Thinning, Grinds, and Food Release

[tostadas]

As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.

Don't know about the science behind it, but it's definitely noticable. I can confirm that fractions of a mm behind the edge have a considerable difference in performance. Your calculation example is not exactly accurate because in reality the thickness of a "flat ground" knife from spine typically does not go from 2mm down to 0. But rather probably something like 2mm down to 1mm (and then a very abrupt angle change at the very end).

At 10mm behind the edge, I would consider anything 1.1mm or under to be pretty thin, assuming that it goes down to around 0.2mm @ 1mm behind the edge.

 

[stringer]

As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of conductivity will be measured in fractions of a millimeter. How does this help with food release? It would seem to this newbie that the amount of convexity would have to be more than that.

I don't add convexity to improve food release. I do it because I like my knives to be as thin behind the edge as possible for the task at hand. I dislike harsh shouldered bevels and zero bevels are too fragile. A convex edge is easy to maintain (except for maybe aesthetically) and is the best of both worlds. Plus, when you get used to sharpening this way you can adjust bevel angle on the fly and make the tip really pointy and the choil really stout. The fact that food release is also improved is just an added bonus. I used to think you need a thick spined wide bevel knife to enjoy the benefits, but now I believe that you can sharpen even the thinnest lasers this way.

 

[Blank Blades.]

As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.

You would be surprised. I mean if you go up to the choil shot I did if my tojiro gyuto, that thing is very thin behind the edge. Having the little convexity that is there makes all the difference.

It's like someone with an untrained eye looking at a very different gyutos and thinking they are pretty much the same knife because they dont look that different. when in reality the small details are what make them different from each other.

 

[ian]

As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.

The knife will probably be thicker than that. .4mm at 10mm behind the edge is not a realistic measurement. You should expect .8-1mm thick at 10mm from the edge. .5mm at 5mm from the edge.

That said, it doesn't take a lot of convexity to make a difference, in terms of food release, in terms of the amount of sticking you feel as you cut, and in terms of edge stability.

 

[stringer]

Here's another thread where you can see some pictures of what a convex grind looks like compared to a typical factory microbevel. This knife was generally left on a prep table for anyone to use at a busy hotel for 12 hours a day for three years.

I also show how I start converting the factory flat grind into something more convex.

https://www.kitchenknifeforums.com/threads/old-beater-meet-new-beater.44563/

 

[KKL81]

As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.

Assuming that a crappy knife will be like 0.75mm thick behind the edge, your numbers gives 1mm thickness 10mm behind the edge and 0.875mm at 5mm. Just keep the 1mm, thin the 0.875mm to 0.5mm and the 0.75mm to 0.1, no problem.