Once all 12 lining notches are at the correct depth and angle, (7 on the bass side and 5 on the treble side under the soundboard) the soundboard should fit down tightly to the binding around the entire perimeter of the rim. This can be tedious. Clamp the soundboard up for a dry test. When satisfied, glue the soundboard to the rim.
Manufacturers have templates and laser cutting machines that are precise down to a thousandth of an inch. Don't be surprised if you have to work with your hand-tooled lining notches to get a good fit with all of the braces at the same time.
Clamp up the entire top/rim connection for a dry test before applying glue. Make sure that the entire perimeter of the soundboard is in contact with the lining and that the braces scallop ends pass through the notches cle@nly. Discovering a misaligned notch in the lining after applying glue can ruin your whole day.
Woody's method is to lay in the perflings with a minimum amount of Titebond glue and blue masking tape. After only a half hour the already-bent bindings can be laid in. Before the bindings are laid in on top of the perflings, however, one scarf joint is cut to join the treble and bass side bindings at the heel. Glue is applied to the rabbet on the upper bouts, then, the bindings are laid in and wrapped with twill tape.
The lower bout rabbet then has glue applied and the remainder of the bindings on both sides are wrapped with twill tape from the waist to the butt. A scarf joint at the butt finishes off the installment of the bindings on the back side. The soundboard side of the guitar has the bindings installed and bound with twill tape by the same method. Be sure and support under the sides to accomodate the arch in the back when wrapping the soundboard binding with twill tape.
The scarf joint at the butt end must be made in situ to complete the binding glue-in process. At that point, the rest of the bindings and perflings are in place with the glue drying. So, work scant and make that scarf joint as tight as possible. You might need 50' of 3/4" twill tape, but it does an excellent job of holding in the bindings as the glue dries.
LINING THE BACK To install lining on the back side of the rim, one proceeds just as on the soundboard side of the rim. The rebar is already in place, so, the layout of each section the kerfed lining might have to be adjusted... but not much. For instance, a strip of lining might have to end with portion of a full block in order to be tight up against the rebar and/or square to the soundboard. This is only a cosmetic consideration, and only then, when the rebar/lining joint is visible through the sound hole. What looks worse is when the rebars are not parallel and perpendicular to the soundboard.
Check out the lining/rebar joints on an old Martin box, i.e when they used wood strips for side reinforcements, as I have described here. Nowadays they use tape, which is just as good structurally, but it’s not wood. The wood/rebar joints of the old days are incredibly clean and tight. That’s a detail that says something about the maker.
GLUING UP THE BACK
A very satisfying day is the day that the back is finally glued to the sides, thus, closing the box. Before the back is glued to the rim, however, put the rim with the attached soundboard in the mold and, using a dowel for a spreader at the waist, make sure that the sides are tight up against the mold and that the notches and back braces are still aligned. When satisfied with the fit of the back braces in the notches, the back can be glued and clamped to the rim. Make sure that the spreader can be taken out of the box through the sound hole after the back is glued on.
When building an instrument without a mold, which is how I learned to build guitars...(thank you Charles Fox, 1976), symmetry is always a challenge. This free-form set up allows adjustment to the shape of the sides as they are drying and cooling right after bending. One can see the shape of both sides and adjust to match if needed.
The second strips of lining will be approximately twice the length (~110mm) of the first strips that are in place up against the tail block. Glue and clamp the second strips in place remembering to keep a space for the rebar between the lining sections, and glue the lining strip just proud of the edge of the side. The rebar will be installed after all of the kerfed lining is in place on soundboard side of the rim.
Proceed around the soundboard edge of the rim with the same, repeating steps as above. When the heel block is reached, the number of blocks in the last strip will probably differ from the others. There is nothing sacred about the spacing between each rebar, but it should be the same on each side of the rim, square to the soundboard edge of the rim, and parallel to each other. One should end up with 6 or 7 reinforcing strips on each side of the rim (depending on the length of the rim, of course).
The equal number of lining blocks per section (~15) should have kept the rebar locations at equal intervals as you move around the side. The rim is now ready to have the rebar installed.
On the inside of the guitar, the scalloped end of each brace is marked where it begins to pass under the binding. The top is then removed to allow final thicknessing of the scallop ends down to 2 mm.
A 2-mm deep notch is then cut through the rim for each brace end. All of the brace ends pass completely through the side of the guitar.
