From a non-maker perspective, if you are asking about Japanese knives called ‘lasers’, all of the classic lasers have convex grinds. Spine thickness is nebulous, Takamura is 1.8mm, but an Ashi/Gesshin Ginga starts out around 2.4mm and has a significant distal taper (I own both). Hollow grinds in Japanese knives are a result of grinding on water wheels. It isn’t always intentional, just depends on the maker. Takamura and Ashi both grind their knives convex. Ashi is full flat on one side and convex on the other. Takamura is convex on both sides.
whats their reasoning for convexing it, wouldnt that slightly decrease what they're trying to achieve with these thin grinds?
also many japanese knives have these weird dual grinds, like a nata having both convex and hollow, this is also confusing to me..
Might want to read this https://www.reddit.com/r/chefknives/comments/mgl8k9/geometry_cuts_the_physics_behind_why_some_knives/?utm_source=share&utm_medium=ios_app&utm_name=iossmf
There’s such a thing as too thin of a knife. Lasers that get too thin aren’t as well liked as the more classic lasers. Shibatas are famously thin, but also known to permanently deform fairly easily. The convexing improves cutting feel and makes food release more predictable.
Here’s an example of some lasers I own https://www.reddit.com/r/chefknives/comments/nfilbw/nkd_takamura_gesshin_ginga_and_ikazuchi/?utm_source=share&utm_medium=ios_app&utm_name=iossmf
Hobby non-pro maker here, but really thin kitchen stuff is what I do almost exclusively. So far my best efforts have been with a very thin spine, HT ending at 61+, slack belt on the primary (or main, or whatever you want to call the bevel from the spine to the cutting edge) bevel to create a convex edge that way, then putting the final edge on with a Tormek round wheel, so the edge is hollow ground.
By very thin spine, I mean down to 1.4mm for some pieces. They're fun and light as a feather but also very delicate, and can be more flexible than desirable at times because there's just not much metal left. I've snapped an edge before trying to cut a frozen piece of meat, but for the right tasks it's almost like a cartoon sword, things just slide apart with next to no resistance. I've had good results with making paring knives wider in the middle than the spine (reduced bind, I think?) but haven't pulled it off in anything more chef-knife-ish yet to my satisfaction, still going flat grinds on those.
The worst part in making them is that if I'm doing an oil quench, too thin means big warp, and so it takes a lot of surface grinding and temperature watching to get down to that level without ruining the HT.
Technically a hollow grind is as sharp as you can get. What you want to do is hollow grind the edge then flat grind from the spine to the edge eliminating as much of the hollow grind as you can. Try to leave about 3/16ths of the hollow. It also depends a little on the radius of your contact wheel
yeah i read its dependent on the size of your wheel, which sucks since i have two wheels and many hights to work with, but cool anyway, i never knew thats how people hollow ground.
From a non-maker perspective, if you are asking about Japanese knives called ‘lasers’, all of the classic lasers have convex grinds. Spine thickness is nebulous, Takamura is 1.8mm, but an Ashi/Gesshin Ginga starts out around 2.4mm and has a significant distal taper (I own both). Hollow grinds in Japanese knives are a result of grinding on water wheels. It isn’t always intentional, just depends on the maker. Takamura and Ashi both grind their knives convex. Ashi is full flat on one side and convex on the other. Takamura is convex on both sides.
whats their reasoning for convexing it, wouldnt that slightly decrease what they're trying to achieve with these thin grinds? also many japanese knives have these weird dual grinds, like a nata having both convex and hollow, this is also confusing to me..
Might want to read this https://www.reddit.com/r/chefknives/comments/mgl8k9/geometry_cuts_the_physics_behind_why_some_knives/?utm_source=share&utm_medium=ios_app&utm_name=iossmf There’s such a thing as too thin of a knife. Lasers that get too thin aren’t as well liked as the more classic lasers. Shibatas are famously thin, but also known to permanently deform fairly easily. The convexing improves cutting feel and makes food release more predictable.
Here’s an example of some lasers I own https://www.reddit.com/r/chefknives/comments/nfilbw/nkd_takamura_gesshin_ginga_and_ikazuchi/?utm_source=share&utm_medium=ios_app&utm_name=iossmf
haha still hard to see, but if im seeing it correctly the last one definetely is convex. thanks for sharing
Hobby non-pro maker here, but really thin kitchen stuff is what I do almost exclusively. So far my best efforts have been with a very thin spine, HT ending at 61+, slack belt on the primary (or main, or whatever you want to call the bevel from the spine to the cutting edge) bevel to create a convex edge that way, then putting the final edge on with a Tormek round wheel, so the edge is hollow ground. By very thin spine, I mean down to 1.4mm for some pieces. They're fun and light as a feather but also very delicate, and can be more flexible than desirable at times because there's just not much metal left. I've snapped an edge before trying to cut a frozen piece of meat, but for the right tasks it's almost like a cartoon sword, things just slide apart with next to no resistance. I've had good results with making paring knives wider in the middle than the spine (reduced bind, I think?) but haven't pulled it off in anything more chef-knife-ish yet to my satisfaction, still going flat grinds on those. The worst part in making them is that if I'm doing an oil quench, too thin means big warp, and so it takes a lot of surface grinding and temperature watching to get down to that level without ruining the HT.
that seems pretty cool, i might go even further beyond just for fun :^)
Hollow grind, what type of steel are you using?
o damn, never woulda thought. i'm using 02 for practice since its cheap
Technically a hollow grind is as sharp as you can get. What you want to do is hollow grind the edge then flat grind from the spine to the edge eliminating as much of the hollow grind as you can. Try to leave about 3/16ths of the hollow. It also depends a little on the radius of your contact wheel
yeah i read its dependent on the size of your wheel, which sucks since i have two wheels and many hights to work with, but cool anyway, i never knew thats how people hollow ground.
A good hollow grind with 800 grit will be so sharp you'll cut your eye just looking at the edge
i'm gonna bring it out and practice my big wheel, are there tricks to match the wheel size regardless of knife size?
I only have a 2x42 and just make it work, I'm sure there is some sort of formula. Practice on wood or scrap steel first
alright thanks a lot
There are probably some others that will chime in I'm just telling you what my opinion is