When it comes to tools, the good news is that a vast selection is offered in the marketplace. Unfortunately, there are some really bad tools in addition to some really good ones. Compounding the problem, most turning tools are not delivered properly shaped or sharpened and need a good deal of user tuning (grinding to the correct shape) and honing to work properly (see chapter 5 for information on grinders and sharpening jigs).
Most aspiring turners try to use tools directly from the package, doing nothing more than honing to a sharp edge. They are disappointed by the results and blame themselves when things do not go well. The fact is that most people take to turning like ducks to water if sharp tools of the correct shapes are placed in their hands. If you follow my prescriptions for tool shapes and sharpening in this chapter, you will find learning to turn an easier process.
Turning tools are available in three materials: high-carbon steel, high-speed steel (HSS), and powdered metal technology steel (PMTS). Traditionally, turning tools were made out of high-carbon steel, which is iron with 3/4 percent to 1 ½ percent carbon as the principal alloying element. Such steel is often referred to as “water-hardening” steel because it must be quenched in water during hardening.
Water-hardening steel tools are still widely available, but in the last two decades manufacturers have increasingly switched to high-speed steel for their premium turning-tool lines. HSS tools are more expensive, but they hold an edge substantially longer, thus requiring less frequent sharpening. HSS also has the quality of “hot hardness.” Whereas carbon steel cannot be heated higher than 430°F without drawing the temper, HSS maintains its hardness at much higher temperatures and is thus more immune to damage from burning and overheating due to excessive grinding. HSS is more expensive because tungsten, cobalt, and molybdenum must be alloyed into the steel in addition to carbon.
Another desirable alloying element is vanadium, which forms vanadium carbide in the steel structure. Vanadium carbide is highly wear resistant, which makes for better edge holding. In conventional steel making, alloying elements in the right proportions are mixed while molten and poured into a mold to form an ingot. The problem is that during cooling, vanadium carbide “freezes out” first, creating areas of greater and lesser concentrations of the vanadium carbide. At vanadium levels much above a 4 percent, “stringers” are created in the resulting ingot that are so hard that they make the steel difficult to machine or grind.
PMTS can have vanadium levels as high as 15 percent. This type of steel is created by spraying a powdered mixture of the desired proportions through a nozzle into an inert-atmosphere furnace where tiny spheres of metal are formed. The resulting powdered metal is then rolled into sheets and bars by using conventional cold working processes. The alloys of the original molten mixture become evenly distributed through the PMTS, giving it a homogenous structure that is free of stringers.
THE HARDNESS OF TOOL STEEL is measured in the Rockwell C Scale, which measures the penetration of a specially shaped diamond into the material under a specific load. Readings are expressed as Hardness Rockwell C (HRC). Under the C Scale, a diamond would measure 100 HRC and a metal file would measure about 64 HRC. As it arrives from the mill, steel is about 30 HRC, but all turning tools need to be much harder than this to hold an edge.
To harden the steel, it’s put through a heat-treating process. The first stage is hardening. Freshly forged high-carbon tool steel is heated to cherry red then quenched in water. This leaves the steel at full hardness, around 64 HRC. The hardness is then tempered in a process called drawing. The steel is heated to a predetermined temperature, which draws back the hardness to the desired level, typically 58 HRC to 60 HRC for gouges and chisels. Without drawing, the steel would be too brittle; the drawing process actually toughens the tools. High-speed steels have properties (imparted by the alloying of tungsten and molybdenum) that make them more difficult to heat-treat but on the other hand more difficult to damage due to overheating during grinding or use. Heat-treating of HSS requires heating to much higher temperatures during the hardening process. Instead of being quenched in water, it can be quenched in moving air. The oxide formed on the surface in air would be unacceptable, however, so heat-treating is actually done in a vacuum or in inert gas atmosphere furnaces.
PMTS is expensive and much more difficult to machine. However, turning tools made from such metal hold their edges a long time. Some kinds of PMTS are not high-speed steels, so they should be given the same care to prevent overheating during grinding as carbon-steel tools. Many PMTS are HSS, though, and in fact the best high-speed steels are now made by powdered metal technology. Examples are M-4, MA2, and T15. When purchasing PMTS tools, it is best to check the manufacturer’s instructions as to grinding temperatures. There are a few small manufacturers (such as Jerry Glaser Engineering Company) making tools from PMTS.
If you’re one of the lucky few for whom money is no object, I recommend that you buy only HSS or PMTS turning tools. If, like most of us, you have to watch your budget, begin with high-carbon steel tools or a mix of carbon steel, HSS, and PMTS tools, then upgrade as your budget permits. Remember that generations of turners have produced wonderful results without the benefit of HSS or PMTS. With carbon-steel tools (and some PMTS), you just have to be more careful not to overheat the metal during grinding. By using a grinding jig (see pp. 92-98), this is a simple matter nowadays.
Premium tools are offered in two types: standard and long-and-strong. Standard tools are for spindle work, while the more robust long-and-strong tools are for heavy-duty faceplate work. You would only need long-and strong tools if you progress to turning large bowls.
When buying tools, avoid commercial sets, unless they are such bargains that you cannot pass them up. Sets tend to include only two or three tools you really need, while the rest eventually become expensive scrapers.
Throughout this article, I will speak of short, medium, and long bevels to describe grinding angles. This age-old way of describing grind angles is an excellent one for comparing two identical tools. A thick tool with a short bevel can be confused with a thin tool with a long bevel, however. To avoid this confusion, the chart above connects bevel length to inclusive angles of grind. In general, scrapers are ground to short bevels, but the resulting burr is what does the cutting. Faceplate tools are generally ground to medium bevels and spindle tools to long bevels.
Tools to Start
IF YOU’RE JUST STARTING OUT, you may be confused about what tool to buy
first. I would build a set of HSS or PMTS tools in the following order:
- ½ -in. spindle gouge
- ½ -in. or %-in. bowl gouge
- ¾ -in. to 1Y4-in. roughing-out gouge
- 1 -in. or larger skew chisel
- 1/8 -in. parting tool
If possible buy HSS or PMTS tools. However, you can get by with a carbon-steel skew chisel since, barring calamity (i.e., an edge-first fall onto a concrete floor), it can be sharpened exclusively on stones. Similarly, you can easily make scrapers from any available piece of steel.
GRINDING ANGLES FOR VARIOUS BEVEL LENGTHS
|Bevel length||Grind angle|
|Short||65° to 85° (typically about 75°)|
|Long||25o to 30o|