Parabolic grind for food release on vegetable knife?

[Nathan the Machinist]

I've seen a lot of things tried for food release on soft wet materials. I've been thinking about this a lot recently. I get potato duty here pretty frequently and I don't like it when the potato sticks to the side of the knife, I want it to pop off. I have some pretty good kitchen knives that cut very well in general, but they're not so great if you have a bunch of soft wet stuff like potatoes.

I have noted that some crappy Cutco knives with their short hollow grind actually do a pretty good job for this. They may not cut well, but they do pop off the sticky food pretty well.

The knife I usually grab for this is a cheap Old Hickory carving knife that I modified with a thin hollow grind. It looks like this except I reground it:

It's funny when you consider I have a nice assortment of kitchen knives and could make anything I want, but this $10 knife is the one I grab the most. It's a little unconventional, but I like it. The combination of the short blade height and hollow grinds I added seems to pop through the food pretty well and the food doesn't want to stick.

So I've been thinking about this. From my point of view, it seems to me that an ideal grind for something like potatoes would be a steep single bevel vegetable knife with a grind that starts off thin and almost flat and increases in curvature as it goes up ending in something like a 3" hollow grind to pop the food off. Varying the curvature of the grind like that wouldn't be a traditional geometry because it wouldn't be practical to make on conventional tools but it wouldn't be a problem with modern techniques. So, I've had this idea bouncing around in my head for a little while and I'm about ready to start playing with it so I wanted to ask you guys if you've ever tried something like this and what are your thoughts?

I understand that a short height and hollow grind on a kitchen knife flies in the face of conventional wisdom of what makes a good kitchen knife and I'd like to hear from some other experienced makers and users.

 

[Frank Niro]

Boy, have you something to talk about here ! I always believed a fillet knife should be flat ground not only so it would lay flat but so a hollow wouldn't create a pocket that would fill and defeat it's purpose - just a bit of course. I also carried this through on my thoughts of kitchen knife bevels but only made a couple that in truth the users in the house never seemed to grab on a regular basis.
I'm sure interested in your go ahead Nathan and know you may soon have an answer for us.
Frank

 

[jdm61]

Ummm, Nate, what do you think that some folks use your curved platens for? Even heard of a "S" grind?

 

[Nathan the Machinist]

Ummm, Nate, what do you think that some folks use your curved platens for? Even heard of a "S" grind?

I love the S grind, it's awesome! Good food release in general and cuts great. But for sticky stuff where cutting performance comes second to food release sometimes a short hollow works better at getting potatoes to let go. I mean a severe deep hollow. Doesn't really cut well though so not real popular in the kitchen. So I was thinking, flat on one side, curved on the side where you need release, and flat down at the cutting edge with increasing curvature as it goes up. Not an S grind, but seriously funky. Does anybody do that? Any suggestions?

 

[Bill DeShivs]

Holes.

 

[Daniel Fairly Knives]

I really like some form of V grind with a bit of shoulder blended in for food release.

Forged Japanese kitchen knives are a great example, on some the V shape is forged in and a low single or double bevel is added for the shoulder effect.

A single bevel or hollow added to the V shape will add even more to the effect... at least in my experience.

 

[jdm61]

I have heard that the Shigefusa blades have some hollow and are thicker at the spine that a lot of Japanese knives, but they scrape those with sens. For veggies how about a really thin nakiri with the grind only coming up about 1/3 to 1/2 way and ground on say a 72 incher? Or now that you looked down the asymetrical path, how about a Nate special semi-western usuba maybe ground like a really thin, tall kamisori with hollows of varying radius on both sides?

I love the S grind, it's awesome! Good food release in general and cuts great. But for sticky stuff where cutting performance comes second to food release sometimes a short hollow works better at getting potatoes to let go. I mean a severe deep hollow. Doesn't really cut well though so not real popular in the kitchen. So I was thinking, flat on one side, curved on the side where you need release, and flat down at the cutting edge with increasing curvature as it goes up. Not an S grind, but seriously funky. Does anybody do that? Any suggestions?

 

[Willie71]

On a taller knife, such as 1.5" +, I use a 70/30 offset edge, flat ground on the non dominant side, and convex on the dominant side. Max 400grit lengthwise sanding. It won't be as good as a short knife (I use a 5" long parer for potatoes as a specific one purpose knife) but this geometry makes a pretty good do everything knife. :thumbup:

 

[12345678910]

We also use old hickory in the kitchen, must be they are 35 years old
Thin of course, but I think less width.


Paring knives reground thinner to make up for the width lost in sharpening, they are 3/4 of their origional height.
Broken off tip reground too.

The total surface area of my parer is a tiny fraction of what your big knife is.

Add to that the cutting style, I'm cutting against my thumb and letting things drop.




