Contents:
1. A Multi-Size, Multi-Shape Solera
2. A Kerfing Jig Using a Portable Circular Saw
3. Free-Plate Tap Tuning Experiences
4. A Tool for Stringing a U-Bass Style Bass Ukulele
1. A Multi-Size, Multi-Shape Solera
This is a technique I'm using for ukulele construction, but it could equally apply to classical guitar construction. It started off simply as a solera which could handle many different sizes and shapes of instrument, but as the idea progressed, it went beyond that. The solera, although perfectly flat, also permits:
* soundboard doming specific to the instrument size,
* raking the neck to a desired angle, and
* attachment of the bridge to the soundboard before the sides and back are yet attached.
The Basic Concept
When I set out to build ukuleles, I decided to use the techniques of classical guitar construction with which I'm familiar - specifically, assembly on a solera, a slotted neck joint, a scarfed head joint, and a domed soundboard. I have 7 instrument outlines I'm working with, corresponding to the four most common size of ukulele (soprano, concert, tenor, and baritone), but also sopranino and two special shapes of tenor (one circular, one tear-shaped). I'm also building a bass ukulele, but it's the same size and shape as the baritone.
It would have been impractical for me to store seven more soleras in my small shop, so I made a single one, drawing the outlines of the different shapes on the solera and extending the clamp slots inwards sufficiently to clamp any sized instrument from all directions and at the critical positions. Note: since this photo was taken, the side slots have been extended inwards so that they reach closer to the smaller instrument outlines.
The elongaged slot on the center line provides a variable position for the soundhole clamp. The small hole on the green line is for the soundhole clamp for the circular tenor, which has an offset soundhole. Since this photo was taken, a recessed area has been created in the lower bout in order to assemble with a pre-attached bridge (see the last three photos in this topic).
The solera uses the same clamps used with the guitar solera, including the side block clamps and (square) spool clamps shown here, and the cam clamps shown further below. When joining the sides, I can no longer use the guitar solera's wide soundhole clamp on ukuleles, but switch to the more narrow version shown above.
Doming the Soundboard
The normal way to dome a soundboard when a solera is being used is to recess a shallow cavity into the lower bout of the solera, such that the deepest part of the dome will be underneath the bridge. This can't be done on a multi-sized solera, because the required doming areas would be all different (and because the heights of the domes should probably vary based on the instrument size). So instead, I position cardboard underlays between the soundboard and the solera. The underlays are made of multiple pieces of posterboard, each having an area cut out to shape the dome (the largest cutout being in the top piece).
Above is the underlay for concert ukuleles. The 4 pieces of posterboard I used have a combined thickness of 1.5 mm., so that will be the dome size. (The outer line you see on the underlay is just a pencil outline used for positioning). For other sizes of ukulele, I use other degrees of doming, using a different number of cardboard pieces, and / or pieces of other thicknesses.
My experience is that it takes some experimentation to determine the cutting positions for each of the cardboard pieces, in part because with this approach, the slope is not continuous, but is in small steps. The pieces are very lightly glued together, to keep them in position but without adding any appreciable thickness.
In the first of these three photos, the lower harmonic bar is being clamped onto the soundboard. There is very slight doming at this position. Next, the first strut is being clamped down. Finally, three struts are being clamped down into the dome, using five cam clamps. Neither the struts nor the harmonic bars are pre-shaped to the desired curve. The clamping pressure and the dried glue force the bracing and soundboard into the domed position.
Joining the Soundboard to the Neck / Head Assembly
The next stage in which the solera is used is in joining the soundboard to the neck / head assembly. To do this, the underlay must again be placed under the soundboard, and underlay strips of equivalent thickness must also be placed on the neck extension of the solera. I use a small piece of wax paper under the joint to prevent it from sticking to the underlay cardboard.
With this solera, you can even angle (rake) the neck, by using a succession of underlay strips of increasing lengths along the neck extension, in a manner similar to how the shape of the dome is built up. I'm not doing that for ukuleles, for two reasons. First, the slots I cut at the heel for the sides are not cut at a compound angle. Secondly, my measurements indicate that the effect of the 1 to 2 mm of doming can dealt with through designing the fretboard thickness and the saddle height accordingly.
