Shaping the top’s bracing is part art and part science. There is over 100 years of tradition in steel string bracing but most luthiers develop their own methods. Perhaps the majority of bracing used today is derived from CF Martin’s research and development. The bracing directly affects the tone of the guitar so needed attention should be given to this step in the building process.
I use very sharp chisels to shave wood from the braces. If the chisel is sharp enough, the wood should come off in curly scraps. It is very easy for the chisel to cut the top if it should veer from the brace so I take great care and use two hands to guide the chisel.
Carefully using the chisel to shave the brace.
The X bracing is shaped to have a point while the tone bars are more rounded. All the brace ends are sloped toward the top until they are even with it.
Carefully maneuvering the chisel to shape the brace and to avoid cutting into the top or a finger.
Once the initial chiseling is completed, I use 150 grit sandpaper to smooth the braces. Sitka Spruce bracing is very quick to sand so it requires very little pressure. Once the sanding is complete, it is time to determine if any further shaping is necessary to achieve the desired tone of the top.
The intial shaping of the braces is completed.
There are many “scientific” methods of testing the results of bracing including deflection testing and Chladni patterns. I prefer tap tone testing. This is where you use your ears to determine the pitch, sustain, and overtones of a top. I strive for a pitch between G and A.
This top is currently at A# and it has wonderful overtones but not enough sustain. I will gradually sand off some of the width of the X and finger braces but none of the height because the height of a brace contributes more to its stiffness than its width. The process is to spend five minutes in sanding followed by tap tone testing and this repeats until the top is at G# or A and has sustain of at least six seconds.
Dan has selected a small “Routen” logo made from Mother-of-Pearl. I have all my Pearl and Abalone inlay materials custom made by Andy DePaule in Oregon.
The Mother-of-Pearl logo against the Ziricote headstock.
To inlay the logo, it is necessary to route a channel in the headstock to accommodate the letters. The channel must be as close to the size of the logo as possible and deep enough so the logo is slightly proud of the Ziricote face veneer. This is very time-consuming because it requires precision.
I use a 1/32″ downcut router bit in my Dremel tool that is attached to a special base for fine routing. I have a pump and tube connected to the base to softly blow away the sawdust as I route. This helps keep the work area clear for precise routing. I have built a headstock jig to firmly seat the neck for routing.
I have a pdf template of the logo and I cut out the logo shape and glue it to the headstock. The position is centered and 3/8″ from the top.
The guitar neck clamped in the headstock routing jig.
The logo outline glued to the headstock. The “R” is coarsely routed.
Using the Dremel, base, and pump I slowly route the outline first slightly undersized and work inward with each letter. Once the initial route is completed, I use the actual logo to place in the channel. It is too large at first and I use a series of colored pencils to trace the shell on to the glued-on template and I route to the colored line.
It takes about three hours to complete the routing, sand off the logo template, and clean up the headstock before gluing.
Routing out the “R” by drawing the outline and routing just shy of the line.
Slowly routing the logo channel. If you ever need a task to help with patience, this is it!
After routing, the channel is cleaned of of all excess debris. I place a base of polyvinyl glue in the channel and carefully press in the shell logo. A piece of waxed paper is placed over the logo and I clamp a piece of plywood over it to press the logo even with the headstock. This is left to dry overnight.
After several hours of this process, my arms, eyes, and brain are tired!
Today the Waverly tuners were delivered. They have a beautiful gold finish with Ebony buttons.
Waverly steel string tuners for a slotted headstock.
Now back to the top. After drawing out the bracing patterns on the inside of the top, I cut out the outline of the top oversized by 1/2″. I use the 9″ bandsaw for this task and I do not have to be extremely careful at this stage but I use this step as practice for when I do the final cutout.
Carefully cutting out the outline of the top.Close-up of the cutting out process.
Bracing patterns are a luthier’s signature and perhaps the most important tone-shaping variable. The exact placement, height, width, material, strength and shape of the Spruce braces will impact the sound of the guitar. The top will have a slight dome for extra strength so I use a 25′ radius. This is accomplished by sanding an arc into the bottoms of each brace using a 25′ template.
