Diddley Bow

If you've seen some of my other Instructables or Youtube videos, you may know that I build instruments from time to time ... usually snare drums, hand drums, or other percussion instruments. Some day I plan to build a custom 5 1/2 or 6 octave Marimba, but today is not that day my friends.

Recently, I decided I wanted to make a few smaller stringed instruments ... a 3-4 string cigar box being one of them and two variations of a diddley bow. I don't actually know how to play a guitar, so I figured the fewer strings, the better.

I didn't have the build logistics fully figured out, but I did have the design. I I wanted the body to be made from a drum shell cutoff (a leftover or scrap of a drum shell), the neck to be made from a wooden dowel, and all hardware to be available at a hardware store. In addition to that, I wanted it to be an acoustic/electric hybrid.

Since I'm using a drum shell cutoff for the body of the diddley bow, most of the body was complete, but I still needed a front and back. I decided to use poplar since I had some sitting in my shop. Padouk or bloodwood would be really cool, but I'm cheap.

The board I had was 3/4" thick and I wanted it to be around 3/8" for a thinner look and more resonance. 8" is too tall for my bandsaw, so I used the table saw. In multiple passes, I cut a groove into each edge of the board. This left a middle section which I then had to finish cutting with a hand saw, but it only took a few minutes.

To remove the high spots and achieve a consistent thickness, I ran the boards through the planer and then the drum sander. My drum sander has 80 grit paper on it, so I currently use it more as a thickness sander than a finish sander.

You could just glue the panels to the shell edges, but I seem to have a love for over complicating thing and I like when parts interlock. Basically, I'm making a round rabbet on the panels.

I cut this rabbet using my shop made trim router radius jig, which is a variation of John Heisz's design. Since I don't want to drill a hole into my finished surfaces, I attach pivot blocks to the poplar boards using carpet tape. Another block is attached to the jig to keep things level. Put the pin in the pivot block, the router in the jig, hit the power, and slowly cut your circle. The first pass is the hardest because you're in the middle of the board and not really cutting an edge.

I always start at a larger radius than needed and sneak up on the cut until the drum shell fits perfectly. I want that extra "lip" anyway to cover the edge of the drum shell.

Once the circle rabbets are routed, they are roughly cut out using the bandsaw. Note: It's better to leave more material than less. If you cut too much, you won't have enough to cover the shell edge ... I speak from personal experience.

My drum shell cutoff originally had some cheap mahogany venner and gloss topcoat. I sanded that off using an orbital sander, sprayed a coat of primer, and then a few coats of flat black.

A 1" poplar dowel will extend all the way through this shell, so I need to mark two points 180 degrees from each other. The more precise the better ... or else I'll have a lopsided diddley bow and no one wants that. I happen to have a drum layout mat since I occasional make drums. You could use some geometry or even print out a version of this type of mat. The layout mat I use is sold by Drum Foundry and I recommend it to any drum builders.

Once I had my circumference marks, I marked the center of the depth and drilled 1" holes using a forstner bit in the drill press. Removing this much material didn't leave me with a lot of confidence in the overall strength of the shell, so I decided to add blocking to these two ends. Since I was already doing that, I decided to a 4 additional smaller blocks, which provide for screws to secure the back panel. If you are making an acoustic version, you could just glue on the back panel, but I want access to the wiring should I need to make any repairs.

The end blocks were cut from a scrap of poplar. I used the actual shell to draw the arcs, cut them proud using the bandsaw, and sanded them to fit using the oscillating belt sander. The smaller blocks were cut from sections of a 1" dowel. Again, I used the actual shell to draw the arcs, cut them proud using the bandsaw, and sanded them to fit using the OSS. The height of these blocks was determined by the space between the panels when the back is attached ... remember it has that rabbet. I snuck up on cuts until they fit.

Glue up of the body starts with the front panel. Just spread glue on the circular rabbet, add the shell, and add some clamps. I used some cauls in an attempt to even out the pressure.

Second glue up was the larger end blocks. Nothing fancy .. .glue and clamps. Clean up any squeeze out before it fully cures.

