This Instructable shows how to take an ordinary classical guitar (a cheap one, preferably), and cut it down to the smallest size possible for practice on the road, especially in hotel rooms. The final guitar fits in a large suitcase and is very quiet, basically like an electric guitar not plugged in. It is not loud enough for performing or playing around a campfire, etc, but is OK for practice alone.
It only requires a cheap nylon string guitar, basic tools, and a few parts you can get at any hardware store. It took me about a week working in the evenings to finish, with most of the time being waiting for glue or varnish to dry.
Note: this is a follow-up to this instructable (in case you want to know more about the whole development process): https://www.instructables.com/id/Travel-Practice-Guitar-with-video/
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Step 1: Get a Cheap Classical Guitar
I got a cheap guitar on an online auction site for around USD$30, used. The guitar had some damage, which probably made it cheaper than otherwise, but there are a lot of inexpensive used guitars available. The exact model of this one was Kasuga Guitars G-130.
Step 2: Cut Off the Guitar's Back and Remove Bracing
Just use a saw to cut the back right off the guitar, cutting lengthwise along the sides. The leftover parts of the sides at this stage will keep some of the rigidity and prevent the neck angle from changing, so don't cut them off completely yet.
You're going to be gluing/screwing parts onto the back of the soundboard, so remove the bracing so it doesn't get in the way.
Step 3: Cut Off the Guitar's Head
Just saw it off right above the nut. Leave a little space for where you're going to attach the strings.
Step 4: Put a New "back" on the Guitar
Cut out a piece of the original guitar's back (or another piece of thin plywood) the size that you want the final guitar body to be. It only needs to be long enough to reach from just below the bridge to the neck joint.
Note: the picture actually shows after the next step, with the rest of the soundboard already removed. I forgot to take a picture after attaching the back and before cutting off the rest.
Step 5: Cut Off the Rest of the Soundboard and Old Sides
With the new back attached, the guitar should have enough rigidity that you can cut off the upper and lower bouts and the butt end of the soundboard. This leaves you with the basic shape that the final guitar will be.
Now you can also cut down the overhanging bits of the back to the final shape.
Step 6: Make the New Sides
With the back and soundboard attached, you can measure the areas where your new sides will go, and cut them out of the old guitar's back or other plywood.
Step 7: Attach the New Sides
I used wood glue and some small screws.
Step 8: Shape and Sand Down the Headstock
You'll need to cut an angle on one end of the headstock as shown, because the strings will be coming around the butt of the guitar at a very low angle.
Also sand the finish off of the flat side of the headstock that will be attached to the back of the guitar.
Step 9: Attach the Headstock to the Back of the Guitar
I used glue and a number of screws.
Step 10: Head-end String Attachment
You'll need a way to attach the strings at the head (the far end of the neck). I drilled seven eye-bolts into the end, and threaded a long bolt through them, and capped it off with a nut. This allows me to just tie the strings to the bolt, one between each two eye-bolts. This needs to be pretty strong because it holds all of the string tension for all six strings.
Step 11: Butt-end
The strings need to be able to go around the butt end smoothly so that the tuners can function correctly. If there is too tight of an angle, or if the strings get caught at the end, they will break while you are trying to tune them.
Some rollers would be ideal here, but I couldn't find any good ones, so I bought some metal tubes and screwed two of them so that the strings go around them as shown. This works OK, but I still need to be pretty careful while tuning up. This is an area where a creative person may be able to make improvements.
Step 12: Finish the Guitar
Now the basic construction is done. I put a couple of coats of varnish on, and painted black bindings around all the edges just for looks. Then you can put the tuners back on and string it up.
My final product is 72cm long and fits in my large suitcase as shown.
Step 13: Video
The video shows an overview of the process with pictures and a short performance. You can hear that it's very quiet, really only good for practicing.
I hope you find this useful and get some good ideas from it. Please share if you have something similar or any good ideas about this kind of construction. Enjoy!