Flat grind versus Hollow grind

S

steve porter

Joined
Jan 2, 2001
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I am relatively new to the world of knife making. All my knives to date have been flat ground. I'd like to try hollow grinding but at the moment don't have a large enough contact wheel.My Question here is are either of these grinding method better then the other, and which one would help provide better edge holding abilities.
Any feedback would be greatly appreciated

Thankyou
Steve
 
Steve-

I doubt anyone is going to reply directly to this. It has been asked many times, and there is never a definitive answer. I think there are as many answers to this as there are knifemakers.

If you search the archives you'll find the arguments to this question.

Mine are on there too
wink.gif


Nick
 
"Generally" speaking, hollow grinding seems to be not quite as difficult as flat grinding. I primarily flat grind but hollow grinding (for me) does not take as long to grind.

Another "general" statement that is "generally" true is that you can get a hollow ground edge sharper but a flat ground blade will hold an edge longer and is tougher just as a result of the blade geometry.

Nine times out of ten the above is true but there is always that exception to the rule.
 
Here is the general run down:
1) Hollow Grind- Thin edge that takes a razor edge,but the edge is the weakest of all the grinds, works good for skinning and slicing chores great.
2) Flat Grind- can have a thin edge but wont be as keen as a hollow ground edge,But the edge is stronger during ruff duty jobs such as chopping,works great for skinning slicing and chopping.
3)Convex Grind-The srongest of the grinds but wont take as sharp of a edge as the rest.This grind is the best for ruff duty use such as chopping,it holds it's edge the longest of the three,works great for skinning,chopping but not fine cutting chores.
The flat grind has the best of both worlds as it will hold a keen edge but has strength for ruff duty chores...
Hope this helps,
Bruce

------------------
Bruce Evans Handcrafted Knives
The soul of the Knife begins in the Fire!!!!!
Member of,AKTI#A000223 and The American Bladesmith Society
asmallpicofbruceforforums.jpg
 
When I first started making knives I only flat-ground because that was the only thing I knew how to do. After two and a half years I learned how to hollow-grind. From my experience I can tell you that hollow-grinding on a rubber contact wheel will give you longer belt life, more aggresive cuts and cooler grind than flat grinding.
Flat-grinding is difficult to re-enter after taking your blade off the platen because there is not a groove to fall back in.
Everything about the 3 different grinds is true: hollow being the weakest and convex being the strongest. But I cannot believe that 3 blades, heat-treated and ground 3 different ways to the same thickness and the same angle on the edge, will have different edge-holding abilities.IMHO.
 
I have been flat grinding for 15 years.
This year I switched to hollow grinding.
I hollow ground a few blades for s few orders through the years.

For folders I feel a hollow grind is best after testing. A folder is NOT suppose to get the abuse a big fixed blade gets.
As for being easier I dont think so . Ever grind that is right side to side and at the edge is an intense process.
Flat grinding after you learn how to do it right is about the same.
I use a 14 in wheel to give the blade more strength and high grinds . They come out semi flat. There is not the deep groove to hold the blade grind in so its a biatch like flat grining. The advantage is the belt bump from a hard platen imho. I can get better finishs on the rubber wheel .
The hollow grind does slice MUCH better .
It not for chopping though when using a small wheel. Flat grinds kick butt for this purpose.
With the 14 in wheel I can make a big blades and they chop great. As stated its semi flat.
Its the best of both worlds IMHO with a big wheel.


------------------
Web Site At www.darrelralph.com
MADD MAXX !
 
good advice Darrell, use a BIG wheel. I understand a lot of old stuff was holowground, but on such large wheels that it hard to detect. As for me, I have always wondered what you'd end up with it you took a typical small wheel hollowgrind, you know with the full thickness spine above the "hollow", and cut the thick spine off. A filet knife? That thick spine and the "step' between it and the "hollow" always turned nme off on a lot of hollow ground knives i've seen. Seems awfull in the way to cutting.
 
