Saturday, August 14, 2010

Knife Sharpening

Bones said...
One thing I can never seem to do properly is sharpen blades. Care to share any tips/techniques? I understand there are knife sharpening kits available but would be interested in using commonly available tools.

Hi Bones,
Check "sharpening" on teh topics on the lower left column. I've written some about it. 

Knife sharpening is one of the hardest skills to master. A lot of people think they can do it, but take a blunt piece of steel and turn it into a blade you could easily shave with? Few people can do it. It takes years of practice, but a few good tips and having the right tools will help reduce the learning curve significantly.

Probably the easiest way to sharpen knives if you don’t yet master that skill is to get a knife sharpening system like the one you probably have in mind. Good sharpeners sometimes use it if they want to sharpen a knife quickly. I don’t own one myself but the Lansky kit has had a good reputation for as long as I can remember.
Lansky Deluxe 5-Hone Sharpening System

There are a million different ways to sharpen a knife and everyone has his method they swear by. The first thing I do with a new used knife is take a good look at the edge, checking for dents or rounded edges. If the blade has been abused and there are dents and chipped metal I use a belt grinder to remove them. This of course eats up a lot of metal so its not something you want to do often.
If the knife needs a lot of sharpening (it wont even cut through paper properly) I use the more coarse side of the wet stone so as to get a half way decent edge. Here I use elliptical movements, keeping the edge against the stone at a 20-30 degree angle depending on the edge of the blade. The trick and one of the hardest things to do is keeping the blade at the right angle as you move it, and do so again when you change to the other side.
A few tips here:
1)       Go slowly. Visibly check that the angle is correct. This is specially important because its almost impossible to achieve the exact angle on both sides.
2)       Use a red marker on the edge of the knife. This will tell you if you are making contact where you should, and if the angle is right.
3)       Place the knife in the angle you believe to be right and while keeping it that way, look around from other directions to verifiy.
4)       Do 5-10 eliptic movements on one side, then change to the other. If you don’t do this often enough you’ll end up with a wire edge. That is a very thin layer of metal that rolls over the edge. While this can be pretty sharp, its not the real edge. You can feel it with your fingernail by dragging it through the edge. If your finger nail catches on the edge, you’ve got a wire edge and you have to keep sharpening until you remove it.
5)       When using a water stone, you want to eventually achieve a very thin paste on its surface, this paste sharpens nicely.
6)       Use all of the surface of the stone to is full extent so as to not ruin it.
7)       Good stones aren’t cheap. This is one of the" you get what you pay for" things. The $1 chunck of grinder junk will ruin your knife. I did that as a kid, then I learned better and bought a nice two surface Japanese stone. It wasn’t cheap but I’ve had it for decades and its still my favorite stone.