Next, cut a two-block section of kerfed-lining stock (~15mm total width). This will be the width of your reinforcing strip. Use the two-block lining section as a spacer to mark where the next lining strip will begin.
That's it for explaining the assembly of the guitar box and binding. Next month will have some explanation of what to watch for in cutting the dovetail to join the neck to the body. Woody uses and LMI dovetail fixture.
Now the soundboard side of the box is lined and the rebar is installed. The side reinforcements will protect the sides from splitting if the guitar is dropped... like this 1938 herringbone, Martin D28 that Woody put back together a few years ago. The owner had dropped it on a concrete floor. Woody had to take the back off and repair.
It didn't have any side reinforcements.
It helps to maintain the symmetrical shape of the guitar if the reinforcing strips and the linings are glued to the guitar sides while they are in the mold.
THE FREE-FORM FIXTURE
Woody’s shop only has two dreadnought molds so, when bending more than two sets, improvisation is necessary. The free-form set up pictured below was generated spontaneously out of need and it turned out to be more than adequate. In fact, as one of the guitars being built is a Mini size, the sides could not be held in shape in the standard dreadnought mold. The free-form fixture pictured is very simply built. It can hold the sides in any shape while they cool and set. The sides might stay in the free-form mold a few days or a few weeks depending on Woody’s informal production schedule.
Before the top is glued in place, the notches for the back braces should be laid out and cut in a manner similar to the top braces. The notches for the back braces are easier to layout because, unlike the top, the back braces are all square to the centerline of the back.
After the blocks are installed, the spreaders are removed and the kerfed linings and spruce reinforcement (rebar) strips are installed.
KERFED LININGS_ Adjust the position of the rim in the mold so that one inch of the soundboard-side edge is visible outside of the mold. This will allow easy clamping of the kerfed lining. Clamp the rim in place from the back side of the mold.
Working on the soundboard side of the rim at the butt end, begin by cutting two strips of kerfed lining with an equal number of blocks. (7 or 8 blocks, ~55mm) The number of blocks varies with the length and shape of the rim. The important thing is that these two strips must be equal length. Glue these lining strips on both the treble and the bass side of the tail block, just one mm proud of the edge of the rim.
The box is now closed. The last major effort on the box is to rout channels for the purfling and bindings. The first thing that you will need is a set of roller guide bearings. These will allow you to control the depth and width of the rabbet. They take a little practice to get used to, so, always check your depth and roller set up on a piece of scrape wood first. Adjust to keep the rabbet very slightly smaller than your binding purfling plan. That is, the bindings and purflings should be just proud of their respective rabbets.
Install the rebar so that it reaches across the full width of the side, edge to edge. With a small square, lay out the rebar so that it is square to the bottom of the kerfed lining which should be parallel to the soundboard edge of the side. Mark the perpendicular line with a light pencil mark and glue the rebar in place. Repeat for each rebar. The final result should be 6 or 7 equally-spaced reinforcing strips, parallel to each other and square to the bottom of the soundboard.
Finally, the short pieces of lining (the two-kerf blocks) are glued on top of the rebar ends as seen in these photos.
Keep the centerline of the router parallel to the side of the guitar and let the base of the router tilt.
Woody made about 35 of these spool clamps one rainy afternoon. They are very handy.
18' of 3/16" all thread
35 ea.__ nuts, washers and wing nuts
6' of 1¼” hardwood dowel
sheet of 1/8” cork board
Remember, there are two ledges to be cut, one for the perfling and one for the binding. Cut the perfling rabbet first. Your perfling selection might have to coordinate and fit into the back strip. This will require hand work in mitering multi-line perfling to join the back and butt strips. Also, some nice things can be done by incorporating continuous perfling into the heel cap. Be sure to have a design in mind before the binding is cut. If there is no perfling (which is the easiest thing to do), the edge binding and the back strip can just butt (most manufactured guitars are built this way). Take a look at some of your favorite guitars the next time you are in a music store. There is no harm in copying, or modifying a design that you like.
The Journal entry for December is complete. This is the 7th chapter in a comprehensive, step-by-step overview of the process of building a guitar at home. The 1st chapter was in June, 2020.
If you follow Woody until next June, you will have a complete, step-by-step description of the entire process of building an acoustic guitar in a home shop.
Below is a list of chapters and where we stand right now. Seven Home-Shop Guitar Building chapters have now been posted in the Luthier's Journal since June, 2020. The 7th chapter is posted below. There will be one chapter each month going forward, and we will finish the complete Overview in June 2021. That's the plan anyway.
