ROUTING FOR THE TRUSS ROD

Thickness Sanding

     Thickness sanding of tops, backs and sides to final rough dimension. Basically bump-and-grind woodworking, lots of dust must be captured and exhausted to the outdoors. The work is spread over several days.

     The Performax 16-32 drum sanding machine (pictured here) is about as small a thickness sander as a guitar maker can get away with. Initially, while the plates are still separate, Woody likes to take the top thickness down to about 0.140" and the back to about 0.130". After gluing the bookmatched halves together the target thickness is 0.120" for the top and 0.110" for the back.

    Every thickness sander must be kept tuned up to ensure that the thicknessing is even across the entire sanded surface and end to end. The machine pictured is about 15 years old and it has its quirks. But Woody knows what they are and makes adjustments. ​ 

     It's a good idea to rout for the truss rod before slicing the neck into three sections for laminations. The key thing is to have the edge of the roughed-out neck parallel to the centerline so that a fence can guide the router perfectly down the centerline of the neck.


     Woody uses a shaper table for this operation, but for many years I used a Woody-built fixture to hold the neck firmly in place with a hardwood fence to guide the router.  The router moves and the work is stationary. With the shaper table it's just the opposite. The heavy router is stationary and the relatively light-weight neck moves. There is, unquestionably, more control with the shaper table.  

​     The neck of a steel string guitar can be the nemesis of guitar makers and players alike. It is essentially a stick attached to a box. The neck can shrink, twist and bend without the least bit of naughty behavior on the part of the player or the maker. 

     Corrective measures, therefore, must be taken proactively while the guitar is under construction in order to counter the forces that will be acting on the neck. 

     Six steel strings collectively pull on the neck with about 175 lbs. of force. The composite nature of the neck and fingerboard also creates stability challenges. That is, the neck and fretboard are made of a variety of very dense materials like fret wire and a truss rod, which do not shrink, and not-so-dense materials like ebony and mahogany which shrink and swell at different rates. Add to this that some fretboards are bound with plastic bindings to counter fretboard shrinkage issue. These bindings create issues of their own. Woody binds the fretboard with wood bindings made from the fretboard itself. More on that later.



     The kicker is that shrink/swell issues re-occur on a cyclical basis related to the weather and time of year... more specifically, the ambient relative humidity of the air surrounding the instrument which differs from season to season and from city to city. 

     Some instrument makers (like Woody) have incorporated laminations into the construction of the neck (as seen in these photos). This stabilizes the neck and allows the neck to be a bit thinner. Also, it's necessary to rout the neck for a truss rod that operates in both directions. That is, the truss rod will pull the nut end of the neck back, or push it forward as needed. 

     Begin with a stock mahogany plank (889 x 76 x 22 mm) (35 x 3 x 7/8 in.). From that plank cut 3 blocks to make up the heel (75mm, 55mm, 50mm). True the joining surfaces.

     Next cut a scarf for joining the head of the neck to the arm.

In the photo above:


Top: Straight plank of mahogany neck stock

Middle: Arm and built-up heel blocks assembled

Bottom: Headstock scarfed from the end of the arm and turned over to be glued to the top of the scarf.


In the photo below:


     The scarf joint is cut and the headstock is glued under the arm of the neck. This is how Woody learned to do it from Charles Fox back in 1976. He has tried both ways and has found that there is no substantial difference...except in the layout of the scarf on the neck stock, which is very different.


MUST KNOW: 

     In this presentation, the dimensions and discussion of building the guitar neck assumes that the headstock is glued up as shown below, i.e. under the arm. The location of the nut and the scarf is entirely based on this choice. 

The Guitar Neck  

     Neck stock is roughed out and laminated together. This particular style of laminated neck is unique to Woody guitars (as far as I know). There is some geometry involved and careful attention must be paid to symmetry about the center line. The objective of lamination is to strengthen the neck and headstock where it joins the arm (under the nut).

Joining the Top and Back

     The two book-matched halves of the top and back must be joined and show no glue line.

     There are several ways to do this, as there is more than one way to do just about everything, but the top and back joining method must address two important details. 

  • ​     The two halves of the top (or back) must be kept flush with one another at the joint.


  •      When the two halves of the top (or back) are pressed together at the joint, both sides of the book-matched set must be held down to avoid buckling as pressure is applied from the edges.


        To keep the joint from buckling, and to keep the joint flush, see the set up photos below. Two long strips hold down the work on both sides of the center joint. Opposing wedges squeeze the joint together from the edge.  Be sure to underlay this set up with wax paper.

August 2020   Luthier's Journal


Chapter 03_ 3-Piece Neck; Top and Back

     OK. That ought to give you something to think about for a few weeks. If you are interested in Woody Adventures, a couple more chapters have been added.

     If you are not familiar with the WA stories, they are a journal of Woody's adventures in becoming a luthier in Fairbanks, AK back to 1975. I was 27 years old. Adventure is the right word.


Woody Strings for Sale 


      Now, 45 years later, I am 72 and just about ready to retire from luthiery. I am planning to sell my entire Woody Strings shop. In the shop there is enough wood to build about 40 guitars; 35 mandolins; 6 violins and all of the tools and equipment that you see on these pages...plus 6 or 8 finished dreadnought guitars and a complete set of guitar repair tools and supplies. Woody made a living as a string-instrument repairman for 15 years.

