SHAPING THE BRIDGE

EQUIPMENT: Using a clean, quality spray gun is the only way to even hope to get a quality finish.  Control is everything and cheap spray guns can be extremely frustrating when they clog, spit, spray erratically or just plain don't work at all.


     I once visited a professional refinisher to get some tips on buying a spray gun. His comment was that "None of them are worth a sh_t!"


     I've since learned that he is right... IF YOU DON'T CLEAN THE GUN RELIGIOUSLY. If you don't know how to clean a spray gun, there are many videos on line that explain how. Once you know how, the trick is to clean the gun immediately after use... every time. It takes about 3 minutes.  

       

     The saddle needs to carved to compensate for the varying string diameters. The whole story as to why compensation is needed is a bit tedious to get into here. Suffice it to say that tension on the string is one of the determinants of pitch. Thicker strings required more pressure to fret and, thus, the pitch is raised further than on the thinner strings.  That's part of it. 


     The other part is that the vibrating string length of thicker strings is shorter (conversely, the dead length is longer). Thus, the amount of compensation of the 'E' string is greater than the compensation of the 'e' string. 


     For a more complete explanation Google: "Guitar String Compensation"


SHAPING THE NECK

    HVLP       (High Volume,    Low Pressure)           

     The guitar bridge is shaped from a rosewood or ebony blank. The exact shape and dimensions of the bridge are somewhat optional. Woody isn't trying to re-invent the wheel so wJs bridges are fairly standard. Length and width dimensions might vary by a couple of millimeters, but there are a few dimensions that the guitar neck and fretboard will dictate. These critical dimensions are the neck angle, scale length, and the taper of the fretboard.  That is, the thickness of the bridge and the spacing of the strings at the saddle will vary with the neck angle and the taper and radius of the fretboard.


     Woody guitars use a standard 25.4" scale length. The width of the fretboard at the 14th fret is 57 mm, the width of the fretboard at the nut is 43 mm, and the center-to-center spacing of the strings at the saddle is 57 mm. The fretboard has a 12" radius.


     As noted in the sketch above, these dimensions are "advisory". So too is the thickness of the bridge which is determined by the neck angle. Woody likes the bridge to be 9 mm thick in the center and 3 mm thick on the wings. All of these dimensions are relatively standard for a dreadnought guitar. There is nothing sacred about these dimensions, however, and each luthier will have their own preference. 

Rails

     The gun pictured above costs less than $200 and when I bought it I also committed to cleaning it immediately after every use. I've done that and it works great!


     I have described the finishing process previously on this website (September, 2016). There are also quite a few videos on line that explain all that you need to know about the equipment and techniques.


     The one thing that first-time, home-shop luthiers might find surprising (and difficult) is the amout of hand sanding and polishing required to get a high gloss finish like one sees on manufactured instruments. What production facilities have in equipment, experience and capital investment, the home-shop luthier must make up for in hand and shoulder work with multiple grades of sandpaper and sweat! The finish is the first thing that people will see and judge... before they hear the guitar played. That's just the way it is.

       

August, 2018


     Woody Teaches
          Shaping the Neck
          Shaping the Bridge
          Shaping the Nut and Saddle
          Bridge Layout
          Finishing

Power Rough Out

CUTTING THE SADDLE SLOT


     Above are a couple of photos of the jig that I use to cut the saddle slot in the bridge__ after the bridge has been glued to the soundboard. 


     LAYOUT: With the bridge glued to the soundboard (centered and square to the center line), lay out the compensated 'e' string saddle position. On the bridge, mark the front, treble-side of saddle slot about 5mm from the front of the bridge.  Then add 3mm (2mm for light-gauge strings) to determine the break point of the 'E' string (near the back, bass-side of the saddle). These numbers are derived from measuring dozens (if not hundreds) of compensated saddle positions over the years .


     THE JIG: The 'rails' on the top of the plywood jig are perfectly parrallel and at a width that is the same as the router's base.  The bottom of the jig is covered with felt as it will be in contact with the guitar soundboard.  Set the router between the rails of the jig when it is positioned (but not clamped yet) on top of the guitar.


    Slide the router back and forth in the jig and visually position the 1/8" router bit so that it is aligned with the slot layout. The 3mm saddle layout is marked on the bridge with two, parallel pieces of light-colored masking tape.  The position of the router bit is adjusted by moving the jig and the router together.   


     The jig is nearly as wide as the lower bout (~16") so that it can be clamped in place without interfering with the router. The jig and the guitar are clamped down to the underlying workboard.  Standard cam clamps will suffice.


     Visually check to verify that the path of the router bit matches the layout of the saddle slot.  On the top of the jig, mark the beginning and end-of-travel points. These points mark the position of the router base when the bit is at each end of the slot.

     

     Set the depth of cut to ~ 5mm for the 3mm-wide (1/8") bone saddle. This will leave about 7mm above the bridge to shape the top profile of the saddle to match the radius of your fretboard.


     Explaining how to make and use this simple jig is more difficult than actually using it. Check and double check the path of the router bit. Make sure everything is centered and that nothing moves but the router once you're underway. Woody has used this method and jig for cutting the saddle slot for nearly 40 years.

Glue Up

Staying on Course

Simple Shaping Fixture

Dimensions are "Advisory"

​Don't let being great get in the way of being good.


See you next month.

       

     All of the work pictured above happens before the neck is dovetail jointed to the body.  Once the neck is roughed down to approximate shape, and the heel is veryclose to its final shape, the neck and the body are joined.  The remainder of the neck carving takes place after the neck and the body are joined and the truss rod and finished fretboard are in place.


     The final shaping of the neck and fretboard together must be  carefully controlled. The truss rod is already embedded in the neck and, unless care is taken, one might remove too much wood from the back of the neck and the truss rod begins to appear.  This is NOT good.


     Woody uses three simple templates of the desired neck cross section at the 2nd, 5th and 10th fret. These are easy to make from styrofoam and they profile sections the design guitar neck. Each template represents the sectional width, depth and curvature of the finished neck and fretboard at different points down the neck. Check your work against the templates often.

FINISHING


VENTILATION: If your 'spray booth' ventilation system is the same as your home HVAC system... forget it. 


     To spray 6-8 coats of lacquer and sealer on your guitar you need to take it outside of the air that you and your family are breathing (i.e. take it outdoors).  Be mindful of humidity and bugs and you will be OK. Inhaling finishing fumes while you're sleeping is not OK.

    

Saddle Layout

Carve to Compensate Saddle

THE SADDLE