Mitering the tail strip into the back strip.
Chapter 07_ Body and Bindings
CLOSING THE BOX
Notching for Braces
TOP FIRST: In Woody’s shop, the process of closing the box begins with fitting the top (soundboard) to the rim. To do this, the rim is clamped into the mold from the back side. Then the soundboard is centered and clamped to the heel block and the tail block to hold it stationary on the rim. The objective is to hold the soundboard in place without bending it out of shape. If anything, the sides should be re-shaped to fit the contour of the top and not vice versa. The relaxed shape of the top is critical.
When the top is centered and clamped onto the rim in the mold, the intersection of each brace with the rim is marked on the inside and the outside of the guitar. The linings are carefully marked on both sides of each brace, as is the outside of the rim where the brace ends pass through.
The wood bindings (maple and rosewood) are bent on the same bending machine as the sides. In the photos below, bindings for four dreadnought guitars have been bent and placed in the free-form mold until needed.
Bending the bindings in the LMI bender begins by taping the flat and straight binding stock together, side by side on your workbench. Spritz with water and lay them in a foil envelope. Then put them into the LMI bender as if one piece. The tape will keep them from being accidentally skewed across the bending surface. They are easy to bend but, remember, maple and rosewood bend a VERY different rates. So, bend them in separate groups. Bend slowly, especially in the upper bout. Once the bindings have been bent, they are placed in the free-form fixture to keep them in shape until ready to install.
Once the wood is bent and cooled, it should go directly into the mold as pictured here in a Woody-Strings built dreadnought mold. While in the mold, the blocks and lining are glued in. The shape of the guitar is now fixed. The complete assembly of the guitar body and bindings will be the subject of this chapter in Woody’s guitar-building overview.
BLOCKS and LININGS
It is very important to have the guitar sides and blocks in their final shape and orientation when the blocks are glued in. This is achieved by using spreaders to hold the guitar sides in position in the mold as the blocks are glued and clamped in place.
Last month we discussed building a one-off guitar mold out of Styrofoam and Luan. The same applies here for building your own spreader for keeping the sides tight in the shape of the mold as the blocks and linings are glued into place.
Play Safe, stay healthy,
Come back next month for a discussion of Dovetail joints and Carving the Neck.
ROUTING for the BINDINGS
The routing of the binding channel is not a casual undertaking as many hours have been spent to this point in manufacturing and assembling the various parts of guitar box. A slip of the router in this process would be disaster.
First, make sure that the guitar body is secure and will not move. It is important to clamp the box firmly and completely while the binding rabbets are being routed. Also, make sure that the bit is tight in the router and it will not move in or out as you proceed. This can make an irreparable mess. Finally, keep in mind that the objective is to cut the binding rabbet so that the back wall of the rabbet is parallel to the side. More on this below.
The yellow router that is pictured here is actually a laminate trimmer and weighs about 4 pounds. The power is rated at 5.6 amps. It operates at one speed, 30,000 rpm. There are many good, small routers on the market now. There weren‘t when I bought and modified this one. The website noted below provides a review of the most popular brands of routers.
There are a few characteristics to keep in mind when buying a router for cutting the binding rabbet. It should be light and balanced in your hand. It helps to have a tilt base which is necessary on the back of the guitar but not the top (of a flat-top guitar). Otherwise, you might have to fashion a custom skid plate. Woody had to make a new skid plate for the yellow machine. Note the clear plexiglass plate in the photo above. This allows plenty of room for your hand to hold the router where you want it while moving around the edge of the guitar.
The upper bouts of the back are a bit of a challenge as the back is arched and you will need to compensate for that in the router set up in order to keep the rabbet square to the side. The clear plexiglass skid plate pictured above is flexible enough to bend and keep the vertical axis of the router parallel to the side. The area between the heel and the waist is where the arch of the back is most pronounced. It takes practice to keep the router vertical as you go around this curve on the upper bout.
That's when a tilt base could be handy. Problem is, the angle that the back makes with the side varies at every point on the curve around the upper bout. It might be best to work scant and finish squaring up with hand tools… a file and a sharp chisel.
The objective is to keep the back wall of the channel parallel to the side, and the width of the binding channel the same as the rest of the guitar. If the router stays square to the arch of the back, the rabbet that it makes will be tilted toward the outside of the guitar and the width of the binding will be thinner than if the centerline of the router is kept parallel to the side. A tilt base helps in this regard. I have tried to picture this below.