Questions about the various grinds

Mongo

Mongo

Joined
Nov 5, 2001
Messages
8,969
Greetings,
I feel like an idiot on many occasions, this particular time I'm hoping you all can clear up some misconceptions and questions I have. What are the characteristics and differences between the different grinds? Specifically: convex grind, hollow grind, flat grind. I already know what a chisel grind is, and plan to stay away from that one. There are those here that favor certain grinds for the way they cut. One proponent of the convex grind is so very persuasive in his description of it, that I want to rush out and get one. Are there other types of grinds that I have failed to mention? Are some easier than others to sharpen/maintain? Do makers have preferences for a particular type of grind, and if so... which one?
Ah, so many questions...
Thank you in advance for your answers,
Mongo
 
Mongo,

There is not a perfect, one size-fits-all grind. How do I know this? If there was they wouldn't be so much debate and so many methods.

You need to answer these:

What's the blade for? (Wood chopping ax, Wood carving, Boning, fillet, 'camp' knife, meat cleaver, box cutting, skinning, ....)

Who's using it? (Kid, Doctor, Fisherman, Mom in the kitchen, professional butcher, ...)

Then you can answer:

What blade shape?
How long?
How stiff?

Then you can answer:
How wide?
How thick?

Then you can answer:
What grind should I use?



For example the guy that comes out to slaughter our livestock uses a knife with an edge sooooo thin, weak, and soft that he is constantly straightening it. However, it cuts like a son of a gun. He skins a pig faster than you can peel an apple (well not quite ;) ).

However, a knife like that would drive my wife nuts. Because she isn't going to use a steel every 5 cuts. (I didn't check his out up close but I'll bet he kept a 'wire' edge.)

Convex edge? When it's new and good I'll bet you can get a great edge on it. However, after alot of sharpening you're getting into the meat of the blade pretty fast. Then you need to regrind to get that factory sharp edge again.

But even that's not a universal statement. How thick is the blade and how blunt is the convex? .....

I sharpen folks' kitchen knives. Henkels have a thin flat ground blade. I can sharpen those a lot of times before I need to do a double bevel. However, I've done some other flat ground knives that were quite thick. On those I had to first perform a mini-flat grind, before I put on the edge. Otherwise it was soo thick you couldn't get the performance you want, no matter how sharp.

Last week I did some hollow ground kitchen knives. The had a very shallow hollow grind. This was their first sharpening and I got a great edge on them. However, in a couple more times I'll be into the thick part of the steel and the knives will be useless. You'd have to completely regrind.

I think I'm blabbing.... So, I'd better stop. Hope it gives you food for thought.

Steve
 
Mongo,

I got to thinking.

Was your friend talking about the blade grind or the edge grind?

I was answering the blade grind question. However in sharpening you are dealing with the edge grind. (I hope I'm getting my terms right here!)

There are 3 ways to sharpen. They can go by the same names as blade grindings, hence some confusion for me.

Flat - this is done on a stone
Hollow - this is done on a wheel (like the Tormek).
Convex - This is done with a strop

If you have a very thin blade, then using a strop (like a barber) is a good idea. Because it adds strength to the edge. Where as a hollow grind on that thin of a blade might make it too weak.

I mostly sharpen on a wheel so it's a 'hollow' grind. However, the wheel is 8" and most edges are narrow enough that I don't think you can tell a difference between that and a Flat edge from a stone. But on a thicker blade (which makes a wider edge) I believe there is a difference.

I have a thick hunting knive that is OK when sharpened on a stone. However, on the wheel it is wickedly sharp. If I used a strop and got a convex edge I don't think you could cut with it.

So, are you wondering about a Convex blade grind with a flat edge? Or a Hollow blade grind with a convex edge. Or a ..... :)

More Food For Thought,

Steve
 
Thanks for the links. Steve/itrade... the person I was refering to was talking about the convex edge grind, as found for example on the Marbles fixed blades. He promoted a very easily resharpened edge just by stropping. Very easy to do in the field in other words. I think that most of my blades are flat ground. I have two Doziers, they are wicked sharp and I can touch them up on a DMT in a short time. I also have the OVB bowie and a BK-9, which I haven't had to resharpen yet... haven't had the heart to use the former, and haven't beat the crap out of the latter yet. My other blades pretty much consist of slipjoint blades that also seem to be flat ground. My sharpening so far consists of either a Norton india stone for the carbon steels, or DMT stones for the D2 blades. I am pretty much a neophyte to free hand sharpening, and can't seem to get the clamps on my DMT system to hold anything larger that the slippie blades.
Thanks,
Mongo
 
Mongo,

Now you're out of my league. I'm not a stropping kinda guy.

I know guys create a flat edge with a burr and then strop to remove the burr. However, that's different than creating a convex edge by stropping. Something I have no direct knowledge. Sorry.

I have tried a fairly flat edge and then tried to strop to razor sharp but couldn't do it. I just don't know how.

I'm just guessing, but maybe you create a very low angle flat edge, say 10 or 12 degrees all the way out to a wire edge. Then you strop it back into a convex edge. ??

In any case, once the edge has been stropped to death, I'm sure you'll need a re-grind, just like any edged tool. Unless the blade is thin like a razor.

In any case, sorry I don't have a direct answer to your question. Maybe someone else here can shed some light on it.


Steve
 
I put a convex edge on a lot of my camp style knives. You can easily strop them if you don't let them get very dull. I think Laurence uses a very slight convex on his knives and they do very well.
 
i put convex edges on all my knives both convex and flat grind, the thinner the blade the more gradaul sp? un my rhino chop the edge grind is about a 1/4" high on the blade. being convex 220g there is enought steel there to really last and not chip or roll.
 
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