​     After cooling and drying (overnight on the tower) the bent stock is wrapped around a circular fixture, also home-shop built out of 4" PVC pipe. While gluing up the layers, spring clamps are all that is needed. Once all are glued and laid up (to a width of .500"), PVC cauls are used with 2" C-clamps to keep the 15-piece assembly round as the glue dries (overnight).

     The number of rosettes that one can make at the same time is limited by how many circular fixtures one has and how many C-clamps.

​​​ROSETTE


Making Up and Inlaying the Rosette

     With the tops and backs at the rough thickness and center joined, the rosette is made up, inlayed into the top, and sanded flush. Rosettes are available from suppliers, but Woody likes to make his own from wood binding and perfling stock built up around a circular jig. The result is 9-15 pieces of wood bent and laminated to a width of 1/2" and a thickness of ~ 0.080". After curing overnight, the newly made-up rosette is inlayed into a 1/2" circular slot, 0.060" deep, and concentric with the location of the sound hole. It's basic, it's effective, and it's all wood.

​​    The rosette that Woody uses is actually 13-15 strips of maple and rosewood_ bent and wrapped around an MDF cylinder (the tower jig) to cool and stay in the approximate final shape until ready to be glued up.


​​​TONE BRACES

​​

     The two braces (or three, as above) in the lower bout between the cross braces are referred to as tone braces.  The lower bout most significantly impacts the tone and volume of the guitar. The upper bout is primarily structural and somewhat inert relative to the lower bout in terms of tone production. 

     The angle of the tone braces relative to the grain lines also affects the tone that the top will produce. More perpendicular to the grain enhances the treble end.  More parallel to the grain enhances the bass. Dreadnoughts don't need any help with bass.


SOUNDBOARD BRACING

​​

​     Now we are ready to brace the soundboard.  First, the cross braces.  These are the longest braces on the guitar.  Woody uses standard C.F. Martin style cross bracing on all of his dreadnoughts (so far). 


ROSETTE THICKNESING 


When the glued-up rosette comes out of the fixture it is about a 1/4" thick and rough on the top and bottom. The rough rosette is placed in a simple, home-shop fixture with two circular channels.

     The first circular channel is routed to a depth of .200" and is used to flatten what will be the bottom side of the rosette. Here, Woody's Performax thickness sander does the trick nicely. Then the rosette is flipped over and placed in the second routed channel which is only .100" deep.  This takes the rosette down to less than 1/8" thickness which will allow it to be inlayed and sanded flush to the guitar top...again on the thickness sander. 

​​​​October, 2015​   Back and Top Braces


     

     The month of October flew past just as months do when one is busy. Guitar building is on-your-feet work and if you followed me around all day you would be tired. You know, a good tired, a sleep-well tired.

   September ended with the completion of the initial joining and rough dimensioning of the top, back, sides and neck of the several guitars that Woody intends to complete in the next few months (before Easter). Please don't be confused, Woody and I are the same person.  I just get tired of someone talking about my-self all the time.


BRACING STOCK, THE BACK

    The shape and carving of guitar braces is unique to every guitar maker (as is almost everything). The common property of back braces is that they are all arched to produce and maintain the arch of the back.

     Many guitar makers these days use a manufactured, bowl-shaped fixture, lined with sandpaper to produce the arch in the back braces. This is a personal choice of the maker. When one thinks about the geometry of a concentric bowl, however, the arc north and south is the same as the arc from east to west. 

[A picture containing vessel, barrel, indoor, stack Description automatically generated]      The arc from the heel to the butt of the guitar, however, is not the same as the arc from side to side. When produced in a sanding bowl, the brace cross-section will have the same arc across the bottom as it does down its length. This would seem to introduce a number of hard-to-control variables... I must not know everything that there is to know about sanding bowls.


In principle, back braces are shaped like barrel staves. 


ROUTING for the SOUNDHOLE and ROSETTE  


    Woody usually routs the rosette channel, then inlays and sands down the rosette and, as a last step, routs the sound hole.

