Today, four girls from grades 4 through 8 and I built a diddley bow as described in this video:

I picked this project because I wanted to test build a string instrument possibly for use in the fall with my freshmen in physics class. For that, I’m looking to get build time under an hour for a class or 20 kids. This was definitely more than an hour so I immediately looked into ways to speed things up and take the risk of power tools down a few notches.

Materials & Tools

Your diddley bow will consume the following materials:

• 1″ diameter dowel, $4
• Cigar box (cardboard preferred and as large as you can find), free
• Hex bolt 5/16″ x 3/4″ and matching nut, $0.15
• Hose clamp for 1″ diameter, $1
• Guitar string, $2 (est)

And use the following tools:

• miter saw
• belt sander
• Power drill
• Assorted drill bits
• 1″ spade bit (to match your dowel diameter)
• Hole saw bit
• Philips & Flat head screwdrivers
• metal files/rasps or sand paper

Comments on Building

I recommend cutting your neck to 2 to 3 feet long. In a classroom setting, unfortunately, each kid would need their own dowel, about $4 each. If I were to build diddley bows in class, I’d cut and sand the necks in advance to save time.

When drilling the holes in the cigar box for the neck pass through, offset these holes toward the front side of the cigar box. Ideally, the neck will pass just beneath the front as shown here:

Drilling the neck holes also took us a long time today. In a class of up to 20 kids, I don’t see how I could supervise every kid drilling two holes in a cigar box. I’ve posted a possible solution below under Next Steps: a rectangular neck.

When you go to attach the string at the bottom of the neck, I recommend adding a grommet so the string doesn’t tear up or out of the neck. I couldn’t find any pop rivets with the center knocked out, so we skipped this part. I can see that our strings have enough tension they’ll eventually pull out. I need to think on how to improve this part of the diddley bow’s design.

I didn’t struggle with it but several girls had trouble attaching the string to the screw at the top of the neck. Putting enough — but not too much — tension on the string before tightening the screw down was tough. That’s why below under Next Steps I’ve noted that I want to figure out some form of a tuning peg.

Demonstration

Based on watching other diddley bow demonstrations on YouTube, I’m pretty sure my string could use more tension. I know that was the fact with several of the girls’ instruments.

Next Steps

• Try going with a rectangular neck like this guy did with a broken hockey stick. This could eliminate the power drill step of drilling out the neck holes on the cigar box, to be replaced with cutting out a rectangle with a box cutter.
• Replace the pop rivet grommet at the base of the neck with something more readily available.
• Get a tuning peg at the top instead of just a screw. I hope to find a DIY peg idea.
• Play with a pick and a slide — can I make or substitute common materials so I don’t have to buy?

Class Applications

If I go forward with this class assignment idea, I imagine building the same diddley bow with all the kids then getting them to mark off the neck for a complete octave of notes. Alternately, the video at the top of this post has some instructions in it for marking off a series of notes for common blues progression. I could ask the kids to calculate why the ratios in the video work.

The current musical instrument project is wide open: build an instrument and explain how it works. Some kids feel this is too wide open for them. Perhaps we can learn more physics if we build a common instrument and study it in depth.

About Camp Megan

This is a thinly veiled opportunity for me to observe how kids younger than those in my classes handle building a project. It’s sort of physics projects beta testing. My brother named it “Camp Megan” and would like to see me turn this into a real camp instead of just beta testing physics class projects. Meh, maybe, that’s a lot of work.

Check out the first Camp Megan: Catapult Build from earlier this summer.