What grind for my knife

[Andy]

though i know a fair bit about knives (uncle has made them for WS and i come from family history of knife making) i don't have much experence with the different grinds of blade. both my lock knife and sheath knife are hollow grind. i haven't had any use with a high quality flat grind. would this make much difference?

 

[Colin KC]

Hi Andy (what we need is Martyn & some of his lovely drawings)

A hollow grind, from the spine is comparable to a flat grind (a la SAK)

A hollow "sabre" grind is comparable to a WS woody with a secondary bevelled edge.

Both would be treated exactly the same as your hollow ground knives, the exception being, a zero edge single bevelled knife, which would be sharpened across the whole of the bevel.


Hope that helps


Col

 

[Andy]

i was thinking about that pros and cons of primary flat verses the hollow with a secondardy grind

 

[C_Claycomb]

Question is, difference to what? How they cut, how they sharpen, how durable they are??

If you can work through the pages from the link below, there is a ton of info there. You will probably get what you want, and more, from reading it.
http://www.bladeforums.com/features/faqbladegeo.shtml

There are many more factors than just "grind type" that affect how a knife cuts and how it works for different jobs. Height of the grind, type of secondary bevel, if present, thickness of stock and width of blade.

Hope the link helps.

Chris

 

[Gary]

In simplest terms I'd say a hollow grind is usually on a secondary bevel and is mostly produced on knives that are machine sharpened in the factory - secondary bevels arent desirable in a field knife thats used with wood as it has less bite.

Flat grind is generally done on a stone (although I have everal flat grinds which are slightly convex and proof of a belt pr wheel being used) - flat grind is easily sharpened and much better in the field where carving wood is required.

Hope that simplified things for you.

 

[C_Claycomb]

Gary is right that a single flat bevel, as seen on Puukos and the Woodlore type knife makes a very good wood carver. From what I have seen there are two reasons for this, one is that the bevels meet at the edge in a much more acute angle than is normal when using a secondary bevel at the edge. This more acute edge offers less initial resistance. The other factor is that the wide bevel acts as a guide, like the sole of a plane, making it much easier to remove long precise shavings (as for feather sticks). If the bevel is laid flat on the wood, only a tiny increase in the angle makes the edge cut.

Despite hearing it all the time, I am far from convinced that a single flat grind is really easier to maintain in the field. Sharpening the 1mm width per side of a secondary bevel is going to be easier to do in the field than removing metal evenly from the 5mm that make the edge of a primary bevel edge. It is my feeling that in the field a secondary bevel is going to start to form on the edge and those wide bevels are going to need periodic reshaping on a bench stone to restore their flatness. Secondary bevels can be very adequately maintained on rod type sharpeners and slip stones.

Hollow grinding does require a rotating wheel (usually belt grinder these days), but that has nothing to do with whether the knife is made in a factory. Many custom knife makers hollow grind by hand. I would be very hesitant to say that hollow grinding is in any way cheaper or easier than any other sort of grinding. Having just made a Woodlore style knife using hand tools, I would say that this style suits the use of machines more than any other. I would have sold my soul for a belt grinder and platen when I was developing the edge after heat treat!!

The type of grind used for the primary bevel, when a secondary bevel is used to make the edge, had NOTHING to do with how much bite the knife has. Initial “bite” is a function of how acutely the bevels that make the edge meet. You could sharpen a hollow ground blade to have the same edge angle as a puuko and it would bite like a puuko. The usual reason given for not doing this is that it would weaken the blade, the puuko edge is easily damaged and the hollow grind doesn’t leave much metal immediately behind the edge. I don’t see how the edge will be any weaker than if it were part of a bigger flat grind, nor how the thin area behind the secondary bevel would be weaker than if a steeper edge where used. So if you have a hollow ground knife and it doesn’t cut wood the way you want, think about changing the edge geometry before you run out to buy another knife.

