Liquid Inlaid, Laser Cut Guitar Headstock - Made at Techshop

This a laser cut, inlaid headstock for my carbon fiber acoustic guitar project, made as part of a workshop at Techshop. I'm going to show how I designed and cut the headstock shape and inlay using the software and laser cutter at Techshop.

In addition to showing how I made my particular headstock, I will be demonstrating the broader technique of liquid inlay. As opposed to traditional wood inlay - which involves fitting many carefully cut parts into carefully cut pockets - liquid inlay uses a liquid binder, such as epoxy, mixed with colored filler to make inlays with nearly unlimited colors and materials.

Disclaimer:

Before I get started, I want to say that I am NOT an expert luthier (stringed instrument maker). I tried my best to do my own research and follow the plans for my guitar design, but only time will tell if I was successful.

If you choose to make your own guitar, please do your own research using professional guides. There are several amateur luthier communities online, as well as good books. I personally used How to Build Your Own Acoustic Guitar - by Jonathan Kinkead, found at my local library.

Tools & software used

• Adobe Illustrator
• Corel Draw
• Epilog 60 watt laser
• Table router with pattern cutting bit
• Tool for mixing and spreading epoxy - I used coffee stirrers

I used the laser cutter because my inlay was small, and the laser is the best tool for doing fine details. However, many other tools could be used - a router, dremel, carving knives - anything that can make a pocket for the inlay material..

Materials used

• Cocobolo headplate 1/8" veneer - ordered from Luthers Mercantile International. Can also use any hardwood
• Lyptus 3/4" thick headstock base - can be any hardwood, but should be strong to withstand the string tension
• Painter's tape - used for masking off un-lasered surfaces
• Double stick tape - used for pattern routing headstock shape
• Epoxy (slow cure is best) - Can use other resins or binders, but I've only tried epoxy
• Atomized (powdered) brass - Can use many different types of filler - paints, powdered dye, sawdust, etc... The filler should not be chemically reactive with the epoxy. If unsure, ask around and check online.

There is at least one company specializing in this type of product - InLace. They make pre-mixed versions, as well as selling clean resin and pigments. I found some at a local art store, but not in the colors I wanted, and they were charging a lot for the pre-mixed version. For small projects, I'm sure their stuff is great - but I intend to play with inlaying a lot more, so I went ahead and used my own epoxy and pigments to save money.

Pictured is a plate with some of the different fillers I tried before deciding on just one. In addition to the powdered brass, I tried ebony sawdust, gold pigment, silver pigment, pearl pigment, and white pigment.

I designed the file in Adobe Illustrator, but any similar graphics program will work. My design was the guitar's name - WindSong - combined with a logo by pretend maker "Orphalese". In short, the name and logo are inspired by part of one of my favorite books. I discussed more about the story behind my designs in my carbon fiber acoustic guitar video page.

Process

• I started by making rough sketches on paper. I could have drawn directly into Illustrator, but I prefer to start on paper
• I traced the sketch in Illustrator, using the pen tool
• I used the direct selection tool to edit the anchor points of the vectors, until I was satisfied
• I converted all my lines to 0.25 line weight (hairline in CorelDraw) to make the laser cutter use vector cut mode instead of raster etching

The design can be almost anything you want, but you should consider the limits of the tools you are using and the inlay material.
For example, with the laser be aware of charring when making fine details. Although the width of the laser beam is only a few thousandths of an inch, if making a deep pocket you can end up scorching a wider area. By choosing a very small font size, I lost the center parts of letters with loops, like the "O" and "e".

Also, though this inlay was small, when experimenting with larger images, I've noticed that the inlay sags under its own weight towards the middle, creating a depressed inlay when it dries. If making a larger inlay, perhaps use a thickening agent to make the inlay material stay in place while wet. Overall, I recommend experimenting with less valuable materials before doing the final inlay.

I laser cut the headstock in two different vector passes. The first pass cut through the wood, and the second pass was at a higher speed, cutting ~1/2 way through the wood. My settings are for a ~1/8" piece of cocobolo - other species and sizes may require different settings.

Prepare the head-plate

• Wrap the head-plate with painter's tape. This will protect the surrounding wood from charring, and more importantly will create a mask allowing the liquid inlay into the cuts without covering the rest of the wood.
• Focus the laser
• Do an air-pass with the lid open and the red laser pointer on to make sure everything is aligned properly

Pocket settings

Speed: 35%
Power: 90%
Frequency: 500

Cutout & tuner holes

Speed: 20%
Power: 90%
Frequency: 500

In addition to cutting my headstock, I made a test strip using some scrap wood. The test strip includes 6 copies of the logo, allowing me to test different inlay colors.

