Presenting the Carbon Fiber-Bamboo Guitar prototype.

I still have to write more documentation. I am terribly lagging behind, but I’ll definitely have more time in April. Anyway, for now, here are some high resolution pictures. You should compare these against the original 3D images. I am immensely having fun playing the final prototype. Now I am focusing on production.

If you got here from nowhere, you’ll be missing out if you don’t check out the project in full. Nevertheless, pretty images are always nice to see.

(Click images to zoom)

Headstock with locking Grover tuners installed (click to zoom)

Head back (click to zoom)

It’s been a while. My last post was in November 3. Actually there’s one more unpublished post in December about “Sustain” Myth and Science but I need more time to do tests and analysis, so that will have to be posted later. The project is very active, thanks to help from some folks. I am having loads of fun testing the prototype. The guitar sings and weeps like no other. There are two more prototypes underway and the development is now focusing on production. We’ll have more on that later. Now, it’s about time to continue documentation.

The Bind

Stainless Steel Binding (click to zoom)

Binding the guitar using stainless steel proved to be very tricky. This is the first time I used stainless steel as binding material. Plastic is very easy to handle. Stainless steel is many times more difficult. No wonder no one is using this for binding. But the end result is gorgeous and it is all worth the extra effort (image at right).

The first issue was determining the gauge to use. Plastic binding generally ranges in width from 1.5 mm (~0.060″) to 2mm (~0.090″). At 1 mm, stainless steel is very difficult to bend into form. At 2mm, I’ll need a press to force the material into shape. One thing for sure is that I need to improve on metal working skills. For now, I settled for 0.5 mm stainless steel sheets.

Cutting the stainless steel sheets into strips is another matter. Forget about manually cutting stainless steel sheet into 6mm (my desired binding height) strips. I tried, but can’t do it cleanly and quickly. In the end, I settled for either laser cutting or water jet cutting. Both have drawbacks. With water jet, the edges are somewhat serrated with micro cut marks that need to be filed smooth. Laser on the other hand, can’t cut long and thin strips without micro bridges at intervals to hold the sheet into place. Without the micro bridges, the heat from the laser tends to make the strips twist and curl. It is easy to cleanly file and sand the micro bridges.

Binding The Fretboard

The stainless steel strips are glued in using structural epoxy specially formulated for bonding metal and wood. Glue is applied to the back side of the strips and the fretboard, making sure that the surfaces are sanded well for good adhesion. The binding is then placed into the routed-out groove and secured with tape making sure there are no gaps.

Applying epoxy specially formulated for bonding metal and wood.	Securing the binding with tape and wiping off excess glue.
Yet more tape to fully secure the binding and ensuring that there are no gaps.	Final wrap with taut vinyl tape. Now the neck looks like a Mummy!

Binding the Headstock

Before gluing, the stainless steel binding strip is pre-formed for a perfect fit around the headstock’s profile. This is done manually for now. Next time I’ll definitely use a template (water-jet cut) for bending the binding into shape, both for the body and the neck and headstock. After applying glue, the same procedure used in binding the fretboard is applied.

Applying epoxy on the headstock binding groove.	Applying epoxy on the back side of the pre-formed binding strip.
Carefully positioning the binding strip.	Securing the binding with tape: A fully Mummified neck.

Installing Frets

The layered carbon fiber-bamboo-epoxy fretboard has characteristics totally different from hardwood when it comes to installing the frets. With hardwood, the fibers easily grab the barbs immediately after the fret is pressed or hammered in. With CF-bamboo, I had difficulties using the traditional approach to fret installation. First, unlike wood, bamboo end grain splinters easily. There’s barely enough fiber cohesion to make the bamboo end grain reliably grab the fretwire barbs. While I can successfully hammer in frets into bamboo, I am not sure how reliably it will hold the frets in the long run. The carbon fiber outer layer adds to the difficulty. When a fretwire is forced into a tight fret slot, the carbon fiber-epoxy does not seem to sufficiently grab hold of the barbs. The epoxy tends to chip at the edges when the barbs are hammered or pressed. Post analysis shows that the material does not “heal” around the barbs enough to hold the fret in place as wood does.

