True Convex Grinds?

bobbywett

bobbywett

Joined
Jul 23, 2006
Messages
1,231
Hi Folks,

Got a question or 3 about creating a true and or full convex grind.

1.) What knives do you put convex grinds on....ie....Hunters, Choppers/Camp, fighters/bowies?

2.) At what edge thickness do you start your convex grind....ie.... .050, .030, .020....?

3.) How high up from edge to spine do you take your convex....ie.... 1-5th, 1-4th, 1-3rd, 1-1/2 the blade width? I can't tell from the photo's, but I believe that the superb Master Smith Jason Knight has a radical convex on a lot of his fighters?

I know I've got more questions on this topic, but they elude me for the moment. Any and all help would be greatly appreciated.

Thanks,

Bob,

Hershey, PA
 
I never touch mine to a flat platten. I try to get the convex grind to go all the way to the spine. I measure an edge thickness of 0.020" or less before putting a microbevel on mine.
 
Almost all of the knives that I make have a full convex grind clear to the spine. the blades are ground right down to sharp with no secondary bevel. this includes kitcen cutlery folders and all of the hunting camp/choppers.
 
Bill Burke said:
the blades are ground right down to sharp with no secondary bevel.
Click to expand...

OK Bill this brings up another question. I really like the way a full bevel creates a nice sharp edge but how do I sharpen the blade after it is used in the field for a while? Do I go back to my shop, regrind the whole knife to maintain the full bevel or create a secondary grind with a quick touch up on a stone? I like a nice hand sanded or mirror finish on my knives and maintaining a full grind every time I resharpen could take hours.
Gerry
 
I never touch mine to a flat platten. I try to get the convex grind to go all the way to the spine. I measure an edge thickness of 0.020" or less before putting a microbevel on mine.
Click to expand...

Thanks for your response Fiddleback, I'll start to incorporate a higher convex on my blades and try and hold off setting the edge to .020.

Almost all of the knives that I make have a full convex grind clear to the spine. the blades are ground right down to sharp with no secondary bevel. this includes kitcen cutlery folders and all of the hunting camp/choppers.
Click to expand...

Thanks you Bill for reinforcing Fiddleback's notion that the convex can go all the way back to the spine.
 
G L Drew said:
OK Bill this brings up another question. I really like the way a full bevel creates a nice sharp edge but how do I sharpen the blade after it is used in the field for a while? Do I go back to my shop, regrind the whole knife to maintain the full bevel or create a secondary grind with a quick touch up on a stone? I like a nice hand sanded or mirror finish on my knives and maintaining a full grind every time I resharpen could take hours.
Gerry
Click to expand...

I'd like to know that also. I've toyed with no secondary bevel but always have decided to leave it with a micro bevel for ease of sharpening.
 
G L Drew said:
OK Bill this brings up another question. I really like the way a full bevel creates a nice sharp edge but how do I sharpen the blade after it is used in the field for a while? Do I go back to my shop, regrind the whole knife to maintain the full bevel or create a secondary grind with a quick touch up on a stone? I like a nice hand sanded or mirror finish on my knives and maintaining a full grind every time I resharpen could take hours.
Gerry
Click to expand...

A good convex edge is pretty easy to maintain. I find that I can sharpen maybe ten times befor I see a noticeable secondary bevel start to form. What I do then is to start sharpening at a very low angle, after several (up to ten) strokes on each side of the blade i then increase the angle slightlyand repeat until I am at about a 30 degree included angle with very little pressure on the stone. this gives you several minute micro bevals that blend together very easily on a strop. This proceedure sounds kind of complicated and can be a real pain IF you are using some kind of fixture for sharpening but are very easily preformed freehand on a stone with a little practice.
 
Just wondering too, is there a way to sharpen on stones to make the grind go all the way to the spine without a secondary bevel? You know, like maybe laying the blade flat on the stone, and the sliding it all the way from the flat and increase angle until you reach the edge? or do you have to sharpen with a secondary bevel on a stone? I, too, really don't like to mess up the look of a beautiful freshly grounded full convex edge. thanks
 
On his knifemaking video, Bill Moran commented that convexing a blade on a slack belt leaves the blade too convex. Something like the KMG rotary platen helps eliminate this problem, but I still flat grind down to a point and then go to the rotary platen. I think that Scott Gossman does all of his burly field knives fully convexed on the rotary platen.
 