It would follow that a hollow ground blade would slice more easily. Since there is a small space betweeen the blade and the item being cut the blade would tend to be less "sticky." I'm thinking of a slice of cheese and how it sticks to some knives and not others. I can't imagine that one keeps its edge better than another however....

Of course, what do I know? I'm a rank beginner!
smile.gif


------------------
Peter Atwood

email:fountainman@hotmail.com
 
Aside from the thinness -- and weakness -- of the final edge, there's also a substantive difference in the performance characteristics.

Why aren't any kitchen knives hollow ground? Because once you get past the initial edge on a hollow ground blade, the blade widens non-linearly, and this reduces control and performance. Hollow grind is the thinnest behind the edge, and awesome for shallow cutting, but for deeper cutting, flat grind is my choice.

If you want to do a relatively-inexpensive experiment, buy a Spyderco delica (hollow sabre grind) and Calypso Jr. lightweight (full flat grind), and see how they perform. My prediction is, you'll love the calypso in the kitchen!

For a general-use knife, my own preference is that if the maker uses a shallow grind (a sabre grind), I'd prefer a hollow grind to get the edge thin. But if he's willing to do a full-height grind, a full flat grind will be nearly as thin as a hollow grind, and will perform better for a number of important tasks.

Joe

[This message has been edited by Joe Talmadge (edited 01-08-2001).]
 
"which came first, the chicken or the egg"
hallow is generally sharper (though i've made some pretty sharp falt ground knives)
flat generally stronger.
the steel and heat treat determines how well it holds an edge.
 
I agree with what is being said here. It is looking like an intelligent discussion (FINALLY!!!).

Since I do flat grinds only, and have for almost 15 years, I tend to like a flat grind more so than the others.

Other than what has already been stated, this is what I have to add.
If you take 3 blades ground to the same edge thickness (1 hollow, 1 flat, & 1 convex) , heat treat them all the same, and sharpen them all the same, how can you say that the hollow ground blade will be "sharper"? It is my humble opinion that the sharpness has to do with the type steel, heat treat, and the molecular composition of the steel. (If I am wrong then please correct me). I just can't see that hollow grinding the blade makes it more sharp than the others.

------------------
Barry
Jones Knives
"NEW Knives"
http://albums.photopoint.com/j/AlbumIndex?u=126319&a=5922856
"For DUTY and HUMANITY!"
Curly, Moe, & Larry
 
Dumb question, guys:

What exactly is a hollow grind & a flat grind as it related to knife blades?

I'd like to see pics of examples if possible, or maybe a good explanation.

I'm very familiar with a hollow grind , say on a spade drill, or a hog end mill (rake angle on the flutes, looks like this " )" if you look at the end).

I've not seen a knife blade like this , o any pics/explanation is greatly appreciated!

Sorry!
 
Has anybody ever wondered why they only hollow grind rezors,Becuse they are thinner at the edge so it will get sharper.
And a ax is convex ground,it doesnt get as sharp but boy does it hold that edge...
Anybody heard of a Moran edge? I know Jerry hollow grinds but on his big knives he leaves some meat at the edge so he can Moran the edge(I hope this is correct Jerry) I personaly Flat grind and put a moran edge on it,I grind like this because I forge my blades .And like Jim Batson told me "If you are going to forge in the beveles then why not just flat grind,If you are forging in bevels and hollow grinding you are just making more work for yourself"
Alex Daniels has a platten shaped to the radius of a 5 foot grinding wheel so when he does reproductions of the Sheffield Bowies he has the grind correct.This setup is really cool and the hollow grind that you get is hardly noticeable as a hollow grind...
Bruce

------------------
Bruce Evans Handcrafted Knives
The soul of the Knife begins in the Fire!!!!!
Member of,AKTI#A000223 and The American Bladesmith Society
asmallpicofbruceforforums.jpg
 
Steve

Flat grind, hollow grind etc, etc. Who cares, I'll tell you who. As a maker I have my own personal preferances but I'm not buying my knives the customer is. If you restrict yourself to just one grind you can only satisfy one half of your potential customers.
Do yourself a favor and learn to do BOTH grinds.
Personally nothing turns my head and grabs my attention faster than a flawlessly mirror polished hollow grind because I know how much work went into the blade.

