The FretBoil Ukulele

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February 20, 2014
I got this idea when we were canoeing the Boundary Waters with my sister and her sons (my nephews). I brought along an inexpensive ukulele so we could have some music while in camp, and it was nice to have but inconvenient to carry in the canoe since it was too bulky and too fragile to fit in my backpack. My eldest nephew Josh and I each have the same model of JetBoil backpacking stove with a 1.5 liter cooking pot and I thought it would be cool to have a thin and easily packable ukulele that would use the cooking pot as its body, so one could just snap them together in camp and start playing. This year I finally got around to making one as a birthday present for Josh, and here’s the result:

I did most of the machining using my Shark HD 2.0 CNC router. I made the body and neck from laminated quarter sawn white birch, with two of the inner laminations having the grain running at 45-degree angles to the neck to strengthen the area where the neck blends into the body. The top lamination is curly maple and there are five layers total, each 1/8″ thick so the main body is only 5/8″ thick. I made the soundboard from western red cedar, and I made it 1/8″ thick which is quite thick for an instrument of this size. A thinner soundboard with cross bracing would likely give more volume but I wanted it to be sturdy enough to survive being packed in a backpack without much padding so I went with a thicker soundboard and no bracing. I inlaid a single ring of black-maple-black purfling around the soundhole and a double ring around the joint between the soundboard and the maple frame. The bridge is rosewood with a bone saddle, and the finish is about 6 coats of Tru-Oil. The strap is a hiking boot lace, naturally.

Here are two views of the back, showing the spring-loaded latch that I made and the leather gasket I glued around the edge, which keeps the pot from buzzing against the soundboard:

Below are close-ups of the fretboard and headstock. I made the fretboard from bloodwood with inlaid paua abalone marker dots, and it has a 13-inch scale length which is typical (a bit on the short side) for a soprano uke. The tuners are upside-down compared to how they would normally be installed, i.e. the knobs point toward the front of the instrument. This looks a little odd and it is not as easy to adjust because you have to reach around to the front to turn them but it keeps the overall profile flatter this way since they stick up on the same side as the bridge, and this should make it easier to pack in a backpack. Planetary tuners would have been even better (flatter), sticking straight out to the sides, but the standard tuners don’t add much height since they’re about as high as the bridge. I also considered mounting them in a solid headstock with the knobs out to the side but then I’d have to angle it back to make the strings break properly over the nut, so I think that would have been a less packable shape. To make the FRETBOIL text I used the CNC router to V-carve the letters and then filled them with a mixture of epoxy and bloodwood sawdust, and sanded it flush.

Here is a sound clip, recorded with an AKG C3000 microphone into a Fostex MR8 mkII 8 Track Multitrack Recorder in a small room using no reverb or other effects, just the natural reverberation of the instrument. It’s strung with Aquila Nylgut strings with a low wound G string, which are my favorite. My uke playing is a bit rusty and may not win any contests but I think the instrument has a nice sweet voice. This is with the cooking pot’s urethane jacket and plastic bottom cover in place as shown in the photo near the top, which doesn’t seem to have much effect on the volume and I think it improves the sound by damping out some of the tinny quality of the aluminum pot.

Guitar #1

November 2014

I started building my first guitar in the Spring of 2014, and it took about 6 months to finish as I was also learning techniques and making or acquiring various tools and fixtures that I needed. It’s a fairly straightforward design but with a few uncommon features.

I built it from scratch, without using a kit or prefabricated parts. I think building a guitar from a kit is a great way for people to start out but I enjoyed making everything from scratch. The back and sides are Black walnut, with Sitka spruce for the top and all the bracing. The bindings around the edge are curly maple. The neck is Spanish cedar (not a real cedar but more closely related to mahogany) and the fingerboard is Honduran rosewood, which I chose because it’s a good color match for the walnut. The rosette is a simple wood herringbone inlay, and I made the end flash as a stylized “tree” so unlike most tapered end flashes I’ve seen, the pointy end is toward the soundboard:

Some guitars are designed with a headstock that pulls the strings in a straight line when seen from above, which can minimize the resistance as the strings pass through the slots in the nut, but it often requires an asymmetrical headstock to position the tuning machines correctly. I liked the idea of a straight string pull but I really prefer the look of a symmetrical shape, so I designed my headstock to give a very nearly straight string pull but using a symmetrical layout. I made the guitar with a compensated nut, meaning that it’s offset differently for each string, which makes it possible to achieve better intonation where the notes don’t become overly sharp when fretted near the upper frets. It’s still a compromise, as are all equal-tempered instruments, but at least it gets closer to a true chromatic scale.

