The question is how much curvature? The modern Strat has an aggressive 241 mm (9.5″) radius while Gibsons have 254 mm to 304 mm (10″ to 12″) radius. Modern Jacksons, on the other hand, have what’s called “compound radius fretboards” which are really conical fingerboards which start out with a smaller radius at the nut and gradually get flatter (bigger radius) towards the other end. The Jackson is definitely one of my favorite axe in my arsenal. And, for this design, I will definitely have something based on the Jackson. The radii of the curvature starts at 304 mm (12″) and ends (at the 24th fret) at 456 mm (18″).

Compound radius cutting jig

For this to happen, we need, you guessed it: yet another router jig. The router rides on a platform that pivots on a stainless steel shaft which is oriented on an angle corresponding to the conical section with our desired start and end radii (304 mm and 456 mm). Swinging the mechanism back and forth will give you the correct radius at any given point in its entire length, thereby guiding the router over the block to be cut into a fretboard. This web article details this jig quite well: Compound Radius Routing Jig for Guitar Fretboards.

Now we sandwich the fretboard with 8 layers of carbon fiber laid up with laminating epoxy; 4 on top and another 4 at the bottom. The fretboard is vacuum bagged to remove excess resin and to ensure that there are no air pockets or bubbles that can ruin its sonic integrity.

Bamboo fretboard ready for layup	4 layers of carbon fiber
Bamboo fretboard sandwiched in between with another 4 layers on top	Vacuum bagged. Excess resin oozing out.

After 24 hours curing, it’s time to slot the frets. I love jigs. Jigs make tricky tasks easy to do accurately. Inspired by StewMac’s fret slotting miter box, I use another jig for cutting the fret slots. Finally, we trim the sides using a fretboard template with a pattern following router bit.

Released. Nice and smooth! Ready for trimming and slotting.

Slotted and trimmed

Further Reading

1. Guitar Fretboard Radius
2. Compound Radius: Explained
3. Compound Radius Routing Jig for Guitar Fretboards
4. Fingerboard

Next: Pearl Inlays

This installment concludes the Neck-thru construction series. As a final step, the neck is wrapped in 4 layers of carbon fiber to ensure maximum rigidity. We vacuum bag the whole thing to ensure that there are no air-pockets and bubbles and to make the carbon fiber layup hug the shape as tightly as possible while allowing the resin to cure.

Vacuum Bagging

Vacuum bagging is a method that uses atmospheric pressure to hold laminated components (laminating epoxy and carbon fiber) in place until the adhesive cures. Laminated components are sealed in an airtight bag. Atmospheric pressure exerts around 101 kPa (14.7 PSI) inside and outside the bag. A vacuum pump then evacuates air from the inside the bag reducing the pressure inside the bag. This negative pressure creates as much as 82 kPa (12 PSI) pressure differential that compacts the laminate resulting in excellent consolidation and interlaminar bonds. The vacuum also draws out trapped air (air-pockets and bubbles).

Vacuum bagging is a crucial step. I’ll provide some links below detailing the process.

Laying-up the first carbon fiber layer	Laminating epoxy applied in between layers
Yet more layers of carbon fiber	Vacuum bagging the whole thing
Excess resin being drawn out by negative pressure	The carbon-fiber wrap ends at the neck-body heel

Perfection! The Final Result

(Click to zoom)

Perfect!

Further Reading

1. Basic Vacuum Bagging
2. Vacuum Bagging: Basics
3. Vacuum Bagging Techniques
4. Vacuum Bagging Equipment and Techniques for Room-Temp Applications

Next: Compound Radius Fretboard

Now, we install our new Carbon-Glass Truss Rod. We begin by cutting the truss-rod slot using a router. At the headstock-end of the neck, an aluminum block is embedded for additional strength and rigidity. In all guitars, the weakest point is this area where the neck meets the headstock —a critical breaking point. In addition to improved rigidity and strength, any additional support here will enhance tone and sustain. The aluminum block also serves as a foundation that evenly distributes the load of the tensioned truss-rod over a wider surface area. This aluminum block is glued using high grade structural epoxy. The nut sits in direct contact above this block further enhancing sustain.

A cavity at the headstock behind the nut is provided with ample space for a hex key wrench to reach into the stainless steel Allen adjustment screw for tightening the truss-rod. Another cavity behind the aluminum block gives the truss-rod head (see Carbon-Glass Truss Rod) some freedom of movement.

With the cavity routed to specification, we begin installing the truss-rod. The stainless steel anchor at the body-end of the truss-rod is glued, again with high grade structural epoxy. Finally, to ensure against the possibility of the rod rattling, we add some silicone sealer into the channel. The sealer will dampen any unwanted vibrations that can spoil the sonic quality of the neck.

