What is your favourite grind and Why?


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alsask
December 20, 2013, 11:09 PM
Lots of conversation about knife grinds of course and I was wondering what people favour and why.

Myself I like...

1. Convex grind. Probably the easiest to sharpen and supposedly one of the stronger profiles.

2. Scandi grind. Again another easy to sharpen design although it could be argued that it may not be the best when you are splitting a rib cage on a deer or any other high impact type chore.

3. Hollow grind. I find this to be the hardest to field sharpen.

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Yo Mama
December 20, 2013, 11:22 PM
I love full flat grinds, and depending on the blade a good flat saber grind is nice

Sam Cade
December 20, 2013, 11:37 PM
On a big choppy knife I like a full flat or high saber (for a bit more grunt) with a convex secondary.
Machetes end up convex.

Carving or crafty knives I prefer a scandi or full height convex provided the blade stock is nice and thin.

rcmodel
December 20, 2013, 11:45 PM
A hollow-grind should be the sharpest, and easiest to sharpen of them all.
Like a straight-razor!

But what I see is, a lot of commercial blades have a big honk'en hollow-grind.
Just above a bigger, very steep bevel grind, that keeps them from breaking or chipping like a razor would.

So you are trying to sharpen a thick chisel edge, not a thin hollow-ground edge.

You are not really dealing with a hollow ground blade.
You are dealing with a blade that only looks like one, but doesn't sharpen or cut like one.

rc

Sam Cade
December 20, 2013, 11:58 PM
Gerber calls that a "double grind":rolleyes: when they put it on their machetes.

I'd kinda like to see how they cut it.

rcmodel
December 21, 2013, 12:17 AM
The old Buck 100 series were another perfect example!!

They look hollow-ground till you can see daylight through the middle.

But look at the thickness & bevel of the edge you are trying to sharpen to a decent cutting angle!!

rc

harvjr
December 21, 2013, 08:10 AM
Hollow grind for most of the things I do with a knife. I even made a cutting competition knife with a hollow grind and it worked great.

Harv

mole
December 21, 2013, 09:53 AM
I agree with yo momma: "I love full flat grinds, and depending on the blade a good flat saber grind is nice"

GLOOB
December 21, 2013, 02:48 PM
There's a pervasive misconception about knife grinds that tries to associate the primary grind with edge sharpness and durability.

For instance, Wikipedia states that a hollowgrind "yields a very sharp but weak edge which requires stropping for maintenance."

In fact, this statement is completely inaccurate and nonsensical.

Let's take a straight razor as an example. Does the hollowgrind make the razor sharper? The hollowgrind has nothing to do with the final edge. There's no practical way to hone an actual hollowgrind into the edge; that's done with a flat stone producing a flat bevel, just like any other knife, only in the case of a straight razor it's quite acute. Somewhere between 14-20 degrees. This acute angle is what makes the edge of a razor weak. Also, the thinness of the blade behind that edge makes it weak, but that's nothing to do with the grind; a hollowgrind knife can be very thick, as RC noted.

The blade stock of a straight razor is actually quite thick. The average straight razor is thicker than a kitchen knife. The hollowgrind is just there to thin the blade near the edge while retaining a thick spine for rigidity.

When done right, a hollowgrind is great. You can either look at it as a way to get the edge thinner. Or you can look at it as a way to make the spine fatter. Or you can look at it as a way to remove some of the unnecessary material behind the edge, simply to make sharpening easier.

Take, say, a fat 1/4" convex knife with a thick, strong edge. If you put in a shallow hollowgrind starting, say, a few mm behind the edge, and ending a half inch before the spine, the edge would be just as durable and strong, and the knife would still make a great prybar. The big difference is it would be easier to sharpen... and also you could use more aggressive grits without scratching up the entire knife.

But my average everyday knives, I trend towards thinner blades, and full flat or thin convex is my preferred for such knives. But on a sharpened prybar, I would appreciate a nicely done hollowgrind that leaves the right amount of meat behind the edge. Say at least 35-40 mics min. I can make the final edge geometry any way I want, but I cannot put a hollowgrind on a knife, myself.

Sam Cade
December 21, 2013, 03:33 PM
Grind matters immensely as it effects how the material being cut is displaced as the blade moves through the medium being cut.