Searching around for solutions, I found this article in the web offering a different approach, cutting a wider fret slot and using epoxy to hold the fret. Even with hardwood, the author notes that the barbs often lose their grip, and the frets pop out of the slots, leading to buzzing while playing. Surely, I too had problems like this before. That is why I always glue the frets in to make sure they sit firmly in the slots. Doing so also improves the tone considerably. This StewMac article says why: Fret jobs are often too loose. Super gluing your frets improves fret-fretboard coupling resulting in superior tone.

The fretwire is pre-bent to the curvature of the fretboard using a simple fret-bender jig (below). The fretwire slides in at the right and rolls through the middle, then exits the left roller bending it into the right amount of curvature. The amount of curvature does not have to be exact because the frets will be clamped in later.

Fret Bender Jig

To accommodate the binding, the fret’s tang must be trimmed at the ends. I do not have a fret tang nipper yet, but a good end-cutter will do just fine. The end-cutter’s cutting face is ground and sanded to make it as flat as possible for a clean cut without requiring a lot of filing afterward.

Fret End Cutter

Notched Tang

The fretboard slot is cut using a miter saw with kerf that is is wide enough to have the fret tang plus the barbs slip into the slot without resistance. With this method, we will not have to hammer or press the frets in. Since epoxy will hold the frets, we do not need a very tight fit. Masking tape is applied such that only the fret slots are exposed to ensure that excess epoxy does not get into the fretboard. After test-fitting the frets to see if they all fit well into each slot, epoxy is injected into the slots. Finally, the frets are clamped using a clamping caul made from acrylic plastic with strips along the edges to press the fret ends firmly and rubber padding in the middle to evenly apply pressure.

Injecting epoxy into the fret slots	Frets ready for placement
Frets placed. There's no need to hammer or press the frets. The frets slide in easily.	Clamping the frets until the epoxy cures overnight.

Dressing the Frets

After the epoxy cures (I give it ample time, typically leaving it to cure overnight), it’s time to dress the frets. The fret ends are trimmed flush (again using the end-cutter) and beveled using a fret-end file block with an edge cut at a 30-degree angle where a flat file is held in place by screws (below):

Fret-end file block

Fret crowning tool

This method ensures that the frets are seated perfectly and very little effort is needed in leveling the frets. Using a perfectly flat sanding block with a 320 grit high quality sand paper, the frets are leveled starting from one end near the body, continuing towards the nut. After several gentle passes along the entire length of the fretboard, a narrow and shiny flat top should be noticeable on all frets indicating that the frets are leveled.

The fret edges are rounded off using a fret crowning and burnishing tool (above). Starting with 220 grit, proceeding to 400 grit then 600 grit sandpaper held over the tool’s groove, each fret is shaped and burnished until there are no more sharp edges and the frets feel perfectly smooth. The frets are finally polished with a polishing wheel using the dremel.

Further Reading

1. Fretting
2. Super glue your frets to improve your tone!
3. Fret Dressing using “Essential tools” that don’t break the bank
4. How to Install Bindings
5. Fretting Simplified
6. Installing the Frets in a Fretted Stringed Musical Instrument

Here are a couple of snapshots:

The Fret Markers. The motif is the reverse (white on black) pipe-organ keyboard.	Next: Pearl Inlays Zooming in a bit on the fret markers. Mother of Pearl is just so elegant!
Testing the LED lights. Small white LEDs are inlaid in the middle of each fret marker.	The logo. The real thing looks even better than the original 3D rendering.
Zooming in on the logo. The logo is hand crafted. For production, it might be better to have it cut using laser or water-jet.	One more snapshot. The gloss is just to protect the inlay. We haven't even buffed yet. The final result will have a mirror finish!

The Craft

Mother of Pearl Blanks

Shell inlays (not the cheap plastic substitutes) add value to an instrument. You can find real shell inlays only on priced high-end or custom-made instruments. Guitars endowed with shell inlays, from the simplest to the most elaborate, are works of art akin to fine jewelry.

Inlaying decorative shells such as Mother of Pearl (MOP) and Abalone takes time, patience and perseverance to master. The craft involve:

1. Cutting suitable shells into blanks
2. Grinding the shell blanks down to a flat surface
3. Cutting the blanks into the desired shape
4. Routing the cavity from the wood
5. Inlaying the shell into the routed-out cavity

I’m not about to delve into the fine details of the craft but I’ll provide various links below that you can find useful if you want to get serious about this craft. You can also buy books on the subject. My favorite is the definitive bible of pearl work: “Pearl Inlay” book by James E. Patterson.

