How To Kitchen knife grinds and how to grind them?

HSC /// said:
Understood
Most of my customers are qualified sophisticated users who thin their own knives
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Got it. Difference between commercial and custom knives i guess...

(My sister has a 20 year old set of henkels she was getting really frustrated with. I thinned them for her, and now she raves about them...
 
on thickness behind the edge, i make mine as thin as they can go (enough to cut sandpaper usually) then sharpen back a secondary edge enough to prevent chipping. i've seen others use a similar approach.
on how to grind the more complex geometries, my understanding is you start with a rough FFG then round over edges or add divots, so i would start by practising FFGs. these knives aren't convexed like a wood axe or fullered like a cinquedea.
 
Cushing H. said:
But my concern is maintainability over time as the blade is repeatedly sharpened, and the edge walks back into the thicker convexed area, producing a quickly increasing TBE. A FFG will reduce that ongoing increase in TBE.
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With normal sharpening on a whetstone this process should not happen quickly because you're not typically removing a lot of material, and can be mitigated by thinning the blade after some time, or thinning a bit with each sharpening. It's going to happen with a FFG too, so you will have to thin no matter how you do it, so you may as well get the better cutting performance from a convex grind.
 
Michael Black said:
With normal sharpening on a whetstone this process should not happen quickly because you're not typically removing a lot of material, and can be mitigated by thinning the blade after some time, or thinning a bit with each sharpening. It's going to happen with a FFG too, so you will have to thin no matter how you do it, so you may as well get the better cutting performance from a convex grind.
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This discussion has occurred before (and please I only mean that as a statement, not argument). I am very likely biased (if that is even the right word) .... because I am talking about my blades-in-use experience over the course of some 40 years, and much (i.e. vast majority ) of that time pre-dates any knowledge of "thinning" a blade. so yes, if as a user you know enough to thin a blade, my stated concerns go out the window.....

But I STILL have to argue/wonder/raise the point ( :) ) that there is a *difference* between out-of-the-shop performance versus how the performance of the blade evolves over time. I am basically saying we should at least be aware of it (and the customer base and how they can deal with it), and not just say something like "when it left my shop, it was just fine....".

A *really* bad analogy would be that of a car manufacturer who says something like "what ... you cant access that part to fix/remove it? not my problem, I was able to get it into place just fine.....". I have had vehicles that were a nightmare to repair (because you could not trace stuff or could not physically access them), and others that were just sweet to repair/maintain, because things were accessible.

I guess I am just really trying to relate that I am not sure it is the best thing to say "X grind is best" .... because in the end it really comes down to understanding your design versus the knowledge of the user and their expectations of how the thing will perform over time. Hopefully that makes sense???
 
Cushing H. said:
This discussion has occurred before (and please I only mean that as a statement, not argument). I am very likely biased (if that is even the right word) .... because I am talking about my blades-in-use experience over the course of some 40 years, and much (i.e. vast majority ) of that time pre-dates any knowledge of "thinning" a blade. so yes, if as a user you know enough to thin a blade, my stated concerns go out the window.....

But I STILL have to argue/wonder/raise the point ( :) ) that there is a *difference* between out-of-the-shop performance versus how the performance of the blade evolves over time. I am basically saying we should at least be aware of it (and the customer base and how they can deal with it), and not just say something like "when it left my shop, it was just fine....".

A *really* bad analogy would be that of a car manufacturer who says something like "what ... you cant access that part to fix/remove it? not my problem, I was able to get it into place just fine.....". I have had vehicles that were a nightmare to repair (because you could not trace stuff or could not physically access them), and others that were just sweet to repair/maintain, because things were accessible.

I guess I am just really trying to relate that I am not sure it is the best thing to say "X grind is best" .... because in the end it really comes down to understanding your design versus the knowledge of the user and their expectations of how the thing will perform over time. Hopefully that makes sense???
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Yeah that makes sense. Pretty much everything in knifemaking comes down to a tradeoff between different advantages/disadvantages, so you just have to make the right decisions for yourself as a knifemaker and your intended end users. There's nothing wrong with a FFG chef knife, I just happen to prefer the convex grinds based on my experience and feedback from users, but I have made plenty of FFG knives as well. :-)

Any knife of any geometry will eventually wear down from use and constant sharpening, so at some point it's all irrelevant anyway haha!
 
Michael Black said:
Yeah that makes sense. Pretty much everything in knifemaking comes down to a tradeoff between different advantages/disadvantages, so you just have to make the right decisions for yourself as a knifemaker and your intended end users. There's nothing wrong with a FFG chef knife, I just happen to prefer the convex grinds based on my experience and feedback from users, but I have made plenty of FFG knives as well. :)

Any knife of any geometry will eventually wear down from use and constant sharpening, so at some point it's all irrelevant anyway haha!
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That is probably fair and a very sane statement to make. Personally - I guess I take pride in the fact that I have knives that I bought some 35 years ago that are still going strong .... though some of them are DEFINITELY suffering from the "increased TBE" syndrome. somehow, I can not bring myself to thin them .... but then again, I have a 100 year old knife from my grandmother that I wont touch, because if I thin it, that will absolutely destroy the patina. Maybe the difference between a "working tool" versus a "memory" (if that makes sense). for me at this point it seems better to create a new tool, versus destroy the memory???? :)

(Man ... now we have to distinguish between "users", "shelf queens" and "well used shelf queens" ?????? :)
 
If you are going to do a convex grind or just wanting to blend a cheap aid you can use a leather platen. You have to replace it every so many blades but it's handy. I just cut a chunk of heavy leather and use a bit of spray adhesive and stick it on. I take to around .010" ish an then convex on down. It makes using AO belts easier because it damps out the belt bump.
 