     Briefly explained, the router base has two 3/16" holes drilled in it. One of these 3/16" holes in the router base is a distance from center that allows a 1/2" bit to cut a 5-1/2" outside diameter (5” inside dia.) rosette channel. Woody rosettes are 1/2" wide and set 1/4" from the edge of the soundhole. The other 3/16" hole is exactly the distance from center needed to cut a 4" diameter sound hole with a 1/2" bit. 


     Rosette Channel: The soundboard is clamped to a workboard.  A 3/16" hole is drilled in the soundboard and the workboard at the center of the sound hole layout. A 3/16" dowel is set in this hole.  Then the router base slips over the dowel which will allows the router to rotate 360 degrees. The cutter is set to a depth of half the thickness of the top (~0.065") and the rosette channel is cut by rotating the router around the dowel. Once the rosette is inlayed and allowed to cure overnight, the over-thicknessed rosette and soundboard go under the drum sander to flush the rosette with the soundboard to a thickness of ~0.120". The rosette should fill the top half of that thickness.
 

     The process used for cutting the sound hole is similar to cutting the rosette channel except for using the second 3/16" hole in the router base to center the 4” diameter sound hole.

  

     One can see that determining the proper scallop design and brace stiffness is a VERY subjective subject.  So many methods and theories are used that a complete discussion on this page is not possible (and probably not worthwhile). Woody, and all luthiers, must start with a rational plan and then work from experience, intuition and feel.          There is one piece of advice that all instrument builders would agree... "Begin with the end in mind...and... Work scant".  Proceed with carving braces only after drawing the intended shape of the scallop on the brace. Stop, think about what you're doing. Proceed again and stop again. Before you think that you've taken out enough... stop. You can always come back. There’s no worse feeling than comes with carving too much wood off the braces.
 

LAYOUT and GLUE UP

     Woody uses a foam template to place the braces at the 99-degree angle when gluing onto the top. Once the X-braces have been glued down, the final step is to glue on a reinforcement patch over the top of the lap joint (pictured on the right below). This strengthens the joint significantly.

     The soundboard braces are glued in according your bracing plan. Woody uses a 99-degree X-brace pattern. 

​​​​​SOUNDBOARD BRACING STOCK and LAYOUT

    If one went to work for a guitar manufacturer like Gibson, Taylor or CF Martin, etc., one might start out by roughing out bracing stock (after sweeping the floors for a couple of months). There's no big trick to cutting out bracing stock, but one does need to be consistent in keeping the width and height of the bracing stock precise. That's not too hard with basic stationary woodworking equipment. You might be surprised at the amount of bracing that one guitar consumes. Below is pictured a spruce billet and almost enough bracing stock for one guitar.

      At Woody Strings, Sitka spruce is used as bracing stock. From billets or planks, the stock is ripped to a rough thickness close to the final thickness. Then lengths of spruce stock are taken to their final thickness dimension on a Woody's PerforMax 16-32 thickness sander. The final width of the soundboard braces ranges as shown in the drawing below.

     NOTE: The dimensions shown here are for Woody guitars, roughed out bracing stock. The dimensions of length and height will change with Woody’s final shaping and carving of each brace. Width will stay the same. 


​   The photos here are an attempt to show the length and depth of the scallops as Woody has carved them. 

BRACING AND HUMIDITY CONTROL


      In Woody's shop, winter is the best time to glue up bracing... while the ambient humidity is low_ about 35-45%.  In Virginia, winter is the only time when one can count on several low-humidity days in a row.  So, in January, Woody tries glue up bracing on all the tops and backs of guitars that he is going to build that year.

          The braces, of course, are glued on after the soundboard and back stock have been thicknessed and center joined. Then the rosette has to be made and inlayed into the tops. Last winter, all of this activity took about three weeks during which there were about 16 days of outdoor ambient humidity of less than 45%.  The humidity in the shop stayed below 40%.

