http://www.knife-making-supplies.net Check out what's new on this site and the world of knifemaking! Feeder 1.2 http://reinventedsoftware.com/feeder/ http://blogs.law.harvard.edu/tech/rss en-us 2005 Knife Making Supplies .net info@knife-making-supplies.net info@knife-making-supplies.net Tue, 17 Jan 2006 00:56:05 -0800 Tue, 17 Jan 2006 00:56:05 -0800 http://www.knife-making-supplies.net/rockwell-hardness-scale.html the hardness of the steel used.

The Rockwell hardness testing is done by a gauge that forces a diamond-tipped probe, often called a cone, into the metal being tested. The depth of penetration for a given amount of force is measured and converted to a scale of relative hardness. This scale is called the Rockwell C scale. The hardness rating is usually abbreviated Rc.

There are other hardness tests for other types of materials. Because some high-tech knife blades are made out of ceramic, you will hear the mohs scale used. That relates to the hardness of minerals and is not appropriate for steel. Since a ceramic knife blade is a stone, mohs is used for that application alone. The rest of the time, the Rc scale applies.

In the 1960s, a trend was started among custom knifemakers. They began using the Rc rating of their blades as a sales gimmick. That started a race for ever-higher Rc ratings that is still going on today. You don't necessarily want the highest Rc rating you can find. When the rating is in the middle 60s, the steel becomes so hard that it can shatter like glass!

It's too simple to say that the higher Rc rating, the longer the knife will hold its edge. The type of steel has a lot to do with edge-holding ability. Each steel alloy has a hardness range that is optimum for it when used in a knife blade.

You'll notice that the hardness of stainless steel is usually lower than the hardness of carbon steel. That illustrates what was said about the various types of alloys having optimum hardness ranges.

With larger manufacturers, like Boker, Case, Ka-Bar, etc., you can be sure that they are using the optimum hardness range for the steel in their blades. These big companies have often had government contracts, where their blades were tested far more severely than any commercial blade ever would be. And, the government gets real serious when it comes to the metallurgical composition of their products!

The time to worry about Rc is when you buy a knife from an individual maker that brags that he makes all his blades from rasps and hardens them over the kitchen stove! You may get a fine knife from a maker like this - but just as easily you could get something that is worse than useless.

The thing to remember is that Rockwell hardness is one component of knifemaking, just as steel alloy is another. Your best bet is to stay with a qualified knifemaker whose products you can trust.

I've discussed Rockwell hardness as though it magically happens, but, of course, it doesn't. There is a process of heating the steel, quenching it and then tempering it that turns out a product within a certain hardness range. On Tuesday, I'll write about that process and what it means to you.]]> info@knife-making-supplies.net Tue, 17 Jan 2006 00:56:05 -0800 the-rockwell-hardness-scale http://www.knife-making-supplies.net/how-to-sharpen-a-knife.html you should be able to put an edge back on the blade in less than five minutes. Sometimes, in less than one minute!

By far, the larger bench stones are easier to use than the smaller stones. The drawback is that they're not as portable. However, if you plan to do a lot of knife sharpening, you should invest in both medium grit and fine grit bench stones.

The secret to knife sharpening is angles
Most pocketknives need a slightly steeper angle than if you were trying to slice off the top of the stone. Since every knife is an individual, it's difficult to say exactly how much to hold the back edge off the stone as you slide the blade forward. But, starting with the height of two American quarters under the back of the blade will usually get you close to where you want to be. If your knife doesn't get sharp within five to ten passes in each direction (that is, on each side of the blade), the angle you are holding is probably not steep enough.

Should you use oil or water on your stones?
How much oil should you use on your stone? NONE! You CAN use oil, but modern knife sharpening relies more on plain water, and you can even get by using many stones totally dry. The secret lies in a clean stone. You clean a stone with dishwashing liquid and water. The cleaner the stone, the faster it sharpens.

Forget those circular patterns that you saw your father make on the stone. Move your blade across the stone - edge first - as though you were trying to slice off the top of the stone. If the point of your knife has a deep curve, you may have to rotate the blade as the curved portion slides across the stone. If you don't, all portions of the curve will not meet the stone at the same angle.

Natural stone or artificial?
It really doesn't matter which type of stone you use. Both natural and artificial work well if you keep them clean and use a little water for lubrication or clean them more frequently if you use them dry. Soft stones usually sharpen blades a little faster, but the down side is that the stone also wears away faster. The bests bet for all types of knife sharpening is to buy a set of stones with graduated grit sizes, such as Lansky's 5-hone deluxe knife sharpening system. Lansky also provides oil with their sets. It's okay to use it, but remember to dry your stones before you store them away. And, keep them clean!

If you carry a multi-tool that has awls, small chisels, reamers (which have delicate edges) as well as knives, you can sharpen all of them with the Lansky 5-hone set and really put an edge on those tiny tools!

If you travel and take your knife or multi-tool with you, you won't want to carry a big knife sharpening set. Instead, I recommend that you pack Lansky's multi-sharpener to touch-up your blade every day. Just keep that little stone clean with plain hotel hand soap and water.

When someone asks to use my knife, they're always amazed at how incredibly sharp it is. After all, what good is knife if it doesn't cut?]]> info@knife-making-supplies.net Tue, 17 Jan 2006 00:55:01 -0800 how-to-sharpen-a-knife http://www.knife-making-supplies.net/hardening-tempering-knife-blades.html Steel with too little carbon can only be hardened by adding carbon in a case-hardening process.

Each steel alloy has a different temperature at which it must be heated for ideal hardening. The goal of hardening is to produce a homogeneous structure within the steel so there isn't a large collection of ultra-hard crystals and softer areas. When steel is heated to the ideal temperature (for that alloy), it transforms into a product called "austenite." When austenite is rapidly cooled, it forms "martensite." Martensite is the hardest transformation product of steel.

The cooling process, which often involves a liquid, is just as important as the temperature to which the steel is heated. It's called "quenching," and the liquid used is most often some type of oil. However, a few steels require a water quench, and fewer still are hardened by air cooling alone.

If we just hardened the steel into martensite, it would be too hard to be serviceable. It would take a good edge, but it would shatter. A second heating process known as "tempering" is required. In tempering, the steel is heated to a much lower temperature, and it softens and becomes more ductile (pliable).

Once the blade has reached its maximum hardness, it's very brittle and full of stress. Tempering gives it a correct balance of hardness and toughness while relieving much of the stress. Tempering also requires lower heat for longer periods of time, again depending on the alloy and the mass of the steel in the blade. Some blades can also be selectively hardened and tempered - and require terrific control and a master knifesmith.

There are too many technicalities of hardening and tempering steel to cover them adequately in this small space. If you're interested in this subject, you might want to get a knifemaking book. There are many to choose from, so I won't make any specific recommendations.

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