Wood Turning

Woodturning is one aspect of woodworking which is now exceedingly popular as a hobby, source of supplementary income or full-time occupation. There is a large range of wood-turning lathes on the market, from tiny machines for modellers to huge ones on which really large work can be performed. In between these extremes there are many makes of the most popular size for serious work – 762 mm between centres. Such a machine will accept work up to 762 mm in length, which is long enough for table legs.

They are limited in capacity and capability but they can produce many useful but smaller examples of the turners’ craft, and can provide a good jumping off point for any one anxious to try out or develop his skills at turning.

There are also reasonably priced universal woodworking machines which include a lathe. With a much greater capacity than the drill-powered lathe, they also provide other operations such as band or circular sawing, planing and slot mortising. Some are basically a lathe, with the other operations carried out by attachments which can be added as the need arises. They are a sound investment for the keen woodworker.

Another term which relates to the size of a lathe is referred to as the swing. This is the distance from the lathe bed to the centres, which determines the maximum diameter that can be turned on the right-hand side of the headstock.

A lathe with a 102 mm swing will turn work up to a maximum diameter of 203 mm. Thus the term ‘swing’ indicates the maximum radius of work.

Many lathes, however, are designed and equipped so that faceplate turning can be carried out on the left-hand side of the headstock, a facility known as ‘rear turning’. Because there are no restrictions imposed by the lathe bed the diameter of work which can be done with rear turning is up to three times the diameter possible on the right-hand side.

Basic principles

If a block of wood is held horizontally between points on which it can be made to revolve it is possible to hold chisel-type tools, on a suitable rest, against the wood and gradually shape it in the form of a cylinder with parallel sides, or cut to give an elaborate profile. Similarly, if a block of wood is fixed to a revolving plate the tools can be used to hollow out and shape the block to make a bowl, platter, vase, table lamp and so on.

The lathe has a headstock in which revolves the spindle. Almost invariably the machine is powered by an electric motor. Usually there are stepped pulleys on both spindle and motor which enable different speeds to be provided as the drive-belt is re-positioned on the pulleys. Speeds usually range from around 750 r.p.m. for large diameter work to 3,000 r.p.m. for work of small diameter.

When wood is being turned it is really the speed of the wood at its periphery which is important, rather than its r.p.m., I.e. the feet per minute speed of the wood as it passes the cutting tool. Too high a speed should be avoided, as this will result in dust being removed rather than shavings, which should be the aim. Ideal speeds cannot be achieved, especially for faceplate work. If, for example, a fairly large bowl is being turned, then the speed at which the wood passes the tool at the rim of the bowl is very much greater, for a given r.p.m., than the speed at which the wood passes the tool near the centre of the bowl.

For turning between centres, or spindle turning, a device called a live centre is placed into the hollow spindle in the headstock. This live centre grips one end of the wood. The other end is held on a fixed point or dead centre, on which the wood revolves. The dead centre is held in the tailstock, which is a sliding fit on the base, or bed, of the lathe. The headstock is fixed to the bed. An adjustable tool rest is mounted on the bed. It can be moved along the bed and locked in any position within the maximum capacity of the machine.

The live centre, also known as the driving centre, can be removed from the spindle and a faceplate screwed onto the threaded nose of the spindle. On this can be fixed a wood block of roughly circular shape. The tool rest can be adjusted to allow for both the hollowing of the block, and exterior shaping.

When wood is mounted between the centres it has its grain parallel to the axis of rotation. This is known as spindle turning. When wood is mounted so that the grain is at right angles to the axis of rotation it is referred to as faceplate turning. There are subtle differences in technique between the two, especially with regard to tool sharpening and handling. They have a tapered shank, known as a morse taper. Tapers are number-graded according to their size. Most lathes up to 762 mm between centres size take a number-one morse taper and the headstock spindle and tailstock barrel are bored with a tapering hole to suit. The mechanical principle of the morse taper is the circular wedge, and even a small amount of end pressure creates adequate friction for a positive grip between the two surfaces.

Work is also held on chucks, of which the most common is the screw. This has a fairly heavy gauge wood screw which is both renewable and adjustable, so that the amount of projection can be varied. Screw chucks of this type can be used for mounting wood where the grain is parallel to the axis of turning, or at right angles to it. Because the wood is held by a single screw its capacity is limited, and this applies especially to the length of a piece of wood when it is being held at its end. The greater this projection the greater is the levering effect of the cutting tool – the screw in end grain has limited holding power.

Other types of chuck include collet chucks, one which incorporates a coil spring to grip the work and one, recently introduced, where it is claimed that the work piece can be held by one of six different methods.

This type of faceplate is drilled for screw, the usual way of mounting work on a faceplate. Different handed threads are used at the centre of such faceplates according to which side of the headstock they are to be used: standard clockwise thread for right-hand side of the headstock and anti-clockwise thread for left, or out-board side.