With the wood and mask cut by the laser, it's time to make the inlay material. Before inlaying my real headstock, I chose to test out different colors. Fillers can be almost anything, but some liquid pigments like paint can slow the resin drying. I used epoxy as my binder and tested a total of six fillers:

• Ebony sawdust - from sanding my fretboard
• White liquid pigment - designed to color epoxy and polyester resin, bought from TAP Plastics
• Powdered (atomized) brass - all powdered pigments bought at local art store Douglass & Sturgess
• Gold powdered pigment
• Silver powdered pigment
• Pearl powdered pigment

A good rule of thumb when mixing dry filler with epoxy is a 2:1 ratio - use twice as much filler as epoxy binder. After mixing, add more filler or dilute as necessary. With the liquid filler, I only used as a small amount, adding a few drops at a time until the resin is the color I wanted. My white got contaminated before drying, so I cut it out of the test.

Any type of epoxy will work, however it's best to use a slower curing epoxy instead of 5 minute epoxy. Slower cure epoxies tend to dry more crystal-clear and bubble-free than quick dry epoxy. EasyCast is a good 1-1 mix epoxy for this type of work that is commonly sold at arts and crafts stores.

Apply the inlay

(My real headstock is not pictured here, because I forgot to take pictures when applying the inlay - this is a "stunt double" made from scrap wood.)

1. Measure out the epoxy resin and hardener. Try to be exact - mix inside a measuring cup, measure both by weight. Follow the directions for whatever resin you are using - my epoxy was 1 part resin to 1 part hardener.
2. Mix the epoxy well according to the resin directions. When the two parts are mixed, add the pigment - start with the 2:1 ratio for pigments, and add more if necessary. After mixing, the epoxy shouldn't be dry, it should still flow as a liquid.
3. Smear the mixture over the pocket. Don't worry about any mess - the purpose of the painter's tape is to make a mask that can simply be peeled away later. Put it on thick to make sure it fills everything - but beware of bubbles.
4. If you see bubbles forming, you can use a blowdryer set on low or a heat gun to quickly heat the epoxy, bringing bubbles to the surface. Don't point the heat source directly at the epoxy, which can scorch it - just wave it over enough to raise the bubbles.
5. Leave the epoxy to dry over the mask
6. Once dry, peel away the tape and scrape away excess epoxy. I used a block plane to scrap my pieces - it's also possible to use a knife, chisel or sandpaper.
7. After scraping away the excess material, use sandpaper to make the inlay completely flush with the wood. If using real metal, such as powdered brass, you can use very fine sandpaper and polishing compound to put a shine on the metal.

Between the different fillers I chose to try, I liked the brass and ebony the best. The ebony came out very clean, and it looked and felt almost like a natural wood inlay. The brass unfortunately had some bubbles inside, but with just a little sanding it was already shiny - and since the brass is real metal, it can be polished to shine like real metal.

I really preferred the ebony, but I didn't think there was enough contrast on my cocobolo blank, so I used the brass instead.

The entire headstock is ~3/4" thick - too thick for the laser cutter to make by itself. Therefore I cut the thin head-plate on the laser cutter, and used the table router to copy the shape to a larger base wood. The base wood should be hard and strong, enough to withstand the tension from fully loaded strings - I used some scrap lyptus from another project.

(Again, the piece being cut in photos is not my original Colcobolo, it's a stunt double with a piece of MDF for the base. The last two photos are the real headstock.)

Pattern routing

1. Use double stick tape to attach the head-plate to the base wood
2. Install a pattern routing bit into the table router
3. Align the bearing on the bit with the edge of the head-plate veneer
4. Cut into the base wood with the router bit, gripping the opposite side firmly. Get a firm grip on the wood, but keep your fingers as far away as possible.
5. Guide the work, keeping the head-plate veneer pressed against the bearing to copy the shape

After routing the shape, I permanently glued the head-plate and base together. I could have done this before routing, but I wanted to be able to keep the inlaid head-plate removable in case I made a mistake while cutting the base.

To install the headset I cut away the back of my carbon fiber body to accomodate it, and I finessed it into place with a file and sandpaper until it fit inside the carbon fiber neck, just under the fretboard. I left a little bit of carbon fiber under the headstock, between the tuners.