Wednesday, May 28, 2014

Flat Top Tele - Great Indoors

So go unlock the door
And find what you are here for
Leave the great indoors
The great indoors

In designing the neck block, there were a few means and methods I considered.  Flat top acoustic guitar neck blocks are typically made from a piece of lumber with the grain oriented from top to bottom panel, perpendicular to the direction of the strings.  A dovetail joint with some glue, or a tenon joint with one or more bolts through the joint, counter the forces from the strings that would otherwise separate the joint.  With a solid-body electric guitar, the neck bolts attach the neck to the bottom portion of the body, and the grain of the body and neck both run parallel to the direction of the strings.  Both of these designs makes use of the strong bending direction of the "body" part of the joint.  Since there will be neck bolts attaching the neck to this guitar's body like an electric guitar, I am orienting the grain of the Flat Top Tele like a solid body Telecaster, parallel to the strings.

Early in the design process, I considered the proportions of this guitar and decided on a body side dimension of about 3-inches.  Not having access to a band saw, my design constraints include the limits of using tools currently in the shop and readily-accessible lumber dimensions.  These factors drove the decision on making the 3-inch side dimension with a build-up of layers of 1/2 x 5-1/2 inch and 3/4 x 7-1/4 inch red oak hobby boards.  The process is similar to making a glulam beam.

Keeping things as simple as possible, I choose the top layer thickness such that it would not be necessary to route the neck pocket cavity.  With the acoustic bridge and saddle I'll be using, a 1/2-inch thick top layer should produce a setup such that the neck set angle can be fine tuned by shimming the neck pocket.  To achieve the width of wood I need for the upper bout dimension, I am also building up each layer from the 5-1/2-inch and 7-1/4-inch wide boards.

To avoid any weaknesses from lining up the joints, I will use a stagger between the layers.

Here are some pictures during fit-up, clamping and sanding of two slabs formed from 7-1/4-inch wide boards.

I used a full-sized drawing to make a template of the upper bout portion of the body, to keep final shaping to a minimum.  The template is cut from a piece of the red oak with the grain in the direction perpendicular to the neck block layers, as an easy way to provide an initial straight edge to work from in shaping the layers.  Here are pictures from before and after rough cutting the template with a jigsaw.

Next came trimming and sanding of the template, and then some experimentation to determine a procedure for using a combination of tools to shape the multiple cut-out slabs.  I knew this would generate a lot of sawdust, so I set up my plunge router in a portable saw table for using some drum sanding attachments and a flush trim router bit in the Great Outdoors.

I used a few screws to attached the template to an excess piece of red oak.  After getting used to handling the setup to minimize kickback working with and perpendicular to the grain, I had some initial success shaping the outside curves of the upper bouts and cutaway.  Hoping to complete the shape of the template with this practice piece, I began shaping the inside curves.  While working cross-grain on the inner curve of the bass side, the wood chattered in my hands and shook out of control.  In the blink of an eye, I had broken a piece off of the practice piece and had damaged the template.  I moved on to the inside curve of the cut out, with a much firmer grip, and similar results.

It was clear that using the router this way would not produce acceptable results.  Plan B calls for a few more steps and will make use of other means and methods for making the tricky cross grain inner-curve cuts.  The improved template will have extra portions joining the upper bout curves to the central portion of the neck block slabs.  This will provide stability as well as a convenient way to check alignment of the pieces during shaping and assembly.  I'll use the router to cut the outside curves, and I'll use the router and/or a combination flat drill bits, straight saws and drum sanders to cut and trim the inner curves.  I'll hold off on removing the extra portions of the neck block, until after gluing together and belt sanding all of the layers smooth, and just before attaching the bent-sides portion of the body to the neck block.

With so much design and building effort going into making this large neck block, I began considering an Ovation soundhole design that would showcase all of this craftsmanship.  I found some replacement parts on eBay and started visualizing the finished guitar in the comfort of the Great Indoors...

Tuesday, May 13, 2014

Flat Top Tele - Springtime Blues

Now, baby but I'll see you
Baby, in the spring
Just after the bluebird begin to sing.

With winter and some recent mandolin repair projects finally behind me, I got back to thinking about this project.  As much as I'd like to make an acoustic guitar body in the shape of a Telecaster, the sharp curves at the cutaway and where the body meets the neck can not be made with my home-brewed steam chamber and bending iron.  Instead, I will use a large neck block method of construction that is common in f-style mandolins for this prototype.  As with the difference in sound envelopes between f- and a-style mandolins, I expect the large neck block will somewhat reduce the sustain while adding some attack, enhancing the projection of the instrument compared to one built with a bent wood acoustic sound chamber with a minimal neck block.

It's been said that the best sound comes from the instrument that’s on the verge of collapse.  To put it another way, the art of stringed instrument building is a balancing act between providing structural integrity and allowing the front and back panels to vibrate freely.  A small box is inherently stiffer than a larger box, so the bracing in this guitar will be intentionally minimal to get the most pleasing sound out of it.  The bracing pattern I chose is similar to a design by Ettienne LaPrevotte from a guitar he made in Paris, ca. 1835.  LaPrevotte participated in numerous international competitions to improve the sound of his guitars. Here is a picture during the build of a modern copy of a LaPrevotte by Ian Watchorn.

Tacoma was a modern-day company known for innovations, such as non-traditional sound hole locations and minimal bracing patterns.  The bracing in some Tacoma models resembles the design by LaPrevotte.  In the Tacoma bracing below, two relatively deep main structural members run in the long direction of the guitar with a transverse member notched into the main members.  A small bridge plate sits just in front of the bridge plate and between the two longitudinal members.

Borrowing elements from LaPrevotte and Tacoma, the Flat Top Tele will have an H-shaped bracing pattern and an oval-shaped sound hole.  Here are scaled drawings of the final bracing and top panel layouts.