12-11-2018

Sharpening Knives - Equipment for freehand sharpening

As a point of reference, here are the supposed "grit equivalents" for the Sharpmaker rods.

I own a pair of DMT Duosharp diamond stones. One is fine/x-fine with 600 and 1200 grit (25 and 9 micron). The other is coarse/x-coarse with 220 and 325 grit (60 and 45 micron). These are big (2.5 by 8 inches) and cost about $60 each. So I have:

Note that the green should be comparable to the brown sharpmaker rods. The difference is that the ceramic makes smooth cuts, whereas the diamond tends to make scratches. Some people are entirely satisfied with an edge sharpened on the brown rods (x-fine DMT).

the Spyderco Goldenstone is equivalent to the standard white rods (3000).

On the way is a Spyderco 306UF 3x8 inch stone, which is ultra fine (8000). It comes in a nice leather pouch, just under $80.

If you watch the videos by jdavis882 where he discusses his "beginner kit" for freehand sharpening, it consists of:

I have the DMT DuoSharp plates. Many people prefer the Diasharp plates. The Diasharp have diamond over the entire surface, only on one side and are made of a plate of metal. Most people say they will both do fine. Light pressure is the key, both for good results and life of the plates. The DuoSharp plates are "interrupted" with holes -- this makes them better for removing lots of metal, because the swarf ends up in the holes rather than clogging the plates. The Duosharp are more economical since you get two plates in one.

You can buy smaller Diasharp plates (2x6 inch) and save some money, but the bigger plates give you more feel for what is going on and what angle you are holding.

It turns out I have the Knives Plus Strop. It is 8 by 2.5 inches, and comes loaded with chrome rouge. They say it should last you a lifetime, and it is well regarded.

Also available are the Spyderco Bench stones in a 8 by 2 inch size in plastic cases. These sell for $48 each, and you can buy coarse, fine, and extra fine, just like the sharpmaker rods.

Rough Rooster presents his beginner kit as 3 plates, all are DMT Diasharp.

He says that if he had to just have one plate, it would be the 600 "fine".
He sprays water (mixed with a few drops of Dawm detergen).
He says he has tried the Atoma brand plates and does not like them because of the way the plates are made. Atoma puts the diamond on in a pattern of patches, he would prefer even coverage like the DMT plates.

The 325 plate will yield an edge that will shave hair. The 220 plate (x-coarse) really removes metal fast, and can be handy to speed up a big repair or reprofiling job -- if used with care. His coarse looks like a 3x8 and the others look larger as indicated. DMT sells both a 4x10 and a 2.5 by 11.5 plate. He never says, those dimensions are my guesses. DMT says you get 5 carats of diamond with the 10 inch plate.

More advice

A fellow says that he got the following recommendations from BBB (big brown bear), who has Youtube videos you ought to watch. Get a King Neo 800 grit water stone and 1 micron diamond spray. Use the spray on a smooth leather strop.

Some searching finds: "King NEO is a splash-and-go 800 grit stone from Matsunaga Stone Co". So, this is a Japanese water stone. You can get it in 2 sizes, ST-2 is 210x73x25mm (8.26" x 2.87" x 0.98"). There is also a bigger ST-3.

Just for the record, Spyderco has 3 bench stones: medium, fine, and ultrafine.
At this time I have the 306UF, which is white - the ultrafine stone - big (3x8 inches).
The Medium (302M) and Fine (302F) and the smaller Ultrafine (302UF) are 2x8 inches.

Do you need diamonds?

This seems to be controversial. I have seen claims both ways by people that are supposed to be smart. It seems that most experts use diamond plates. The big trick is to use really light pressure. The usual claim is as follows:
Aluminum oxide and silicon carbide are softer than vanadium carbide, so you need diamond, boron carbide, or cubic boron nitride to abrade it. The aluminum oxide and silicon carbide will only abrade the steel matrix and chromium carbides, not the vanadium carbides. If you sharpen high vanadium steels with standard abrasives, you'll get the steel sharp, but will have torn the carbides out of the edge and so you're not getting any benefit from them and your edge won't hold any longer than a low-alloy steel would.

The claim is that with these high vanadium steels, you must use diamond at sizes below 10 microns (as a rule of thumb), if you want to shape carbide grains rather than expose or tear them out.

Here is a table of Knoop hardness values: 

Glass                            530
Tempered martensite at HRc60     700          Value questionable
Quartz                           820          Silicone dioxide, Arkansas stone
Cementite                        1025         Iron carbide
Chromium oxide                  ~1200         Green compound (with alumina)
Zirconia                         1600         Zirconium dioxide
Zirconia toughened alumina       1700
Chromium carbide                 1735
Molybdenum carbide               1800
Tungsten carbide                 1880
Aluminum oxide                   2100         Alumina
Silicon carbide                  2480         Maybe harder due to hardness anisotropy
Vanadium carbide                 2660
Boron carbide                    2750
Cubic boron nitride              4500
Diamond                         >7000
Feedback? Questions? Drop me a line!

Tom's Knife Info / tom@mmto.org