Routing the truss channel	Aluminum reinforcement block
Gluing the anchor using structural epoxy	Truss-rod installed!

Routing the Body

For the body part of the neck-thru section, we will route the pickup cavities, the bridge height adjustment screws, the string ferrules where the strings pass through the body and the tail block —a piece of aluminum at the bottom that terminates the strings and where the ball-ends are anchored with easy access at the back.

Body side view transparency

For this design, we will have 3 single coil (DiMarzio Area 69) pickups. The pickups are body mounted and can be installed from the back of the guitar (how many times have you ever wanted to change pickups without having to loosen or take off the strings?). For that reason, the pickup cavity goes through the entire neck-thru body but not through the entire body (see figure at the right).

The body top also has a mild curvature which we will shape using yet another jig. That’s what we will do first. The images below show the jig in action. The jig rides on two rails with the router mounted on an acrylic plastic base which is mounted on two wooden sides with the desired curvature. I use this type of jig anytime I need some curvature —works well all the time.

Curvature-shaping jig

Jig shaping the body top

You might be guessing that I use a variation of this jig to shape the fretboard as well, but no, I did not. This guitar design has a compound radius fretboard for which this type of jig is not suitable. More on that later.

Now let’s move on to routing the pickup cavities. It starts with proper preparation and layout. I have prepared beforehand acrylic plastic templates for single and double coil pickups for standard Strat and Les Paul style pickups. I cover the entire area with masking tape and draw the outlines first. It was tempting to use the Strat’s pickup positions which give it its distinctive sound, but 1. I use a slightly shorter 644mm scale (25.35″) and 2. I have 24 frets (the Strat has 21). 1 is not a problem —it can be scaled. The real deal breaker is 2. The Strat’s neck pickup sits at around the 24th fret position. Hence, for this design, I compensated a bit and came up with a hybrid Ibanez Jem (I am a proud owner of two of these lovely Jems) and Strat layout. I use the acrylic plastic template to guide the router using a pattern following bit. Before routing,I pre-drill the cavities using Forstner bits to minimize the router’s work.

Layout

Routing the pickup cavities

Finally, at least for the neck-thru body, we drill the top string ferrules, the bridge height adjustment holes and the aluminum tail block. The bridge height adjustment is also accessed from the bottom. There will be no unsightly screws at the body’s top.

Drilling the top string ferrules. I love laser guided drills!

The tail block at the bottom

Further Reading

1. Neck Construction Tips and Techniques
2. Truss Rod Installation

Next: Neck-Thru Construction (part 3)

The "Log"

Influences

I like the basic idea behind the original Steinberger design. The idea is to keep only what’s needed —the bare essentials that define an electric guitar. The idea actually started from Les Paul himself when he started building “The Log” which became the precursor to the legendary Gibson Les Paul. The Log, as he likes to call it, is essentially a Gibson neck glued to a 4×4 block of solid pine. The body sides were added only for appearance to make it still look like a guitar. An ugly contraption, but I digress.

Classic Steinberger

Ned Steinberger, the man behind the Steinberger, got rid of the body sides and also got rid of the headstock altogether. It is also one of the first of a breed of guitars that used modern materials such as carbon fiber and graphite.

Developed in the late 70s, the Steinberger was ahead of its time. It still is. However, the headless and bodiless design never really took off as its inventor intended. Except for a few devoted followers, guitarists in general never got used to it. Later designs kept the headless neck but added at a body. Some designs also include a headstock. I think these moves are attempts to win the hearts of the general public. Looks matter and for some reason, guitarists are rather conservative when it comes to shaps. Is this perhaps because the guitar’s shape evokes the graceful female figure?

Following the basic premise that the essential factors that make an electric guitar is the neck, just enough body to allow a bridge and a tailpiece that anchors the strings, pickups, and of course the tuners, we’ll start with the middle neck-thru section. This is the most crucial part of the guitar and should be structurally sound and sonically excellent.

Cycfi Neck-thru design

In the section on bamboo preparation, we detailed the manufacturing of the composite material intended for the construction of the central neck-thru piece. This consists primarily of laminated bamboo interspersed with carbon fiber. In this section, we will walk through the process of actually shaping the material into our final neck-thru form.

Cutting the Outline

Trimming with a bandsaw

Compared to hardwood, bamboo planks are a lot more difficult to machine. Router bits and planer blades easily get dull because of the tougher grain structure. Also, while bamboo is very tough, it is very easy to tear-out the bamboo’s perfectly unidirectional grains. It is best to remove as much material as possible prior to routing. A bandsaw cuts excess material very close to, but outside the outline. 6 mm (¼”) bandsaw blades make sawing intricate curves easy while wider 12 mm (½”) blades are good for straight lines. Inner cavities are best pre-drilled using Forstner bits.

