Hollowing-out

with the plunge router

The body can also be hollowed out from above with a router. For this a sufficiently large additional baseplate will have to be fastened to the base of the router to make it possible to rout all across the width of the body. If you use a clear plastic plate, you will be able to follow what's going on under it.

Another option would be to fasten two long battens like skis on the two bars of the edge guide of the router. There ought to be some form of dust collection on your router.

Making a hollow body

Hollowing out the body

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A body made from two pieces - a top and a bottom - allows hollowing out parts of it. This adds an additional acoustic element to the sound of an electric guitar but also increases the likelihood of feedback at higher volume levels.

Make a template for the outline of the hollowed-out parts. If you leave wood in the middle, the pickup and the bridge can be mounted as usual if you make this middle part wide enough in the bridge area. The bottom part of the body in picture 1 is 40mm (15/8") and the glued-on spruce top 6mm (1/4") thick. The hollowed-out areas are 34mm (15/16") deep and not very wide so that they can be cut out with a router. Remove as much as possible with a Forstner bit before cleaning everything up by guiding a router bit with shank-mounted ball bearing along the template. This leaves fewer shavings and is less of a strain for the router bit. Set the depth of cut to the point of the drill bit so that the marks left by the point can be routed off later. There should be at least 6mm (1/4") of wood left under the hollowed-out parts; the shavings are best removed by sucking them off.

If the body is to be hollowed out all across its width, the top will have to be thicker to allow bolting on the bridge. I made the bottom of the body (2) 30mm (13/16") and the top 15mm (19/32") thick. In this case the hollow-out has to be 24mm (15/16") deep.

If you have one, use an overarm pin router and mount the template on the back of the body. I made a kind of upside-down (reversed) overarm pin router (3), consisting of a table-mounted router and an arm with a pin of exactly the same diameter as the router bit. The additionally stiffened arm is adjusted so that the pin is situated exactly above the router bit. My bit is 19mm (3/4") in diameter and the pin is a short piece cut off a 19mm (3/4") dowel bar. It is tensioned by means of a rubber band as shown in picture 3. The template, which in picture 3 is still lying on the

body, is fastened on the back of the body. Then place the body (with attached template) between the pin and the router bit on the table. By guiding the index pin along the template a precise line can be followed (4); the shavings will fall through the hole in the router table. By going about the job systematically and regularly checking whether any areas have been left out the hollow-out will become quite clean (5). This is a very safe approach too, as the router bit is completely covered and can never cut any deeper than to the depth set. With a conventional overarm pin router the body is easily lifted by shavings so that more than originally intended is removed.

Making the top

A lot of guitar tops are “bookmatched”: A board is bandsawn lengthwise through its middle (a technique known as resawing) and then the two halves are opened up like two pages of a book and glued together as shown above (6). The result is a surface with an almost perfectly symmetrical grain pattern. To be able to make such a precise parallel cut at such a great height of cut the fence has to be set extremely accurately. This is why I use an additional board screwed to the fence. Better than a long fence is a very short guide fence just in the area of the blade as this allows small corrections of the blade drift. The blade I am using in picture 7 is rather narrow; use a wider blade than that if at all possible.

Be careful when resawing wood. If anything should go wrong because, for instance, the bandsaw tension is badly set, or the piece is pushed too strongly, the sawblade might bend and suddenly come out in the middle although the cut may look fine at the top and bottom. So keep your fingers clear of these areas. As a matter of principle you should always use a push stick for pushing the wood anyway. If the bandsaw has been correctly set, making such a difficult cut should, however, not be too much of a problem.

After both halves have been jointed they are glued together as shown in picture 8. The weight of a clamp or a hammer is sufficient to keep the pieces flat, and only little pressure (exerted by wedges) is needed for pressing the two pieces together.

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Wedges

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Photo: Stewart-MacDonald's Guitar Shop Supply

Fancy guitar tops

If you can afford the wood, it is also possible to glue pretty-looking tops of curly, quilted, flamed or bird's eye maple onto a solid-body or semihollow body .

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Gluing on the top

After the glued top has been sanded flat cut out the body shape by sawing just outside the drawn line (1). Use all the clamps and weights you have for gluing on the top (2). The pressure of the clamps can be spread more evenly by using cauls.

After the top has been glued on the body template is screwed on and the body is routed flush as described on the solid-body model (3). Again the holes for screwing on the template could be placed in the neck pocket and pickup cavity area. I was lucky enough to have wood wide enough to allow making the ash bottom and mahogany top from one piece. Use a router bit with end-mounted ball bearing for routing a thin glued-on top flush with the already-routed body (4).

Binding

Often bodies look better with a binding. The rabbet needed for this purpose can easily be made (at least if the guitar top is flat) with a rabbetting router bit (6). Since it is much easier to scrape the binding flush with the body than vice versa, the rabbet should be made about 1/10 mm (0.004") less wide than the binding is thick. For the same reason the rabbet depth is also set to 1/10 mm (0.004") less than the height of the binding. In

Ball-bearing

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picture 7 you can see the rolled binding being used to check whether the router is correctly set. Rolling together the binding also makes it easy to sand away any bits of it that may be too high. The binding should protrude over the body only very slightly. Before starting work on the body practice on a piece of scrap wood. When everything is fine cut the rabbet(s) on the body (8).

When you buy a binding from a guitarmakers' supplier it is normally made of celluloid and is therefore an acetate. Consequently, the best solvent to use for gluing on the binding is acetone. Brush it generously on to the binding and into the rabbet (9) over a length of about the width of your hand. Press the binding against the rabbet and secure it with adhesive tape. Then apply acetone over the next section and again tape on the binding. Repeat until the whole body is bound. After about six hours the tape can be removed and the binding can be scraped flush with the body using a scraper.

Soundholes and f-holes are best routed with the help of a template. I normally use a 5mm router bit and a 10mm template guide (10). In my case the template has to be made 10/2 minus 5/2 = 2.5mm larger all around. Fasten it with double-sided tape. If any shavings should fall into the body, they can easily be removed with a vacuum cleaner. Soundholes can also be lined with a binding (11).

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Binding cement

When ordinary celluloid binding is cut into small pieces and left soaked in a glass of acetone overnight a creamy mixture - so-called binding cement - is formed which can be used for correcting mistakes and replacing missing bits of binding. It takes about a day before it is dry and any further work can be done on it. Be careful, though, when repairing guitars: acetone attacks nitrocellulose lacquer!

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