This is a 25′ radius plexiglass template that I use to draw the arc on the brace bottom.
Spruce bracing cut to size, radiused on the bottom, and ready to glue.
I drill a 1/4″ hole into the center of the two transverse braces to accommodate the truss rod adjusting Allen wrench that may be needed for future neck adjustments. Transverse braces are the braces between the soundhole and neck.
This 12-fret to body design leaves more room between the soundhole and the neck joint so I am modifying my transverse bracing. I am using Mahogany for the lower transverse brace because it has greater mass than the Spruce. The upper transverse brace is oversized Spruce 5/16″ wide and 1/2″ tall.
I use a thin film of special luthier’s polyvinyl glue on the brace bottoms. To clamp the braces in place while they dry, I use a special “go deck” that I built that allows insertion of Ash “go bars” between the top of the deck and the top of the braces, exerting many pounds of downward pressure on the braces. I made “go bars” out of Ash because of their strength and bending ability. The Cedar top is placed in a 25′ radiused “bowl” so it conforms to the shape of the braces during gluing. After five minutes I clean up glue squeeze-out and let the top and braces set overnight.
Gluing the X bracing in the go deck.
Complete view of the go deck during brace gluing.
Next: back to the neck headstock to route in the Routen logo.
The outline of the Concert body shape was drawn on both sides of the Cedar top. On the exterior side of the Cedar I drew in the rosette channel and purfling lines on both sides of the rosette. The interior of the top will contain the bracing, perhaps one of the more important contributing factors to the sound of the guitar. I use a traditional X bracing design that was developed by CF Martin and perfected by James Goodall (in my humble opinion) and slightly modified by me! I drew the bracing outlines directly on the top and I will dimension the bracing to fit perfectly within these patterns.
Using triangles, square and rulers to draw the bracing outlines on the top.
The next step is to insert the rosette and purfling lines. I use a Dremel tool with a special circular base I obtained from StewMac, a major supplier of luthier tools. First I route out the rosette channel. I made a rosette from a wood called Bocote that has beautiful lines of browns, blacks and tans. It looks awesome against the Western Red Cedar! Next I route out two narrow purfling channels on both sides of the rosette. I will use purfling made of Koa/Maple/Koa to compliment the Bocote.
The Dremel tool with a StewMac circular base for routing the channels.
After routing out the channels, I test the rosette and purfling to make sure there is a snug, but not too tight fit. This time it is perfect and I do not have to re-route. I clean up the channel bottom and sides using 220 grit sandpaper.
Concentrating on getting the rosette and purfling channels routed for a perfect fit.
Now it is time to glue in the rosette. A thin film of luthier”s glue is spread on the bottom and sides of the channel. The rosette is inserted and pressed into place. The glue squeezeout is wiped off after rubbing a thin film on top of the rosette. I place wax paper over the rosette and I use a caul that applies equal pressure to the entire rosette.
The rosette fits perfectly in the channel.
The caul applies even pressure on the rosette. I keep the caul on overnight.
The completed rosette and purfling with the soundhole cut out.
The same process is repeated for the purfling lines: apply glue, position the purfling, press into place, clear excess glue and clamp with the caul. After the glue has set (over 24 hours), I use a sanding block with 220 paper to even the purfling and rosette with the top. It really looks beautiful with this combination of natural woods.
I really want to thank my wife for taking all the pictures. She prefers to remain nameless but she is a great help!
Next up is bracing the soundboard.
After the glue has set for over 24 hours, I remove the joined top from the jig. Using my favorite tool, the scraper, I micro plane the top to remove the glue squeezeout and level the top. To sand the middle of the top to the desired 130/1000″, I use a random orbital sander with 150 grit sandpaper. I frequently measure the thickness of the top using the caliper jig. The perimeter areas of the top will reach 110/1000″. With the middle of the top thicker than the perimeter, the top can act like a speaker cone – it has strength and elasticity. The next step is to draw the outline of the guitar on the Cedar and begin planning the rosette. I also have been squaring the headstock and I drew the headstock outline on the top of the neck. I am waiting for delivery of the Waverly tuners before I proceed any further with the neck.