------------------
Robert
Flat Land Knife Works
rdblad@telusplanet.net
http://members.tripod.com/knifeworks/index.html
 
OTE]Originally posted by Joe Talmadge:

Why aren't any kitchen knives hollow ground? Because once you get past the initial edge on a hollow ground blade, the blade widens non-linearly, and this reduces control and performance. Hollow grind is the thinnest behind the edge, and awesome for shallow cutting, but for deeper cutting, flat grind is my choice.

If you want to do a relatively-inexpensive experiment, buy a Spyderco delica (hollow sabre grind) and Calypso Jr. lightweight (full flat grind), and see how they perform. My prediction is, you'll love the calypso in the kitchen!

Joe I don't totally agree. The hollow grind will not bind or hinder any more than a flat it really depends on how the grind is ground and the style of the knife. For exsample I have a CS voyager that will cut better than a flat ground knife in thick material, and another hollow ground knife that will cut through even better than the CS. Truthfully I like all grinds just depends on how they are ground and on the style of the knife. Hard to beat the hollow if done right on cutting .
 
A few years back, I had a mess of broken cultivator tines. These were a little less than 2" wide, about 1/2" thick, and had the radius of a 20" wheel.
I sent a few pieces off to some makers to modify up platens out of.....some liked the idea, but one (Wayne Goddard) had a better idea...he took dimensional 1" X 2" hardwood and made several different "platen toppers".
If I recall, he was going to do one in a radii of a 6' wheel, only less then 12" long, & bolt it to his flat platen.
More 'n one way to skin dat kat!
wink.gif
 
What was being hinted in the "general" statements are basically the extremes. Well of course if three different blades had the exact same edge thickness (the same heat treatment and steel being a mute point, why would you do it any other way?) then sharpness and edge retention would be the same, that is only common sense.
BUT
As Bruce Evans pointed out, this is why razors are hollow ground. They don't have to be that strong but the edge is super thin so they may take a really fine edge. On the other end of the spectrum an axe is convex ground for strength and abuse.

Lets look at it from a different direction. If you were going to make the sharpest knife that you could possibly make, which grind would you use??? It all depends on the application and what grind is best suited for it doesn't it....


[This message has been edited by C L Wilkins (edited 01-09-2001).]
 
<font face="Verdana, Arial" size="2">Originally posted by BARRY JONES:

Other than what has already been stated, this is what I have to add.
If you take 3 blades ground to the same edge thickness (1 hollow, 1 flat, & 1 convex) , heat treat them all the same, and sharpen them all the same, how can you say that the hollow ground blade will be "sharper"? It is my humble opinion that the sharpness has to do with the type steel, heat treat, and the molecular composition of the steel. (If I am wrong then please correct me). I just can't see that hollow grinding the blade makes it more sharp than the others.
</font>
Click to expand...

Barry --

If the very edge is the same, then I agree, I expect them all to cut the same, provided I'm cutting with just the very edge. In many materials, I won't see any difference in performance -- although the user may see a difference is difficulty-of-sharpening, when it comes time to resharpen (the flat grind will have more metal to grind away).

But cut a little deeper in binding materials, and in the hollow ground case, there's less metal behind the edge to push through the material. In the flat ground case, the amount of metal is increasing linearly. Again, in many materials, you won't notice a difference, but in some materials you might.

Lastly, keep pushing through a very binding material. When the material hits the non-linear expansion of the hollow grind, it tends to wedge. The flat grind tends to shear the entire way through.

db posted a contrary position, but I'm not sure how contrary it is. I am over-simplifying somewhat when I say it's just deep cutting that makes or breaks hollow vs. flat grind. It really does depend on the material, but I can't quantify it better than that right now. If the material is especially hard and especially binding, then it's really easy to see the difference when deep cutting, in my experience. If I can find some time, I'll do some experiments with a delica and calypso, both sharpened to the exact same edge, and come up with some concrete examples where the performance characteristics don't match.

 
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