Why you should freeze your tools?
Cooling your tooling to -300˚ below zero can double or triple the time between sharpenings. And here's the real kick: it's impressive and companies that offer this deep cryogenic freezing are becoming more common. However, here's what you absolutely need to know before you try...
Magazine: Popular Woodworking Title:
Why You Should Freeze Your Tools
Author: Christopher Schwarz
Issue Date: 12/2001
Volume Number: 125
Page number: 58
About 150 years ago, Swiss watchmakers noticed that extreme cold changed the properties of their metal clock parts for the better. So after manufacturing their gears or what have you, some watchmakers would then store the parts in caves during the cold swiss winters and let them freeze.
Unwittingly, they had given birth to what is now commonly know as cryogenics. During the last century, toolmakers and metal heat treaters have explored what extremely cold temperatures do to tooling, metals and other materials. And they have come to som remarkable conclusions. For certain types of metals, cooling them to -300˚ below zero can make them at least twice as resistant to wear as untreated metal.
The wear resistance is permanent. You have to treat your tooling only once, and it will remain that durable forever, experts say. And the price of cryogenically treating your tools is becoming quite reasonable. We found that treating about four pounds of metal will cost you about $30 to $50. (If you treat a lot of items, the cost can be as little as $1 per pound -- and prices continue to drop). Cryo labs themselves are also becoming more common because commercial heat treaters are investing in the technology so they can offer the service to their customers. If you live in an industrial area, you'll propably be able to find a cryo lab locally. But even if you live in the sticks, there are cryo labs you can ship your tooling to for treatment.
So what's the catch? If cryo is so amazing why doesn't anyone sell cryogenically treated planer knives or router bits? Many of the manufacturers we talked to, including Freud, had experimented with the process in it's early days and found that it had little or no effect.
That's not surprising, says Bill Bryson, author of the book "Cryogenics" (Hanser Gardner Publications) and the president of the company Advisor in Metals in Milton, New Hampshire.
"Back in the 1970's it was a free-for-all, and it hurt the industry," Bryson says. "People were dumping tools in liquid nitrogen and they were cracking, or they weren't tempering the tools after the (cryogenic) process."
As a result, cryogenics got a bad rap in the steel and tooling industry, Bryson says. Not only for the early mistakes that were made but because some people thought that cryogenics would hurt sales. If tooling lasted twice as long, they might sell only half as many tools.
But during the last 30 years, heat treaters and cryogenic advocates began figuring out more about how, why and when cryogenics works. Andy today, most people in the industry acknowledge that it works well for certain types of metals, Bryson says, particularely the more complex alloys (more on that later).
In the home woodworking market, we've seen only a few cryogenically treated tools on the market. A few years ago, Vermont American announced it would sell "Ice Bits," cryogenically hardened screwdriver bits. Hock Tools recently began offering a line of cryogenically treated A2 plane blades. The cryo blades cost between $5.50 and $12.50 more than the same-size high-carbon steel blades. And toolmakers Bridge City Toolworks and Steve Knight, owner of Knight toolworks, also offer cryogenically treated blades.
But cryogenic treatment can help woodworkers with a lot more than plane blades or scredriver bits, Bryson says. Just ask James Larry Poole of P&K Custom Cabinets in Lula, Ga.
A couple years ago Poole sent out his carbide-tipped sawblades, router bits and sharper cutters to a lab for treatment.
"It really makes them last longer," he says. "I had one sawblade in particular that would just 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 crankshaft and pistons. So when a friend of his from the racing business started a cryolab, 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 the 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 sequenched (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 Austentite to martensite is never 100%. If a tool is carefully heat treated, it might end up with 90% martensite and 10% austenite. Commercial heat treating typically results in about 75% martensite, Bryson says. In low-quality tooling, it can be as slow as 50% martensite.
By carefully cooling the tooling to -300˚ below zero and then thoroghly retempering the metal, nearly all of the austenite is transformed into martensite. Bryson says it's proven to be 99.9% 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 vine 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 resharpened.
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 the treatment, Bryson says, that's when you see 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.
- Warmer Cryo: Some labs use dry ice to cool the tools. Dry ice with take the temperature down to -109degrees Fahrenheit. This process works, but you won't get a full transformation of austenite to martensite.
- Quick Dip: Some labs dip the tools into liquid nitrogen (-300˚), leave it there for a short period of time, remove the tools and let them return to room temperature. This process can cause the tools to shatter from thermal shock. it also can transform only the outer layer and leave the core untreated. Many of the experts we talked to do not recommend this procedure.
- Long Bath: Other cryo labs use gaseous nitrogen to reduce the temperature slowyly; they keep it there for 20 hours or more (using either gas or liquid nitrogen), and then slowly return the tools to room temperature. Bryson says he's tried a variety of methods, and the equipment he prefers (and sells to other cryo labs) takes the temperature down using gas and then soaks the tools in liquid nitrogen. Either process works, however.
One of the keys to getting the best results is to choose a lab that has some knowledge of heat-treating and metallurgy and is willing to soak the tools for a long time, says Randall Barron, professor emeritus at Louisiana Tech University's Depeartment of Mechanical Engineering. Barron's pioneering research in the 1970s, 1980s and 1990s helped convince many industries to use the process in manufacturing.
Barron's studies showed that bringing the temperature down to -300˚ below zero created a more durable tool. Plus, his research showed that soaking the tools for hours was what led to the creation of the micro-carbides, which lend additional wear resistance.
No matter which process is used, after the tools return to room temperature, the tools need to be retempered because the new martensite is fragile and can shatter, experts say. This retempering process is almost always included in the price for the cryo treatment.
Bryson recommends that the tools be tempered at 300degrees to 350degrees for two hours for every inch of thickness of the tool. He also says you should make sure that the items are not stacked on top of one another during tempering.
How Well Does it Work?
This, of course, is the big question. Some of the claims seem outright outrageous. A dowel maker claimed his A2 knives lasted 800 percent longer. A titanium aircraft bit that once lasted for 15 holes was replaced by a common bit that had been cryogenically treated that would last for 200 holes.
Most cryogenic labs will tell you it's reasonable to expect your tooling to last two or three times longer between sharpenings. Considering how inexpensive cryogenic treatment can be, you'll make your money back after one sharpening.
In August, we sent a batch of tooling from our shop here at Popular Woodworking to a cryo lab for treatment -- everything from a chisel to 12" jointer knives. We're going to compare the durability of these tools with the identical untreated tooling we recently install in our machinary.
Next year, we'll let you know what we found. But even if we find out that cryogenic processing really works, don't be surprised if you don't see cryogenic planer blades for sale in woodworking catalogs.
Professor Barron says that one of the studies he did in the early days was for a manufacturer of razor blades. The company wanted to see if the cryogenic process could improve the dies they used in making the blades.
"I asked if they wanted to treat the razor blades to make them last longer," he says with a chuckle. "They said no, because then they might not make as much money."