking for.
 
Any reason not to do a flat grind? I'm guessing though that you should have plenty of tension on your belt, ensure you keep the angle even during each pass and use nice even pressure. Let the belt do the work, don't force the blade into the belt to take off too much.
 
Most of what folks are calling "convex" grinds are actually about 90% flat ground, with just the last 1/4" or less of the edge "convexed". This actually has a lot of advantages in that the flat grind lightens up the overall knife, while the convex edge adds a great deal of strength compared to a complete flat grind.

The way I accomplish it is to flat grind the blade, leaving a very small flat on the edge of approx. .020-.040. Then when I'm on a 400 grit belt, using a small slack belt area built into my platen, I convex the edge until its sharp.

One of the biggest issues that plagues knife owners is when a maker puts huge edge bevels on a blade, making it extremely difficult for the owner to resharpen....or in some case it won't sharpen at all. The other down side to this is that large edge bevels create a great deal of cutting resistance, which can make even a very sharp blade, seem dull.
 
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I've never seen a convex sabre grind. Is that what you're referring to? I convex grind my blades on my rotary platten. REALLY tight during the before heat treat initial grind so that the grind approaches flat. Then nice and loose after heat treat to give me the edge.
 
Yeah, I would flat grind initially and instead of grinding down to a thin edge, leave it a bit thicker. Once you have nice even "thick" flat grinds, switch to a slack or rotary and "round off" the grind so it convexes to the edge. That way you get the sharp grind line and a convexed main bevel.
 
Garrett Schmidt said:
Yeah, I would flat grind initially and instead of grinding down to a thin edge, leave it a bit thicker. Once you have nice even "thick" flat grinds, switch to a slack or rotary and "round off" the grind so it convexes to the edge. That way you get the sharp grind line and a convexed main bevel.
Click to expand...

I'm with Garrett, on this one.. thats what i do, flat grind to .028 - .020 edge, heat treat then convex edge......on slack belt.
 
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70% of my grind is done on the flat platen, 30% on the rotary. Final edge is done on the slack belt.
Scott
 
if you are talking about a saber grind, like a convexed mora, i would say to do a regular saber flat grind leaving a bit extra and then after heat treat taking the rest off on a slack belt like everyone else already said.

its a bit trickier than doing it all the way to the spine, but not too hard. i would suggest getting some scrap and playing around with some old belts.
 
The blade im doing is a little screwed up as far as grinds. It was a challenge I felt as though i need to take and on top of that its an order. I Have a 1 1/2" hollow grind that rises on the blade just over an inch and for the rest of the blade i decided a convex that only rose 5/8" on the blade for the rest out to the tip. I just didnt want to loose the grind lines form the hollow to convex. I see what you mean by flat grind first, that will give me the lines im looking for. I appreciate the help-josh
 
A not widely known secret of the crispness of Randall grinds, is that the saber division line was lightly hollow ground to accent the line. At least during the seventies. If you put a straight edge on the wedge of one of this vintage, you can see it. I was told this personally by Pete Hamilton, of Randall Knives. One could do this, then blend into a gentle convex, as easily as a blended flat grind. Similar to a Buck grind, but not as obvious. The hollow of the older Bucks, served no purpose, other than weight reduction, and a sharply defined saber line. Nearing the edge, they might as well have been flat, or convex, as far as the final result.
 
yes, a 14" wheel hollow grind looks very flat to the untrained eye, but will leave a VERY crisp ridge line if done properly.

Personally I do it the way Ed Caffrey described
 
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