grinds: hollow, flat, convex

A

ayz

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Jul 5, 2004
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i've always gotten the basic gist of these but unclear to the specifics. i was wondering if there was an FAQ or if someone could explain to me the exact differents between the types of grinds, as well as how you can tell what kind of grind a knife has just by examining the edge
 
A search would give you more info than you ever care, but here's a graphic exagerrating the differences:
knifegrinds.gif


All three are great when done properly. They excel at different things. A flat grind is flat. You can sight from edge to spine and the grind is flat all the way along. Hollow grinds are concave, meaning they go inward toward the center of the knife, and they have a distinct look and sort of "round" the reflections in them. Convex grinds can sometimes be hard to spot, but sight from tip to butt and they look kind of round, and usually end at a "zero edge" or with a tiny, tiny microbevel. If you look from edge to spine, you really see the roundness of the grind, too.

Then you can have sort of compound grinds. I have a Bark River ELK that has a deep hollow grind, but the edge is convex, so it's both to a certain extent. Or you can have a flat grind with a convex edge, or a flat grind with a (technically) hollow edge (but for all practical purposes it's really more or less flat). Look at a lot of knives and the differences couldn't be more obvious.
 
so i guess my question is what is a convex grind good for?

i know hollow is best for slicing

flat is better for chopping

i assume convex is better than flat at chopping in the sense of not chipping but cuts worse?
 
Convex grinds are really misleading. I have a knife I made myself from 1/8" 1084 with convex grind to a microbevel and the edge is THIN. It is one tough bastard. I cut copper wire, scrape, do all kinds of abusive things to it and no problems. Try something like a Bark River Northstar. Fairly narrow blade, almost 5/32" stock, and what looks like a thick convex grind to a zero edge. That thing slices like there is no tomorrow. When I got mine I took it in the kitchen thinking "This is going to suck" and I was amazed. If you really want to experience what a convex edge can do, I would look at most of the Bark River knives because the majority of the blade have full convex grinds, although occasionally you'll see an oddity like the ELK that has a compound grind. They are unbelievable. In terms of function, I like the convex grind the best, but I make most of my knives with flat grinds because proper sharpening of a convex blade would ruin the nice finish I put on my knives! Sad, but true!

Furthermore, in theory, proper sharpening on a convex knife will not change the edge geometry. As metal is removed, it is, theoretically, removed equally from edge to spine, so the knife will perform as well after 1,000 sharpenings as it did after the first. To a certain extent, this can also be said with a hollow grind. Flat grind geometry can change over time, with the edge getting thicker and thicker with each sharpening, until you need to regrind the angle of the flat to thin it out. I've never used a knife THAT much to see this effect, but that's the idea.
 
I have a list from a book that has some info. From "How to make your own knives" By Jim Mayes.

I'll summarize it here for you.

Differentgrinds-copy.jpg


Flat V grind=good choice for skinning, and carving. slicing ability above average with only fair resistance to abuse.

Modified V= General purpose grind. Also called the Saber grind or Scandi grind. Probably the best GP grind actually. Good slicing ability usually but not as good as a flat, higher resistance to abuse than flat.

Hollow grind=Outstanding slicing ability usually. Weaker usually because it is ground thinner so it can have a low resistance to abuses. Used to pry or when hitting a bone can nick or break the edge and/or past the secondary bevel.

Concave grind=Very similar to hollow grind only full concave on the blade. Abuse resistance is usually poor but slicing is high.

Convex= High resistance to abuse. Long edge life usually. Seen primarily in large choppers, machetes, axes, cane knives. Traditional sharpening of these was done with a file or course stone. Slicing ability on the bigger tools is quite poor.

Tanto= Sabre or Mod V grind with reinforced point for higher resistance to stabbing and prying due to increased thickness.

Chisel grind=One side of the blade or cutting tool only. Such as wood chisels. Usually strong, and easy to sharpen. Most often used in general utility tools.

Modified V w/fuller= High saber grind with fullers or blood grooves as they were called and made famous in WWII. Also seen in flat grinds on occassion. The real purpose is believed to be weight reduction in bigger knives and swords. Pretty much the same in all categories as the Mod V grind but perhaps less able to widstand abuses although this is argueable.
 
STR, that's good information, but it's almost too general. SOOOOOO much of a knife's performance is based on multiple factors that you can buy a "flat ground" knife that doesn't do any of the stuff it's supposed to do, or could excel beyond what it's supposed to do. Thickness of stock, finish of the knife, the edge geometry, heat treat of the knife, etc all play into it, big time. I'm constantly surprised by knife performance in my testing, so the grind is a part of the full story.
 
Sorry I thought all that was asked for was general info on the subject. Rest easy though. I'm sure Cliff will chime in shortly and then you will have your full of more than general info.
 
Chiro75 said:
Flat grind geometry can change over time, with the edge getting thicker and thicker with each sharpening, until you need to regrind the angle of the flat to thin it out. I've never used a knife THAT much to see this effect, but that's the idea.
Click to expand...
It depends on the extent of the flat grind, the rate of growth of the edge is proportional to the angle (ok it is not exactly linear, but it is to a fine approximation) and of course the initial edge thickness is rather critical.

If you sharpen something from Boye which is 0.005" thick behind the edge, you have to wear away ~1/4" of steel to even reach the same edge thickness that most knives come with anyway.

This issue is mainly significant on shallow sabre ground knives which are are the limit of edge thickness for decent cutting ability anyway. Even then though the solution is to just have them reground as necessary, it takes years of use.

As for what the grinds are used for, as Chiro noted you can't generalize as one grind does this and another does this, there are hollow ground axes and convex ground light utility knives.

The actual curvature of the grind (convex/flat/hollow) is secondary to the actual cross section of the knife and the general shape of the blade. Ref :

http://www.bladeforums.com/forums/showpost.php?p=3128609&postcount=3

-Cliff
 
STR said:
Why not just give him the whole link ...
Click to expand...
Because that post contained the info I wanted to present which was specifically :

"...in general look not only at the type of grind, but its he nature and use the following few simple rules to get a feel for performance :

-as more metal is removed you lose strength this will make the knife easier to bend, so a thin spine makes the whole blade easier to bend and a thin edge makes the edge easier to ripple, a thin tip is also easier to bend / deflect

-as more metal is removed the cutting ability increases, note the only part of a knife which matters is what the material exerts pressure upon, so if you are cutting hemp the edge geometry is very critical, but if you are chopping soft woods the whole profile is significant

Note how these go in opposite to one another, you can't maximize strength and cutting ability at the same time, you have to decide how much of one you are willing to sacrifice.
Click to expand...
Individual posts contain links to the full thread, they are in the top left hand corner.

-Cliff
 
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