Oh man, that kind of sounds like a rant :-? it wasn't meant to honest!!

Chris

 

[Gary]

I disagree about bevels and sharpening - maybe its a personal thing but I find a single bevel - where you can lay the whole bevelled surface on the stone far easier to sharpen than a secondary bevel where you have to try and maintain the correct angle through out the whole stroke while sharpening.

Of course if you use a lansky system of something then ya - makes no odds but when push comes to shove can you sharpen your knife on a piece of stone from a river bed?

As I say personal choice comes into it and we do have the luxury of being able to buy and use all manner of gizmo's and gadgets - but having used knives all my adult life I wouldnt look twice at a secondary bevel and it I did it'd be to grind it out (hands on experience talking).

One point to bear in mind however is butchery - a single bevel does fall short here and if I am butchering big game or fish I will run my single bevel over a steel to give it a minor secondary bevel, this helps the blade slice into the meat and avoids rapid dulling caused by bones.

Maybe we should say for a hunting knife a secondary bevel is advantagious and in the same vein for a bushcraft knife a single bevel is best.

 

[Celtic Dragon]

Or just carry 2 knives 1 for bushcraft and 1 for butchery. Yeah, another excuss for collecting more blades :-D :-D :-D . Just what we needed, a vaild excuss!!!

ATB
Simon

 

[Andy]

shame I'm a veggi then isn't it
since reading this i have re shapend my knife so that the secondary bevel is at an angle just off hitting the spin of my knife when on the stone. which has helped a lot

 

[coutel]

A flat grind with a slight convex edge (Moran grind) is my favorite...

It can easily be stropped on leather or course material to keep it honed....



kevin.

 

[Gary]

Coutel, never played with these. I usually grind it out if its on the bevel but i have seen them and they look interesting how wide is the bevel? Couple of MILs? or do you go for the whole blade being convex like a bronze age sword?

 

[coutel]

Coutel, never played with these. I usually grind it out if its on the bevel but i have seen them and they look interesting how wide is the bevel? Couple of MILs? or do you go for the whole blade being convex like a bronze age sword?

Gary.

There are several variations.....

One way is a total flat grind bevel from spine to edge, but instead of taking it to a razor edge on the flat, leave it slightly blunt then convex it on the edge only.

Or you could put a slight convex from edge all the way to the spine.An overated example would be like an axe grind.
You can pretty much put a convex edge on anything.

The convex should blend in with the bevel so there is no actual bevel seen (bevel edge?).


In fact, whenever anyone strops a blade on a leather, even if it has a secondary bevel or flat edge .. would be putting a slight convex edge on.

I find it an easy edge to maintain if you dont let it get too blunt.
If it gets very dull/blunt then you just need to re establish the convex edge again....pretty much like anyother type of grind...horses for courses.

kevin :-D

 

[Stuart]

There are many people out there who know far more about knives than i do, But it is my business to know what a good bushcraft knife is so could i quote Kevin McClung a moment

"Sheffield, England was to straight razors what Detroit was to automobiles. Their only serious competition for sales in Europe and America came from that other historic cutlery mecca, Solingen, Germany.

Around the middle of the nineteenth century, beards came back into vogue in a big way. Contemporaneous to this was the romantic popularization of the Bowie knife. Sheffield had been producing large numbers of flat ground Bowies, but the demand in America far outstripped their flat grind production capability. The decline in straight razor sales offered the perfect solution so far as the British marketing types were concerned. To wit, make hollow ground Bowies. The production advantages were obvious. The hollow grind is simpler and faster to accomplish, as it removes far less stock than a flat grind. The equipment was already in place and lying nearly idle, due to the decline in razor sales. Thus began the age of the hollow grind, a decision driven by capital expediency rather than dedication to quality."