Jeweler's Saw

While the art of inlaying has changed little over the centuries (the craft began in East Asia during the Tang dynasty), it is a lot easier now than it was before. Modern tools certainly made inlaying easier. The versatile Dremel rotary tool is an indispensable tool for routing inlay cavities as well as for cutting, sanding, trimming and deburring shell pieces. You can buy precision jeweler tools that are well suited for fine shell work such as the Jeweler’s Saw with fine blades from 35 teeth per inch (size 5) to 84 teeth per inch (size 8/0). If you do not want to go through the messy trouble of cutting and grinding the raw shells, you can also buy rough-cut shell blanks ready for cutting your design (that’s what I do) or even pre-cut shells for typical designs such as Les Paul square or trapezoid fret markers, dots, diamonds, etc. Finally, if you have access to laser or water jet cutting services, you can get extremely accurate results with minimum effort —simply draw the design using a vector drawing software such as Inkscape, Corel Draw or Adobe Illustrator.

Cutting the Blanks

Skipping the laborious first step (preparing the blanks from raw shell), I start out with some nice Mother of Pearl blanks. You can buy either plain or figured blanks. There are various grades. Exhibition Grade is the most expensive. It is flawless in every respect with no discoloration, no wormholes, no growth fractures and no undesirable flaws. AAA Fancy Grade is like exhibition grade but with only one flawless side. A Grade is almost like AAA with one flawless side but with potentially small flaws that can easily be avoided. Standard Grade is the cheapest entry-level grade. I buy from an MOP supplier in ungraded bulk. I grade the blanks myself and choose only the highest grade. Some blanks may have rather nice features except for one or two flaws that can be avoided.

For the prototype, I manually cut the logo using a Jeweler’s saw. For production, it might be better to have the shapes cut using laser or water-jet. For most of the work, a medium size blade will suffice. For more intricate curves, I use a finer blade, but I never had the need for sizes finer than 1/0. It takes time to master the use of the saw and it is perfectly normal to break a few blades before becoming proficient.

Rule 1: be patient.

Rule 2: be patient.

Rule 3: be patient!

Rule 4: see rule 1 to 3

Shell cutting sawboard

So you know I love jigs. For cutting the shapes, I devised two jigs. For the fret markers, I needed a jig that will give me accurate and repeatable round corners. I built a jig with a small adjustable swinging clamp (see image below). The jig is positioned adjacent to a table mounted Dremel with a small drum sander. The distance from the pivot to the edge of the drum sander will be the round corner’s radius.

The other jig is a standard sawboard for cutting the pearl blanks. You can easily construct this jig from plans provided in the links below, or the easy route: just buy one from StewMac. I built mine from plans I got from “Pearl Inlay” book by James E. Patterson (see picture at right). It is very similar to the one from StewMac. I use a small aquarium air pump and hose for the dust blower —a must if you want accurate results.

Cutting the logo with a jeweler's saw and a pearl cutting sawboard	Patience! Tons of patience!
Smoothing with a needle file	Shaping the fret markers using a round corner shaping jig and the Dremel table-mounted.
Smoothing the truss rod cover after cutting	The truss-rod cover ready to be placed

Routing the Cavities

I use four routers: a 1500-Watt Makita 3600H for heavy routing, a 1200-Watt Ryobi ERT241200 plunge router for moderate routing, another 400-Watt Ryobi EVT400K trimmer router for light duty routing and trimming and finally, a Dremel rotary tool for precision routing. The Dremel is not just a router. It is such a versatile tool; indispensable for intricate work, including, but not limited to, routing. I love this tool!

The Dremel is the perfect tool for routing out the inlay cavities. I use a Dremel router base and various small end-mill bits. I’m quite disappointed with the plastic Dremel router base. While it gets the job done, I’m not quite happy with the fine adjustment. I’d probably get a StewMac Precision Router Base soon or build one myself.

To transfer the design to the material to be routed out, a thin layer of white water-based paint is first applied. A fine point inlay scribe traces the shapes’ contours while holding the inlay pieces down. Smaller, more intricate parts may be temporarily glued down using spray adhesive.