        Woody doesn't have any type of mechanical humidity control in the shop (maybe we should).  When I see from the weather report that we are in for 3-4 days of dry conditions, I am ready. These tops and backs were center-joined last winter so, when the weather is cooperating, I am prepared to go into the shop early and stay late... glue up braces all day and sleep well at night.

     All of the back braces can be clamped at the same time to this type of workboard/fixture to form the shape of the back into the proper radius. All braces were finish-carved after they were glued to the back.


September, 2020


Chapter 05_ Rosette and Bracing    

    Cut between the lines which should be the width of each of your cross braces and only halfway through the brace. Use the bandsaw blade to carefully hog out all of the wood between the lines. WORK SCANT and you should still see all of your lines when you're finished cutting with the bandsaw. Being too tight is not a problem. You can always shave a bit more off.


​Play Safe, stay healthy.


    Come back next month.


                                                 Woody​​


GLUE and ​​​SCALLOP or...

      On a hand-made instrument, braces are always carved in place. This allows the builder to modify the stiffness of the top and back relative to the density and stiffness of the wood in each brace. Woody uses a 25 mm, #5 sweep Swiss gouge to remove wood from the braces.

November 2015


  • ​Efficiency

  • Resonance

  • Bending

  • Bracing 5 Guitars



    Before cutting out what will be the sound hole, the disk that will be removed from the hole must be secured (see 4 brads in the photo below) so that the disk will not get in a fight with the router bit when cut loose from the surrounding soundboard.  This is very important.

     The dimensions given here for plate thickness are approximate and depend on the type of guitar and the unique stiffness of the soundboard species. It seems that there is only mild consensus among luthiers on final soundboard thickness ranging from 0.095" to 0.125" depending on the model of the guitar. (dreadnought/Sitka spruce here) Soundboard thickness influences tone significantly. Equally as important, however, is the pattern and stiffness of the top bracing and the player’s intended string gauge and style of attack. 



     In October the goal was to put braces on the five tops and backs started last month. Also in October, at the Richmond Folk Festival, I met and talked with Wayne Henderson (guitar maker). He is a very unique person. That was great fun. Then, back at the shop, an old (50's) Gibson ES 150 came off the rack and had some renovation work which will be discussed here on a later date.


    As is often the case in writing up these journals, with so many words of explanation it might seem as if the process is more work than it actually is. Woody made up, inlayed and surfaced in place four rosettes in about 3 hours, albeit spread out over several days.

    One final note about bracing several backs at the same time. It is likely that these backs will not be built into a guitar body for several months. Therefore, to maintain the heel-to-butt contour of the back while hanging free in the shop, Woody has cut out an arched fixture (caul) in the longitudinal curve of the back. With one clamp and this contoured caul, the back will stay in shape until it's time to glue it to the sides of a new guitar.


That's it for this month's addition to the Complete Overview of Home-Shop Guitar Building. When I'm done you can save these pages and put them together... you will have a complete book on how to build a guitar in your home shop.

BACK BRACES


    The shape and carving of guitar braces is unique to every guitar maker (as is almost everything). The common property of back braces is that they are all arched to produce and maintain the arch of the back.

     Many guitar makers these days use a manufactured, bowl-shaped jig, lined with sandpaper to produce the arch in the back braces. This is a personal choice of the maker. When one thinks about the geometry of a concentric bowl, however, the arc north and south is the same as the arc from east to west.  The arc from the heel to the butt of the guitar, however, is not the same as the arc from side to side. When produced in a sanding bowl, the brace cross-section will have the same arc across the bottom as it does down its length. This would seem to introduce a number of hard-to-control variables... I must not know everything that there is to know about sanding bowls.

     In principle, back braces are shaped like barrel staves.


  • Top and Back Joining

  • Bracing Explained

​     The rest of the braces are glued in according your bracing plan. Many of the various bracing schemes are available online.  Many are free, some are not. The one thing that they all should have in common is that brace ends are scalloped and tucked in under the cross brace or lining, or both. Pictured to the right is an example of what I mean.

