Monday, July 11, 2011

Taking a knife from dull to razor sharp

Don't you hate it when you buy a new knife and it comes out of the box dull? I don't know why manufacturers do this. Or maybe you have a knife that came sharp but has gotten dull and you can't seem to get it back sharp. I have no trouble keeping a sharp knife sharp, but once it gets super dull I (used too) have tons of trouble getting it back to sharp.

I recently ran across a knife I bought as a boy. It came dull and no matter how hard I worked on it I could never get it sharp. In the past few years I have learned a little about sharpening things, so I decided to take another crack at it.

This knife is about 20 years old and made by Western Cutlery.

Before we get started lets define what a sharp knife is. The test I use to determine if a knife is sharp is what I call the "arm hair test". If the knife will shave the hair off my arm without pulling, then it is sharp. Some people use a tomato. If the knife cleanly cuts a ripe tomato without tearing or squashing then it is sharp. This test works well also, but is not quite as stringent.

It's so dull it squashes tomatoes instead of cutting them.

Usually, the reason a knife is hard to sharpen is because the angle of the edge is too steep. When it is being passed over the stone, only the top portion of the edge touches the stone. It never gets sharper because the actual edge is never touched. In order to fix this problem a new, shallower edge needs to be applied to the knife. It is important the edge is not too shallow. A very shallow edge is weak and will dull easily. The proper angle for your knife edge is between 17 and 22 degrees. There are lots of web sites that can help you determine the correct angle of your knife edge.

The first step is to grind a new edge. This can be done by hand, but will take a long time. I have a craftsman electric knife sharpener. It is inexpensive and does a great job of slowly putting the foundation for an edge. Don't use a bench grinder unless you really know what you are doing. It can overheat the blade and ruin the temper. Be sure you are grinding at the same angle for the entire length on the edge.

Messy but quick

Next use a wet stone the get the edge close. If the foundation edge is ground evenly and thoroughly this will not take long. Try to match the angle that you ground in step one. Fifteen to twenty swipes on each side and you have a good edge. Most people will stop here, but we want a razor edge.

Been using this stone for most of my life.
Buy a good one and it will last forever.

Lastly, the secret to a great edge are porcelain rods.

The perfect end to a sharpening adventure!

Lightly pass the edge of the knife at a very slightly steeper angle that you did in the first two steps. This will create a strong, sharp edge. It should only take about ten swipes per side. If it does not, go back to step 2 and work on the edges foundation some more.

Even a crude picture is better than 1000 words

That's it! Sharpening a knife is not nearly as hard as it seems. The trick is all in the angles of the edge.

You don't have to go through the entire process with each knife. If it already has a good edge then you might just have to do step 3 or steps 2 & 3.

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