It’s just someone holding a piece of steel against a big, spinning rock.

October 13, 2023 12:37 PM

TW Lim writes about knife-sharpening as a process less about making a knife objectively, maximally sharp than about making a knife be what what it needs to be to do its particular job, in Forming an Edge. Don't miss the electron microsopy.
posted by cortex (20 comments total)

I finally happened across a method that keeps the laminated stainless/carbon 240mm gyoto consistently sharp day-to-day. I gave it a good sharpening on 3 levels of water stones about a year ago. Since then, before each use it gets a bit of stropping on a piece of leather with a little 1 micron diamond powder occasionally applied to it. It stays scary sharp despite almost daily use.
posted by Mei's lost sandal at 1:04 PM on October 13, 2023 [2 favorites]

I like using a rasp because you know it's cool.
posted by clavdivs at 1:36 PM on October 13, 2023 [2 favorites]

Right before reading this I was reading some biological developmental systems theory about the complex interactions among genes, environment, epigenetic processes, etc. that take place as organisms develop.

So now I understand: knife sharpening = organismal growth.
posted by airing nerdy laundry at 1:52 PM on October 13, 2023

This is facinating - I'm going to conjecture that different types of steel will sharpen differently even if using the same sharpener due to variations in carbide size and density.
posted by porpoise at 1:58 PM on October 13, 2023

I'm only slightly knowledgeable about knife sharpening but... how can this "Ho's knife" grind even work? For one thing, a 2-degree cutting edge would be destroyed the first time it touches a carrot, wouldn't it? Secondly, you'd have to regrind the entire knife face every time you want to touch up the edge (which would be frequently since the edge would get destroyed within a minute of use).

Yes, a perfectly triangular cross-section seems like a child's idea of what a knife should be, but there's a good reason no actual knife looks like this - or so I thought until I saw this.

Does this make sense to anyone else?
posted by splitpeasoup at 2:03 PM on October 13, 2023 [3 favorites]

I agree, I question whether that knife really had a 2° angle.

I have a chef's knife where the entire blade tapers, both from top to bottom and from handle to tip. The metal is still thick enough overall, even at the edge at the tip, that just the edge itself is sharpened at a 12-15° angle, leaving a small but clearly visible bevel. The blade is plenty sturdy yet still thin enough to be an absolute joy to work with, just slices through food like it's slicing through soft butter. And like Mei's lost sandal, I keep it razor sharp with a butcher's steel (which just pushes the very edge back upright where it's microscopically bent over to one side, rather than removing metal to create a new edge). I last sharpened it on stones something like a year ago; granted I don't use it every day but I do use it frequently and it doesn't yet need resharpening.
posted by Greg_Ace at 3:10 PM on October 13, 2023

Also, this needs a "knifeTheUniverseAndEverything" tag!
posted by Greg_Ace at 3:14 PM on October 13, 2023

This video featuring the inventor of Magna-Cut steel — which is slicing off a big chunk of the market for premium knives, hunting, camping, pocket, and kitchen alike — has some of the best discussion of edge geometry, heat treatment, toughness vs. hardness, and specific brands of steel and their characteristics I have seen yet.

It also appears to be sponsored by Buck Knives, though it doesn’t talk about Buck knives generally or specifically, but it does seem to constitute an announcement that some Buck knives will now be made with Magna-Cut. A long, long overdue refreshment, in my opinion.
posted by jamjam at 3:31 PM on October 13, 2023 [3 favorites]

slicing off a big chunk of the market

ISWYDT!
posted by Greg_Ace at 3:41 PM on October 13, 2023

I tried and failed to come up with a more subtle version of the same metaphor just for you, Greg_Ace. Sorry!
posted by jamjam at 3:50 PM on October 13, 2023 [1 favorite]

Are you not feeling very sharp today? No worries, sometimes you just have to cut and run.
posted by Greg_Ace at 4:09 PM on October 13, 2023

This is facinating - I'm going to conjecture that different types of steel will sharpen differently even if using the same sharpener due to variations in carbide size and density.


