Machinery

The wood lathe

The wood turning lathe is one of the oldest pieces of equipment for fashioning articles from wood. Known to the Egyptians as early as 1400 BC, it has been developed over the centuries with improvements that have culminated in the modern variable-speed lathe (see Fig. 1).

The bed is the backbone of the lathe on which other components are mounted. It may have its own stand or be bolted to a sturdy bench. The headstock houses the speed change pulleys and the main bearings supporting the headstock spindle. Some modern lathes now have electronic speed control, which can maintain the torque necessary for turning. Equipment, like chucks, face plates or a spur centre, is attached to the spindle depending on the work being undertaken. Along the bed may be a tool rest holder and a tailstock. A belt round the headstock pulley is connected to another stepped cone pulley, which is attached to an electric motor mounted in the stand. By taking the tension off the belt, which is achieved by lifting the motor, then moving the belt onto a different sized pulley (always keeping the belt on the same positioned pulley above and below) speeds can be altered to suit the activity being undertaken (see Fig. 2). For example, sanding would be performed using a medium to fast speed whereas turning a large or unbalanced piece of timber would be done using a very slow speed.

Figure 1. The Woodfast lathe

Figure 2. Pulley system for changing speeds.

There are three basic operations performed on the lathe:

Turning between centres, also called 'spindle turning', where the work is held between the drive or 'live centre' in the headstock and a free wheeling or tailstock centre at the other end.
Face-plate turning, where the work is held on a face plate or chuck attached to the headstock.
Chuck turning, where the work is held on a chuck attached to the headstock.

Wood-turning chisels and how to use them

Two classes of chisel are used in turning:

Cutting chisels that are intended primarily for achieving a peeling action: the gouge, skew chisel and parting tool.
Scraper chisels that are used only for scraping, including the round-nose, square-nose, spearpoint and combination chisels.

Broadly speaking, a cutting action (with the chisel at a tangent to the work) is like 'peeling a potato' and is used for between-centre turning. A scraping action (with the chisel at right angles) is like 'getting the mud off your shoes with a boot scraper' and is safer and more suitable for face-plate work (see Fig 3).

Figure 3. The cutting and scraping action

Materials used to make chisels

Carbon steel chisels are generally cheaper than high speed steel (HSS) chisels but will blunt more quickly than harder materials. High speed steel produces a lasting edge but costs a little more. There are other alloys/materials being experimented with but, as yet, they are very expensive and scarce.

Cutting chisels

The following cutting tools (see Fig. 4) have different uses and are all explained below.

Gouges

The square-ended gouge is used for roughing down stock when turning between centres (see Fig. 5).

Figure 4. Cutting Chisels

Figure 5. Use a square nosed gouge for roughing square to round

For cylindrical cutting

Place the gouge, convex side down, on the tool rest near the middle of the cylinder, a little higher than necessary.
Raise the handle gently (which lowers the blade) so that the bevel (the angle that has been ground) rubs lightly on the rotating stock (but doesn't cut), then slowly lower the cutting edge onto the work surface until cutting starts.
Gently move along the cylinder, maintaining the same angle of attack, coming off the end of the work. Next, go back to the middle and repeat the process in the other direction. If you are turning from square, initial passes will feel very bumpy until round is nearly complete.

SAFETY: Do not start a cut from either end of the piece of work as the gouge could lift a splinter by digging in from the end of the grain.

Cutting hollows (coves) using a spindle gouge

Mark the size of the hollow with a pencil.
Select a suitable size gouge (12 mm for general work).
Place the gouge flat on the rest and push it gently into the stock (a scraping action) to remove most of the centre portion.
Now place the gouge on its side with the bevel at right angles to the axis of the stock, with the handle slightly raised (see Fig 6a(i)).
Roll the gouge from the side to the horizontal position, moving the handle outwards and downwards, guiding the cutting edge to stop at the centre. Use the bevel to control the cut. Note that each cutting stroke begins at the top or shoulder (largest diameter) and works down to the bottom of the hollow (smallest diameter). See Figure 6a(ii) then Figure 6a(iii). The same operation occurs from the left and right sides of the hollow. You should swap the position of your hands to make the process easier. Gouges may be used to form straight cylinders, hollows, general shaping and beads if a fine shallow gouge is used. They give a very good finish, which needs little sanding. A deep fluted bowl-turning gouge may be used for face-plate work and generally produces a better quality finish than a scraper (but is more difficult to master).

