I saw one of these somewhere a while back and always thought it would be fun to play with. A quick Google came up with several including the one in this picture. It's available online for about $33. I'm no kind of musician and I've never built a musical instrument before but this looks simple enough. I'd rather just make one.

Step 1: Materials:

Looking at the image I found on google there is no reference to tell exact size but I'm not really worried about making it accurate. I'll guess it looks to be about 5" x 7" x 1".

For most of the parts I was looking for stuff I had sitting around. This is the parts list for what I ended up with.

(2) - 3/16" plywood - 5" x 7" for the top and bottom
(2) - 3/4" x 3/4" x 3' pine - 5" and (2) 7" for the frame
(2) - 1/4" dowel - 2-1/2" to support the keys
(1) - 3/8" aluminum rod - 4" to hold down the keys
(1) - 3 1/2" nail - cut to 3-1/4"
5/8" x 18 brads - optional
(2) - #6-32 x 1/4" T-nuts
(2) - #6-32 x 1" round head bolts
street sweeper bristles - enough to make 9 keys about 2-1/2" - 3-1/4" each.

I had to buy the T-nuts and bolts but the rest I was able to scrounge. The "keys" were made out of street sweeper bristles. They're easy to find if you get out and walk much, just keep an eye on the street.

Step 2: Cut Out the Wood Parts

Cut two 5" x 7" plywood sheets for the top and bottom of the box and the 3/4" pine into 4 lengths at a 45 for the sides - 2 @ 5" and 2 @ 7". Glue and (optionally) nail the sides onto the bottom with small brads, then set it aside. I didn't mind using brads to hold the bottom together while it dried. They won't show much but you could just clamp it instead. Just be sure to set them in deep enough so they won't stick out and scratch things.

Step 3: Front Face

Measure and mark the two points to drill for the T-nuts, don't make the holes too large for the T-nuts or they will fall out easily. I drilled 5/32" holes for the T-nuts 2-1/2" apart and about 1-1/4 from the one end. Measure and mark the 1" hole centered about 4-1/2" from the same end.

I drilled the 1" hole part way through the back then turned it over and drilled the rest of the way from the front to avoid splitting either side of the plywood.

When I was done I found that 4-1/2" seems a bit too close to the T-nuts you could move it a half to an inch further down. Also I found out that a 1" hole seems to make the higher notes sound louder, epically the B key. A smaller hole would tend to shift the emphasis to the lower notes. Using a 1/2" drill gauge held over the 1" hole seemed to bring out the F note.

Drill the 3 holes and tap the T-nuts into place with a hammer.

Step 4: Assemble the Box

Assemble the rest of the box (Careful not to knock the T-nuts loose!). Brads wouldn't look good on the top so just use glue and clamps. Be sure to use some sort of pad between the clamp and the box. They aren't shown in the picture because I forgot and ended up with some clamp marks to sand out.

- set it aside to dry

Step 5: Dowels and Rods

Cut the aluminum rod to 4" and file the ends flat. I clamped it in the drill press and use the file to smooth and round the end off and used ultra fine sand paper to "clean" the aluminum. Carefully measure and mark the holes for the screws to attach the rod then drill the 2 holes at 1/8".

Cut the head and point off of the nail (3-1/4") and file the ends flat. Put it in the drill press to round the ends and clean as with the aluminum rod.Cut 2 lengths of the 1/4" dowel to 3-1/4". Flatten both dowels along the length just enough so they don't roll easily. Hollow out a channel on the side opposite the flat of one of the dowels to "cradle" the nail in place. I did this using a motor-tool while holding the dowel in a vice.

Set these parts aside for now.

Step 6: Sanding and Finishing

When the glue has dried, take the clamps off the box and start sanding. Sand the edges flat and sand off any imperfections or pencil marks from the front and back. I like to sand off all the hard edges and corners just enough so it feels good in my hands.
Dust it off carefully and put a coat of varnish on it. I put the bolts in the T-nuts so I could hang the box up to dry without it touching anything. When the varnish is completely dry rub it down with fine sand paper or steel wool to get a nice smooth finish. Put as many coats of varnish as you like.

Step 7: Final Assembly

Assemble the whole thing as pictured. You don't need to glue the dowels or the nail in place, friction will hold it down when it's fully assembled. Be sure to place both dowels close to the aluminum rod (about 1/2" center to center) or the keys will bounce and buzz when you play it.

Insert one street sweeper bristle and tune it roughly to a C note. Mark it and "cut" it to length, actually I just put it in a vice and broke it. File and sand it carefully to round and smooth the ends, if you don't it will make a sound scraping across your finger prints or worse scraping off your finger prints! Re-insert it under the "clamp" and do the same for each of the notes you want, I added a total of 9. If you want more you'll have to either make the whole thing bigger or space the keys closer than I'm comfortable with. I put in keys for C through G then A through D in this pattern:

====C
======A
========F
==========D
============C
==========E
========G
======B
====D

The pattern was suggested by a friend that had a bit more experience with musical instruments than I have, but other people have since made other suggestions so arrange them in any order you're comfortable with.

When they're all in, tune them carefully and tighten down the screws until you don't hear any buzzing when you play it.