"Look no further than the flat grind for best general utility in a knife blade. Why? Because it is the least specialized. It suffers from none of the weaknesses of the other three from a user stand point, but it is slightly more costly and time consuming to produce, for the simple reason that as much as 60% of the stock must be removed by grinding, as opposed to the 10-30% removed by bevel or hollow grinding. The results are well worth the extra effort. Flat ground blades have a better strength to weight ratio and cut a wide variety of materials with less effort. The edge does not suffer weakness from excessive thinness, nor does the blade transition from edge thickness to full stock thickness too quickly, rendering the blade too fat to cut deeply with ease. The British had it right when they were selling flat ground cutlery to the discriminating buyer, who really needed a first class knife. As soon as faddish popularity kicked in, and everyone had to have a "Bowie knife", they started cranking out the hollow ground stuff"

Or Joe Talmadge at www.Bladeforums.com :

"The hollow grind is done by taking two concave scoops out of the side of the blade. Many production companies use this grind, because it's easier to design machines to do it. But many custom makers grind this way as well. Its great advantage is that 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 can chip or roll over in harder use. And the hollow ground edge can't penetrate too far for food-type chopping, because the edge gets non-linearly thicker as it nears the spine."

"The flat grind endeavors to provide an edge that is both thin and strong, and leaves a strong thick spine. The grind is completely flat, going from the spine to the edge. This grind is harder to make, because a lot of steel needs to be ground away. However, the edge ends up being fairly thin and so cutting very well. Because the bevels are flat, there is plenty of metal backing the edge, so it's much stronger than a hollow grind. It is not as strong as a sabre grind, but will outcut that grind.

The edge on this design also penetrates better for slicing and chopping. The hollow grind expands non-linearly as you go up the blade, the sabre grind expands linearly but very quickly. The flat grind expands linearly and slowly. Kitchen knives are usually flat ground, because when chopping/slicing food you need to push the blade all the way through the food. This grind is an outstanding compromise between strength and cutting ability, sacrificing little for either."

If you wish to learn a little more about knife blades etc please see the following links

www.bladeforums.com/features/faqbladegeo.shtml
www.capeforge.com/sharp.htm
www.arrow-dynamics.com/articlegrind.htm

 

[Gary]

Cheers Kevin, I have a Black Jack U1 with that kind of edge - forgot about it.

Dont like the sound of the bevel from spin to belly - thats more razor than knife.

But as you say courses for horses.

 

[sargey]

Flat ground blades have a better strength to weight ratio

mr mad dog is wrong on this point! :shock: a hollow ground blade most closely approximates a T beam girder of all the four grind styles. a more solid grind might have greater resistance to twisting, but it's greater solidity equates to greater weight. i would suggest that a hollow grind gives the greatest strength to weight ratio.

But many custom makers grind this way as well. Its great advantage is that 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 can chip or roll over in harder use. And the hollow ground edge can't penetrate too far for food-type chopping, because the edge gets non-linearly thicker as it nears the spine."

and?

"The flat grind endeavors to provide an edge that is both thin and strong, and leaves a strong thick spine.

this quote contradicts the previous quote.

The hollow grind expands non-linearly as you go up the blade, the sabre grind expands linearly but very quickly. The flat grind expands linearly and slowly. Kitchen knives are usually flat ground, because when chopping/slicing food you need to push the blade all the way through the food. This grind is an outstanding compromise between strength and cutting ability, sacrificing little for either."

more contradictions.

i think that part of the problem is that relatively little of the nomenclature describing knives is standardised.

we have four different basic grinds, two straight ie: flat (i mean full flat) and sabre, and two curved, ie: hollow or concave and convex, appleseed, moran or rolled edges. (that last term is also used to describe damage to the edge where it has been bent out of alignment, and rolled over) confusing eh?

but i don't think this is sufficient, we should have blade geometry, and edge geometry.

a well designed axe will have a convex edge like a symmetrical appleseed, then there will be a hollow behind this edge that doesn't come into contact with the substance being chopped, then you have the full thickness part of the head around the eye. all the GB axes follow this pattern. the appleseed part of the edge should follow a geometry that precludes the rest of the axe head coming into contact with the substance being cut and so keeping friction to a minimum.