If you're considering cutting board duty, I have a granton edge stainless santoku
It's pretty stickless on wet watery vegies like peppers. but starchy potatoes,

I'm using chef techniques to hold the potato down and keep it together while I draw the knife through and away.

 

[zhyla]

Seems like those silly knife sets that stack inside each other would win out in this particular case.

The simplest solution is to choose to not care what is on the far side of your blade.

 

[butcher_block]

stiction will always be an issue with taters but ballancing a slight convex edge on a flat ground knife works ok better is to then hollow out reight behind the edge but you can make this too extreme if not careful and since ever chef has a different thought on how much wedging vs food release they want stock knives will always be tricky (customs as we all know can be tuned for the buyer )
going asymmetrical is great so long as you know the buyers left or right handed

 

[stezann]

I use just athin stock single bevel edge, 1 inch tall blade. Short bevel, a bit convexed through honing.
Using my left hand finger to lay down the slices if stubborn...not always a concern, but i'm interested in your experiment

 

[tim37a]

I completely eliminated the problem by buying OreIda crinkle cuts.

 

[Nathan the Machinist]

Okay, so here's what I figured out. A short bevel and steep hollow grind like I was talking about does indeed pop the potato off pretty well, but it cuts with too much binding and drag. I made a couple prototypes and settled on a parabolic grind that is fairly flat towards the edge and ends a little higher than I originally planned with the curvature ending around that of a 6" grind. I ended up varying the grind height and curvature a little so it was more conventional at the tip where you make most of your slicing cuts and more abrupt toward the heel.

I laid the blade over on its side to mill the parabola which leaves a scallop from the cut. For the first prototype (which I didn't even harden) I just left them in there and I think the scallops helped the food release so I decided to leave them in there as a design element, but reduce the step over towards the tip to reduce problems in slicing cuts.

Per you guys suggestion I left it a little tip heavy. I put the center of balance at the point between your index finger and thumb when held in a pinch grip (once the handle is installed). I dropped the edge a bit for clearance to a cutting board.

So, anyway, that's what I came up with. We've been using the prototype in the kitchen a lot this week and I felt it was ready for a short run of a few to get some out there.

What do you guys think?

 

[bravodelta]

Nathan, is this the kitchen version of the CBT on my Busse HG55? As a person with more time that I care to remember in commercial kitchens long long ago, I used a "cullenshiffe" equipped Santoku to cut probably cut a metric ton of taters with good success. I also believe that proper knife technique in the kitchen can mitigate some (but not all) of the sticking issue, especially with taters. Now, soft cheeses are a disaster! In have always wondered if the hand hammered type finishes found on high end Japanese chefs knives accidentally helped with "sticktion".

Keep up the great and innovative research!!

 

[Nathan the Machinist]

^ I wasn't familiar with that term I had to look I up. But yes, I think it's driven by the same basic concept, it's turning an artifact of the manufacturing process into a design element. In my case, the geometry I wanted for the blade didn't lend itself to direct side or end milling so it needed to be surface milled. This works out well for a single bevel vegetable knife because it can be laid flat and I liked the way they worked in the prototype. It's not something I've done before and I'm not sure I how I would apply it to other blades. I have to surface mill geometry that can't be milled directly pretty frequently, but I usually try to minimize it's prominence, just in this case it worked for me so I tried to accentuate it.

 

[james terrio]

Cool ideas here. The only way to really find out would be to do long and exhaustive testing, preferably on video. And even then, those who like flat grinds will still like flat grinds, etc.

And others who prefer stuff like this:

... are pretty much beyond help anyway

I have always wondered if the hand hammered type finishes found on high end Japanese chefs knives accidentally helped with "sticktion".

Many, if not most, claim that's no accident. Those makers certainly know how to provide crisp finished surfaces when they want to, so I'm sure they have a reason for not "bothering".

Overall I think for sticky stuff like taters and cheese, a short single-beveled blade makes a great deal of sense. Probably thicker than normal, simply for stiffness. "Fancy" grind or not... there's simply less surface area for sticky stuff to get stuck to.

 

[Nathan the Machinist]

Here's a better shot of the actual parabolic grind

It's less drastic than where I started

The idea is the short bevel and pronounced hollow at the top of it kicks the food off without the poor cutting characteristics of a short hollow grind.

 

[Patrice Lemée]

Thanks for the pic Nathan, great for visual people like me. :thumbup: Gotta try this.

 

[tim37a]

Nathan,

Could you get a grind like that with one of your radius platens? What do you think the edge thickness before sharpening should be - maybe .020 with a 20* inclusive bevel. Given a 1 1/4" high blade, grind the parabola about 1" high?

The rest of you guys feel free to join in regarding these measurements, too

Tim