Knive sharpening.

[amakah]

Can someone tell me why some knives are sharpened from both sides unlike chisel which are always sharpened from one side. I would have thought that due to the angle on the finished item you would get a much sharper blade with one side sharpening.

 

[peterw3035]

I've been reading up & collecting together some gouges & chisel for letter carving, gouges are ground on outer face and straight chisels ground on both faces. A side axe is ground on one face but most axes are ground & sharpened on both. It all depends on the application & use but it needs someone better than me to explain the geometry

 

[paulrbarnard]

Can someone tell me why some knives are sharpened from both sides unlike chisel which are always sharpened from one side. I would have thought that due to the angle on the finished item you would get a much sharper blade with one side sharpening.

Chisels are actual sharpened from both sides. You only put a bevel on one side but the back also contributes to the edge.

Some knives only have a bevel on one side like a chisel. It comes down to what and how you are cutting.

 

[pgrbff]

Japanese cooking knives often have bevel on one side. Here is a randomnly chosen explanation. Some marking knives are also bevelled on one side making it easier to scribe an accurate line.

 

[pe2dave]

(guess). Push a chisel into wood it 'self guides' away from the bevel.
Push a knife into meat / bread it *should* go straight down? I.e. single bevel not helpful

 

[amakah]

Hello all, Thank you for your most interesting views on this subject. I think that if you want a really sharp edge it would be better to sharpen from one side only and leave the other side flat as the angle would be much less than what it would be if sharpened from both sides. I like the point about cutting bread but surely a really sharp knife would be better as it is not difficult to control a knife when cutting bread.

 

[--Tom--]

Hello all, Thank you for your most interesting views on this subject. I think that if you want a really sharp edge it would be better to sharpen from one side only and leave the other side flat as the angle would be much less than what it would be if sharpened from both sides. I like the point about cutting bread but surely a really sharp knife would be better as it is not difficult to control a knife when cutting bread.

I’m not sure why you think this? A triangle is still a triangle.

I have knives I grind at around 3 degrees per side which gives an inclusive angle of 6 degrees. At that fineness the edge won’t stand up to much real use so they get a bevel added of around 10 degrees per side which gives an inclusive of 20 degrees.
If I ground from just one side at 6 degrees and then put a 20 degree bevel on one side the edge angles would be the same. Go lower than 20 degrees at the edge and you’ll likely experience microchipping and other forms of edge failure.

The problem with only sharpening one side would then come in use where the knife would steer away from the bevel and make straight cuts need more focus and steering by the user. Possible but one of the signs of a well made kitchen knife is that it won’t steer and cuts straight.

Japanese single bevel knives are made with very specific single purposes. And the aren’t typically flat on the side opposing the bevel. Having a hollow ura to make it easy to polish the steel at the apex, and in a yanagiba acting to reduce the pressure on the fish being sliced.
Butchery knives like Hankotsu, honesuki, garasuki etc being slightly different as the edge geometry is designed to allow cutting cleanly along bones etc.
Sharpening single bevel knives is a much more involved process than double bevel which have become the norm for general use for good reason.

Other knives like marking knives are single sided to cut along an edge without any offset caused by a bevel. But the back is pretty small so easy to keep lapped. On bigger stuff it would be a nuisance without a hollow to reduce the contact area.

 

[paulrbarnard]

Hello all, Thank you for your most interesting views on this subject. I think that if you want a really sharp edge it would be better to sharpen from one side only and leave the other side flat as the angle would be much less than what it would be if sharpened from both sides. I like the point about cutting bread but surely a really sharp knife would be better as it is not difficult to control a knife when cutting bread.

I think you have a fundamental misunderstanding of an edge. An edge is the intersection of two planes. The sharpness is a function of the included angle between both planes. It makes no difference is it is 10 degrees on both sides or 20 degrees on one side. The only difference will be in how the blade handles. The cut, unguided, will try to follow the center of the angle. A chisel has a large flat back which you register on the work to stop it following that natural center of the angle. A knife with equal bevels will tend to cut straight on its own. Given there is no difference in sharpness with the same included angle the choice you make comes down to the use you have for the tool.