so according to that last quote i copied, all those gransfors axes are of a pretty poor design :shock:

not to mention that all our favourite sabre ground scandi knives are pants too! :shock:

but these quotes never bring into account the idea of a final bevel or not. back to the idea of blade geometry and edge geometry.

the one part was correct, a thin edge does penetrate better, it is also inherantly more fragile.

the best way to get the thinnest edge with the most meat to back it up is a convex edge. it's also traditionally the most complex edge to resharpen using either flat stones or secured linear sharpeners like the lansky or edge pro rigs.

the scandi grind being a short sabre grind with no secondary bevel offers the best penetration in wood. it is the easiest edge to sharpen freehand on flat stones, it takes more labour but less skill. this edge is relatively very fragile. it's penetration and it's fragility are essentially due to the relatively acute (thin) angle found at the edge.

a flat grind can be essentially the same as a sabre grind. the variance is essentially dependant on the angle between the faces. a sabre grind will tend to be steeper than a flat grind. but what about that final bevel?

if you take a hollow grind to it's ultimate, with no final bevel. you have the geometry of a straight razor, the sharpest and the most fragile of the lot. if you take a hollow grind and a convex edge you have a very efficient cutting tool. a thin but strong edge with minimal friction due to contact with the material being cut. the optimum grind for hunting knives. many folks don't like the lack of "feel" when carving. difficult to sharpen free hand with flat stones.

the convex grind, full convex from spine to edge. possibly the sturdiest and sharpest combination of the lot, also possibly the heaviest. just a slightly convexed scandi/sabre grind? flat grind with a convex secondary bevel? or as already mentioned a hollow grind with a convex secondary bevel?

so thems your choices in basics. if you want to get specific you have to start taking the actual angles of geometry into account.

sorry if i bored you :-?

cheers, and.

 

[coutel]

....(snip)
not to mention that all our favourite sabre ground scandi knives are pants too! :shock:

.

I am very interested in this subject as I am attempting to come up with a knife that would satisfy bushcraft needs, but away from the generic 'woodlore/RM ' design which seems so popular....I just dont want to repeat/copy it.

The generic 'woodlore/RM' and scandi's are popular, but I cant understand why they are not a full flat grind rather than the sabre grind (short bevel).......sargeys and stuarts posts sums up a lot of what I thought anyway....

Taking into account edge/bevel geometry... would one single flat grind all the way to the back be an improvement?


thanks.
Kevin.

 

[coutel]

.....snip

Dont like the sound of the bevel from spin to belly - thats more razor than knife.

But as you say courses for horses.

Gary.....

Just to clarify.......a convex from edge to back would be more like (what I think of anyway) , an 'axe'.......The 'razor' profile would be more of a full concave/hollow grind.

kevin.

 

[Andy]

not at all. I've been told I'm too obssed by my knife. but i don't think people here would say that. maybe I haven't seen many cheap flat ground knives other than the mora which seems a bit think to me (2mm at spine) what would you think to pputting a flat bevel on a butchers boning knife. it gets a bit thinner towards the edge but not much could i grind my own from one of these. i can get a victorinox ne for about £10

 

[Hoodoo]

Taking into account edge/bevel geometry... would one single flat grind all the way to the back be an improvement?

The problem with a single flat grind is that if you lay the knife on the flat to sharpen it, you are now trying to remove a lot more metal than if you had a scandi grind. Also, every time you sharpen, you will be cutting away at the spine of the knife, which will weaken it. A full flat grind with a small bevel will not give you the same cutting performance as a scandi imo. However I do like full flat grinds but I convex the edge and this gives me great performance and makes sharpening easy.

 

[Andy]

so what do people think to grinding down a butchers boning knife? is the mora knife a bit thin?