​     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.


September, 2020


Chapter 04_ Bracing and Rosette    

​Play Safe, stay healthy.


    Come back next month.


                                                 Woody​​


​​​​​LAYOUT and  GLUE UP

     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 when it is not in use which is 98% of the time.

    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 and height of the braces can be done before or after the braces are glued to the back. Here I glued them, then carved them to final shape. These back braces are 15 mm tall between the scallops.

​​

​​    Yes, my guitars have six back braces instead of four.  All that needs to be said here is that, based on Woody's experience, there is a reason. More on that later.

    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.

​​

​     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 below is what happens when Woody gets over anxious and tries to bend the rosewood too quickly on the pipe.

Back clamped to the Caul

​​     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 soundhole 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 degrees is my own.  I've seen it 98 and I've seen it 100.  Go figure.)


     TONE BRACES: The two braces 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 tems 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.


    PREPARING 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, and set up of the guitar fretboard.


      Once the arc of the cross braces has been carved, 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 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 arrows in the picture point to the edge of the brace that will receive the glue.   It is critically important to orient these braces properly before cutting. 

 

Spruce Bracing Stock 


    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. 23"(L) x 1"(H) lengths of spruce stock are taken to their final thickness dimension on a Woody's PerforMax 16-32 thickness sander. The final thickness ranges from 0.250 - 0.325" thick depending on its intended application. 

     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 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.


​    Contoured Back Caul

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 soundhole.


     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 soundhole with a 1/2" bit. 


     Rosette Channel: The top is clamped to a workboard.  A 3/16" hole is drilled in the  soundboard at the center of the soundhole layout. A 3/16" dowel is set in this hole.  Then the router base slips over the dowel which will allow 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".


     Soundhole: The process used for cutting the soundhole is similar to the cutting the rosette channel except for using the other 3/16" dowel-pin hole to center the (4” dia) diameter soundhole.

  

​     ​BACK BRACING


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


     The photos shows two fixed-caul workboards that Woody uses exclusively for this purpose. One has four ribs (cauls) and the other six. A third, not shown, has five ribs.  It just depends on the type and size of the guitar being built. Today it's a 6-brace dreadnought back.


     Every brace gets clamped at the same time to this type of workboard/fixture to form the shape of the back into the proper radius.


​     LAYOUT and GLUE UP: The soundboard braces are glued in according your bracing plan. Woody uses a 99 degree X-brace pattern. 

     

TOP AND BACK BRACING



     Now we are ready to brace the top and back.  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). It looks like this.

    The rosette that Woody uses is actually 13-15 strips of wood_ 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.

​    One final note about bracing several backs and tops 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, I have cut out an arched fixture (caul) in the design radius of the back. With one clamp and this fixture the back will stay in shape until it's time to glue it to the sides of a new guitar.



    Before cutting out what will be the soundhole, 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 fly out when cut loose from the surrounding soundboard.  This is very important.

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



     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.

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.

  • 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 on line.  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 below is an example of what I mean.

​     CUTTING THE LAP JOINT: Set the bandsaw table to 9 degrees as shown in the photo below.  Tape the braces together making sure that the edges to be cut are flush. Both braces 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".


     Cut between the lines which should be the width of each of your cross braces and only half way 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.


     Woody uses a guide 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). This strengthens the joint significantly.


Top 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 I am building are intended for use under medium gauge, bronze wound steel strings.  These tops will have cross braces which are 0.310" (~8 mm) thick. Initially, the brace height will be 0.620" (~16 mm).  The braces are shaped before gluing and scalloped after. This way the maker can attempt to accomodate the varying degrees of stiffness of brace stock. The transverse brace (above the sound hole) is ~ 9.5 mm wide and 19 mm tall before shaping.  It shouldn't change much with shaping.  


     All other braces on the top and back of these guitars are 6 mm wide.  Of these, only the long tone braces are scalloped in the area of the lower bout below the "X" bracing.


     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.


     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. 


​     I've taken a couple of photos where the shadows of the braces show the length and depth of the 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). 



Scallops (briefly):

     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 of discussion here. 


Back to the Basics:

    Notice, in the upper bouts, the cross braces are not scalloped. 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.

     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 .120" deep.  This takes the rosette down to approximately 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 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... and sleep well.


     But first, rosettes and soundholes.

Simple

November 2015


  • ​Efficiency

  • Resonance

  • Bending

  • Bracing 5 Guitars

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. 


     In principle, back braces are shaped like barrel staves.