Engineers’ type dividers or the more traditional woodworkers’ wing compasses are used frequently before and during actual turning operations. Prior to mounting a block for faceplate work it should be cut approximately to circular shape to eUminate projecting corners and reduce vibration during preliminary turning. The wing compasses are a convenient means of marking out for this. During turning they are used to scribe out circles indicating where cuts are to be made. The compasses are set to the required diameter, one leg is placed on the centre of the revolving work, and the other lightly trailed against the work in order to scribe the working line.

Outside calipers are used far more than inside ones but both have their place in the turner’s tool kit. Simpler patterns of calipers are available without the screw adjustment. Lateral marks, required on a piece of wood during turning to indicate shoulders, steps, sinkings and similar features, are done by pencil, the marks being transferred directly from the rule to the work while it is revolving.

Tools

Tools used by the turner are relatively few but they are made in many sizes and weights. For the drill-powered lathe small tools are available and for larger machines tools called iong-and-strong’ are quite popular. The principal tool is the gouge.

This is sharpened in a number of different ways according to the type of work it has to perform.

For the initial shaping in spindle turning a fairly large gouge of about 32 mm should be used. This is sharpened with its end square. Although all turning tools need grinding from time to time it is not usual to same way that bench chisels and planes have. This type of sharpening is required on a gouge for concave shaping on spindle work.

The third manner of sharpening is shown at. This gouge is prepared for faceplate work and has a bevel of 45 degrees. It can be steeper without loss of efficiency. Only relatively narrow gouges are used for faceplate work, rarely more than 13 mm CI2 in. Patterns known as long-and-strong are popular for bowl turning, when 10 mm is considered to be an ideal size. Many turners use gouges straight from the grindstone, and gain the cutting action from the burr so produced.

The parting tool, shown at, is included in all’sets of turning tools and is in frequent use. It is used for squaring off ends, forming shoulders, and reducing diameters at specific points on the work. It is a very useful tool but it does not cut cleanly because of the nature of its cutting action. An end squared off with a parting tool would need attention from a skew chisel if the end of the work is to be seen.

A skew chisel is used to make smoothing cuts for finishing and for cutting shoulders, beads, vees and convex curves. The exact angle at the end is not important but it is always policy to use as large a skew as possible, depending on the nature of the work. The heel of the chisel is used to bite into the work and the toe must trail, allowing the waste to curl off in a thin shaving. This is because in use there is the ever present danger of the toe digging into the work. Therefore, the wider the chisel the further the toe is away from the wood.

Tools shown at, and are classed as scrapers because they scrape the wood rather than cut it. They are used more on faceplate work. The most common of the scrapers is the round nose, used for finishing hollowed out work where a gouge cannot operate. Scrapers are ground with a steep bevel and work best when used straight from the grindstone.

Cylinder or spindle turning

Spindle work can, and should, be carried out entirely with tools that cut the wood. Such tools are gouges and skews. When used properly both are capable of removing long, continuous shavings from the wood – to the delight of the turner and amazement of the onlooker. The ability to remove very long shavings does depend to some extent on the species of wood as some respond to this technique better than others. When the wood is properly cut with the gouge and skew the surface is usually left smooth, and does not require much sandpapering.

Using the gouge and skew correctly is a knack acquired by experience, and until the proper way of using these tools is mastered the beginner will in all probability resort to scraping. This is, undoubtedly, easier and safer but scraping does not cut the wood anything like so cleanly as the gouge and skew. ^

This has the result that the surface is left fairly rough, necessitating a lot of work with glasspaper. On long, slender work scraping can cause the wood to bow while revolving, as the wood will tend to resist the pressure and lower cutting efficiency of the scraper.

Stock to be turned between centres usually starts off by being square. Sufficient waste must be provided at each end for mounting and subsequent parting off. These locate the centres for mounting in the lathe. It helps if a diagonal at one end has a small V-cut sawn in it, as shown, and the centre of the other emphasised with a bradawl. It is also worth while, and saves time in the long run, if the corners are planed off the wood to reduce it to octagonal section. This lessens the work turning tools have to do, and also reduces vibration.

If the wood is rather hard, a pronged centre can be tapped home with a hammer, as shown. Live centre and wood are then returned to the headstock, and the tailstock positioned so that the dead centre engages in the small hole made by the bradawl at that end. The tailstock is then locked in the bed and the barrel is screwed up and tightened to drive the centre into the wood, then slackened off a little to permit free rotation. A spot of oil at the tailstock end reduces friction and prevents the possibility of burning, but a rub from a candle is even better as it will not penetrate and discolour the wood.

The tool rest is now adjusted to within 3 mm of the wood, and about the same distance above its centre. As a precaution, the work should be revolved by hand to ensure it does not touch the tool rest.

