Popular Woodworking 2001-12 № 125, страница 38

WHERE TO GO FOR CRYO

If you can't find a cryogenics lab or a heat treater locally, here are a few labs across the country that provide the service. Please contact them for pricing and shipping information.

Advisor in Metals Bill Bryson 336 Governors Road Milton, NH 03851 603-755-9232

Applied Cryogenics Bruce Medlyn Fort Smith, AR 800-734-7042

Down River Cryogenics Mike Pate 606 West St. Whitehall,AR 71602 501-397-7189

ADS Cryogenics Aaron Bennett P.O.Box 3401 Crestline,CA 92325 909-338-6756

Advanced Cryo Techniques Jim Sabinas 110 E. Center St. North Fort Wayne,IN 46554

Cryogenic Services Jim Younger 18308 West 79th St. Viola, KA 67149 316-545-7555

York Cryogenics Leon Patterson 3945 Farm Road York, PA 17402 717-309-0639

Cryotron, LTD Gordon McKay 75 E.Shep St.

Spruce Grove,Alberta Canada 780-960-0960

ticular that just would not wear out."

Poole used to be involved in car racing, and he had heard about the benefits of cryogenically treating some car parts, including crankshafts and pistons. So when a friend of his from the racing business started a cryo lab, Poole decided to see if it would help his tools.

"You really can tell the difference," he says. "I get twice the life at least... so it's worth the money."

But before you start gathering all the cutting tools in your shop to take to a lab, there are some things you need to know.

In a Nutshell:What Cryo Does

There's a little science here, but it's easy to digest. When tooling is made, the manufacturer heats it to make it hold an edge. During heat treatment, the structure of the steel changes. As it is heated, the steel has a structure that is called "austenite," which is softer and has a coarse, irregular grain. When the blade is quenched (reduced quickly in temperature), the austenite changes into "martensite," which has a finer grain and is more resistant to wear.

The problem is that the transformation from austenite to martensite is never 100 percent. If a tool is carefully heat treated, it might end up with 90 percent marten-site and 10 percent austenite. Commercial heat treating typically results in 75 percent martensite, Bryson says. In low-quality tooling, it can be as low as 50 percent martensite.

By carefully cooling the tooling to -320° and then thoroughly retempering the metal, nearly all of the austenite is transformed into martensite. Bryson says it's proven to be a 99.9-percent transformation or more.

All tooling will benefit from cryogenics, Bryson says. But if the steel is an alloy containing cobalt or tungsten, the cryogenic process will create very fine micro-carbides, which add even more durability to the edge.

The alloy A2 steel, which is now found on some hand plane blades, contains carbon

and chrome, so it reacts well to cryogenic treatment. High speed steel (HSS) contains molybdenum (which makes the tool resistant to heat), chromium and sometimes tungsten, which makes it ideal for cryo treatment. You'll find HSS in your planer knives, your jointer knives and in other cutting tools. As a rule with metals, the higher the alloy content, the better the cryogenics will work.

But what about carbide tools? Will saw blades and router bits benefit from cryogenic freezing? According to Bryson, that depends.

If the carbide is newly manufactured and not recycled from old carbide tooling, cryogenic treatment works, Bryson says. Carbide that has been reclaimed or recycled is not improved.

"And we don't know why," he says.

In new carbide, cryogenic treatment strengthens the binder between the individual carbides, he says. Cryogenically treated bits should last twice as long between sharpenings, Bryson says, though some people report even longer times between sharpenings.

Beware of the Thin Film

Perhaps one of the strangest aspects of cryogenic treatment is something that experts have yet to fully explain. It seems that after a tool has been frozen and then retempered, some report you won't get the added wear-resistance until the tool is re-sharpened.

Bryson says there's a layer of metal that's between .00007" and .0001" thick on the outside that remains untreated. After you remove this layer by sharpening, the tool works great. Bryson calls this the "Thin Film Phenomenon," and he says it's one of the reasons some people thought cryogenics was a crock in the early days. People would treat their sharp new tools, put them to use and see almost no difference in the tool's life. But if you sharpen the tools after treatment, Bryson says, that's when you see the the full benefits of cryogenic treatment.

How to Shop for Cryo

There are several ways to cryogenically treat tools, and experts say some are better than others.

60 Popular Woodworking December 2001