Top and Back Joining
Steps in Building a Guitar
An overview of the steps and skills necessary to build a guitar will be posted here each month. To follow the journal monthly, just hold the cursor over the Luthier Journal page in the navigation bar at the top of the page. A drop-down menu will appear with the journal entries listed by month. The journal will be updated during the first week of each month. The intention is to document guitar construction activities in the Woody Strings shop for a period of one year as several guitars are being built.
It might be necessary to explain here that Woody Strings is the registered trademark and business name of the luthier's shop. We are located Richmond, VA. Woody is not a real person but the nick name of luthier and owner of Woody Strings, Joe Lenzi. As referenced here, Woody and I are the same person.
The methods shown here work... with the space and equipment available to Woody Strings. There's always more than one way to skin a cat, however, and your shop might be different. Submit questions to Woody@WoodyStrings.com. Woody will be happy to respond.
Objective: To Build 5 guitars this winter, 2015-2016.
This could be a challenge for the size and equipment in the Woody Strings shop. Nonetheless, there will always be a guitar to work on while another guitar is waiting for glue to dry, or jigs to become free, etc.
Start Work: Sep_1_2015
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 Pro Max 16-32 drum sanding machine (pictured here) is about as small a thickness sander as a guitar maker can get away with. At this point, the target thickness is about 0.110" for the back and sides, and 0.125" for the top. This thicknessing should be done before the book-matched top and back are joined.
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).
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.
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. Multi-piece backs are a bit more challenging to join but can be visually quite interesting.
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 simple, it's effective, and it's all wood.
Once the rosette is inlayed, the over-thicknessed top goes back under the drum sander to flush the rosette with the top and take all to a thickness of ~0.110".
The dimensions given here for plate thickness are approximate and depend on the unique stiffness of each spruce blank. Across the written discussions on the web and elsewhere, it seems that there is only mild consensus among luthiers on final top thickness ranging from 0.095" to 0.125". My belief is that top stiffness influences tone significantly in the guitar. Equally as important, however, is the pattern and stiffness of the top bracing which will be discussed at a later date.
The Guitar Neck
Neck stock is roughed out and laminated together. This particular style of laminated neck is unique to Lenzi 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 keep it from twisting.
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 month to month 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 to a certain degree. 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.
Below is a photo of the Woody Strings necks that were built up and roughed out this month. Notice the maple laminations sandwiched between lengths of mahogany. We will discuss truss rods later.
23" lengths of Sitka spruce are dimensioned for bracing stock. The stock 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 sitka spruce that bracing consumes. Below is pictured a spruce billet and almost enough stock for one guitar.
The work described to this point has taken place at Woody Strings in Richmond, VA during the month of September, 2015. As the intention is to make five guitars this winter, each operation has been performed five times.
Play music and sing everyday and check us out again next month. Submit questions to Woody@WoodyStrings.com. Woody will be happy to respond.