There is one other requirement. I have already added headplates to all the neck / head assemblies, with the front edge of each headplate being positioned squarely and vertically against the nut position. That means that the front of the headplate rises above the level of the neck, as shown in these photos:
With a solera built for one size of instrument, the headplate would lie beyond the end of the solera neck extension, so there is no issue. But with a solera built for many sizes, the headplates of smaller instruments will fall onto the neck extension at some point. To allow this, there has to be a depression in the extension to let the front of the headplate lie low. The four depressions below correspond left to right to the required positions for 12-fret-to body tenor, concert, soprano, and sopranino ukuleles. For 14-fret-to-body tenor ukuleles, and also for baritone and bass ukuleles, the headplate lies beyond the neck extension, so there is no issue.
Below, you see the two sets of cardboard underlays while the neck / head assembly of a concert ukulele is being joined to the soundboard. The rightmost clamp, which is holding the dome down, is actually not necessary at this stage, because the bracing adhesives have already dried.
Completing the Assembly with the Bridge Pre-Attached
Once the soundboard is attached to the neck / head assembly, the exact position of the bridge and saddle can be determined (given a nut of a known thickness), and therefore the bridge can be glued on. This has the benefit of not having to deal with clamping through the soundhole and fumbling around with cauls over the bracing, as is required when the bridge is attached after assembly. It is extremely important however, that assembly of the soundboard, neck, and sides be done exactly in line; otherwise the bridge will end up being skewed in relation to the neck.
To permit this, the solera has been modified by cutting out a rectangle spanning the area into which the bridges will fall for the 7 sizes of ukulele I am building. The cutout has then been sliced into four removeable strips.
Here, two strips have been removed, because for concert ukuleles, the bridge will fall into the middle area of the cutout. For other sizes of ukulele, other strips would be removed. Note: the strips stay in place when the solera is raised up on blocks or by means of clamps, because the solera has been built up by a layer of hardboard glued to its underside, with the clamping slots extended through the new layer. (I used pegboard because I had a piece of the right size - the five holes you see are meaningless.)
Footnote: The ability to install the bridge prior to soundbox assembly eliminates the difficulties in clamping the bridge through the soundhole after assembly, as intended. However, it has to be done very carefully. I've found out from experience that if the parts are not accurately lined up, you can end up with an assembled instrument in which the bridge is not completely in line with the strings. A temporary solution can be found in notching the saddle, but in the long term it will be better to remove and reset the bridge..
When I decided to start making my own kerfed lining, I did a little research to find a suitable method, but wasn't completely satisfied until San Diego luthier Len Laviolette passed this technique on to me. Len Laviolette (www.lavioletteguitars.com) is a maker of superb classical and jazz guitars. Len gets full credit for the technique shown here, but you'll also see my own enhancement (the sled).
The Basic Jig
The concept is to use a jig which allows a portable battery-operated circular saw with a thin-kerfed blade (the carbide one that comes with the saw, or a thin plywood blade) to cut a kerf in several strips of lining at once. The circular saw runs along wooden tracks that keep it at the right height above the bed in which the lining strips are positioned against a backplate. Here are some photos that demonstrate its use. The first three are of Len's setup:
The curve in the horizontal piece allows for the hand to move closer to the cut position while holding down the lining strips, which are fed in left to right (left being at the bottom of the photo). Note that these four guitar strips have already been cut, and Len has re-inserted them into the jig for the photos. The next two photos show how the tracks in the jig position the saw.
Above, you can see the index mark in the back bar, just to the right of the cut position (from the operator's perspective). After each pass, the strips are moved to the right, with the last cut visually positioned at the index mark.
Jig with Sled
The next three photos are of my own version of the jig. Mine is made from scraps I had in the shop, and looks somewhat different from Len's for a few reasons, not the least of which is simply the dimensions of the materials I used to make it. You can see that mine does not have continuous tracks - they are broken in the middle, but they work the same.
The main difference difference however, is a sled which runs along the jig bed from left to right, allowing the strips to be moved along in unison more easily. The sled in turn required a fixed-dimension bed to slide along - hence the pieces of MDF at the front and back of the jig, suporting the tracks and defining the boundaries of the bed. The sled was a later addition to the jig, and also required the tracks to rise up by 1/4" (hence, more pieces used in the construction).
Here you can see the sled to the left, resting on a piece of 5/8" melamine board (the same dimension as the base of the jig). The sled is 24" long by 4 1/8" wide and 1/4" thick. The base of the jig has a lip on the underside at the front, allowing it to butt against the front of the workbench. At the left end of the sled is a stop block. A small piece of 1/4" plywood, visible in the centre of the photo, serves as a hold-down pad.