Figure 6a. Turning hollows or coves with a fine gouge

Figure 6b. Turning beads with a skew chisel

Skew chisels

Skew chisels can be used for finishing cuts on cylinders, vees, square shoulders and convex curves, and for turning beads. When skew chisels are sharp, and used correctly, they give an excellent finish, which needs virtually no sanding. They should not be used for scraping as this action quickly blunts the tool (see Fig.7).

For finishing cuts

Hold the chisel on the rest with the cutting edge well in advance of the handle.
Lower the skew until the work rubs gently on the bevel (but not cutting).
Raise the handle so that the cutting edge is lowered for the desired depth of cut, which is controlled by the bevel.
Gently push, allowing the chisel to cut in the direction in which it is being advanced without taking too much off in a single cut.

HINT: It is helpful to set the tool rest parallel to the work piece so the skew chisel can be guided along it

To turn a bead

Cut two vees at the outer edges of the bead to give clearance for the final cuts.
To 'roll' the bead, begin with the skew chisel held flat on the rest at right angles to the axis of the stock at one side of the bead and with the cutting edge high. The point of the heel, which does all the cutting, must be very sharp, with the bevel ground flat.
Roll the chisel over from the horizontal position, gradually lowering the cutting edge by raising the handle, at the same time swinging your arm slightly to one side. See Figures 6b(i), (ii) and (iii).
Turn the other side of the bead in a similar manner. Changing hands makes this easier.

SAFTEY: Never use the upper part of the skew chisel cutting edge (especially the top point because if it touches the rotating wood it will suddenly dig in).

For turning shoulders, after roughing out with a gouge, cut in with the toe of the skew, finishing along the axis with the heel of the skew chisel (see Figs 8 a & b).

Fig 7. Skew chisel in operation: Bevel must rub on work to support cutting edge and control depth of cut; cutting chisels are sharpened by grinding and honing to the same angle

Figure 8 a. Top and side view of turning a shoulder with the toe of the skew chisel

Figure 8 b. Heel finishes to the shoulder

Parting tools

The parting tool (a narrow tool that is shaped to cut and produce its own clearance so that the edge will not be burnt; see Fig. 9) is designed to cut grooves and shoulders straight into the stock to a desired depth, as well as parting off a finished job from waste.

Figure 9. Correct angle for parting tool use

Scraping tools

Although scraping tools (see Fig. 10) are best suited for face-plate work, they can also be applied to between-centre turning, as in Figure 11a and Figure 11b.

While scraping is slower than the cutting method of turning, and produces a rougher surface, it is easily learned and demands less skill. The degree of accuracy that can be achieved is another reason it is recommended, particularly for patternmaking and beginners.

Flat and convex surfaces are produced with flat, combination or spear-point scrapers; hollows are turned with round-nose, combination or bowl turning scrapers.

Figure 10. A variety of scrapers - ground angle can vary from 45 to 75 degrees

General rules for scraping tools

Set the tool rest so that the chisel can be held at the horizontal with its cutting edge close to centre height.
Preserve the cutting edge by 'backing off' occasionally to prevent overheating.
Aim to make the tool take off fine shavings rather than dust: this will be less abrasive to the cutting edge. Such an effect can be achieved if the tools are sharpened by merely grinding on a wheel and leaving the burr to act as the cutting edge.
Virtually any profile can be ground to suit a particular job. For example, a scraper that is ground to hook to the left is ideal for turning an inside lip at the top of a bowl.

Figure 11a. Scraping hollows with a round nose scraper

Figure 11b. Scraping beads with a spear point scraper

Turning between centres

How to mount stock

Mark diagonals on both ends of the stock to locate centres.
Plane corners along the stock (for easier roughing to round).
Cut saw kerfs about 3 mm deep on the diagonals on one end of the stock; note the saw cuts must be at 90° to each other, which will not be the case if the stock is rectangular (see Fig. 12).
Seat the spur centre, which fits in the headstock spindle of the lathe, with prongs in the kerfs at the point where diagonals intersect (see Fig. 13). Locate it with a soft hammer or mallet.
Remove the spur centre and thrust the tapered end firmly into the headstock spindle of the lathe.
Place the stock in position, wind the tailstock spindle in to about half of its travel, insert a centre with a ball bearing then advance the whole tailstock until the revolving centre point almost touches the end of the stock where the diagonals intersect, lock the tailstock to the bed.
Wind the tailstock spindle in while slowly rotating the work back and forth by hand until no free movement is felt; the tailstock centre will be properly embedded in the wood and lock the spindle.
Select the appropriate tool rest and set it up approximately halfway up the side of the wood (about level with the axis or point in the tailstock) and close to the wood.
Make sure the work rotates easily by hand without catching on the rest and get your teacher to check everything before you start the motor.