      That's why I am documenting Woody's procedures for home-shop guitar building one last time. By spring of 2021 I hope to have recorded a comprehensive overview of Woody Strings...the shop, the tools and machines, the fixtures...everything.

      If you are interested in some or all of this, contact me.


Woody@WoodyStrings.com 




     In regard to making the joint surfaces straight and true, below are some photos of a light box that I made in the shop one morning just to help me make better top and back glue joints.

     Woody made this light box from and old drawer ~24 x 16 x 4" deep. It has a 1/4" plexiglass top. Inside are three 18" fluorescent fixtures and a 10-foot strip of LEDs sewed onto bias tape. 

     The light box helps pick up areas of the joint where the two halves of the top (or back) are not quite touching. 

GLUING UP THE SOUNDBOARD and BACK


    The real trick in gluing up the soundboard is to get the two glue surfaces straight, square and true. After that, it's just a matter of pressing the two surfaces together.


     By not clamping the hold-down cauls directly over the joint, the squeeze out can be cleaned while it is still wet. If not done now, it becomes a problem later when trying to clean the hardened glue off the soft spruce. To clean the other side, leave the top (or back) in this clamping rig for only 30-45 minutes. Loosen the wedges first and then remove the hold-down cauls. Take the top out carefully. Clean the not-quite-hard glue from the other side with hot water quickly applied and removed. Dry with paper towels immediately.  (See above: Take Your Pick/Fire and Water)


      The back is glued up the same way as the top but the backstrip must be inserted between the two halves as in the 2-piece mahogany back in the photo. Multi-piece backs, like the 4-piece, rosewood and walnut back in the photo, are a bit more challenging to join but can be visually quite interesting.


​     Once the plates are dimensioned to the rough thickness, the center joints of the back and top are trued up, glued and joined. Truing up the edges to be joined is done by hand on a shooting board with a three-foot level to achieve a glue joint in which no light is visible when held together.


     One finds that a lot​ of guitar building in a small shop is done by hand. When tolerances and budget are tight, and the shop is small, hand tools with a good feel and a good eye, will get you where you want to be quicker, cheaper and with far less airborne dust. (a major concern if your shop HVAC is the same as your house).

LAMINATED NECK


       Now you have the rough out of the neck. When all of the glue has set up (24 hours), next thing to do is to rip the entire assembly into three pieces from end to end. The three sections will sandwich the two maple laminates between them.
     These rips are commonly parallel when you see a 5-piece laminate neck. This is where Woody does his laminate neck a little differently. 

     Woody rips the roughed-out neck on a converging angle as seen in the photos below. This complicates the process which was not simple to begin with. It strengthens the neck allowing it to be thinner and it also strengthens the head-to-neck area of the scarf which is commonly a point of severe damage if the guitar falls over backwards and lands on the head.

CONVERGING LAMINATE LINES


             Before these rips can be made they must be laid out very carefully. Then, they must be cut as straight as you possibly can to maintain symmetry around the centerline and truss rod channel. 

     Lay masking tape down the centerline and on each step of the heel so that your cut lines are symmetrical and clearly visible. Woody uses his trusty nine-inch band saw (with a sharp blade) to make these two long rips down the length of the neck. You will save yourself a lot of heartache if you cut these rips straight. These joints are about 24" long and each has two sides that must be straight, square and true. Woody recommends a 36" long butcher-block table covered in sandpaper to true up these surfaces . 

​Play Safe, stay healthy.  Come back next month.


Woody​​


     Traditional 'Wedge and Twine' method of joining of the top and back plates (pictured below)  is still used by many luthiers, including Woody. It is a good method but a little tricky in the set up. Pictured below are 14 pieces of wood laced together with about 30 feet of twine. If one did this five times a day for a year it might be quicker than the 'wedge and workboard' method described above... but not better. 

     As mentioned at the start, it is the truing of the joint surfaces that determines the quality of the glue joint. 

     Glue the built-up heel and arm seperately from the glue up of the headstock scarf.  Make sure that the joined surfaces are square and true.

     When gluing up the scarf, likewise, make sure that the joined surfaces are square and true. Be sure that centerline of the headstock is a true extension of the centerline of the arm. Then clamp it up dry and, in the waste areas on both sides of the nut, drill tiny holes through the headstock and into the arm. Insert brads that will keep the headstock from sliding around when it's clamped up with glue. The brads should be snug in the drilled holes.

     The dimensions shown above are finished dimensions. The 378 mm dimension from the back of the nut to the back of the dovetail should be increased to 388 mm when locating and cutting the scarf. This will allow 10 mm for truing up the scarf joint before gluing. It also allows room to later sand off the back of the dovetail if it's more than 15mm deep. 

     The 3 heel-block dimensions shown below (75mm, 55mm, 50mm) include this 10 mm allowance. The critical thing is to have 363 mm from the back of the 6 mm nut to the 14th fret. The finished dovetail adds 15 mm. 

     Note that new pages have been added to the Navigation Bar: 


     Table of Contents     Index By Subject 

GLUING UP THE NECK


     In Woody's shop the guitar building process  begins with cutting and gluing up the neck stock. Often Woody will build several necks at once to be a little more efficient with machine set up and use. Woody's methods for making a laminated neck will be presented here.