Storm W said:
If you are going to do a convex grind or just wanting to blend a cheap aid you can use a leather platen. You have to replace it every so many blades but it's handy. I just cut a chunk of heavy leather and use a bit of spray adhesive and stick it on. I take to around .010" ish an then convex on down. It makes using AO belts easier because it damps out the belt bump.
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Sounds good. I will keep that in mind.
 
F3 felt works really well for convexing the grind. The corners round out, so I may put leather over it to see if it will stay more even side to side.
 
I haven't finished a knife yet but this thread reminded me that I had a bunch of convex platens that I never used. I ground a bunch of knives and sharpened one and tried it out. I think that is the way to go. Its still only at 50 grit and will get a lot thinner but you keep a nice stiff spine and keep the blade as thin as possible. It cuts like nothing else I have tried. I Like my knives to cut as well as possible and if things stick oh well. To be able to keep the blade thin as possible most of the way up I think will make a huge difference. You could probably make one out of hardwood that would last for several blades. Mine are from Nathan the machinists. I don't know if he still sells them from time to time. They don't fit my grinder so I had to glue them to a platen. I recommend giving it a try. Once at least.
 
Storm - convex platens are for grinding concave blade grinds - AKA Hollow Grind. Nathans convex platens simulate large wheels for hollow grinding wide blades and doing urasuki.
A convex grind is a blade that slowly curves to the edge instead of a flat main bevel and a secondary edge bevel.
 
The convex platens are typically called radius platens.
 
Taz said:
The convex platens are typically called radius platens.
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Which is humorously all sorts of wrong, since they are chord segments and the number used is the diameter, not the radius. That is why I usually call them radiused platens.
A 36" radius platen" actually simulates a wheel that has an 18" radius.
 
Stacy E. Apelt - Bladesmith said:
Storm - convex platens are for grinding concave blade grinds - AKA Hollow Grind. Nathans convex platens simulate large wheels for hollow grinding wide blades and doing urasuki.
A convex grind is a blade that slowly curves to the edge instead of a flat main bevel and a secondary edge bevel.
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Did I not word that well? Yes a hollow grind. I finally broke them out. I did a batch of blades with very thin hollow grinds. They are 8 thousandths or so in the middle and and come up a bit and then down to near zero at the edge. I have been doing near flat grinds as thin as I can grind them with a tiny bit of convex but these seem to cut even better. With the really hard to grind stuff I'm hogging them out with the wheel first. I got in a car accident last year and have a bunch of unfinished blades that I have been sitting on. Willie71 Willie71 did up a bunch of M2 and M4 at 66Rc and it takes a bit of grinding. I finally got back where I can do my own stuff so I got some S35VN and the odd AEB-L blades in the pile too. I have some flat grinds to compare them to as well.

I know that people often use them for Japanese knives or S grinds but I am doing more or less just a very large hollow grind. I don't know yet how the food release is on them but I prefer that my knives just cut as well as possible. For me it's it's a quest for the knife that I can get as thin as possible and as hard as possible and to realistically hold as fine of edge as possible without chipping or breaking under intended use. I'm not super interested in Japanese style knives. Just simple functional knives. I don't claim to be the best maker out there but I have worked out a few things to be able to make what I do
 
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Stacy E. Apelt - Bladesmith said:
Which is humorously all sorts of wrong, since they are chord segments and the number used is the diameter, not the radius. That is why I usually call them radiused platens.
A 36" radius platen" actually simulates a wheel that has an 18" radius.
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I usually call them radius platens as well. I guess I just said convex or it popped up as a word option on my phone. I'm not doing anything fancier than a hollow grind and I just go with what's written on the back and then blend it into the blade. I'm a hobby maker and I have 20 or so blades in progress and that's a big batch for me. Especially since some of them are big Bowie's. If I get them done in a month it will be a miracle. Lol
 
I agree, the radiused platens are great for getting those long hollow grinds to lighten a big blade. It also looks very good.
 
I want to try my 36" radius platen from AmeriBrade. I have 2 Japanese White #1 san mai blanks to grind out and I want to try to keep some of the kurouchi finish up near the spine. I did a flat/convex grind on two of them and they are almost too thin at the spine when I finished them! Many of the high end Japanese knives with the visible shinogi line use a very shallow hollow grind, like the Konosuke Fujiyama series. I think the radius platen will work really well on thin, slicey EDC type blades, too.
 
Question regarding the grit progression to grind a convex. Is it typical to use a 36, 80, 120? What belts typically follow up after this in order to achieve a belt finish?
 
Diego_B said:
Question regarding the grit progression to grind a convex. Is it typical to use a 36, 80, 120? What belts typically follow up after this in order to achieve a belt finish?
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For convex, I would do a flat grind pre heat treat leaving about 0.04" on the edge. I'd use 36 grit and then clean it up with 120.
After heat treat, I'd convex going 50, 120, 220, 320, 400-600.
 
Are scotchbrite belts a worthwhile thing to get for this? I have used cork belts before but I figure that the scotchbrite would be better in this case thinking that it has a little better finishing value than a cork would on a convex grind?
 
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