    When the bottom of the brace is perpendicular to the vertical centerline of the section, it is relatively easy to shape on a 6 x 48 stationary sanding machine, and then glue in place tightly. That is the method used here.


GLUING THE BACK BRACES

     Gluing up back braces is much more straight forward than top braces when you have radius cauls to hold the back in an arch shape as the braces are glued down. Woody uses a 15-foot radius for the arch of the back.

     The photos show a fixed-caul workboard that Woody uses exclusively for gluing and clamping back braces. In Woody’s shop, the number of back braces depends on the type and size of the guitar being built. Shown here is a 6-brace dreadnought back.    


    The guitars under construction for this journal are all dread-naughts, not like the arch top Gibson shown above.  I mentioned the Folk Festival and working on the Gibson as excuses for not getting as much done on the D's as planned.


Back Braces:

    The shape and carving of flat-top guitar braces is unique to every guitar maker (as is almost everything). The common property of back braces is that they are all arched to produce and maintain the arch of the back.


     Many guitar makers these days use a manufactured, bowl-shaped jig, lined with sandpaper to produce the arch in the back braces. This is a personal choice of the maker. When one thinks about the geometry of a concentric bowl, however, the arc north and south is the same as the arc from east to west.  The arc from the heel to the butt of the guitar, however, is not the same as the arc from side to side. When produced in a sanding bowl, the brace cross-section will have the same arc across the bottom as it does down its length. This would seem to introduce a number of hard-to-control variables... I must not know everything that there is to know about sanding bowls. 


    When the bottom of the brace is perpendicular to the vertical centerline of the section, it is relatively easy to shape on a 6 x 48 stationary sanding machine, and then glue in place tightly. That is the method used here.  


     Woody prefers using six shaped braces to achieve the curve of the back. To do this, six brace molds (made from ordinary 1 x 2 pine) serve as templates for the braces. These molds then become cauls when fixed to a work board, as shown below. The final shaping of the braces can be done before or after the braces are glued to the back.  I prefer shaping them before gluing. Here I glued them, then carved them to final shape. These back braces are 15 mm tall all the way across.

​​

CUTTING THE LAP JOINT

     Set the bandsaw table to 9 degrees as shown in the photo here.  Tape the braces together making sure that the edges to be cut are flush with one another. With both braces taped together, the notches for the lap joint are cut at the same time. I have a 9" bandsaw, so I have to keep the 'upper' end of the braces on the throat side of the blade.  The upper part of the brace is about 7-1/2" long.   

​​SCALLOP then GLUE 

​​​​​CONTOURED BACK CAUL

​     The stock for these circular bends is wood binding stock from LMI or StewMac (maple and rosewood, .250" x .080"). Maple and rosewood strips (.250" x .020") are also part of the lamination. These thin ones don't need heat.

      Pictured here is what happens when Woody gets over anxious and tries to bend the rosewood binding stock too quickly on the pipe.

LOWER BOUT SCALLOPS

     Many, many guitars have been made without scalloped braces and they sound great! Some luthiers believe that scalloping braces is incorrect and weakens the brace unnecessarily.

  C.F. Martin used to scallop braces quite a while back (in the 1930's and 40's) when their primary top wood was Adirondack spruce which is much stiffer than Sitka. When quality Adi quartersawn became more expensive, they quit using it and they quit routinely scalloping their top braces. I've restored several Martins from this vintage in which everything, BUT the scalloped bracing, needed repair.  Martin now produces very good sounding instruments without scalloped braces, but their HD models feature scalloped bracing (something for everyone, I guess).


​​​PPREPARING THE X BRACES

     Cutting the cross-bracing lap joint is straight forward and relatively simple if one is careful. First shape the bottom of each cross brace. That is, shape the edge that will be glued to the top.  Woody shapes the lower bouts of the cross brace to a 30-foot arc leaving the upper bout ends flat and straight down to the lap joint.  Other luthiers will cut these braces differently...but only slightly. Keeping the upper bout flat will assist with assembly of the box, joining of the neck with the proper neck angle, and set up of the guitar fretboard.

