I had a PM earlier today (or yesterday now), to post up a how-to on sharpening. It's something I've meant to do many times but gibbed it as it's a large subject. I have posted bits and pieces before on Boards, so I will shamelessly pillage those posts to flesh out this one!
Well, here goes, I may need to use a few replies to fit in all the pics I want to use, but we'll get there in the end!
I want to make it clear how to go about making a sharp knife out of whatever finish the factory left on your knife. So to start we'll look at what grind the factory (or maker) has put on our knife.
Meat the Steal.
I'm a fan of Alton Brown so you can expect these horrible puns!
There are about six knife grinds, and real quick here's the highlights.
Hollow ground, done on large round grinding wheels gives a thin edge with less metal behind the edge. Good for slicing but bad for chopping.
Full flat, tapers from the very spine to the edge in one Vee shape, may have a tiny micro bevel right at the edge.
Sabre ground, the knife sides remain even until halfwayish down the blade, then taper to meet at an edge. Tapered lower down the blade it's Scandi ground, mainly used in scandinavia, the knife is flat until maybe five mil. from the edge then a bevel is made to bring to the edge, may also include a micro bevel.
Chisel ground, common on Japanese cutlery to leave a shiny surface on the face of the cut.
Double bevel, often used on a fine thin blade to leave a bit more beef at the cutting edge, handy if your knife is chipping out but you want to keep the fine slicing geometry behind the edge.
Convex grind, what I usually use on softer western kitchen knives. Has an apple seed profile so has a nice sharp edge but with a bit more support behind the edge so less flopping of your edge and less aligning needed in use, also good for outdoorsy knives, machetes and axes!
These are the basic ones that you probably have, there are some variations but these are the basics!
The other big variable we have to look at is the steel itself, what is your knife made of? How was it heat treated and how hard did it get?
This will dictate what angle you will sharpen at, I like to sharpen at the thinnest angle the knife can tolerate without failure. Some knives will be 5 degrees a side, some 25 degrees. It all depends.
Japanese steels are generally hardened to a higher level than French/German kitchen knives. This means they will hold an edge rather than roll it, so less need for a steel to realign the edges.
They are also usually carbon steel laminated with softer cladding (Hitachi White paper or blue Paper steel).
Sometimes like my Hattori some of the Japanese "Super" steels are used that are not allowed to be used outside Japan unless under licence (Cowry X, VG10, S30V, S90V, BG42)
What this means is you can go for a thinner angle and the steel will take an hold that edge, the downside is too thin and the brittle core can chip on you instead of folding like a Sabatier/Henckels/Wusthoff et al.
Traditional Japanese knives are usually specific to various cutting tasks. A Deba is for cutting up heavy fish like a big tuna so is thicker and generally chisel ground (beveled only on one side, also makes some knives left or right handed).
A Nakiri is a light cleaver like knife and used for vegetables mainly. Any heavier work it can chip like a mother (or like my Shinichi Watanabe mukimono!).
There are some Japanese blades that are more multi-purpose and similar to Western knives.
A Santoku, "three virtues" close to a medium chef knife in use, has a pointy enough point, enough belly for rocking chopping cuts and enough length for slicing and mincing.
A Petty which is basically a paring knife, can be long or short but is a great prep knife and peeler but the lack of length can mean slicing is more awkward.
A Gyuto or "Cow Sword" is like a big chef knife more than a dedicated carver (Sahimi) and does what it says on the tin. It's a long knife with a decent belly for long gliding slices and also good for winter squash and Pumpkin carving!
Most western knives are "Rostfrei" or Stainless, this means that they "stain less" than high carbon steels, unless you have a knife made of Spyderco H1 which replaced carbon with Nitrogen and does not react or corrode at all! (It's an Austenitic work hardening tool steel, mad stuff!
OK, but how would I sharpen the damn thing!
Well basically, you rub the steel against an abrasive until both sides (planes) meet each other. This can be done using stone (water or oil), abrasive ribbons on a loop (belt sander) Diamonds or sheets of abrasive known as "Sandpaper"
I have all of these, but for someone starting out the easiest and cheapest option is abrasive sheets. The technique is largely the same for any edge, exceptions excepted!
The main choice now is backing material (or substrate if ya need to get fancy). A flexible backing like a foam mouse mat gives a convex edge, very Bark River. I like it for softer Western Kitchen knives or cheaper stainless knives as the convex supports the edge. A knife prone to rolling can be made a star using a soft backing and an edge trailing stroke.
The other option is a very hard and flat backing. This is the "Scary Sharp" method, can be done with float glass, granite surface plate, or my cheap favourite is a cheap mirror on a rubber mouse mat.
