INTRODUCTION TO WOODTURNING
Chapter 3: The tools
The range of woodturning tools on the market today is enormous. Ashley Iles, for example, produce 350 different woodturning tools. These are all standard tools made in a range of sizes in carbon steel or high speed steel. In addition a number of manufacturers are making some highly specialised (and very expensive) tools, such as the Stewart System. Most beginners, however, will only be able to afford a limited number of standard tools so they will have to make some careful choices. My suggestions for the minimum basic set of tools is given at the end of this chapter.
But, before coming to the choice of tools the beginner needs to understand the functions of the different types and the reasons for some relatively subtle differences in shape and form. The difference between carbon steel and high speed steel also needs to be understood.
When I started turning at the beginning of the eighties only carbon steel tools were available, but since then high speed steel turning tools have become ubiquitous. High speed steel, which is harder than carbon steel, was originally developed to enable higher cutting speeds to be used when machining metal. Because of this high speed steel tools retain their edge longer on wood.
Nevertheless, each type of steel has its advantages and disadvantages. These are discussed later in this chapter. There are three principal types of tool: scrapers, chisels, and gouges. Gouges can be sub-divided into three further types: bowl gouges, spindle gouges, and roughing out gouges. Chisels and gouges are usually described as cutting tools, because they are designed to sever rather than break, or tear, the wood fibres. In contrast scrapers are often perceived as crude tools which simply tear out a shaving. However, when employed with care, and the correct technique, scrapers can be used to sever the fibres and leave a good finish. It must be pointed out, too, that chisels can, on occasion, be used for scraping.
However, there is a clear distinction which can be made between chisels and gouges on the one hand and scrapers on the other. This concerns the attitude in which they are used. When employed in the cutting mode chisels and gouges are used with the bevel rubbing and the wood moving onto the edge of the tool (see also Chapter 6). In contrast scrapers must never be used with the bevel rubbing and the edge must be trailing. Except in very special circumstances this means that a scraper must be used with the tool pointing downwards. (See Diagram 3.1) If a chisel is used for scraping it must be held in the same attitude as a scraper, that is, pointing downwards.
Diagram 3.1 Attitude of scraper in use
Scrapers are mostly made from rectangular bar and are usually ground with a large bevel angle. The size of the bevel angle is not critical, however, and some turners may make it relatively small. Like a chisel, the cutting edge of a scraper can be skewed, but it can also be a variety of other shapes. Some of the most common, which a beginner may wish to use, are shown in Diagram 3.2. They can be made from either carbon steel or high speed steel and the same shapes are used in both materials.
Diagram 3.2 Some shapes for scrapers
Like scrapers chisels are usually made from rectangular bar but the bevels are ground differently. Chisels usually have double bevels, and the bevel angles are smaller than those normally used on scrapers (see Diagram 3.3).
Diagram 3.3 Bevels on chisels and scrapers
The cutting edge of a chisel can either be ground square across or it can be skewed (see Diagram 3.4).
Diagram 3.4 Square and skewed edge chisels
Carbon steel chisels have always been made with a rectangular cross-section. High speed steel skew chisels can also have a rectangular cross-section. Some, however, are made slightly oval in section with one edge rounded (see Diagram 3.5, section A-A). In the smaller sizes this can make them a little flimsy, particularly when they are made overlong. Until recently the cutting edge of a skew chisel was always ground so that it was straight (as in Diagram 3.4) but in recent years some turners have made it curved (as in Diagram 3.5).
Diagram 3.5 Oval section HSS chisel with curved cutting edge
3.4 Parting tools
Parting tools are narrow chisels. In principle, as their name suggests, they are used for separating the waste material from either end of the finished piece of work. In practice they have a number of other uses. They come in a variety of shapes and sizes, some of which are shown in diagram 3.6.
Diagram 3.6 Parting tools
3.5 Bowl gouges
Because bowl gouges are often used with a long overhang between the cutting edge and the rest they need to be stiff and strong so that they will not bend or flex in use. Books written before high speed steel came into use refer to the ‘long and strong’ bowl gouge. This is a carbon steel gouge which has a deep ‘U’ section. It has been superseded by the high speed steel bowl gouge which is made by milling a flute into round bar. This gives a very different cross-section (see Diagram 3.7).
The long and strong carbon steel bowl gouges were ground so that the cutting edge was square to the axis of the tool, as shown in Diagram 3.7. Also shown in this diagram is the shape of the a high speed steel bowl gouge. It can be seen that in this case the wings are ground back. The way this is achieved is described under sharpening below. (See Section 4.4)
Diagram 3.7 Bowl gouges
Sizes normally refer to widths but high speed steel bowl gouges are measured in a very peculiar way: from the inside of the flute to the outside of the bar (see Diagram 3.8). Although these tools have only been available for a few years the reason for the way in which they are measured seems to have been lost in the mists of time. Anyway, the unfortunate result of this system is that, in effect, there are no standard sizes. Differences in the size of the flute in relation to the diameter of the bar can lead to very different gouges with the same nominal size. Note that it is the size of the flute which really determines the size of the tool. The diameter of the bar determines the strength of the tool.
There are in practice quite substantial differences between manufacturers and I suggest that when building up a set of bowl gouges an attempt should be made to stick to a single brand.
