Spyderco Forums

For those of us who like Convex Ground knives Spyderco might like to give consideration to producing a true convex ground knife. Something like a MiniManix in .187" thick 440B steel would seem to be appropriate.

I agree, that would be super cool.

HOWEVER, I don't think they would want to alienate sharpmaker users. When you get a spyderco knife you know that you can count on the grind being one that is compatible with the sharpmaker as far as I know. You never get something too obtuse to hit the edge.

Funny you should ask that right now JDEE. Just yesterday, while searching for something else, I came across a post by Sal from a few years back explaining why the convex grind does not work well in practice.

http://66.113.178.251/forums/showthread.php?t=7911

Another technical thread, great!
Deacon, good that you dug out that old thread, as it contains good information about creating and maintaining a convex grind, as well as the link to the convex grind F.A.Q.
Seems to me you don't need a knife with a factory convex grind. Get a flat ground knife - some sand paper and a mouse pad will let you create it on your own, see here:

http://home.nycap.rr.com/sosak/convex.htm

That's how the hamaguri grind on the Lum Tanto gets shaving sharp. :)

A convex edge is the cat's meow when done correctly, but a pronounced secondary bevel can usually yield very similar results and is easy to maintain.

Thanks for the link to Sal's thoughts. My "wish" is probably "pie in the sky" given the cost of producing a true convex ground blade. Of course all blades can have the edge convexed, and many end up that way more by default then intent, but a true fully convexed blade can be a delight to use.

Pardon my ignorance here. I would think the advantage of what we normally refer to as a full flat grind is that it creates a blade with the most gradual "wedging" action possible. I would think the advantage of a hollow ground blade, partial or full, would be that it creates the thinnest possible cross section for the first quarter inch or so of the blade's height, so it will take a very keen edge. But I would think the advantage of both the saber grind and convex grind would be that they give greater rigidity to a long blade by retaining a greater volume of steel for any give blade than the others. But, since I can only see that as beneficial in a sword, what other benefit does it provide in a normal size knife?

Well, you can sharpen them in the field very easily. A bit of stropping on your jeans is all it takes to get 'em hair poppin' all over again.

BTW, go to knifeforums, and check out the bark river knife and tool board, there's a lot of information on convex grinds there.

The Deacon wrote: But I would think the advantage of both the saber grind and convex grind would be that they give greater rigidity to a long blade by retaining a greater volume of steel for any give blade than the others. But, since I can only see that as beneficial in a sword, what other benefit does it provide in a normal size knife?

A proper ground convex blade with the right steel and heat treatment IMO provides you with a stronger blade and with more steel behind the edge gives you a tougher edge less likely to chip. I have fully convexed and sabre ground blades from less then 3" up to 5" and they out perform any flat ground blade I have with the possible exception of slicing although that depends on the profile. They are easier to maintain and their edge outlasts any traditional flat ground blade I have with similar steel. If you don't like fully convexed blades, fair enough, but that doesn't mean that those who do shouldn't have access to them in the Spyderco range if they want them. That has been one of the good things about Spyderco they offer something for everyone.

keep forgetting my old posts when folks ask for help and info... not a lot I haven't tried.

Should see the edge on my 'fly now. about a 11-12deg inclusive edge, flats on the stone or paper, then about 5deg elevation to kill the burr after. Usually get by on stropping every week or so. Doesn't shave but **** it'll cut all day. Blade is nothing pretty though after 4yrs of abuse & experimenting with it.

convex has it's place when you want to prevent edge deformation from contact. By having a convex edge, the edge is supported by the full width of the blade and will not roll or chip, though it may dent if you hit something hard enough.

A super thin, zero grind, bevel has the advantage of the edge being fully supported by the full blade and no shoulders for the material to grab. But it chips, and rolls rather than dents(unless it's a low HT).

I think the reason production knives are not convex is due to lack of skill/patience with the general user. They want a quick touchup when the knife gets dull, not sitting there removing material from the entire bevel to create a whole new edge when they destroy it.

By putting a convex EDGE on a flat ground knife you get the best of both worlds. No shoulders for material to grab, strong edge, and easier matanence and repair when the edge needs work. Look to the old FB01/02 with mirror polish and convex edge for an example of this as a production knife.

Some custom makers do the same thing but they usually start with thicker material. I've got a tichbourne h5 with a sweet example of this. Flat ground, convex edge with a perfect transition. thick material though. Just TRY and kill the edge on it... doesn't shave though. My tichbourne h7 is a flat ground, 17deg edge(34deg inclusive, from george's hand), and that 440c will work all day long and still shave after some heavy dirty use. Edge maintance with the h5 is just stropping it, the h7 needs a benchstone.

Convex edges aren't hard to form, they're easier to maintain with a little skill, and they cut better in dense/stiff material. But the general user doesn't like em, so we have to make em ourselves. Just grab the sandpaper and mousepad, sit down and have fun.

vampyrewolf wrote:
I think the reason production knives are not convex is due to lack of skill/patience with the general user. They want a quick touchup when the knife gets dull, not sitting there removing material from the entire bevel to create a whole new edge when they destroy it.

The other reason is that they are more costly to produce. That's why I said my "wish" is probably "pie in the sky" as I double that a company like Spyderco could produce a full convex blade that would be within the pockets of knife buyers. I think Sal alluded to this in regards to the original Moran FB01 (of which I have one) and that was only a convex edge. But we can dream can't we?

The Deacon wrote:[...]But I would think the advantage of both the saber grind and convex grind would be that they give greater rigidity to a long blade by retaining a greater volume of steel for any give blade than the others. But, since I can only see that as beneficial in a sword, what other benefit does it provide in a normal size knife?

I'm no expert either, but SD knives and tactical knives (folding prybar type :D ) come to mind.
The tanto style that Bob Lum used has this type of reinforced convex tip for better penetration of armour, while the main part of the blade has a hollow grind for better cutting ability. So a convex ground SD knife should be reasonable?