Pattern Bit

12.7 mm (½”) diameter, 19 mm (¾”) long pattern following bits (with bearing on the shank) guide the router through templates made from 19 mm (¾”) thick MDF board. It is best to cut slowly with successive 6 mm (~¼”) deep passes. As a general rule: don’t attempt to remove too much wood. Multiple passes work much better than removing a lot of wood at one time. Use the router as a precision cutter.

The router bit rotates counter-clockwise. In some places, the counter-clockwise movement of the bit will cause splinters when the blade pushes the end-grain outward. In this case, it is better to flip the body where the template is at the top then use a flush trim bit with the bearing at the end instead of the shaft. A hand-held plunge router serves this purpose so I do not have to change bits and flip the workpiece.

Routing the body	Routing the head
Flipping the template and using a flush-trim bit	Drilling the machine-head holes

Shaping the Neck

End Mill

For shaping the back of the neck, my favorite tool is the trimmer router with a solid carbide 4-flute 12.7 mm (¼”) end mill. These are typically used for machining metal, but are surprisingly well suited for shaping bamboo. As always, treat the tool with respect. This is a dangerous tool.

After rough shaping, the belt-sander is another indispensable tool. Every once in a while, the neck profile is checked against profile templates made from acrylic plastic to make sure that the shape is true to spec. For those intricate curves, the Dremel is a very capable and versatile tool.

Shaping the neck-body heel	Using a trimmer router with end mill
Smoothing with a belt sander	Checking against profile template
The versatile Dremel with a fine cutter bit	This time with a drum sander

Further Reading

• Les Paul, Chasing Sound
• Steinberger History
• Steinberger
• Routers Go Left!
• Go with the grain on curves to prevent splinters
• Tips to Reduce Router Tear-Out

Next: Neck-Thru Construction (part 2)

Do we need an adjustable truss rod? Unlike wood, carbon fiber is not affected by temperature or humidity. Some guitar builders using carbon fiber proclaim that they don’t need to install a truss rod because necks made from carbon fiber are already stable and will not shift, warp or bow over time. However, while that may be true, these builders miss a crucial point: neck relief. The neck should not be perfectly straight.

Strings oscillate side to side and also up and down. This oscillation is most pronounced at the center (the 12th fret). A little bit of neck relief —a slight bow— is required to allow the strings to vibrate freely. You can check neck relief by placing a ruler across the frets or capo at the first fret while pressing down at the last fret. The clearance at the half-way point (typically the 8th fret) is the neck relief. There is no ideal value for neck relief. It will depend on a few factors, most importantly your playing style. However, for an electric guitar, 0.025 mm (0.001″) string relief is typically recommended. This value is sub-millimeter, so be sure to use a feeler gauge if you want to be precise.

So, do we need an adjustable truss rod?  Yes. It is the only means to make the neck relief adjustable. Different string gauges will pull from 40 kg (88 lbs) to 50 kg (110 lbs) of force. The string’s tension naturally tends to bend the neck giving it a a slight concave curvature. The stiffness of the neck and the truss rod counteracts that force. An adjustable truss rod will allow us to control just the right amount of relief. Too much and the action will be too high making the guitar a pain to play. Too little and the strings will not have enough freedom to vibrate freely which will result in string buzz.

Fit and lite

Allow me to present the carbon-glass fiber truss rod. I’m quite pleased with the results. A truss rod of comparable strength made from steel is at least 3 times heavier. A stainless steel rod 6.3mm dia. 510mm in length weighs 127 grams whereas our hybrid carbon-glass fiber rod (the one I am using) 4.8mm by 10mm, 510mm in length is just 41 grams.

(Click to zoom)

Truss Rod Head

Truss Rod Tail (anchor)

The rod is made of 8 layers of carbon fiber (right now, I am using carbon fiber twill weave cloth but in the future I intend to use unidirectional carbon fiber cloth). 4 layers + 4 layers of carbon fiber sandwiches 6 layers of fiber glass weave for a total width of 4.8mm.

The head is machined aluminum alloy with a stainless steel allen adjustment screw. The adjustment screw has a finer thread than typical truss rods. This gives us finer control over adjustment of relief. Recall that we merely want 0.025mm of relief. The rigidity of the combined bamboo and carbon fiber neck is more than adequate to counteract the string’s pull. All we need is a little nudge.