Figure 14. Lathe accessories

Figure 12. Seating spur centre

Figure 13. Cutting kerfs to locate spur centre

Face-plate turning

Small face-plate jobs offer a good introduction to wood turning. Excellent results can be obtained with a minimum of skill and practice, and it is possible to turn some items completely with the use of only one tool such as a round-nose scraper or bowl-turning scraper. Care is needed in locating the stock on the face plate, and various chucking methods may be employed. Five of these methods are described and shown below. A tailstock may be used to add support to the job until it is turned concentric.

5 Methods of chucking

There are a number of expanding-type face plate chucks on the market. The development by Bruce Leadbeatter of microwave seasoning for woodturning highlighted the need for a special chuck for green-timber turning. Leady's chuck fitted that use (see Fig. 14). This system requires a shallow insert to be drilled in the base of the work piece that just fits the chuck, which is expanded to grip the work.
There are also chucks that are designed for gripping a turned spigot at the base of the work piece like the Nova chuck. The spigot is removed when the bowl is turned and sanded (see Fig. 15).
By first screwing a wooden backing plate to a face plate, a seasoned work piece can be attached in two ways: using four blobs of quality hot glue or by gluing a piece of cartridge paper (with PVA glue) between the backing plate and the work piece, clamping and waiting 24 hours for it to dry (see Fig. 16). Both methods are carefully separated with a chisel later.
Turn a recess at least 5 mm deep in the base of the stock then turn a wooden jamb chuck to fit. The plug must fit tightly and have a true shoulder to bear against the base. A similar method to this involves screwing the top of the stock to a face plate. The total outside surface (base and side) can be turned and a spigot formed on the base. A wooden plug is then turned that the base will fit in. Turning the inside then gets rid of the screw holes.
Use a screw centre-a lathe accessory designed with a threaded point to hold small stock for turning, for example, drawer knobs (see Fig. 17).
Use cup chucks to support turnings such as goblets, eggcups, mugs and vases in which the end grain runs parallel to the axis of the lathe, therefore requiring lateral stability (see Fig. 18). First, turn a taper on the end of the stock to correspond with the taper of the chuck then drive it firmly into the chuck with a mallet.

Figure 14. Expanding type chuck - the Leadbetter chuck

Figure 15. Nova chuck

Figure 16. Face plate with glue method

Figure 17. Screw centre chuck

Figure 18. Cup chuck

Describe a process to produce a bowl using a lathe

The easiest way to get started is with a blank that has been generally cut into some form of rounded shape equidistant from the center point using other tools such as a bandsaw
Once the blank is into a generally round shape, punch a hole in the center point using an awl and then mount the blank to the chuck on the headstock, tightening it with the chuck's wood screw.
The first task is to complete the rounding of the shape, for which you may want to connect the tailstock to the center point opposite the mounting point on the headstock for stability.
Position the tool rest parallel to the two center points, and about 1/8 of an inch from the highest protruding point on the stock, while rotating the piece by hand.
Turn on the lathe at a low speed and begin rounding the blank using a roughing gouge until the blank is smoothly and consistently rounded to the desired diameter.

Next, remove the tailstock and re-position the tool rest so that it is parallel to the face of the blank (that was previously connected to the tailstock). Turn on the lathe slowly and begin turning the outer face of the bowl using a rounding gouge or a bowl gouge. Continue turning until the outer shape of the bowl is complete.
Then, you'll need to cut a recess into the bottom of the bowl to accommodate the bowl chuck that came with your lathe. Check the instructions on your bowl chuck to determine how deep and at what diameter to cut the recess. Once you are confident that you've cut the recess properly, remove the blank from the headstock, attach the bowl chuck to the blank and install it into the headstock. Rotate the blank by hand to make sure that it is spinning freely.
To hollow out the bowl, position the tool rest parallel to the face of the blank and turn on the lathe so that the blank is rotating slowly. Use two hands on a bowl gouge and gradually begin making light cuts to start hollowing out the center of the bowl. Make very gradual cuts to remove the center material, focusing on developing an inner shape to the bowl that matches the outer shape of the bowl until you have the desired, consistent thickness of wood between the inner and outer shapes.
Finally, use your bowl gouge or a scraper to create a consistent lip of the bowl, whether that be a rounded shape transitioning from the inner to the outer portions of the bowl, or more of a squared-off shape. Make very shallow cuts on the lip, as any cracks in the blank can easily catch on the edge of the cutting tool and gouge the piece.
Once you've completed your basic bowl shape, you can sand and apply the finish of your choice.

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