Tapered router bit

4-flute end mill

I start off with a 4-flute 3.18 mm (1/8″) solid carbide end-mill to cut larger chunks of material close to, but without touching the outline. I then finish with a fine solid carbide cutter tapered router bit. These bits taper from 0.48 mm (0.019″) to 0.8 mm (0.032″)) —perfect for fine inlay routing.

The headstock painted with white water based paint and scribed with the inlay pattern.	Routing the logo cavity. The small hose is connected to a small air pump to blow away dust.
Cavity fully routed out with the logo. The layer of paint easily wipes off with a damp cloth.	Gluing the inlay pieces with black epoxy. Making sure that excess glue is wiped off, the logo is now ready for leveling and sanding.
Rough routing with 3.18 mm end mill	Detail routing the fret markers using fine tapered router bit

Further Reading

1. Pearl Inlay (book) by James E. Patterson
2. Mother of Pearl
3. The Inlay Pages
4. Pearl Inlay by Sean J. Barry
5. Mother-of-pearl
6. Inlay (guitar)

Next: Neck Dressing

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)

Selected Bamboo culms are sliced into straight strips 25 mm wide 1.2 meters long. You would want to choose large diameter culms that are more or less straight to begin with. Not all parts or the culm can be utilized for our purpose. Only the middle section is usable. The lower part of the culm near the roots, while having a larger diameter and thicker wall, has nodes that are spaced too close together. The upper part, on the other hand, is too small in diameter.

To cut the bamboo into straight strips exactly 25 mm wide, I devised a special double rip saw using two circular blades. A pre-cut bamboo section, 1.2 meters long, is strapped firmly in place while a movable assembly carrying the double-rip saw and motor cuts through the entire length of the bamboo section. After each cut, the bamboo is turned a few degrees clockwise and the next pass is made, repeating until the entire diameter of the bamboo is consumed.

At this point, only the internal nodes will be holding the bamboo section together. Applying a moderate amount of pressure will easily crush what’s left of the internal nodes that are still holding the bamboo. We shave off what’s left of the nodes and any protrusions. This can be done initially with a sharp knife and later with a jointer, then cleaning up with a thickness planer.

Treatment

The end result is a bunch of nice and straight bamboo strips. The strips are sun dried and air dried for 3 weeks. After drying, the strips are boiled in water for 30 minutes to eliminate its natural starches and sugars, making them unattractive to termites and other pests. This will also make the bamboo less prone to shifting, expanding and contracting due to changes in temperature and humidity. The strips are then dipped in a 60% borax-40% boric acid solution for further preservation. Both boric acid and borax are great as insecticide and anti-fungal preservatives. After treatment, the strips are sun dried and air dried again for a few days until they attain 10% to 15% moisture content. Now the strips are ready for lamination.

Lamination

The strips are grouped into 25 mm and 50 mm bundles, vertically oriented with their narrow edges facing up. Vertical orientation has better structural strength compared to horizontal orientation (with their wider edges facing up). Laminating epoxy (the same formulation used for laminating carbon fiber) is used to glue the bamboo strips. 2 tonnes of pressure is applied while allowing the epoxy to cure using a small press constructed just for this purpose (picture below). The epoxy resin slow-cures in 24 hours (faster if moderate heat is applied).

Laminating press

Laminated Bundles

The planks undergo another thickness planer session to even out any irregularities. After making sure that the planks are perfectly squared up, we are now about to prepare one end of the planks for a 14 degree scarf joint. This will later become the neck-thru’s headstock.

A jig is utilized to cut a smooth surface, exactly 14 degrees, using a router. The jig serves as a guide for the router, mounted on a movable acrylic base. The router base slides over two edge guides while the cutter bit cuts the surface material at the desired 14 degree head angle. The result is very accurate and easily repeatable. This jig can be found in Patrick Spielmans book “Router jigs and techniques”. A complete description of this technique can be found here.

Squaring-up the planks —another thickness planer session	Scarf-joint jig
Gluing the scarf joint	The final scarf joint —perfection!

Two outer 50 mm planks and one inner 25 mm plank make up the central thru-neck construction. These are laminated together with up to 6 layers of carbon fiber for optimum structural strength. The image below shows the layering.

Laminating the first carbon fiber layer	Yet more layers of carbon fiber
All good and ready to press	View showing the 14 degree scarf joint

Finally

Another 24 hours of curing. Our patience has paid off. We have a nice bamboo-carbon-fiber plank ready for routing and shaping! Yeah!