Third glue up was the four smaller blocks. I couldn't do these at the same time as the end blocks due to lack of space for all the clamps.

Last step was to drill the 1" hole for the dowel through the new end blocks. Since the front is attached, I couldn't use the drill press set up and had to do my best with the hand drill. It actually worked out.

Yes .. that is a honey bear glue bottle .. "Glue Bear." It works great if you want a lot of glue fast ... not so much for precision work.

The back panel attaches with screws in six equidistant locations and for this I am using some geometry techniques.

1. Find the center using my shop made disc center finder.
2. Use my shop made trammel or beam compass (John Heisz design) to circumferential mark where I want the screws.
2. Use that same trammel setting to mark the six location. I used my mini compass (John Heisz design) to depict how this is done, but in reality, it didn't have enough span and I had to use the trammel.
3. Drill the six holes to the diameter of your screws.
4. Place the back panel onto the body and use it to transfer the holes to the internal blocking.
5. Remove the back panel and drill the holes in the blocks with a bit just a tad smaller than the screw so it has some bite.

Due to the added blocking, positioning of the 1/4" audio jack and volume knob were limited. I went for a lower offset space for the audio jack, which is similar to an actual guitar. For the volume knob, I initially wanted to have it on the front face, but since the body is so small, it was actually in the way when trying to play the diddley bow ... I decided on using the space directly across from the audio jack.

I marked a vertical line the shell and then found the center point so the holes would be in the middle of the shell's depth. I used a shop made awl to mark the holes and create an indent to help guide the step bit.

I ran into a small problem with the audio jack not being long enough to make the through the shell thickness. My solution was to hollow out a cavity with a dremel, which was quick and easy.

I needed to draw a straight line down the length of the dowel, so that I could drill holes in the same plane. I figured the easiest way would be to just lay the dowel on a flat surface and scribe it with a pencil. I'm not sure if the dowel had a bit of twist of if I just wasn't 100% precise when it came time to drill. If I had to do it again, I would dry fit the handle to the body and use a chalk line to make the mark.

The Bridge
The first hole location was for the bridge, which is a bolt that will screw into a T-nut recessed in the poplar dowel neck. A shallow 3/4" hole was drilled with a forstner bit for the flange, drilled further with a 5/16" forstner bit for the T-nut's shaft, and finished with a 1/4" forstner bit for the bolt. I drilled all the way through and got some blow out (dangit), but I needed to use the 1/4" to mark the hole location on the front body panel. With the neck removed, I drilled the panel from inside the body until the tip just pierced through. I then flipped the body to finish the hole from the front ... thereby eliminating blowout.

The Nut
The second hole was at the other end of the neck and is for the diddley bow's nut. I used the exactly same process as I did for the bridge.

The Tuner
The tuner assembly gets intersecting holes.

The first hole is perpendicular to those drilled for the bridge and nut. To find the 90 degree offset to each side of my scribed line, I used a seamstress tape and some guess work. A shallow 3/4" hole was drilled at both marks with a forstner bit for the T-nut flange. These two holes are then drilled further with 5/16" forstner bit ... and they end up connecting since we are dealing with 1" dowel. I also ended up having to grind down the shafts of the T-nuts in order to make a space for the guitar string to actually be strung (I used the OSS).

The second hole is on the same plane as the bridge and nut bolts and it ends up being more of a slot than a hole. This is the area where the string will connected to the tuning peg. I drilled it out with a 1/4" forstner bit .. starting in the middle and elongating as necessary until the string doesn't bind against the dowel. Hopefully the last picture in this set helps this make sense.

The tuning peg is a 1/4-20 thumbscrew with a hole drilled through the shaft to accept and hold the guitar string.

To bring out the wood grain, I used 50/50 boiled linseed oil and mineral spirits. This was done prior to assembly because it was easier and no electronics could be damaged.

For the diddley bow's pickup, I used a simple piezo trigger. To help keep it centered and make glue up easier, I drilled a shallow recess with a 1" forstner bit. I used superglue as my adhesive of choice, but epoxy would also work.