To wit:
A short hollowgrind similar to a pocket knife fails miserably in a big chopper. Not only is it fragile due to a lack of support to the edge, the abrupt transition to full stock thickness acts as a brake, limiting the depth of the cut.
It doesn't matter how sharp the edge is in this case, the lim-fac is the primary grind.
http://www.thehighroad.org/attachment.php?attachmentid=191618&stc=1&d=1385428822

http://www.thehighroad.org/attachment.php?attachmentid=191656&stc=1&d=1385506406

Sam Cade
December 21, 2013, 03:37 PM
So, to reiterate, blade performance is often a function of the entire cross-sectional profile of the blade.

Gordon
December 21, 2013, 03:47 PM
Full flat grind, hollow grinds are nice on razors.

Sam Cade
December 21, 2013, 04:11 PM
Agreed Gordon. I like a full hollow razor on the rare occasions I shave my mug. I can feel a difference between a FFG and a FHG my beard is so thick.


http://www.thehighroad.org/attachment.php?attachmentid=191592&stc=1&d=1385358590

alsask
December 21, 2013, 04:17 PM
There is one blade grind I definately do not like and that is the serrated edge. It is OK for kitchen bread knives.

There have been a few knives that have caught my eye from time to time and I passed them up due to serrations.

GLOOB
December 21, 2013, 06:41 PM
A short hollowgrind similar to a pocket knife fails miserably in a big chopper. Not only is it fragile due to a lack of support.

I agree that a fat convex grind is the way to go for a splitting axe. Or a knife that wants to be a splitting axe.

The misconception is that a hollowground knife's edge is "fragile due to lack of support."

If you take a CARBON steel kitchen knife (some stainless knives - cheap or high end, doesn't matter - are too brittle) and you hack on a tree with it, the edge will roll and/or chip. But the damage is limited to a small fraction of an inch past the edge. A hollowgrind doesn't need to go that thin. On top of that, the damage is all starting at the cutting edge, due to the acute edge angle on the kitchen knife. Just by slightly changing the final edge geometry by setting in a more obtuse microbevel to the appropriate depth, that carbon steel kitchen knife can hack away all day without failing. As could a hollowground knife with the appropriate grind and edge.

This begs the question, why are so many pocket knives so thick to where they even need a hollowgrind at all? Why is the blade on a Mora knife only 0.080" thick, and the blade on a Kershaw Blur abour 0.125" thick? Partly, it might be because that specific Kershaw uses a more brittle steel. But mostly, it's market demand. That's the kind of knife that people want to buy. They like the weight, look, or whatever. And it makes a better prybar.

If you have steel at least say, maybe, 30-45 mics (depending on the steel) thick behind that final edge bevel, and a crack goes back far enough to reach the hollowground area, the entire blade was going to snap in two, anyway, regardless of the primary grind.

Now consider that no matter how fat you make your primary grind, you still have to put an edge on it. That edge angle is what determines whether the edge on your 2 lb, 1/4" thick chopper is going to fail or not. The type of alloy and heat treat, plus that edge angle are primary determining factors on whether the blade is going to snap while chopping. The thickness of the spine affects lateral strength, primarily. And the thickness of the primary grind approaching the edge does affect cutting ability (sticking vs splitting) where chopping wood is concerned, I agree. But it does not add significant strength to the edge.

Sam Cade
December 21, 2013, 07:56 PM
Are we really going to have to have a discussion involving the stress/strain curve and Poisson's ratio in order to prove conventional wisdom correct?

Sam Cade
December 21, 2013, 07:59 PM
Meanwhile, over at A.G Russell

Blade Geometry for noobs.
http://www.agrussell.com/Articles/a/105/

GLOOB
December 21, 2013, 08:06 PM
the edge is extraordinarily thin, and thin edges slice better. The disadvantage is that the thinner the edge, the weaker it is. Hollow ground edges
From your link. This is sooo wrong, I don't know where to start.

1. A hollow ground edge is not necessarily "extraordinarily thin." In fact, I have a Kershaw Selectfire and a Sodbuster which are my only hollowground knives. The secondary bevel on these knives is in the neighborhood of 35 degrees, as from the factory. This means the edge of these knives is well thicker than a factory Mora, which is around 24-25 degrees. Of course, the factory angles don't necessarily matter. You can change these as you see fit. The important thing is that the hollow grind part of my sodbuster mike'd out at around 30 mics at the thinnest, IIRC, which is thick enough to support w/e edge you want to put on it. Have you ever seen a knife chip out or fold beyond a secondary bevel 30 mics thick? I never measured my Kershaw before regrinding it, but it never chipped out or folded. Either one of these knives has a much more durable edge, OOB, than a factory Mora.