Using the scraper to micro plane the Cedar top.
The outline of the headstock shape drawn on the neck.
Random orbital sanders are efficient tools – all you have to do is guide them.
The Master grade Western Red Cedar top is extremely stiff with very tight annular rings so I plan to bring the center thickness to 130 thousandths of an inch (130/1000″). I am using accurate calipers to measure the starting thickness. I will create a gradient from the center to the perimeter of the top, bringing the perimeter to 100/1000″.
Measuring the starting thickness of the Cedar top.
Using my Performax drum sander, I carefully remove thin layers from the top. It takes over 100 trips through the sander to arrive at 140/1000″. I will use a random orbital sander, a scraper, and sanding blocks to achieve the final thickness but this will happen after joining.
Thicknessing using the drum sander.
The bookmatched top pieces need to be joined using a butt joint. This is an extremely important join as the top radiates as a whole and the join should never fail with the continual stress exerted by the movements of the top. In order to ensure the stability of the join, I prepare each Cedar half using a trim router and 1/4″ straight bit. I run the router several times along the edge of each piece. To test the evenness, I hold the two pieces together in front of a bright light source to see if there is any “candeling” (any light showing through). Fortunately, the first candeling test is successful.
Using the trim router and routing jig to prepare for the top join.
Using rope to join the top pieces together.
To join the top pieces, I use a method developed by Spanish luthiers over 200 years ago. I built a jig that uses rope to pull together two thin pieces of wood while keeping them flat. I apply a thin line of glue on each side, place it in the jig, and wrap several runs of rope in four positions along the width of the top. I then insert Mahogany wedges under the rope to pull the tops together by tightening the rope.
Inserting Mahogany wedges under the ropes to tighten.
The Cedar top glued and drying in the joining jig.
The headstock outer veneer is Ziricote to match the back and sides. I sandwiched light Maple veneer between the Ziricote and deep green dyed Ash veneers and glued it to the headstock. The deep green veneer, although only 1/32″ thick, will help contrast dark Zirocote to the Mahogany. I often use Ebony for this but I feel the deep green will look beautiful behind the Waverly tuners.
Clamping the headstock veneers
Today I routed a channel for the truss rod and then fashioned a Mahogany spline to cover the rod and couple the spline to the neck. I then drilled two holes through the end of the neck to accommodate the two barrel bolts that will eventually assist in joining the neck to the body. Next I used the table saw and my neck jig to cut out the tenon. I cut a 5 degree angle at the neck end that will be parallel to the body end. Preparing the Ziricote headstock veneer is the next step.
Overhead view of the neck, bolt on tenon and truss rod.
Another view of the tenon.
I started with 1×3 quartersawn Honduran Mahogany and planed it down to 13/16″ and then cut the 8″ headstock from one end. I reversed it and glued it back to the neck blank with a scarf joint using Aliphatic-resin to create a 12 degree angle. Next I used the same Mahogany stock to make a stacked heel. This neck will be joined to the body with a bolt-on using barrel bolts.
Tightening the clamps and cleaning up glue squeeze-out
The scarf joint on the neck is glued using many clamps on a neck jig that I built.
12/2 – 6:12pm – Mark Routen’s Woodshop
Construction on Dan’s guitar has begun! The back and sides are going to be made of beautiful Ziricote pictured below, with an aged master grade Red Cedar top and a Honduran Mahogany neck. Dan has elected to have a Concert body shape with a soft cutaway and the neck will join the body at the 12th fret. This will result in a shorter 24.9″ scale. The nut width will be 1-3/4″ for comfortable fingerstyle playing action and the string spread at the saddle will be 2-1/4″. The Gaboon Ebony fingerboard will have no inlay and I will make a custom all-wood rosette. The headstock will be slotted with Waverly tuners. The finish will be a water-based lacquer for the top, back and sides, and a hand-rubbed oil varnish neck.
The preliminary preparations have begun: this is my 19 th guitar build but the first with a 12th fret body join and slotted headstock and cutaway. I created full-scale schematic drawings of the body shape, bracing patterns and neck template.
Red Cedar top, Ziricote back, mahogany neck.