Shape of the sustain block

Make a full-scale drawing of the lengthwise-cut body shape on thick paper and cut it out as a template. Form the sustain block accordingly and round off its edges.

Lengthwise-cut sustain block

Curve must run out horizontally

Gluing up the sustain block

An alternative to making a sustain block by shaping one solid piece is to glue it up from several already lengthwise-shaped slices (see figure below). Rough-saw the slices and then shape them on a table-mount- ed router with the help of a template. Use dowels for aligning the pieces during gluing.

Making a semi-acoustic body

By making a semi-acoustic-body guitar you get quite close to building an acoustic guitar. I use 2mm (0.08")-thick Finnish birch or airplane plywood, which is resin-bond and water resistant, for making this type of body. Unlike ordinary plywoods, this has no voids, is sanded on both sides and is made up of thin layers that make it very strong. It would also be possible to use solid wood (e.g. maple), but most of the commerciallyavailable models are made of plywood. To make a semi-acoustic body you need two thin plates of wood large enough to cut the body from them (1) and one narrow piece which has to be wider than twice the height of the body's sides and a bit longer than half the body's circumference (2). The sustain block (3), which extends through the whole length of the body, should be made from rather light types of wood such as mahogany, basswood, spruce or alder. It has to be as high as the middle of the body and about 100mm (4") wide. The block in the photograph is about 51mm (2") high. Together with the top and bottom (each 2mm / 0.08" thick) the height of the body will be 55mm (2.08") in the middle and 45mm (13/4") at the edges as the side strips will be 41mm (15/8") high. Make the sustain block wide enough to allow bolting on or gluing in the neck. You also need four 6mm x 10mm (1/4" x 3/8") wooden strips for the lining (4) and four thin strips (5) for binding the body. These strips have to be half as long as the body's circumference.

Any cutaways have to be considered when laying out and making the sustain block, which is best done with a bandsaw. Since the block will be glued to the top and the bottom, its shape will have to be made to match their curve (6). To make the top and the bottom of the body evenly curved a light lateral curve should be sanded which should become increasingly flatter towards the ends. At both ends the sustain block has to be as high as the sides (in my case it is 41mm thick). It is obviously easier to make a body without domed top, especially when building your first-ever semi-acoustic guitar. If you decide not to make a domed top, just make the block the same height as the sides.

Bending the sides

Bending the sides might at first glance appear tricky; but there is no reason why with a bit of practice and careful work the first attempt should not be successful. However, always practice on a piece of scrap wood before you start on “the real thing”.

Wood can be bent to a certain extent when exposed to steam, and it will later retain any shape it has been forced into. Even several-centimeter -thick wood can be bent provided it is exposed to steam for a sufficiently long time. An example of this plastic quality of wood is the well-known coffeehouse chair of the Viennese company Thonet.

The sides of a guitar are only 2mm (0.08") thick and will therefore bend much more easily than thicker wood. The simplest bending device that could be used would be a tube heated by a gas flame. A tube with an ovalor drop-shaped crosssection offers a variety of radii for bending, but a round one that corresponds in diameter to the tightest curve of the sides will do as well. Apart from that it is also possible to use a tube with a greater diameter (7cm to 8cm / 23/4" to 3") for greater and a thinner tube for smaller radii. An electrically-heated bending iron, however, is a more comfortable tool.

Before bending the sides the wood has to be put in hot water for a few minutes. A bathtub or the saucer of a window planter will do nicely for this purpose. Do not put more than one piece of wood in at a time and put some weight on it to make sure it remains under water. How long the piece has to remain there depends on the type of wood used and on one's own experience: five minutes are quite normal, more than twenty minutes should not be required.

Fasten the tube horizontally in a vise and heat it by positioning a blowtorch so that its flame burns into the pipe (7). The tube is at the right temperature for bending when a drop of water “dances” on it. If it evaporates immediately, the tube is too hot, and if nothing is heard, the tube is too cold. The gas flame will have to be regulated or even switched off temporarily as the tube

Supply Shop Guitar Macdonald's-Stewart Photo:

Bending iron

Instead of using a heated tube you can also use more comfortable, electrically-heated and adjustable bending irons.These are available from suppliers of guitarbuilding tools.

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Fox Universal Side Bender

Bending is made very easy with an apparatus developed by the American Charles Fox. Its blueprint is available from Luthiers Mercantile International (LMI).Their catalog, which can only be recommended, also includes a detailed description of how to use this side bender.

