Читать книгу Classic Handplanes and Joinery - Scott Wynn - Страница 17

Carbon added to iron makes it harder and more wear-resistant. Carbon content of about 0.5% to 0.6% is about the lowest amount found in tool steel. The low-carbon steel is used for hammers, blacksmith tools, etc. A carbon content of about 0.8% makes a steel file hard (about 56–58 Rc). Carbon above that level does not increase the steel’s hardness, but raises its wear resistance. A carbon content of 1.3% is about the highest. The highest-carbon steel is used for razors, engraving tools, etc. A carbon content of about 1.05% is a good average—hard with good wear resistance, and yet not fussy or sensitive to heat.

Tungsten, added in small quantities, can impart a tight, small, and dense grain structure and the ability to attain a keen cutting edge. It also enables steel to retain its hardness at higher temperatures and has a detrimental effect on the steel’s forgeability. A tungsten content of 4% (with 1.3% carbon) is so hard that it is difficult to grind with an emery wheel.

Manganese makes steel sound when first cast into ingots, and easier to hot roll or forge. Practically all tool steel has at least 0.2% of manganese. Steel can contain up to 0.5% manganese before it is considered alloy steel.

Silicon facilitates casting and hot work. It usually is used in combination with manganese, molybdenum, or chromium. All steel has 0.1% to 0.3% silicon. Steel with 0.5% to 2% silicon content is considered an alloy.

Chromium increases the hardness penetration of the steel. A thick bar of plain carbon steel will be hardened to a depth of only ³/₁₆" (5mm) from its face during heat treatment. Adding chromium allows the bar to harden all the way through. Because most woodworking blades are less than ³/₈" (9mm) thick, it is not really an issue for woodworkers. Chromium increases the steel’s wear resistance under impact and heat, but does not necessarily increase its hardness. Steel with chromium content of 4% and higher is called high-speed steel.

CARBON STEEL

When manufactured properly, carbon steel sharpens optimally, holds a sharp edge, and resharpens easily—the three basic requirements of a woodworking blade. Its manufacture can be varied slightly to accommodate different woodworking tasks. Many variations exist, based mostly on the quality of ingredients and manufacture, how much it had been hot-worked, and what incidental alloys may be included.

Type	Pros	Cons
White steel	• A forged, very hard, and serviceable Japanese steel capable of getting and keeping a very keen edge, making it ideal for use in difficult-to-plane softwoods and most hardwoods	• While white steel’s long, angular grain structure allows it to take a very keen edge (keener than blue steel), it is less durable in use with abrasive woods than its blue steel cousin
Blue steel	• Both blue steel and white steel get their names from the wrapping paper the mill uses to identify the two. Also forged, blue steel has an addition of tungsten, making it more serviceable in hard and abrasive woods	• Even more expensive than white steel
Cast steel	• A forged, very pure steel • High quality and highly predictable • Takes and holds an edge ideally suited to woodworking	• No longer manufactured • Like blue steel and white steel, the blades always need to be forge-welded (laminated) to a softer, more tensile steel
“Plain” carbon steel	• Very serviceable, but undistinguished blades, unless forged • Easy to shape and harden • Perfect for making specific blades for specific tools; try one of the 10xx steels, such as 1095	• Quite a bit of variation in quality, which can be hard to identify until the blade is used • Usually manufactured with unworked bar stock

ALLOY STEEL

An allow steel allows a blade to imitate some of the qualities of a good hand-worked carbon blade without the cost of handwork—with generally limited success. Generally, they are particularly suited for hard-use conditions. While they may not get as keen an edge as a finely wrought carbon-steel blade, their capacity for keeping their edge is excellent. As a result, they are a viable choice for joint-forming planes (as opposed to joint-trimming planes) where the stress and heat of deep, repetitive cuts and impact all take a toll on the edge (Figure 1-3).

Alloyed steels require different sharpening methods, increasingly so as the alloy content grows. The greater the alloy content, the less effective are water and oilstones, necessitating a diamond stone or paste. The technique and the amount of time is about the same, though, once the different abrasives are employed. Each alloy type has its own advantages and pitfalls. Read on to learn more.

Type	Pros	Cons
Chrome and tungsten vanadium	• These blades are workhorses and very durable • Well suited to general, heavy work • Great for many miscellaneous tasks around the shop • Recommended for forming work	• Since they are coarser grained, they are not suited for making fine, tearout-free shavings in many woods
PM-V11	• Consistent grain size • Great durability • Easy to sharpen • An all-around blade steel • Recommended for joint forming and trimming • Handy when the wood gets harder and blade angle higher when A2 is no longer sufficient when fine tuning	• There is tougher steel available, and ones that can be made sharper
D2/M2	• Extremely durable edge • Suitable for high impact, abrasion, and high temperatures	• With the possible exception of high-angle blades used with tropical hardwoods, its coarse grain structure makes it unsuitable for most plane blades
A2	• Affordable quality and highly consistent content • Finer grained than chrome and tungsten vanadium • High performance across a spectrum of tasks and difficult woods • Recommended for forming and trimming work	• Method of sharpening depends on the manufacturer; some may be sharpened with waterstones, while others may require diamond stones • Not ideal for stock removal
O1	• Shows greater endurance in shaping tasks than carbon steel • Easy to sharpen • Takes a keener edge than A2 • Good choice for trimming	• Not as durable as A2
Highspeed steel (HSS)	• Its durability is ideally suited for very high blade-angle planes (60° or above) such as a rabbet plane used on tropical hardwoods	• Not recommended for general use in planing • Impossible to hone on more common sharpening stones (diamond stone or paste are needed for sharpening) • Doesn’t get as sharp as carbon or other alloy steels • Has a coarser grain than other alloy steels, so it has limitations

FIGURE 1-3. This dovetail plane uses a chrome vanadium blade.

FIGURE 1-4. Blades of A2 steel are usually marked. The one at left was cryogenically treated and is labeled as such.