I came up with the ellipse-in-ellipse bridge shape to echo the arched headstock. I used black walnut for the bridge because it’s much less dense than ebony for example, and a ligher bridge can be more efficient at transferring the vibrating strings’ energy into the soundboard, but it still has sufficient stiffness and resistance to crushing. I thinned down the area behind the strings to save weight and also to make it thin enough to flex just a little as the soundboard distorts under string tension, which I think should make it somewhat less susceptible to glue failure in that area.

Here’s a short sound clip, just me playing a little open chord melody, and I’m not yet proficient enough to exercise the full range of the fretboard so honestly I don’t know how it compares to other guitars but I think it sounds decent. To my ears it seems to have a nice rich bass, which I expect is largely due to the deep body. As far as I can tell it doesn’t have any wolf tones or other sonic problems and I haven’t had any problems with fret buzzing.

Guitars #3 & #3

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December 25, 2014

These are the second and third guitars to come out of my shop, a matched pair. I built one for our 13-year-old grand-niece Emily while working with our nephew Josh and teaching him to build one for his wife, and we finished them just in time for Christmas (I took these photos on Christmas morning just before packing them up for delivery). They are medium-small gutars (known as 00-size) and made to the same specs although of course they’re not quite identical. The tops are Sitka spruce and I cut the backs and sides from the same curly maple board, so I call them “sister guitars”. The necks are Spanish cedar and the fingerboards are Granadillo, which I chose for its reddish color to coordinate with the cherry bindings.

Because of the timing, wanting to apply several coats of finish per day at intervals and trying to get them done in time for Christmas, it wasn’t practical for my nephew to come over and do the finishing on his so I did the finish on both of them together. I did the soundboards in French polish with U-Beaut hard shellac. We then polished them by hand, which took quite a while to get a decent sheen and my arm was pretty sore afterward so I promptly ordered a Shop Fox Buffing Assembly for next time!

I finished the backs, sides and necks in Tru-Oil with a satin finish. I used a cherry backstrip to separate the two halves of the back so the reversing grain pattern of the curly maple doesn’t clash at the center.

Our nephew and his wife recently bought a house with a wooded lot. I spotted a small rotting maple stump in his woods and said “hey, there’s guitar parts in that stump!” We resawed the stump into veneer about 1/8 inch thick and dried it, then cut a bunch of rosette segments from it. The rosettes each have 9 segments and I made a plexiglass form just to hold them in a circle for visualization, then we spread out all the segments we’d cut and let the recipients design their own rosettes by arranging the segments as they liked. When finishing them I intentionally left some of the worm holes in the spalted wood rather than filling them in, as I think it gives them a nice earthy character.

I used the same elliptical bridge design that I created for Guitar #1, but I carefully tweaked the dimensions to further reduce the weight.

This was my first time doing shell inlay other than simple dots, and I created the dragonfly design from a photograph I took many years ago. I cut the inlay pocket and the shell on my Rockler CNC Shark Routing System and after a few tries on scrap wood I got a pretty decent fit. With the light curly maple headplate there’s no easy way to hide gaps like one could on a darker wood. The wings are paua abalone and I cut the body from black mother of pearl for contrast.

Our grand niece has been learning to play on a borrowed baby Taylor guitar and our nephew’s wife hasn’t had one of her own before so this is the first guitar each of them has owned. We delivered the guitars on Christmas day and they were both delighted!

4th Axis Harmonic Drive

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After finishing my Modular CNC Controller I built this 4th axis attachment for my CNC router and my milling machine. This will let me machine parts such as gears, and carve 3D patterns wrapped around cylindrical shapes. In the Part 1 video I build the main drivetrain components, using a harmonic drive gearbox to get precise angular positioning and high torque with low backlash.

