My daughter's school's music class was in need of a storage solution for 30 Ukuleles, and this is the design that the music teacher and I collaborated to come up with.

Supplies

Materials

1 x sheet of maple veneer plywood
7 x 8' 2x1 pine boards
1 x 8' 4x1 pine board
1 x 2' 4x1 maple board
4 x castors
16 x 1 1/4" bolts and nuts
32 x 3/4" washers
Stain of preference (I used light oak)
Finish of preference (I used paste wax)

Tools

Squares
Rulers
Jigsaw
Table saw
Drill
Router table (round over)
Palm router (round over and pattern)
Assortment of sanders
2 or more long clamps
As many small squeeze style clamps as you can get your hands on

Step 1: The Sides

There was a cart we had seen online that had sides shaped like a Ukulele, and that was a must have part of the design.

I started by measuring our Ukulele and thought about the height I would need for two rows, and the width I would need for it to be stable on two wheels. Some quick googling and mathing gave me a scale factor that helped determine the exact sizes. Despite all my measuring, my wife had to help freehand some of the curvature so it looked proportional.

I created a symmetrical paper template by folding a large sheet in half vertically, and then cutting both sides at once. I could then transfer the paper template to the plywood and rough cut two pieces. One of the pieces was cut to its final dimensions, and then used it as a template to cut the opposing side with a template bit in a trim router. Rounding over all of the edges, and spending some time sanding and filling voids leaves a nice edge (even though it's plywood).

Also pictured was my initial thought for how the shelves would be positioned, and where the Ukulele would sit.

Step 2: Fitting Rails

Since the sides of the cart are made from plywood, I wasn't sure how to join the rails (1x2" pine boards). They don't really need to hold a lot of weight, but the force of pushing the cart around and the general abuse from young children was cause for concern. I landed on butt joints with dowels. This helped with alignment, sheer strength, racking, and additional glue surface.

Pictured is a test fitting with scrap wood, and my process for sanding dowels to fit (they're never perfectly sized for the hole you need). I created a makeshift lathe by chucking one end into my drill, putting the other end in a scrap of wood with a hole in it, and using some sandpaper to decrease the diameter.

Not pictured are a couple of jigs I made out of maple (because it's harder) to help line up the holes I drilled in the ends of each rail. A trick to keeping them straight with a hand drill is making sure you're at 90 degrees, and then using a wrench or ring on your drill bit to keep you from wandering up or down.

Step 3: Attaching Rails

I used squares and rulers to line up 1 hole per rail, and then drilled through both sheets so one dowel hole would be all the way through, and perfectly in-line. Then I could use metal dowel centers to punch a location for the blind hole. In this way, each rail is joined with 2 dowels on each end, one through and one blind.

Pictured is some of my layout process, and a test fitting.

Step 4: Finishing Rails

Gluing it all together was a bit of an issue. The dowels made lining everything up and holding it square easy, but I didn't have clamps long enough, and fitting it all together before the glue started to set up was problematic. I ended up doing one side in stages, clamping it all together with some rails only dry fit, and then the other side all at once. Luckily I was able to use two clamps together to span the distance. After glue up was complete I flush trimmed the through dowels, and sanded things smooth.

Pictured is the clamping using longer boards to spread the pressure evenly, and the flush trimming of the through dowels.

Step 5: Adding the Neck

I cut out the neck pieces and finished them as I had the body. I also attached them and the last rail pieces in much the same way that the rest of the rails were attached. The only difference is that I added through dowels that only showed on the inside, and only blind dowels for the top rails, since I though it was more visually appealing.

Pictured is more layout, sanding the through dowels smooth, and a picture of things finally coming together.

Step 6: The Nubbins

I had been messing around with ideas for keeping the Ukuleles in place and providing a visual indicator for where to put them. I landed on creating these little nubbins between the spaces where the necks would go, and attaching them with the same glue and blind dowel joinery (except only a single dowel) that I used elsewhere. I cut out 36 little pieces, used a table router to round over all of the edges that wouldn't touch the rail, and then spent more time than I'd like to admit sanding them smooth on an upside-down orbital sander.

Pictured is a jig I made to help drill holes in the small pieces, my sanding station, the glue up, and a test fit.

Step 7: Wheels & Finish

To add the wheels, I just added a small board perpendicular to the the wide boards at the base of the cart to provide a bit more meat, drill through holes, and used bolts to attach. These are the only mechanical fasteners on the structure.

For finish, after sanding smooth, I applied stain and paste wax.