It consists of a form and two steel slats heated by three 150-200-watt light bulbs. The wet guitar side is placed between the steel slats, and the tight curve at the waist is pressed down on the form while its underside is supported by a metal bar. The steel slats are pulled tight towards the form and the heat is left on for about ten minutes. After cooling down the bent side is removed and occasionally touched up on a bending iron.

A new version of this bender uses slats made of spring steel, thus eliminating the need for the support bar.

Silicone heating blankets

Another approach for bending sides is to use a silicone heating blanket on a form. The blanket has to be as wide and as long as the sides of the guitar and it should work with a low voltage. One source for such silicone blankets is Watlow (www.watlow.com), which has branches all over the world.

must not get too hot to not burn the wood too much. Deep burns on the outside of the wood are almost impossible to remove - so be careful when placing the outside on the bending tube.

Start bending at one end, slowly pushing the wet piece of wood over the tube while pressing lightly all the time. The heat will lead to the formation of vapour. At some point the wood will start to bend and you can shape it - do so carefully and “with feeling”. Putting on cotton gloves makes the heat more bearable for the hands. By varying the pressure and the speed at which the thin wood is pushed over the tube the radius of the curve can be varied. When the desired curve has been reached continue bending for a little while; after bending is finished the wood will spring back slightly. Be careful throughout the bending process as the thin wood can easily break.

Take the bent piece from the tube and hold it for a short while until it has cooled and the curve is stable. Now is the time to find out whether the wood has really been bent: on the hot tube a curve is easily produced simply by pressure; if the wood loses its curve after it has been released, it has not been bent enough yet. The wood bends properly when its fibers are saturated with water vapour - the moment when this is the case can be felt, but patience is required.

To get the right curve constantly check your progress against a drawn outline and correct the curve if necessary. The latter can be done by hand by bending the piece the other way or by placing it with its outside on the tube and by rocking it until you get the right curve.

When you have finished bending the first side of the body leave the second piece to soak in water and then proceed as with the first piece; try to bend it as symmetrical to the first side as possible. If the body is asymmetric in shape bending the second side will be easier as you as you don't have to make both sides perfectly identical. After both sides have been bent put the two pieces away and leave them to dry overnight.

The morning after you will inevitably find that the curves will have changed slightly. The original shape can, however, easily be restored by bending the two sides over the tube for a short time. This final bending should take place before the lining is glued on as the curve of the sides will keep changing with changes in air humidity.

A lot of guitarmakers use forms into which they put the sides after bending. Thus symmetry between the two halves is much easier to achieve, but the sides will still have to be bent just as precisely. Making forms is worthwhile if all or most of the guitars you build are of the same shape. If this isn't the case, it should nevertheless not prove too difficult to bend the sides precisely even without the help of such equipment; but a bit of practice is obviously always helpful.

With symmetrical bodies I usually bend only one piece of wood from which I then cut two pieces with a tablesaw (1). This is faster and guarantees that the two sides are perfectly symmetrical. Be very cautious and wear goggles as the blade guard has to be removed for sawing. You could also use a bandsaw for this purpose.

The sides above (2) were bent with the Fox Universal Bender (shown on the next page). I just bent one side (a little more than twice as wide as needed) and cut it lengthwise into two parts on

the tablesaw. Then I sawed off the top parts, flipped them over 4 and joined them again.

Gluing the sides to the block

The sides are glued to the sustain block. In the cutaway this is best done by cutting out a small square-cornered piece from the sustain block and using a specially-shaped caul to allow stable positioning of the clamp (3). I would advise you to make the sustain block wider than in picture 3 to have more space for the neck pocket. If the body is to have a pointed horn, a caul that fits

on the body horn (4) will ensure a good glued joint. If the sides 5 are fastened at the lower end of the body with two screws and a shaped caul (5), you will not need to place a clamp along the

body. The screwholes can later be hidden by covering them with veneer. This piece of veneer also serves to embellish the joint between the two sides.

Making the lining

By using reinforcement strips (lining) the gluing area at the edges of the body top and bottom can be increased. Take a few 6mm x 10mm (1/4"x 3/8") wooden battens and make a few cuts in them so that they become flexible: the cuts should be made close to each other and should be quite deep; always make sure, however, that the battens are not sawn through entirely.

Such cuts are best made with a hand saw with taped-on depth stop (6), a tablesaw with very thin sawblade or - and this would

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Depth stop