The number of strips that can be cut in one pass depends on the width of the bed. In my 4 1/8" bed, I can cut twelve 11/32" ukulele lining strips at once (or six guitar lining strips). The strips have been preshaped on a router table so that one edge is rounded - that's the edge that will be exposed when the strips have bleen glued into the instrument. Whether the rounded edge is up or down in the bed when you make the cuts depends on whether your intent is to have the kerfed side inwards or outwards when glued to the instrument sides. Here's some installed lining, kerfed side inwards:
Tips
Depth of Cut
The first challenge in using the jig is to get the right depth of cut. It takes a little effort to adjust your saw to the right depth - you need enough of a kerf to allow bending, but you don't want to go too deep and leave the strips weak. Once you get the saw adjusted to the right depth, it helps to not use it for any other purpose.
Alignment
An ongoing challenge in using the jig is to keep the strips in line as you move them along, and especially as you adjust them left and right to get them to align exactly with the index mark. The stop block on the sled and the hold-down pad help, but aren't enough on their own.
Above is a close-up of the hold-down pad. Since taking this photo, I've curved the right side of the pad so that it can get right up to the curved track bar and hold the lining strips down more securely. I also have a small hold-down pad (also with a curved leading edge) which is useful when nearing the end of the strip. Sometimes I place a piece of tack cloth under the hold-down pad to keep the strips from shifting (visible here at the leftmost arrow).
The rightmost arrow shows another technique that helps when the sled is fully loaded with twelve strips. A loose piece of wood of the right thickness (e.g. a popsicle stick or two) is packed between the closest strip and the front support board, keeping the strips snug enough, but not too tight in the bed. The same can be done at the right side of the jig, to keep the strips snug after they are kerfed.
If the strips still get a little out of alignment, you can re-align them by inserting a cabinet scraper into the last slot cut while you position the strips at the index marker.
Breakout
A third challenge is in avoiding breakout in the lining strips as the blade exits. If the lining strips are held snugly against each other, the chances of breakout are reduced. If it happens, it's most likely to be in the strip furthest from you, especially if that strip is nut snug against the backing board.
I find that by stopping the saw before the blade has exited the last strip, breakage is minimized. But if it happens, and you don't yet want to replace the backing board, one remedy is to use a piece of scrap wood as the last strip, or as I have done, a lining strip that already has some defects..
End of the Strip
You can not kerf right up to the end of the strip, if your right hand is operating the saw, and your left hand is holding down the lining strips. I've learned to accept that each strip will have a few inches of waste wood.
Installing the Lining
My shop-made lining doesn't have the precision of bought lining, in part because I eyeball the alignment at the index marker, and in part because so far I've been using a rather splintery wood (meranti). Of course, that doesn't matter too much, because the fundamental purpose is to hold the instrument together. Before installing lining around tight curves, I weaken each kerf by almost, but not quite, snapping it. Moistening the unkerfed side of the strip can help this bending to go more smoothly.
3. Free-Plate Tap Tuning Experiences
Under Construction
This topic will pass on my experiences doing free-plate tap tuning for classical guitars with strobe tuning software, using the method described in Roger Siminoff's book "The Art of Tap Tuning". In short, the book has some shortcomings (repetition, ambiguity, and if you're a guitar maker, perhaps too much focus on mandolins), but the method that it describes does work. The DVD that comes with it is excellent. Siminoff doesn't give you the magic answer if you're looking for that, but he does provide a method. The book is well worth the money, if you plan to read it a couple of times, invest the time to assimilate it, and try it out.
I don't mean to suggest that the book has given me all the answers, or that I've come anywhere near mastering the art of voicing guitars. Far from it. For me, gaining this skill remains one of the great challenges in building instruments.
Free-plate tap tuning is just a technique which allows preliminary voicing to be done before the instrument is fully assembled. A luthier may choose to do additional voicing after assembly, for example by shaving braces or thinning parts of the top further after the assembled instrument is strung up.
With free-plate tap tuning, you need to build a frame within which the soundboard can be clamped, such that it is held firmly all around its perimiter, and will not rattle when tapped. The position of the clamping must correspond to the position of the sides in the completed instrument, so that the area of the soundboard free to vibrate is the same now as it will be. You then tap each brace (fan strut or harmonic bar) and measure the ensuing fundamental frequencies of each brace using a strobe tuner (or as I did, with Strobosoft software), and then shave or sand each brace, re-tapping and re-measuring as you proceed, until you reach the tone you want to achieve.