 

[Jacob]

...one of the signs of a well made kitchen knife is that it won’t steer and cuts straight.

One of the signs of slicing competence is the ability to steer the knife.

Other knives like marking knives are single sided to cut along an edge without any offset caused by a bevel. ...

You offset the offset of the bevel by leaning the knife to the side. Absolutely no problem - as with nearly all sharpening issues it's much simpler than the enthusiasts say!
It doesn't do to overthink these things or you may suddenly find you can't use these tools, as per this example -
it's actually easier to mark with a normal double bevelled knife

 

[--Tom--]

A competent user can always get a get good result.
The question of does sharpening just one side make anything sharper than sharpening both is no it doesn’t.

 

[aet1]

Hello all, Thank you for your most interesting views on this subject. I think that if you want a really sharp edge it would be better to sharpen from one side only and leave the other side flat as the angle would be much less than what it would be if sharpened from both sides. I like the point about cutting bread but surely a really sharp knife would be better as it is not difficult to control a knife when cutting bread.

When I had a sandwich shop I found the knife sharpened on both sides cut straight and gave better slices when I cut loaves or ham.

 

[Jacob]

A competent user can always get a get good result.

True, by definition.
It doesn't follow in any way that obsessing about angles will make you competent, in fact if the complexity of modern sharpening is anything to go by then the opposite would seem to be true.
Just remember one angle; 30º (or 2 x 15º), and get plenty of practice in!

 

[baldkev]

Hello all, Thank you for your most interesting views on this subject. I think that if you want a really sharp edge it would be better to sharpen from one side only and leave the other side flat as the angle would be much less than what it would be if sharpened from both sides. I like the point about cutting bread but surely a really sharp knife would be better as it is not difficult to control a knife when cutting bread.

If you consider a truly sharp blade ( a straight razor, often hollowground ) , is usually sharpened both sides, can cut hanging hair with barely any contact..... but it wont last long chopping carrots ( or wood ) . A knife, generally, has to be sharp and durable
so I'd echo the comments about it being dependent on it's use. As @paulrbarnard said, the back of a chisel ( to get the best results ) has to be lapped and polished on the back, even if its only the last few mm of the blade, like jap chisels as this makes a noticeable difference

 

[Pabs]

. An edge is the intersection of two planes.

Case in point I just cut myself on the side of one of my morticing chisels... I'd been a little over zealous about it all...

 

[Chris_Pallet]

Can anyone recommend a kitchen knife sharpening stone kit ?
I'm looking online it's just Amazon recommend, rather something not imported...

 

[--Tom--]

A 1000 grit will cover most bases- Shapton professional is a very good stone and comes with a case that doubles as a holder. Being splash and go (rather than needing soaking) also means easy to use whenever needed.

 

[Pabs]

agree with Tom. 600/1200 or similar will give a very serviceable edge,
just to add: be wary of the cheap combination stone as they are poorly graded if at all.

also be wary of falling into a never end black hole of obsessive polishing and submicron obeisance

 

[Hornbeam]

The theory with a single bevel knife is that when you run the unbevelled side against the straight edge with the blade perpendicular to the work piece, then you mark exactly where the straight edge is. This is why you need a left and a right ground knife. You can achieve similar results with a knife ground on both sides but you have to angle the knife so the bevel against the straight edge is vertical

 

[Pabs]

The theory with a single bevel knife is that when you run the unbevelled side against the straight edge with the blade perpendicular to the work piece, then you mark exactly where the straight edge is. This is why you need a left and a right ground knife. You can achieve similar results with a knife ground on both sides but you have to angle the knife so the bevel against the straight edge is vertical

was this supposed to be in the marking knife thread?

 

[Hornbeam]

was this supposed to be in the marking knife thread?

It was supposed to be in this section as the original question was why some knives were sharpened on both sides. I guess it could probably go in the marking knife section as well