Part 2: Designing The Middle Section
This post describes the design of Thor’s body’s middle section. The design incorporates both traditional and innovative design elements. The body’s middle section is made of 25mm (1 inch) Ash, with multiple layers of top carbon fiber and covered by a removable carbon fiber bottom. The printed circuit boards, pickups, and sustain drivers are all mounted in the middle section. A neck pocket is included, into which the neck is bolted. The strings pass through the body through string ferrules. A fixed bridge is mounted on top and can be adjusted in height at the bottom with M5 Allen screws.
The first Alpha prototype featured a neck-thru design. A continuous plank spans the entire middle section from head to body. I switched to a bolt-on neck design with Thor, but I kept the “middle section”: that plank of wood that sits at the middle. Here’s a look at the middle section of the first Thor prototype:
The original Thor prototype, as seen in the image above, also had a body frame that contained the magnets that held the bottom cover in place. The original Alpha prototype did not have that frame.
The middle section and the body frame were initially separate components. We combined the body frame and the middle section in the production version. We’ll simply refer to both as the middle section. Here’s a quick video of the middle section and bottom cover:
To CNC Or Not
Previous Thor prototypes (there were a few) were all hand-crafted one-offs. For production, a big question was whether to use CNC. I had all the designs in 3D CAD anyway! In the end, since we only have less than 20 instruments to build for the first batch, I decided to keep it handcrafted, but with special custom-made jigs and routing templates for consistent and well manufactured results.
First, I had to digitize the design from the original hand-made model. Here’s a never-before-seen alpha master (picture at the right). This is what we use to create our molds.
Because the back covers had to fit perfectly, I had to recreate the design in digital form. There were minor differences between the original CAD and the actual master, and the molds derived from it. I traced the bottom cover using a 50 mm grid, scanned the image, and re-traced the shape in CAD software. Because my scanner was not quite accurate, I had to calibrate the grid by applying skews and distort edits in Photoshop to have the lines align to the digital grid of the same size. I don’t have a large scanner, so I had to cut the trace into four A4-sized parts, and align each part later in Photoshop.
And now that I’ve captured the shape in digital form, I can perfect the design of the middle section, with manufacturing in mind:
I love this design. There is plenty of room for the Infinity electronics. I dislike small, cramped cavities. I got rid of the big chunk of wood that that ran through the middle section. In the end, when the pickups, drivers, and circuit boards are installed, that will be mostly routed out anyway. Unlike the previous Thor prototype, this one has an unobstructed clean space for the controls as well as ample provisions for expansion.
I cannot overstate the significance of carbon fiber’s resonant and acoustic properties. CF is extremely vibrant and resonates very well across the entire audio frequency spectrum. The body design reinforces that desirable property of CF. We’ll see later that multiple layers of carbon fiber will be laid on top of this wooden middle section. The top resonates, and the vibration is transferred to the bottom carbon fiber cover via the middle section.
Compared to solid-body guitars, the guitar is acoustically louder, but not as loud as an acoustic guitar and without the unwanted low-frequency resonances that cause howling feedback when played loudly.
Another feature inherited from the Alpha project, is the balanced weight distribution. The rationale is that guitar should neither be neck-heavy nor body-heavy. The center of mass should be somewhere between the 22nd and 24th fret:
That’s all for now. We’ll have more of the middle section and CF top next time in Part 3 of the Manufacturing Thor series.
Nice work! I’ve been building guitars with a similar frame architecture for a few years now. I work in aluminum but I’m looking forward to hearing your carbon fiber machines in action!!
This is a very heartening report, Joel, as was Part 1. Thanks so much. Everything you’re doing makes a lot of sense – I’m ALMOST as excited about the sonics and mechanics now as I am about the electronics!
So great Joel, so glad I jumped in on this project! I’m even more stoked now, knowing that you’re hand building the first batch. I love your attention to detail! I’m on the edge of my seat waiting for part 3!!!