The tail is anchored to the other end of the neck near the body using a short stainless steel rod anchor. To avoid galvanic corrosion —when one conductor (aluminum) corrodes when in electrical contact with a different type of conductor (carbon fiber), the whole thing is sealed with a few coats of clear polyurethane.

This is a single action truss rod. Modern guitars are equipped with double action truss rods. A double action truss rod has the ability to pull or push thereby compensating for back or forward bow. We don’t need that. Our hybrid composite neck is guaranteed not to back-bow.

Further Reading

1. Thoughts on Neck Relief
2. String action and setup
3. Adjusting Truss Rods
4. Adjustable Truss Rods
5. Truss Rods
6. Guitar Neck Truss Rods
7. BRW Necks
8. Neck Tilt, String Relief & Truss Rod
9. Truss Rods – How They Work – Including The Bi-flex. – Telecaster Guitar Forum
10. Hot Rod Adjustable Truss Rods

Next: Neck-Thru Construction (part 1)

Luis and Clark Carbon Fiber Cello

Recently, improved manufacturing techniques are reducing the cost of carbon fiber. Carbon fiber is now becoming a mainstream material finding its way into applications that require durability, high-strength, low weight and insensitivity to humidity and temperature changes. Its exceptional strength-to-weight ratio is the main reason why it is a material of choice in the aerospace industry and much later, for F1 race cars and high end sports cars. Now, it is increasingly common in consumer goods such as tennis racquets, golf clubs, archery equipment, tripods, fishing rods, laptops, bicycle frames and parts, aftermarket automotive body-panels and parts, and… you guessed it, musical instruments.

Stockbridge Summer Music’s 18^th season, July 7, 2003, was an unusual event. Cellist Luis Leguia gave the opening recital featuring standard works from Bach, Vivaldi, Faure, and Kodaly, with a cello made not from wood, but carbon fiber. The cello is his creation.  In 1989, he began experimenting on a prototype carbon fiber cello in his basement. The result is an instrument with exceptional sonic quality, projection and volume; good enough for the discerning professional musician. A decade later, Luis Leguia started his company named Luis and Clark and began building carbon fiber violins, violas, cellos and double basses. Now, a carbon fiber cello costs $7,139.

Carbon fiber is stronger than even the hardest wood. There is no comparison. It has a tensile strength of 565 kN/cm² which is more than 10 times than that of steel with a tensile strength of 37 kN/cm. Yet, it is 4 times lighter.

But then again, a strong material does not necessarily make a good instrument. Early carbon fiber composite based instruments sounded dull and lacking in character, noted Charles Besnainou, an instrument builder at the Paris Conservatoire and France’s National Center for Scientific Research. Since 1986, Charles has been studying and building composite instruments. Over time, he has learned the fine art of tweaking the balance between the material’s rigidity and flexibility (its viscoelasticity) to make the response more like “tonewood”.

Does that sound familiar? Is this again another case of “tuning” the material?

From the descriptions above, it is immediately apparent that carbon fiber is a suitable candidate for building guitars which require high strength to counteract the tendency of the strings to pull the head towards the body with a total tension in excess of 45 kilos (99 lbs) while being extremely low weight and thus less fatiguing to carry around.

A process, called a wet layup, involves laminating multiple sheets of carbon fiber fabric soaked with two part epoxy resin and laid up over a fiber glass mold. Before layup, the mold is first prepped by polishing it with carnuba wax and applying a thin layer of release agent, typically PVA, to ease separation when the resin cures. After layup, the laminate and mold are placed inside a plastic vacuum bag. Air is drawn out using a vacuum pump to eliminate bubbles from forming and to remove excess resin. The piece is then set aside to allow it to cure. This is the same process used in fabricating fiber glass composites.

Here’s a small gallery of musical instruments made of carbon fiber:

“The Handle” by XOX Audio Tools	Blackbird Super OM	Carbon Fiber Mandolin by NewMAD
G1 Seven by Gus Guitars	Luis And Clark Violin, Viola, Cello and Double Bass
WS1000 6-string acoustic by Rainsong	Flute by Maltit	Adamas 2080

Further Reading

1. Japan Carbon Fiber Manufacturers Association
2. Carbon fiber
3. Bacon’s breakthrough
4. Carbon-Fiber Cellos No Longer Playing Second-Fiddle to Wooden Instruments
5. A Summer Cello Expedition with Luis and Clark
6. Carbonfibre
7. 6 Sexy Carbon Fiber Guitars
8. Acoustic characteristics of carbon fiber-reinforced synthetic wood for musical instrument soundboards
9. Beyond Rosewood and Spruce – How guitar makers are using space-age composite materials to create new designs and new sounds

Next: Specifications