In the Part 2 video I weld and machine the steel enclosure, install the harmonic drive system, and try it out.

In this video I apply Powder Coating to the housing.


The Harmonic Drive web site has detailed information about the style of gearbox that I used. The Catalog link on that page provides detailed documentation about this family of ultra-low-backlash gearboxes.

I bought the 3-jaw front-mounting self centering lathe chuck from Shars. Any similar chuck should work, provided that it can be mounted from the front.

I bought my stepper motor on Ebay after quite a bit of searching to find one with the specs I wanted, including the 8mm output shaft to fit the coupling on my particular gearbox. Here is a link to a similar Nema 23 stepper motor on, but with the more common 1/4″ output shaft.

Garden Folly

October 8, 2012
Jay and his brother Dave decided to build a folly to support a wisteria vine in the garden. It’s going to be a dome-shaped structure about 8 feet in diameter and 8 feet high, made of rebar with decorative scrollwork. Jay bent the S-shaped scrolls from 3/8-inch rebar with a plywood jig. Using 52-inch lengths of rebar, he first bent one end into a spiral around the jig.

Once the first spiral was bent, he reversed the piece and bent the other end in the opposite direction. To make the folly took a total of 28 of these.

The folly will consist of two pairs of arches crossing at a right angle. Each arch is made from a 20-foot length of 1/2-inch rebar, with an 8-foot length stretching across the bottom. Once Jay had bent a few scrolls, Dave started welding the arches together while Jay continued to bend.

Each of the two sections has 10 scrolls and about 50 double-sided welds. By late afternoon both sections were fully assembled, but not joined together yet.

October 9, 2012
After aligning the two halves and clamping them together at the top, Jay welded the intersections to anchor them together. Then we put cross braces along the bottom to join the ends of the arches into a square base. He welded 2 more scrolls into each space between the arches to fill in the dome shape.

We used the tractor to move it from the driveway into the main garden just south of the house. It may take the wisteria vine a year or two to cover it, as this is an American wisteria that won’t get as large as the Asian species.

Here’s a close-up of the scrollwork joining the arches, and a view looking up from the bottom.

Garden Trellises

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Below are some photos of metal trellises that we built years ago when we lived in Wisconsin.

This was our first garden metalwork project, a hanging trellis made of welded 1/4″ steel. It is 18″ wide and 32″ high. The design is a real circuit called a Darlington amplifier. The plant is Mina lobata, which will get yellow and red flowers that hummingbirds love.

Here are the second and third trellises we made, 73″ high and 30″ wide. The first circuit is part of a Geiger counter, the second circuit is a crystal calibrator, and the vines are morning glory.

Scrollwork Trellis

October 5, 2012
We made a scrollwork trellis for our Dad’s 85th birthday. Jay cut and bent the S-shaped scrolls from 3/8″ rebar, and Dave did the welding.

For the top, we cut off 4 tines of an old garden cultivator and welded them together to support an antique glass lightning rod ball. Then we made a finial on the metal lathe to fit over the top of the trellis and inside the top of the ball. The finial is shiny because we just made it but it will soon rust to match the rest of the trellis.

Sun Trellis

June 4, 2012
Jay and his brother Dave welded up this sun-face trellis for the clematis vine in front of the cottage near the front door. It’s about 7 feet in diameter and is mostly 3/8″ steel rebar, with 1/2″ steel rods for the vertical supports.

Yin-Yang Gate

June 6, 2012
Since we installed the deer fence last year, we have been using pieces of fence tacked over the three openings where gates should be. Jay and Dave set about making a real gate for the front gateway just south of the cottage. This gate is 7 feet square and Jay created a yin-yang sun-moon design for it. Jay did most of the cutting and bending of the rebar while Dave did most of the welding. We used a fiberglass welding blanket to protect his legs so he could work from his wheelchair without setting himself on fire.

The photos below show the finished gate. The sun and moon are 13″ glass disks that we fused in our kiln.