2. Hollow ground "edges." Already this is meaningless. There's no such thing as a hollow ground edge. A hollow grind describes the primary grind, which has nothing at all to do with the edge. You can have a flat secondary, a microbevelled edge, or a convexed edge on a hollowground knife. You cannot put a hollow ground edge on any knife, unless you want to spend hours with specialized equipment to make an edge we already know will be terrible.

Sam Cade
December 21, 2013, 09:14 PM
And the thickness of the primary grind approaching the edge does affect cutting ability (sticking vs splitting) where chopping wood is concerned, I agree. But it does not add significant strength to the edge.

Other than holding it up of course.

The stresses that a knife blade undergoes aren't necessarily linear and are frequently torsional.
Steel behind the bevel increases the stress required to push the edge out of line (rippling), not only laterally, but in-toward the spine.

Cross section, plastic deformation, ad infinitum, ad nauseam. ;)

Fred Fuller
December 22, 2013, 09:52 PM
For a general use blade, I much prefer FFG... it's just slicier.

Zeke/PA
December 23, 2013, 09:19 AM
In my knifemaking days I built a grinder so I could hollow grind. I find it much easier to finish/polish a hollow ground blade. Someone mentioned serated blades. I really don't like 'em but to each his own.

lobo9er
December 27, 2013, 09:13 PM
Convex with a secondary v-edge or micro bevel is petty good too. Easy to maintain with a Strop or stone what ever is available.

GLOOB
December 28, 2013, 04:33 PM
For a general use blade, I much prefer FFG... it's just slicier.

A FFG with a microbevel is very slicey, indeed. A thin zero convex with microbevel is really the same thing, for thinner knives. Basically, it's a FFG that runs out of spine thickness, then the grind line is blended in. Sorta like the grind on a factory Opinel. Sure an Opinel is really slicey, but then again, the blade is too thin to even put on a hollow grind.

The one place where I find a hollow primary grind can actually outslice a FFG or convex is in a block of cheese, all else nearly equal - meaning on knives thick enough to have a hollowgrind, so maybe over 0.1" thick. There comes a point where the hollow grind gives the cheese less place to stick.

Well, on the other hand, in most other matierials a FFG defacto has the thinnest possible edge for a knife made of the same blade stock. So yeah, FFG is definitely the sliciest in blades of the same size/thickness!

Esoxchaser
December 28, 2013, 05:19 PM
On my work knives it doesn't matter much which grind they have when purchased, they will soon have a hand lapped double bevel flat "grind" I put on with diamond stones. I'll get three to five years out of a hefty work blade till I am into the spine and it takes too much effort to cut anything. Then I donate them to other people..........

Sam Cade
December 28, 2013, 06:18 PM
The one place where I find a hollow primary grind can actually outslice a FFG or convex is in a block of cheese, all else nearly equal - meaning on knives thick enough to have a hollowgrind, so maybe over 0.1" thick. There comes a point where the hollow grind gives the cheese less place to stick.

Turnips (especially big'uns) are a fascinating test medium for slicing performance.

Valkman
December 28, 2013, 06:38 PM
I started out trying to make flat grinds when I first started grinding, but soon went to the hollow grind. I loved everything about it, and if it was good enough for Bob Loveless it was good enough for me.

GLOOB
December 30, 2013, 03:46 PM
The way I see it, a hollow grind is just an auxiliary feature, when done right. Other than cutting cheese, it doesn't seem to make any difference one way or another.

If you grind the bevel on a hollow grind by putting the spine all the way to the stone, then you end up with the same edge as a zero FFG. Obviously, you will need to add a microbevel, same as you would most any zero FFG. Most factory hollow grind knives don't come with an edge that thin, though. The typical hollow ground knife has essentially the same edge as a non-zero flat grind or compound bevel knife, with a thick edge and a secondary bevel at 35-40 degrees, same as 90 percent of knives on the planet. Just like any knife, you can thin the edge, or bring the edge back to fatten it up, you can convex it, etc, etc.

What you can't do is bring the edge any thinner than what you could do with a FFG. (Unless you were to sharpen it with the spine hanging below the surface of the stone, and you don't do that even with a straight razor!) So the only kind of material that should hit and stick on the spine of a hollow ground blade would be something compressible/elastic. And yet, IME, such material like cheese actually sticks less to a hollow ground blade.

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