Diagram 3.8 Measurement of size of HSS bowl gouge
3.6 Spindle gouges
Carbon steel spindle gouges are forged from flat bar to form the cross-section shown in Diagram 3.9. High speed steel spindle gouges can be produced in the same way but they are more commonly made by milling the flute from round bar in a similar way to bowl gouges. The flutes in spindle gouges are, however, much larger than those in bowl gouges relative to the size of the bar. This provides a slimmer tool which can enter the more restricted spaces encountered in spindle turning. The shape of the cutting edge of a spindle gouge has traditionally been described as a a fingernail shape, that is, half an ellipse (see Diagram 3.9).
Diagram 3.9 Shape of spindle gouge
3.7 Roughing-out gouges
Roughing gouges are used in the preliminary stages of spindle turning (as described in Chapter 9). They are normally much larger than bowl or spindle gouges and it is important to note that they should never be used to shape bowls. They are made by forging or pressing flat bar into a half-round section. Some manufacturers of high speed steel roughing gouges extend the wings a little to form a ‘U’ section which flares out slightly (see Diagram 3.10).
Diagram 3.10 Shape of roughing gouge
3.8 Interchangeability of gouges
It is quite common today to find a high speed steel bowl gouge used to perform the function of a spindle gouge. I do this quite frequently myself. The reason for this is that when they are made from high speed steel there is not a great deal of difference in the shape of the cutting edge of the two types of gouges. But there is one important difference which should be noted: for a given size of cutting tip (which is related to the size of the tool) a bowl gouge is very much stronger than a spindle gouge. As a consequence, although a bowl gouge may be used for spindle turning a spindle gouge should not (normally) be used for bowl turning.
3.9 The different types of steel
It is often said that high speed steel tools are easier to sharpen (on a grinding wheel) than carbon steel. The justification given for this statement is that it is less easy to overheat and soften the edge of a high speed steel tool. Although that is true, they also take longer to sharpen (because they are harder) which can make it more difficult to get the desired shape. It is also said that high speed steel tools last longer. This , too, is true, but they are also a lot more expensive. And how long does one want a tool to last? I have been using my 1 1/4in carbon steel skew chisel for eighteen years and I still have more than half the length left.
So, we come to a contentious point. Nowadays, some turners will only use high speed steel tools, and some stockists do not sell carbon steel tools. Nevertheless, I always advise beginners to buy a mixture of high speed and carbon steel tools.
Because of the edge retaining properties of high speed steel I certainly believe it is best for bowl and spindle gouges. The high speed steel bowl gouges are also made from round bar which also provides a better shape than the old, forged, carbon steel forms. For skew chisels and scrapers I find that the edge retaining qualities of high speed steel are not so important. So, for these, I recommend carbon steel; they are easier to sharpen, they are cheaper, and they will last as long as necessary.
3.10 The form of the bevel
The bevel on cutting tools, ie chisels, gouges and parting tools, must be the correct shape: either hollow ground (concave) or flat, it should never be rounded (convex). If the bevel on a tool is rounded it will very difficult, if not impossible, to use it without digging in. (The reasons for this are explained in detail in Chapter 6.) So it is vitally important to get the bevel right. Many novice turners get it wrong; I have seen a lot of tools it would be impossible to use successfully.
There is also the question of the bevel angle to consider. The size of bevel angles is by no means as critical as many pundits would suggest. One aspect of this is that bevel angles are often expressed as a precise number of degrees. In practice it is pretty well impossible to grind, and to measure, to that degree of accuracy. It certainly is not necessary. There is wide disagreement among skilled turners regarding the bevel angles for specific tools. For example one book on my shelves says that the bevel angle on a skew chisel should be 25° (that is 12.5° on each side!) and another suggests that it should be 45°. The truth of the matter, probably, is that skew chisels can be used successfully with bevel angles anywhere between these two figures.
A wide range of bevel angles can be used on bowl gouges without experiencing problems although the most satisfactory angle tends to depend on circumstances. For example, it may be necessary to use a bowl gouge with a large bevel angle (eg 60°) to turn the bottom of the inside of a deep bowl. However, a bevel angle of 40° to 45° will serve for many circumstances. Other angles can be experimented with when the turner feels inclined. In general slightly smaller bevel angles can be recommended for spindle gouges. If the spindle gouge is to be used for cutting beads then a small bevel angle is required so that the tool can be introduced into small spaces.
Generally speaking, however, I believe that tools with relatively large bevel angles are easier for the novice to use than the reverse. Tools with small bevel angles tend to be ‘grabby’, that is to say they have a tendency to bite into the wood. This is particularly true of chisels. In my view most manufacturers supply chisels with the bevel ground to too small an angle. For my students I grind the chisels to a bevel angle of around 45 degrees. But any angle between 35 and 45 degrees will be satisfactory.
3.11 The minimum kit of tools
I would say that the minimum number of tools required to start with is ten. I bought a boxed set of that number when I started turning, more by luck than judgement, and I have never found any reason to think that was a wrong decision. The beginners set of mixed high speed and carbon steel tools I would recommend is made up as follows:High speed steel
It will have been noticed that this list contains 11 tools. This is because have added the 1/8 plain parting tool to my original list - it is a very useful tool. My choice of a carbon steel skew chisel may surprise and irritate a lot of turners. The oval, high speed steel, skew chisel has many devotees. I can only say that I am not enthralled with it, but that is probably a personal idiosyncrasy.