      Once the arc of the cross braces has been carved into the lower bout end, line up the two cross braces side by side so that they both have the glue side down. Make sure that the 'upper' bout and 'lower' bout edges are also side by side.  Now, roll one of the cross braces over 180o i.e., keep upper and lower bouts side by side so that one brace has the glue edge up, and the other brace has the glue edge down. The penciled arrows in the photo below point to the edge of the brace that will receive the glue.   It is critically important to orient these braces properly before cutting. 



      Shown here Woody uses regular cam clamps for glue up. We have used a go-board for this operation, and it worked well. The problem in my shop is space, i.e., storing the go-board fixture when it is not in use which is 98% of the time.


SCALLOPING THE SOUNDBOARD BRACES    

     All of the bracing in the lower bout can be scalloped to lighten the vibrating surface of the soundboard. Do not scallop the upper half to the “X” bracing. This is important. This is the area of critical structural resistance to the torque generated by the pull of the strings on the top. Keep the upper portions of the cross braces at full height and strength.

​​​CROSS BRACING

​​

​     The cross bracing is the most critical bracing in terms of structural integrity of the top. With steel strings and no cross bracing, the pull of the strings on the bridge and top would create a torque that the upper bout and sound hole could not withstand.

     Cutting the lap joint that allows the cross bracing to act as a single unit is essential. Cutting this lap joint is not as difficult as one might think. (The 99-degree intersection is Woody’s own.  I've seen it 98 and I've seen it 100.  Go figure.


SCALLOPED BRACING FOR TONE CONTROL


     The idea of scalloped braces is to reduce the mass and stiffness of the brace thereby changing the resonant frequency of the top. This sounds logical. As a professional engineer, I am intrigued by the measurement and modification of resonance to influence tone. The resonance of the entirely assembled and finished box of the guitar, however, would seem to me to be the critical resonance impacting tone.  The resonant frequencies of the free-standing component parts of the guitar (top, back, sides, neck, etc.) are significant, but how these components interface with each other and the volume of air within the box is the final test.  The physics of the many variables impacting sound and vibration in guitar is beyond our scope in the discussion here.

 

     Woody prefers using six braces to achieve the curve of the back. To do this, six brace molds (made from ordinary 1 x 2 pine) serve as 15-foot radius templates when shaping the bottom (glue surface) of each brace. These templates then become gluing cauls when screwed to a work board, as shown below. The final shaping and height of the braces can be done before or after the braces are glued to the back. Here Woody glued them, then carved them to final shape.

     ​​​​    Yes, Woody guitars have six back braces instead of four.  All that needs to be said here is that, based on Woody's experience, there are structural/ acoustic reasons. More on that later.


CARVING BRACES

     The design of the guitar top braces varies with the model and expected performance of the guitar.  The top braces are a large component of what gives the top more or less stiffness and, therefore, significantly influence the resonance and quality of the tone.

     If the instrument is intended to be played by a heavy-handed flat picker using medium to heavy gauge strings (like me), it should be braced more stiffly than the same instrument intended for use by someone with a lighter touch. This should seem obvious. Even the big manufacturers vary the thickness, height, pattern, and type of wood selected for various types of guitar models and players.

    The guitar tops that Woody builds are intended for use under medium gauge, phosphor-bronze, wound steel strings.  The braces are scalloped after gluing in place. This way the maker can attempt to accommodate the varying degrees of stiffness of brace stock itself.

     When carving the braces, it is good to remember that the stiffness of the brace is relative to the height of the brace far more than the width. I have read that the stiffness of the brace is proportional to the cube of the height.  That means that a brace that is 10 mm tall is twice as stiff as a brace that is 8 mm tall.  Keep this in mind when carving braces.