Step 0:

Have tools. I did this in a machine shop (techshop.ws), but you could likely get it done with a cordless drill, a hacksaw, and a goodly amount of patience.

Step 1:

Have a rack on your motorcycle. This doesn’t cover building a rack.

My BMW already has a factory installed rack, lucky me.

Pick the side of your rack away from your exhaust. Banjos don’t like heat.

Step 2:

Measure your rack. The rails on my BMW rack are roughly 24mm at the widest point. Fortunately, the main rail and the lateral stabilizer down by the passenger footpeg are roughly the same width on my bike.

Step 3:

Find some u-channel metal stock that fits over the mount points on your rack. While you’re there, grab a bit of steel sheet to reinforce the inside of the case (also makes washers unnecessary). Bayshore Metals in San Francisco hooked me up with a bit of scrap 16ga steel sheet and some aluminum stock. The inside spacing of the channel is ~25.5mm, perfect for my use. I believe it is 1 1/4" x 1 1/4" x 1/8" 6061:

Step 4:

Buy nuts, bolts, other materials from any hardware store. I used 1/4" x 1" grade 8 hex head bolts to keep the profile of the heads inside the case lining low. Four nuts and bolts for the main rail, 4 more of each for the stabilizer.

Step 5:

Make sure your metal stock fits over your rack rails, cut to an appropriate size and allow for any weird rack contours. I ground down the sharp corners in an attempt at stress relief:

Step 6:

Put the metal rail on your rack. Hold the banjo case up against the motorcycle. Use a Sharpie to mark where the rail should go.

Step 7:

Figure out where you want the bolts to go. Try to avoid the center, where the resonator is deepest. Try to get the outside bolts as close to the edges of the case as you can while leaving room for the case walls and giving yourself room to work. If you drill the holes in the perfect place near the top of the rail the “ceiling” of the upside down U will hold a face of the nuts when you bolt it together and you won’t need to use a wrench. I did this on a mill with a scrap piece of u-channel stock via trial and error, then switched and drilled my mounting rail:

(I also bent the rail a bit to fit the rack on my motorcycle a bit better. I used a vice and a crescent wrench. With aluminum it’s easy.)

Step 8:

Peal away the lining of the case. On this Deering case it was simply held in place with a moderate-strength adhesive:

(Use a hardy case. I like this Deering case a lot. It was a cheap scratch-and-dent factory second from Deering’s eBay listing.)

Step 9:

Use the rail as a template to drill holes in the case to make sure everything fits correctly. This is why I drilled holes all the way through the rail:

Step 10:

Cut your steel sheet to fit the inside of the case.

I used a medium size piece at the top inside the case behind the rail and a smaller piece at the bottom where the lateral stabilizer goes. If I did this over, I’d take the lining entirely out of the pot section of the case and use one big piece of steel.

Step 11:

Put the metal sheet in the case and make sure everything fits. Use a Sharpie to mark the sheet through the holes in the case so you know where the holes in the sheet should go.

Step 12:

Take the sheet out of the case and drill the first hole. Bolt the rail to the sheet through that hole. Use the rail as a template to drill the rest of the holes, adding bolts as you drill to keep things aligned:

Step 13:

Glue the sheet into the case using a gummy, flexible glue that’s compatible with both wood and metal. I used 3M “27 Spray Adhesive”. Poke bolts through the holes in the plate into the case holes before the glue sets to make sure everything lines up, then mush everything together hard:

(Just before glue and bolts. After the glue I was sticky. Mask the case if you use spray glue, it really gets everywhere.)

Step 14:

Bolt the plate, case, and rail together. Bolt heads go on case side, nuts go on u-channel side. Use Locktite on the threads so it stays together. I used Locktite Blue. Tighten it enough to be secure, but not so much that you crush the wood.

Step 15:

Mount the whole assembly to your motorcycle rack via the rail. If you have a lateral stabalizer (or other additional case mount points) figure out how to attach to these as well. I didn’t document this process terribly well, but here’s a picture of the finished mounts:

(On my motorcyle the lateral stabilizer wasn’t quite in line with the main rail, so there’s a bit of intentional offset and twist to the lateral stabilizer bracket. Just make sure it fits on whatever you’re attaching to.)

Step 16:

Make a bottom clamp to hold the underside of the main rail. I used a piece of u-channel with one of the sides cut off:

(Holes are from test-drilling for Step 7. They’re in the part you throw away. You don’t need them.)

Step 17:

Put the case on the bike. Find a place where there’s clearance on the rack rail for a bolt to pass by. Mark it and drill a hole there:

Step 18:

Drill a hole in the bottom clamp from Step 16 to line up with the hole from Step 17. When you assemble everything the u-channel on the case will rest on top of the rack rail, the bottom clamp will be under the rack rail, and they will be bolted together, securing the assembly to the rack rail. I used a bicycle QR from Bike Friday because it was just the right length. Here it is assembled on the bike:

Step 19:

Use tie-down straps for extra security. This does three things: 1) Helps keep the case from falling apart. The back of the case and the glue joints weren’t intended to support the weight of the banjo, or to handle the vibration of a motorcycle. 2) Gives a backup plan in case something breaks or the QR and clamp rattle loose. 3) Keeps the case from falling open if the case clasps open while you’re riding. I’ve shortened these straps so they don’t flap in the wind too much.

Step 20:

I cut little pieces of bicycle inner tube and placed them between the mount points and the rack. That protects the rack and might dampen some vibration. Pretty optional, though.