Saturday, August 27, 2011

The Fingerstyle Guitar - Notching the Kerfed Linings

Once the kerfed linings are glued to the sides, the sandpaper-lined concave dishes I made use of when shaping and gluing the top and back braces serve their other purpose by helping me sand a drop-off onto the edges of the rim assembly to match the curvature of the back and top plates.

Sanding guitar rims

Kerfed guitar liningsI can then use a Dremel rotary tool to rout pockets into the linings to accommodate the brace ends. Using the more traditional kerfed linings whose saw kerfs face into the guitar body, there's always a danger that if one or both edges of a brace pocket happen to be in close proximity to the kerfs, a chunk of wood will be dislodged as the pocket is cut. With reverse-kerfed linings, however, the individual sections of wood between the kerfs are firmly glued to the sides and serious chipping of the exposed face of the lining on either side of the brace pocket is far less likely, provided some simple precautions are taken.

When routing the brace pockets, it's important that the Dremel is guided in such a way that the router bit's clockwise rotation doesn't contribute to tearing or chipping of the linings as the pocket is cut. This is particularly important to observe where the left-hand edge of the brace pocket is concerned (i.e., with the guitar side facing me). With that in mind, I make my first cut towards me in the direction of the guitar side along this left-hand margin, easing the router bit into the lining for the equivalent of around half the bit's diameter; a second shallow entry cut on the right-hand side of the pocket defines its width. Several light passes are made from left to right until a single recess is created between the two entry cuts. I repeat this process until the recess extends to the guitar's side and make final adjustments until the end of the brace fits snugly within the pocket. It's difficult to avoid chipping entirely, but by guiding the router in the manner I've described, it's of a minor nature and can be easily cleaned up with sandpaper.

I rout the pockets in pairs, beginning at the tail-block end of the body. If the first pair of pockets is accurately marked and cut, the centre-line of the back will be correctly aligned from that point on. If a minor adjustment to the back alignment is required, the pockets can be modified accordingly. The second, and subsequent pairs of pockets can then be more accurately positioned, with correct alignment of the back more firmly established as each pair is cut.

Some builders postulate that because reverse-kerfed linings stiffen the rim assembly once attached, there are resultant improvements in the sound of the instrument. Occasionally, it seems, views such as this are repeated often enough by individuals held in high regard within the luthier community that they become accepted as fact, whether or not they've been held up to close scrutiny. I acknowledge that I have a lot to learn and always try to have an open mind when reading of the experiences and opinions of other more experienced builders, but after looking at popular wisdom such as this from all angles, I'm left unconvinced. For what it's worth, my personal view is that while it's somewhat helpful having a stiffer rim to work with in the course of constructing the instrument, from the point at which the back and soundboard are attached to the rims, any contribution the linings may have made to the rims' stiffness is eclipsed by the strength of the top and back in compression. I suspect that in the finished instrument, the linings - reversed or otherwise - play little part beyond their primary purpose: to provide a gluing surface for the top and back plates.


Friday, August 26, 2011

The Fingerstyle Guitar - Side Reinforcement

For almost as long as I've been building guitars I've followed the lead of others and have fitted kerfed linings to the rims, then installed wooden reinforcement strips to span the sides between the top and back linings. Although this remains common practice, it seems an increasing number within the lutherie community are coming to the view that this could potentially do more harm than good, the thinking being that if the guitar sustains a significant impact, the area of relative weakness created at the intersection of the side reinforcement and the lining could contribute to a crack developing at that point - it makes sense to me.

Guitar side reinforcement

For this guitar then - and for its rosewood and spruce companion - I've chosen an alternative approach which is to to glue cloth bias tape across the full width of the sides at regular intervals and install the linings over the top of it. The rationale for this is that as the glue-impregnated cloth spans the entire side and will remain somewhat flexible, the weak point I've described is largely avoided. In the unlikely event that a crack develops in one of the sides for whatever reason, the tape will provide a measure of protection against the crack propagating along the length of the side - at least until a permanent repair can be carried out.

Useful Links:
Installing Side Tapes


Monday, August 22, 2011

New Wood Purchases

I have a love/hate relationship with our strong Australian dollar at present. It's too convenient an excuse to click the "Buy Now" button when I spot particularly desirable pieces of wood on favourite web sites such as Allied Lutherie's but, of course, it's also of benefit once I've given in to temptation. Resistance is futile, it would seem.

Ample evidence of my recent weakness can be seen below. Those poor souls similarly afflicted with "Wood Acquisition Syndrome" can click the pictures for a closer look. 

European spruce soundboard
European Spruce

Port Orford Cedar soundboard
Port Orford Cedar
European Spruce needs no introduction, but Port Orford Cedar is a relatively uncommon tonewood. Luthier's Mercantile has this to say about it:

Similar in appearance and scent to Alaskan Yellow Cedar, Port Orford Cedar is stiffer, lighter and thus more suitable for soundboards. Indeed, it is highly sought after for the bold, robust, responsive tone that it imparts on an instrument. It is very even textured, with a slight golden-white color and tight, even grain. A great advantage to the builder is that this wood is more immune to splitting than absolutely any other soundboard wood.

The Port Orford Cedar is in transit as I write this and I'm impatient to inspect it, flex it, tap it - and smell it! Aside from its promised tonal and structural advantages, I'm looking forward to experiencing the pungent peppery smell it's said to impart to a completed instrument.  It's almost worth combining it with a back and side set of Claro Walnut for that reason alone given walnut's delicious aroma.  Such an instrument would surely be the ultimate "perfumed guitar"!

Useful links:
Port Ordford Cedar - Stansell Guitars


Tuesday, August 2, 2011

Kerfed Linings

Kerf: a slit or notch made by a saw

Pre-made kerfed linings are readily available from any number of suppliers, but given their expense and fragility, I prefer to fabricate my own, leaving a little more wood between the termination of each saw cut and the opposite face of the lining than is generally present on those available commercially. Even with that precaution, I like to pre-bend the mahogany strips with the aid of a bending iron to match the contours of the guitar side. Breakages are rare, but if I should happen to snap one, it makes sense to discard it, or at least reserve it for areas where the break won't be visible. Given the attention to detail lavished on the other aspects of a hand-built instrument, I find it incomprehensible when I see pictures of the interior of a guitar in which joins in the linings are in plain view through the soundhole. I'm a little uncomfortable too with saw cuts whose spacing or depth varies noticeably along the length of the strip. Using my band-saw and the crude but effective fixture pictured below, I'm able to produce evenly spaced cuts of a consistent depth.

Making kerfed guitar linings

After several less than satisfactory attempts using a router to apply a rounded profile to what will be the inner corner of the strips, I discovered that by planing a series of facets onto the appropriate edge with a small block plane, I could quickly and easily blend them into a smooth curvature with a sanding block. It reinforces the fact that sometimes, the simple, non-mechanised approach is best!