Buried in the recesses of the book is the recommendation to tune each of your fan braces and harmonic bars to different frequencies, to provide a wide spectrum of underlying tonal quality. An example (but not a specific recommendation) is given as to what those tones might be.
The book doesn't describe everything you might want to know. It took me a while to realize that the frequency which you hear when you tap a brace, and which registers in Strobosoft (or which you might have an ear acute enough to interpret) is not the only frequency you hearing. Tapping one brace sets off vibrations not only related to that brace, but also to the other braces. This is of course because the braces are tied together through a common structure (the soundboard). The frequency which registers is simply the predominant, or fundamental, frequency for that tap position. It might be significantly stronger than any other frequency, or only marginally stronger than other frequencies that are nearly as strong.
My experience is that when you use bridge plates, the fan struts become locked-in to a common fundamental frequency, no matter which brace you shave. Since the fan struts span the lower bout of the instrument, their fundamental frequency therefore will define the fundamental frequency of the soundboard*. This is because those fan struts, being in the lower bout, will be more dominant than the tuned frequencies of the harmonic bars. As a result, free-plate tap tuning allows you to control one of the main variables in the tonal quality of the instrument - the fundamental frequency of the soundboard. This will complement anything you do to plan for and to control the fundamental frequency of the air chamber.
* This term might be better named the fundamental frequency of the soundboard structure, because once the first brace is glued on, the soundboard itself is no longer an independent entity.
Without a bridge plate, you can tune the fan braces to different frequencies, as per the Siminoff example, but the fundamental frequency of the soundboard cannot be predetermined by this method.
In my opinion, there are some limitations in free-plate tuning. The clamping only approximates the position of the instrument sides, and is bound to be a little off. The soundboard will actually be somewhat thinner after you have completed the instrument because of final sanding, especially around the perimeter where you trim down the binding and purfling. There will be a finish of (thin) shellac or (possibly not so thin) lacquer on the instrument. The bridge* will be attached, adding some more firmness and weight. The strings and therefore the soundboard will be under tension.
* There is a possible answer in relation to the bridge. If you pre-attach your bridges (see the Solera topic at the top of this web page), and construct a tap tuning frame which allows for the neck being attached to the soundboard, this variable goes away.
Because of these limitations, this free-plate tap tuning method does not predict with any degree of certainty what the exact tap tones will be in the completed instrument. But the method does give you an approximation, and the ability to tune all the braces to different tones (to give a broad tonal spectrum), or to plan the fundamental frequency of the soundboard (if you use a bridgeplate). Either way, you have one more tool at your disposal to voice the instrument.
This topic will be expanded with photos, further explanation, and tap tuning data from my experiences, at a later date.
4. A Tool for Stringing a U-Bass Style Bass Ukulele
Kala's U-Bass has a trap door in the back of the instrument which can be opened to allow the strings to be inserted from the inside. It would have been extremely difficult to build one of those into the slightly arched back of my bass ukulele, so I needed a different solution. I wasn't altogether happy with alternative methods that I had found on the internet.
Aquila Thundergut Nylgut strings each have a stop at the end of the string which will be inside, under the bridge.
The above photo shows my insertion tool - a piece of black ash with a handle and with a notch of sheet metal mounted at the end of a arc. The distance from the sound hole to the bridge is roughly the diameter of a 4-litre paint tin, so that served as a useful template.
The notch, cut with sheet metal shears, is left rough so that it will grab any of the four Thundergut strings. I find it works best when I allow 3/4" to 1" of the string to protrude.
Here the tool is about to be inserted through the soundhole. Note that the tip of the string has been carved to allow it to go through the hole more easily.
Here the tool has just finished pushing the third string up through the bridgeplate, soundboard, and bridge. Because the tool has to navigate around the pickup cylinder and wires, an inspection mirror and flashlight may be useful to check out the inside terrain.
Each string is grabbed with pliers and pulled through, while at the same time the tool is withdrawn through the soundhole.
Strings will often pop out of the notch when they snag on pickup wires. To avoid this, a little electrical tape wrapped around the notch will hold the string in place. After grabbing the string with pliers, the tool will easily withdraw by sliding along the length of the string. The tape is then removed.
A final note: the string holes in the bridge are ramped, to eliminate the sharp edge, and to allow them to stretch smoothly up to the saddle. On the underside, the holes in the bridgeplate are countersunk to help the string find its way into the hole.