 Woodstock D1130 1000 Grit and 6000 Grit Japanese Waterstone 

Once I have an ok edge I turn to the other side of the stone, the one with the finer grit, and start dragging the edge at its right angle towards the direction of the spine, opposite from the direction of the blade. This I do so it doesn’t catch some larger pieces of grit against the edge. The stone is usually much smaller that the knife, even more so when the knife is at 90 degrees in relation to the rectangular stone. What I do is start from one edge of the stone, making contact with the edge sector that is closest to the hilt, and as I drag it to the other side (remember, towards the direction of the blade spine) I move it downwards until I reach the tip of the knife, and the other edge of the stone. 5-10 times on each side. You start at one end of the stone when you do one side, you then start at the opposite end of the stone when you do the other. Side you are also moving downwards to cover the full extent of the blade its more of a diagonal movement, and as you reach the tip you are forced to curve your grip some so as to keep the same angle when the edge curves towards the tip.
Using a bit of water with the fine grit side, you soon have a bit of very nice soft clay on the surface of the stone. When you look at the edge of your knife, this clay should be evenly spread along the edge, a sign that you’ve been keeping a correct angle, like the red marker trick.
After a few minutes of this you have a knife that will shave the hair off your arm, but you can still do better by stropping. For this you can use a leather strop, even a simple leather belt of some thick fabric with polishing paste. You draw it as we did before with the fine grit side of the stone, spine-first along the strop.
What you are basically doing here is polishing the two edges. This makes for a razor cutting edge, the finest edge you can ever achieve.
I often use finger nail polishing pad for this, you get excellent results using it diagonally spine first like you do with the stone.
You can sometimes replace the stomping or fine grit stone with sand paper and a mouse pad or some other foam pad. This makes a very nice convex edge which is both sharp and thick enough for hard work.
Another thing you often hear people say is that they will sharpen a knife for a trip and then have it sharpened again by some expert once they return. To me this couldn’t be further away from the self reliant mentality, or survival mindset.
Its like saying that you don’t know how to reload your gun, so you take a 20 round magazine with you when you go hunting and then have a gunsmith reload it for you. It’s the exact same thing, yet these folks don’t realize it.
What you should do is learn how to sharpen your knife, and at least touch it with a ceramic rod like you do when stropping. The fingernail foam pad I mentioned is ideal for this. Sandpaper can be used but I find the foam pad to be just perfect since you already have a somewhat rigid and flat surface to work with. 

Strop (polish) your blade a at the end of the day or after a certain amount of use and it will always be razor sharp when you need it.



brahma said...

This is the book you need to get to learn how to sharpen a knife. "Razor Edge Book Of Sharpening" by John Juranitch.
It teaches you how to easily use the grinding wheel and rough and fine stones and "SNOOTH" steel to get your relief angles and honed cutting edge. Takes you through every single step and he makes it enjoyable. This is the guy who used to travel around North America with his young daughters to fairs and challenge people to give him any dull cutting tool and his daughters would sharpen it right there and shave him with it. He's no joke though. He has a very respected industrial sharpening company. He also sells some nice but reasonably priced guides you can put on your blade to get the proper angles.

brahma said...

Here's a link to that sharpening book:

ProtegeAA said...

I used the Lansky kit a couple of weeks ago on my Benchmade and Kershaw. It was my first time sharpening them. My coworker showed me how to use it and it was very easy...totally recommend the kit, will be buying one soon.

brahma said...

A friend of mine tried out many inexpensive kitchen sharpeners and came across this one. I wasn't much interested until he got me one. It's awesome.

David said...

Google "knife sharpening with sandpaper" and you'll find good methods, even videos.

I used a Lansky system for decades but now almost exclusively use sandpaper. It creates a convex edge that helps the blade glide through material being cut. Using a carving knife sharpened this way is truly a joy. The only time I'd use a fixed-angle system like Lansky now is to fix a really damaged edge, and then I'd complete the edge with the sandpaper and leather strop. The knife is so sharp you can "whittle" paper with it into fine strips.

Also, if you use a leather strop with a rougher side, put some metal polish (Flitz or any other would be fine) on the leather and then strop. This will work on all but the very hardest steels (I have a blade made from a power hacksaw blade that is so hard that sharpening it is extremely tedious). This method polishes the entire side of the blade (not good for coated blades) and creates something akin to a lightsaber, so smoothly does it cut.

Nolan said...

I use the Lansky system for basic sharpening when I don't want to use a lot of focus. I can get pretty much any knife sharp enough to split hairs lengthwise given an hour with my Lansky.

I only have one knife that is capable of taking and keeping a sharper edge than my Lansky can give. If you are inexperienced with sharpening, then the Lansky is for you. Using a diamond stone to sharpen gives me the best edge, but the functional performance difference is negligible. If you aren't good at sharpening, then use the Lansky. If you want to practice with a stone, then go buy a cheap knife and practice until you can get it very sharp before you ruin a good knife with the stone trying to learn how to use it.

Remember that you blade will come with a certain cutting angle depending upon the manufacturers intention for the knife and it is usually a very bad idea to change this angle dramatically.