The mirror is made of float glass or the reflection would distort! Flat as a flat thing so your edges will be perfect Vee shapes, as much as human muscular control allows anyway. Any hand sharpened edge will be a little convexed by the action of the body in driving the abrasion.
I get my abrasives from any car body work place, you need the paper used for car body work. Available up to about 1500 grit, I then use Micro mesh "paper" to finish and then strop. You can also get Pressure Sensitive Adhesive backed sheets (PSA) of the stuff used to polish fibre optic connections. Same stuff I use on my Edge Pro for polishing, just writ large!
How we Rub
I like an away and back motion. Something in the articulation of the human shoulder makes the side to side stroke a worse option when sharpening. Use one hand or both, just use the same number of strokes on both sides!
On smaller blades I like to make one long stroke, heel to point each time.
Larger knives I go section by section and blend in the overlaps, helps with working up poor areas on a sharp knife.
I do like to press on the blade lightly with my off hand, especially good on flexible blades like fillet knives! These boys are talking about using coins to set the edge angle, and that's fine on a kitchen knife! I like a 15 or 20 degree angle on my harder use knives, mainly so I can easily touch them up on my Spyderco Sharpmaker.
These lads are good! I usually use edge in strokes to minimise burr formation, change to edge trailing when finishing to polish up an edge.
More scary sharp
Use enough grit, not force!
If a knife is like a ruler, go down to 120 grit and make an edge. Most of your work the first time is setting an edge or bevel on your knife. Make the edges meet cleanly and all steps after are refining or polishing the edge you set first day.
Use the minimum grit.
If an edge has been set and is good, just a little blunt. Use the minimum of grit to get the edges back meeting and refine on from there. Many Chef knives aren't blunt, a rub on a loaded strop is enough to keep them going for six months!
Don't wear out your steel prematurely.
The same thing can be done on oil or waterstones. The substrate here is stone so convexing is done by "rocking" the blade, tricky to do. The stone needs to be flat, so before I bought the special stone I flattened all my stones using sand on a lintel or kerb stone.
Sharpening works the same way, away and back.
Keep on keeping on
Once the edge is set, refine and use as appropriate.
I like to deburr during sharpening by lightly slicing some Cork or hard felt.
I use a Champagne Cork, just how I roll
A knife sharpened and honed to mad grit levels on paper or stone can be further refined using strops.
I like leather, but it's just there to hold or carry a bit of polish compound.'
Stroke your blade edge trailing (so you don't cut the strop) and use a little pressure to make the grits work for their keep!
Maintain-A little butt often
To keep your edge in tip top condition, strop often!
A little abrasive, very fine, will preclude a resharpening for months in a busy kitchen. I have stropped on paper, rubber, leather etc. It's just a medium to hold a very fine abrasive. I have several leather strops for hand and machine use. The best I like is "Smurf Poo" and a Longstrider Strop.
Any bit of leather belt and a flat stick will make a strop, using Diamonds or str8 razor stuff all ends the same way, I've used them all!
I like Smurf Poo, Diamonds and Red and Black Razor Paste (Dovo) in that order!
The other touch up option is steel!
A steel should really only be used to realign an edge that has deformed slightly through use. Most steels that come with knife sets are way too coarse and chip or abrade the edge too much. Smooth glass, ceramic or polished steel would be miles better for these regular touch ups.
Most butchers knives and a lot of Western knives are hardened to a lower point than Japanese knives. A butcher will steel before cuts, between cuts over and over until the knife is used up and replaced.
Japanese knives being harder are more brittle, which can be offset by cladding or laminating, using high tech powder steels and by carfeul handling. They are honed and then polished to give a very refined edge. Even a fine ceramic would be too coarse to use even to touch up these edges, I would prefer to see a light touch on a strop loaded with chromium oxide or fine diamond paste.
Diamond abrasives, paste, mounted to a steel like the excellent Fjallkniven or on bench stones like DMT and Eze-Lap are good to cut very hard steels. You need diamond if your knife is made of Super gold powder steel, S30V or better, VG10, Cowry X or most of the newer cutlery steels coming out of Japan (and only licensed for use in Japan).
Diamond because of the shape of the particles will not give as highly polished an edge as stropping with Chromium Oxide (about.5 micron grit) or the other metal polishes like Flitz or razor strop abrasives from Dovo.
Grits are not standard over different systems either, so a 2000 grit sheet of wet and dry isn't the same as a 2000 grit Japanese waterstone. There's a handy chart showing comparisons here.
Scroll to the bottom of the page for the grit comparison charts.