Now we are ready for routing

Further Reading

1. Smoothing a scarf joint with the router
2. Simplifying Scarf Joints

Next: Carbon-Glass Truss Bar

Selection

There are some 1,400 species of Bamboo. The first obvious task is to select the right species suitable for building an electric guitar. Availability is a prime concern, which narrows the alternatives down to a few species that are specifically cultivated for various purposes. Two species are of particular interest:

1. Dendrocalamus latiflorus Munro
   • Common names:
     • English: Sweet Giant Bamboo
     • Chinese: Ma Chu
     • Japanese: Ma-chiku
     • Tagalog: Botong
     • Burmese: Wa-bo
   • Maximum height: 20 meters
   • Maximum diameter: 20 cm.
   • Internode length: 20-70 cm.
   • Spineless
   • Used for construction materials, daily uses and pulp making
   • Straight to moderately arched
   • Distribution: Taiwan, Southern China, Northern Myanmar
2. Bambusa blumeana Schultes F
   • Common names:
     • English: Giant Thorny Bamboo
     • Japanese: Shi-chiku
     • Chinese: Ci-zhu
     • Tagalog: Kawayan tinik
     • Malaysia: Bambu Duri
   • Maximum height: 20 m
   • Maximum diameter: 20 cm.
   • Internode length: 20-60 cm.
   • Spiny branches
   • Arched with slightly bulging nodes
   • Superior strength and durability for construction materials and bridges
   • Distribution: Tropical and subtropical Asia

Manufactured bamboo plank

Manufactured bamboo planks for flooring (alternative to hard wood), typically made in China, are readily available. The bamboo used for these planks is called Moso (Phyllostachys pubescens). This is another giant species which reaches a maximum height of 20 meters and 18 cm. maximum diameter. This particular species is native to China and Japan. I find these ready-made planks to be easily machinable. In terms of rigidity, however, these planks pale in comparison to the other species listed above, especially Thorny Giant (Bambusa blumeana Schultes F). That’s the prime reason why I will not be using off the shelf manufactured bamboo planks.

Also, I will be using only high grade epoxy for lamination. Off the shelf bamboo planks use water soluble PVA, which is a nice glue, but in my opinion, is not good enough. Finally, I also have to consider the need to intersperse Carbon fiber with bamboo. Obviously, with all these in mind, I have to manufacture the planks myself using only the most suitable material.

Flexural strength experiment

What we are particularly interested in is the material’s flexural strength —maximum stress on the tensile side of a loaded beam just prior to failure. The strings want to bend the neck. Guitar strings (light to heavy gauge) pull the nut towards the bridge with around 40 kg (88 lbs) to 50 kg (110 lbs) of force. The material (together with the truss rod) must be able to withstand this bending force. The table below compares various bamboo species along with hard maple and ebony. To test the material’s flexural strength, small strips (10mm x 5mm x 100mm) are subjected to incremental perpendicular force at its end (picture at right) until the material fractures. The force required to bend the material until the point of fracture is then tabulated for each material.

It is surprising to see that the flexural strength of Thorny Giant surpasses that of Ebony. This finding is probably due to flexible nature of bamboo. In the small experiment, bamboo flexes as much as 20 to 30 degress before fracturing. However, while Thorny Giant has superior strength, early experiments with it reveal a crucial problem: it is very difficult to machine using standard wood working tools. Even the best carbide router bits and planer blades easily get dull.

Sweet Giant places third in the chart ahead of hard maple. Compared to Thorny Giant, Sweet Giant is easier to machine. Its nodes are spaced farther apart and the culms are tall and relatively straight with no bulge at the nodes —properties that make it generally more suitable for our purpose.

Given all these data points, here’s the final verdict: We will be using Thorny Giant as a suitable replacement for Ebony to be used as fretboard material. We will also be using Sweet Giant as a suitable replacement for Maple to be used as the Thru-Neck material. As mentioned, bamboo will be interspersed with multiple layers of Carbon fiber and laminated with high-grade epoxy.

Further Reading

1. Zipcode Zoo
2. Bamboo in the world
3. National Plant Germplasm System
4. Phyllostachys Moso
5. Bamboo Information Network
6. Flexural strength

Next: Bamboo Preparation (part 2)