My father likes to flat grind and then finish it off with a hollowed out platen. The customized platen allows him to have more control of the convex grind that it yields. I think he has a couple different platens for more narrow knives or wider knives.
 
jdm61 said:
On his knifemaking video, Bill Moran commented that convexing a blade on a slack belt leaves the blade too convex. Something like the KMG rotary platen helps eliminate this problem, but I still flat grind down to a point and then go to the rotary platen. I think that Scott Gossman does all of his burly field knives fully convexed on the rotary platen.
Click to expand...

In my experiance this can be true but not always. There are a few factors to consider. The tension on the belt, the weight of the belt, the presure you use and the sharpness of the belts.

If you use sharp x weight belts with plenty of tension there should be no problem using a slack belt setup. Of course the grinder can make diferance also.

Of course this is just my two cents
Your milage may vary:)
 
I've done both, grinding each side entirely convex to the spine as well as flat grinding both sides leaving the edge thick (half of the blade thickness) and then convexing the edge area down to a "zero". Comparing two knives with the same profile, the first will result in a generally thicker/heavier blade with shallower plunge cuts while the second will give more deeply defined plunges with a thinner blade overall as well as a little less weight. I wouldn't say either is better in my opinion....just different methods and end results. I prefer the later method because I am a sucker for nice smooth/flat flats and that method keeps those while giving you a decent sized convex portion as well. A well done full convex looks cool too though. To each his own.
 
What ever happened to nice, convex grinds? Are they too difficult?
And what advantage does a convex grind give a knife?
 
A good convex grind is all based on control. If a maker is doing a convex grind and letting the slack belt area determin the the amount of convex on the bevels then they are, IN MY OPINION, doing it wrong. The geometry of the blade and the amount and geometry of convex should be controlled and predetermined not left to chance.
 
Bill Burke said:
A good convex grind is all based on control. If a maker is doing a convex grind and letting the slack belt area determin the the amount of convex on the bevels then they are, IN MY OPINION, doing it wrong. The geometry of the blade and the amount and geometry of convex should be controlled and predetermined not left to chance.
Click to expand...

Bill,
I'm of the same opinion. I shape the geometry of the convex on a flat platen then move to a slack belt to "blend" everything.
Later,
Iz
 
I have only made a few with a convex, however I agree with Bill pretty much to the tee. I have only used it for choppers(1 camp knife, and 2 kuhkri's). I found I just had to not get in a hurry using slack belt...meaning if I wanted to flatten it out a bit I would just not push as hard and let the belt take the material off slowly. I would suspect a tighter grouping of the wheels would make this easier though. I'm just a rookie, but that's my limited experience.
 
Well for what its worth from me and being a new knife maker of less than a year but ive made over 30 knives since i started last december, I started all my first knives with a convex blade . Later I tried a flat grind and didnt like the way it all went and went back to convex . I then decided to try my 10 inch contact wheel for hollow grinding and I love It . I find it way easier even to free hand hollow grind than it is to flat grind period and convex in my opinion not hold an edge as sharp or as long as a convex but not as strong . A convex blade is a work horse for ruff useage taking way more abuse than a thin hollow ground blade. So it really matters what you want the knife to do . My neighbour is ruff on his truck / quad and so on so he would need a more durable blade sucjh as a convex blade. I have a Kmg clone very well made I lighten up on the spring while I have the flat platten on and use it as if im in the slack belt mode constantly watching how slack the belt is with each grit i grind with . I also grind right to the spine and thin the spine by about 1/2 the thickness of what i start with .I sharpen by going to 400 grit and then take it to the buffer and finally the paper wheel. hope this helps kellyw
 
i love this thread.

we do convex grinds on most of our knives and all the swords.

we use water stones from japan. 7 stones for the swords and 4 stones for the knives.

i have a personal knife i use and its convex. i sharpen it with my belt that hold my pants up. i loop the belt on my foot and pull the other end.

at home i will put a thin cloth on a table and then a sheet of 600 grit on top of the cloth. then make one pass on either side lightly. then i feel of the edge. if i like it no more. if i don't i will make one more pass on each side.

then i will take a sheet of paper like 110 card stock and put that on the table with the cloth and swipe a few times. they get sharp for me.
 
Bill Burke said:
A good convex grind is all based on control. If a maker is doing a convex grind and letting the slack belt area determin the the amount of convex on the bevels then they are, IN MY OPINION, doing it wrong. The geometry of the blade and the amount and geometry of convex should be controlled and predetermined not left to chance.
Click to expand...

I agree. I use my rotary platten set really tight, then I wisper the steel away using incredibly light pressure. The result is a grind that approaches flat, but is continuously convex. Very light pressure is especially important at the plunge. My convex blades are ground THIN. I stop between .020 - .010" thick, then microbevel with a slack belt.
 
You must log in or register to reply here.
Back
Top