Make a tenor banjo

A couple years ago, I wrote a post on how to make a banjolele starting from parts bought here and there. I’ve simplified the process to make a 4-string banjo, and it has turned out so well that I just had to share it.

You can see from the picture that the neck is actually on top of the pot. This is the main simplification, which saves a lot of work. The bridge is u-shaped, and it wraps around the neck without touching it. The good news is that you can buy that bridge already made, which again saves you a lot of work. Here’s the list of parts, with some links:

  • A 31 inch maple 1 x 2 board (this length makes the banjo fit within a baritone ukulele bag). It needs to be maple or similarly hard wood so it can take the tension of four steel strings. You can get it at Menards for about $6.
  • Hard maple “floating bridge” by CB Gitty: $5.49 for a pack of two.
  • A hand drum. I used a 10 inch tunable one by Rhythm Band: $23.99 at
  • A set of four tuners, 2 right and 2 left. I used guitar tuners from CB Gitty: $8.29 for the set I used.
  • You’ll need some bushings so the strings don’t damage the wood where they attach: $2.99 for a dozen at CB Gitty.
  • Instead of nut, I used a zero fret plus some stainless steel screw eyes: $1.33 at Home Depot for a set of 4.
  • And of course, some fret wire. You can get 6 ft (which is way more than enough) from CB Gitty for $10.99.
  • Did I mention the strings? For a 21.5 inch scale like mine, I found regular “10” electric guitar strings to work quite well: about $6.00 online.

That’s it for parts. As far as tools, you’ll need a fretting saw (CB Gitty has a nice one), screwdriver, power drill, and a saw. Sandpaper, metal file, and a vise.

Other than polishing the sound, which may take some time, most of the time is spent in shaping the neck. For a 21.5 inch scale, you’ll want a 31 inch piece of 1×2 board (actually 3/4 by 1.5 inch). After cutting to length, I did the following with the help of Craig Johnson, the head machinist where I work, which took him about 10 minutes with the proper tools. It’s going to take you longer with hand woodworking tools, but it can be done as well:

  1. Reduce the thickness on one end from 3/4 inch to 1/2 inch, so the tuners can be mounted. A length of 4.5 inches is enough.
  2. Make a 1/8 inch deep pocked around the place where the bridge would go. This is because the action would be too high without the pocket.
  3. Radius the edges on the back side of the neck. A 1/4 inch radius is comfortable enough to play, but you can do more if you want.

After this, you need to drill a few holes:

  • Four large holes through for the tuners, on the headstock part.
  • Four small holes through for the strings, on the opposite end. Be careful with spacing. You may need to make the holes a little larger on top in order to accommodate the bushings.
  • Four pilot holes for the screw eyes where the headstock section meets the fingerboard part of the neck (see detail). Spacing is critical, as this will set the spacing between strings.
  • After mounting the tuners, a few small pilot holes for the tuner screws.

You can finish the neck once the holes are drilled, which involves sanding and coating with your favorite finish. I used two coats of Danish oil, followed by a single coat of spray-on shellac, which gives a medium gloss finish. On maple, the result matches the finish of the drum quite closely.

I recommend stringing it up and attaching the drum at this point, so you can decide on the scale to use before cutting the frets. The tunable hand drum was easy to attach with a couple angled brackets (forgot when or where I got them), plus plenty of washers. It will appear that the drum surface is touching the wood, but they’ll keep apart from each other once you add the bridge and put some tension on the strings. The original bridge was a bit too tall, so I took off 2 mm from each leg with a file, with the bridge mounted on a vise. I also took off some from the bridge underside so it would clear the neck with no problems.

After that seems to work and you decide on the scale, you can go ahead and cut the slots for the frets. I had a zero fret near the edge of the headstock, and the rest spaced by the fret equation d(n) = d(n-1)*phi, where d is the distance between each fret and the bridge (d(0) is the scale length), and phi is the number phi = (0.5)^(1/12) = 0.9438743, easy to obtain on a calculator by taking the cubic root, and then the square root twice, of 0.5. Then cut the fret wire in 1.5 inch chunks with a heavy duty cutter and press them into the slots (I used the vise for this). Don’t forget to file the edges of the frets with a flat file until they are smooth. I’ve found a final rubbing with a sanding sponge makes them quite nice to the touch.

And then you put the hardware and strings up again, and tune it until it sounds nice. First task is to finalize the bridge position by checking the pitch with open string and at 12th fret. They must be exactly one octave apart for each string. Move the bridge away from the headstock if the 12th fret pitch is sharp relative to the open string, toward the headstock if it is flat. Usually doing this for the 1st and 4th strings is enough. More likely than not, the bridge will end up askew. Then the final tuning. Banjos are very hard to tune because they are so twangy and tend to fool electronic tuners, but I found that a tuner app on my phone gave decent results.

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