Absolutely. This is one reason I think even inexpensive knives with low end stainless steel can perform extremely well. Carbides formed are very fine, and make up a low volume of the steel. So even a cheap pull-through sharpener will yield decent results for many users with this kind of steel, even though it rather coarsely scrapes and shapes the edge into compliance.

For a while, there was a trend to use high alloy, high hardness steel made from specialty foundries in relatively small batches. These were steels intended to be hardened to over 60 Rockwell and form lots of large carbides for extreme edge holding. However, these steels demand relatively careful sharpening with very fine stones/abrasives. Otherwise, carbides tend fracture from the coarse sharpening media and get torn out, leaving edges that might cut via sawing action, but can be outperformed by cheaper, more common types of steel that rely on edge shape to cut. The most extreme example of carbide tearout can be seen if one tries to sharpen a tungsten carbide machine tool cutter with diamond media that's too coarse. The edge will always chip, visible to the naked eye, and negate one of the big advantages of the material.

Interestingly, plain high carbon steel is well respected knife material, despite having no carbide formation. One of the things people like about it is the ease of sharpening!

4° inclusive, is extremely acute for any knife. As shown, it uses what's sometimes called a zero edge, a style of grind that has a single grind on either side of the blade with no separate edge bevel. It almost doesn't matter what kind of knife steel is used with blade geometry like that. It'll cut food extremely well. Of course, there would be tradeoffs. It would be demanding to use, as lateral forces on the blade will take a toll, fracturing and/or deforming the edge. The kind of thing that happens with a hand held tool. And while sharpening is theoretically easy, sharpening a whole flat side is a lot of work and often not very practical. A small secondary bevel is so much easier and quicker to do, and the result is still very good because the width of the new bevel would still be extremely thin.

Yes, I've been obsessed with sharp edges for decades, and sharpen things every day as part of my livelihood.
posted by 2N2222 at 5:16 PM on October 13, 2023 [9 favorites]

Shehan Prull's shop.

If it's linked in the article or above I missed it.
posted by anadem at 5:52 PM on October 13, 2023

Ok so this is excellent but it connects to this which is also excellent and on to this which may be life-alrering.
posted by BlackPebble at 6:05 PM on October 13, 2023 [1 favorite]

The first pass along the whetting stone
creates an edge too fine to last;
the second, more blunting pass
tempers the edge into usefulness.

Taylor Mali, The Second Pass (CW suicide in full poem)
Alternative version with accompanying music, same CW
posted by polytope subirb enby-of-piano-dice at 6:44 PM on October 13, 2023 [2 favorites]

That alternative version of 'The Second Pass' is really wonderful, pseopd.

I had no idea there were people out there doing things like that.
posted by jamjam at 3:52 AM on October 14, 2023 [1 favorite]

A lengthy note about the development and testing of magnacut steel.

https://knifesteelnerds.com/2021/03/25/cpm-magnacut/
posted by sebastienbailard at 4:28 AM on October 14, 2023 [1 favorite]

Not only cooking. Back in the day, the 3 people who ran the bindery in the library of the university where I worked opened the place up on Tuesday nights as a book-binding workshop. I spent a couple of years getting some of my yard-sale reading copies back into usable shape. The boss-boss was the only one in the room who could really get an edge on the knives we were all using. After two years of learning-through-error, I was ready to rebind my copy of An EASY INTRODUCTION to the Arts and Sciences: being a short but comprehensive SYSTEM of polite and useful learning divided into lessons. (1795) by R. Turner jun. LL.D. A quarter-leather binding required, not only paring down a piece of leather to a precise uniform thickness, but also paring the edge to nothing where the leather met the boards - while keeping that edge straight. Needless to say, I had the gaffer whet my knife before I essayed that task.
posted by BobTheScientist at 6:56 AM on October 14, 2023 [3 favorites]

Here's a little ditty I sing when I'm working a blade:

“Knives sharpening knives knives sharpening knives sharpening knives sharpening KNIVES sharpening SHARPENING!”
posted by Ivan Fyodorovich at 8:50 AM on October 14, 2023

Until the voices in your head tell you the knives are sharp enough now?
posted by Greg_Ace at 12:42 PM on October 14, 2023 [1 favorite]