The guitar string runs through a hole at the bottom end of the neck. You could just run it through the wood, but under tension, it will keep cutting into the wood fibers. My solution for this was to use a few rivet bodies. I just separated the bodies from the mandrels/pins and glued one into each side of the hole using epoxy.

NOTE: The neck had to be fit through the body first ... it won't fit once you add the rivets (I know from experience). You could technically thread the neck up from the bottom, but it's a very tight fit and that would be annoying.

With the neck and body connected , I finished the finishing process with 4 coats of spray lacquer. I sanded between the 3rd and 4th coat.

I wanted basic fret markers for a blues scale (I, IV, and V). I've seen people just do this by marking the neck with a sharpie, but of course that look isn't clean enough for me. I wanted the look of an inlaid marker, which I achieved by using a 1/4" forstner bit and 1/4" dowel stock.

Once I found the locations, I drilled holes about 1/4" deep and glued in small sections of dowel. Once the glue was dry, I trimmed off the excess at the bandsaw and then sanded them flush to the neck.

Fret Locations
25 1/2" Scale (Bridge to Nut)
12 3/4" - Octave - equivalent of the 12th fret position [1/2 the total scale]
8 1/2" - Fifth - equivalent of the 7th fret position[1/3 the total scale]
6 3/4" - Fourth - equivalent of the 5th fret position [1/4 the total scale]

When it comes to making/building, I'm a electronics newb ... I'm also not great at soldering, which you'll see very shortly. Since I know nothing about building guitars, I searched youtube for a video on wiring a single pickup to a volume knob and output jack. I then made a fabulous drawing of the wiring diagram.

In my minimal soldering experience, I have learned that it really pays off to tin your wires, which just means applying solder to all of your wire ends before you work on any connections. A guy on youtube tinned the back of the potentiometer, which seemed like a good idea ... so I did that as well. Next I connected my wires to their correlating terminals and then took a stab and soldering the connections. I know enough to heat up the component and do your best at getting strong/even connections, but that's about it. I really try for pretty solder joints, but they evade me.

I've included the wiring diagram so you can see how the components connect.

NOTE: I ended up disconnecting the ground wire to the bridge because it was introducing horrible ground noise and turns out to be unnecessary.

For the volume knob, I used a small section of the 1" dowel left over from the neck. A shallow 1/2" hole was drilled using a forstner bit to accommodate/conceal the nut on the potentiometer. That hole is then continued with a 1/4" forstner bit. The minimum length of this knob is determined by depth of this hole. I made it as short as I could without revealing the hole .. AKA blasting through the other side with the drill bit.

At 1" diameter, the knob looked out of balance on the body ... too large. I used a small washer to draw a smaller circle on the knob, roughly cut off the waste using the bandsaw, and then rounded it out using the OSS.

The knob was attached to the potentiometer shaft using epoxy.

Assembly is quick and easy.

1. Thanks to the rabbet, the back panel locks into place with a nice friction fit. It's just a matter of getting the holes aligned and installing the six screws.
2. The bridge bolt gets inserted through the front panel and threads into the T-nut, which is recessed into the 1" dowel.
3. The "nut" bolt goes through the front of the neck and treads into its recessed T-nut.
4. The string is run from the back ... through the rivet bodies. It is then fed over the bridge bolt, up the neck, over the "nut" bolt, and through the hole drilled in the thumb screw.

Tension is applied to the string by turning it away from the diddley bow body. To hold the tension, tighten the jam nut against the T-nut.

Congrats!! You're ready to rock and and become the envy of your neighborhood. Call your buddy who owns a jug and the old lady who still has a washboard, turn your front stoop into a stage, and see how long it takes the cops to show up.

Materials
8"x1 1/2" drum shell cutoff
1"x8" poplar board
1" poplar dowel
(4) 1/4-20 T-nuts
1/4-20 Bolts
1/4-20 thumb screw
1/4-20 nut
(2) rivets
A guitar string
1" Copper pipe coupler
1/4" Audio Jack
Potentiometer
Piezo trigger