Tools should be held firmly with the left hand near the end of the blade, fingers gripping the tool and palm of the hand partly on the tool rest so as to control lateral movement. Note that the tool is placed fairly high on the wood, the aim being to have the bevel rubbing the surface so that it forms a tangent to the cylinder. The tool should also be pointed slightly in the direction of cutting.

First stage of the cutting is with a fairly large gouge; this procedure is known as ‘roughing down’. It matters little whether the cutting is from right to left or left to right but it will probably be necessary to move the tool rest as roughing down continues. The work should be checked frequently with calipers, set to a little more than the required diameter. It is safer to stop the machine when calipers are being used.

Smoothing a cylinder, and arriving at final diameter, is done with a large skew. It is placed high on the cylinder and positioned so that the centre part of the cutting edge is in contact with the surface. The handle is then lifted and rotated to enter the heel of the cutting edge to the depth of cut required, after which the tool is moved along the work. The skew is held in a similar manner to the gouge and, also like the gouge, it is better to move off at the ends, rather than on to the work.

The bevel of the skew acts as a fulcrum and the handle hand controls the actual cut. Point of contact with the work should be at the approximate centre of the cutting edge, or slightly nearer the heel. If a point too near the toe is used, the wood has a habit of taking control over the chisel, the toe digs into the wood and a piece is split out. Cutting can be carried out in either direction, the chisel merely being turned over.

To square off an end, either the parting tool or skew chisel can be used. This cut cannot be made very deep so the chisel is now placed flatways on the wood, and pushed forward and downward at the same time. To finish off the cut exactly to the line the chisel must be held as shown in. The essential point here is that the bevel of the skew adjacent to the end being cut must be nearly parallel to this end surface. There should be just a fractional variation from this plane, only enough to allow the toe to cut.

For a shoulder with a tenon or a pin, the parting tool is used close to the shoulder line, and a cut made to within about 1.5 mm of the required diameter. Waste is then removed with the gouge, as at. Next, the shoulder is trimmed back to the line with the skew, held as described for squaring an end, and as shown at.

The horizontal cut is also made with a skew. This is seen at and only very light cuts should be taken, with frequent checks using calipers. Such a pin, or dowel, is often intended to fit into a hole so it is therefore wise to check it in a sample hole bored in a piece of waste wood.

Their locations are pencilled in and the parting tool is used to form grooves between the beads. Depths of the grooves should be made equal, about half the width of the bead, and checked with calipers. A diamond point scraper is then used to form the profiles.

Scrapers are initially held horizontally on the tool rest, and the handle moved slightly upwards until the tool is cutting the wood rather than just rubbing it. The edge of the scraper should be on, or slightly below, the centre line. If little more than dust is being removed the tool probably needs sharpening, but scrapers will never remove shavings as do cutting tools. The point, or toe, of the skew is thrust into the work as at A. This incision is enlarged to form a Vee by making the following cuts first at one side, then the other, of the Vee, as shown at B. Depth of cut is increased a little as subsequent rounding is carried out. This must be done carefully in order not to sever the grain as, otherwise, there may be a tendency for some slight surface splitting along the grain. Actual rounding is done from the centre of the bead downwards into the Vee, as in C. This involves quite a compound movement of the tool, controlled from the handle.

The chisel does not move laterally along the tool rest but, for the left-hand side of the bead, the handle moves to the right and is raised so that the cutting edge is lowered around the curve of the bead, and at the same time the tool is rotated slightly so that as it completes the cut the flat surface of the chisel is almost upright, as at D.

As with the bead, alternative ways of forming a cove, or concave cut, are practised: one by scraping, the other by cutting with a gouge. It is always better to use a scraper that is smaller than the size of the hollow required, and the tool is moved in the manner shown.

Forming a cove with the gouge involves rather more skill when compared with scraping, but has the advantage that, when correctly executed, the surface is left very much smoother. This is because, with a sharp gouge, the wood is cleanly cut and with no tendency for the grain fibres to be torn out of the surface, which is always a possibility with scraping methods.

As the gouge is moved forwards, the right hand moves to the right while the left hand rolls the gouge over onto its curved back. This cuts the right-hand side of the cove. The action is reversed for the other side. The position of the gouge at the end of the cut is seen at.

For maximum control the bevel of the tool must always be rubbing on the work. This also produces the most efficient cutting, and therefore the cleanest surface. Approaching the work with the gouge pointing towards the axis of the wood can be compared to using a plane with a vertical blade. The plane would scrape the wood, not cut it, and a gouge used in this manner is reduced to carrying out the inferior action of a scraper.

Most turning work involves curved profiles and as these are either convex or a combination of convex and concave, a lot of woodturning is based on the two fundamental cuts of beads and coves, although the degree of curvature might be much different. The arrows indicate the direction of working, the rule being to work from the large diameter to the smaller one whenever this is possible. Hollow curves must be cut with a gouge or round-nose scraper while convex curves and flat surfaces are formed with the chisel, or square scraper.

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