Do you like guitar? If you're a mover and shaker you've probably noticed they aren't great travel companions, especially if you have other stuff to take with you. Fortunately, acoustic guitars have plenty of built in space.
In this instructable I'll show you how to make an acoustic guitar have a second function: as a backpack!
I picked up a nice used guitar for $35 and made the rest of the modifications at no cost. Check it out in action to see how it operates and sounds. I've been using this guitar with the backpack modifications for 2 years now and have had no problems with detuning, warping, etc. It's survived road trips, flights, camping adventures, and a lot of abuse on both coasts and in between. I've been really surprised and impressed with the durability and sound quality.
Step 1: Materials
OPTIONAL: Old belt, twine/string
Step 2: Prep Work
The first step we will take is to assess the guitar condition. Go ahead and remove or loosen the strings of the guitar so you can get into the guitar sound hole. Now is a good time to wipe down dust/mud/crud off the guitar and give it a little life.
Next you will need to determine what size of a hole you will want to cut inside your guitar. Look inside the sound hole and analyze the braces on the back of the guitar. They will vary for each brand of guitar so you will have to make this decision on your own. Since the braces on my guitar run horizontal and are spaced about 4 inches I decided on cutting a rectangle of 3" by 8.5".
Once you have determined the size of your cut get some scratch paper and draw it out. This will be our cutting template. Next measure on the inside from the very bottom of the guitar to the bottom of where you will make your cut. On the outside of your guitar make the same measurement and then tape down your cutting pattern so the bottom edge of the cutting pattern is exact distance you measured from the bottom of the guitar. You are all set!
Step 3: Cutting
Now take your Dremmel tool and have at it. Make sure to use safety glasses and be cautious when you first start cutting. You want to make extremely straight lines following the pattern because otherwise the edges of the door won't look as nice. If you have access to better tooling feel free to use it, I think a lasercutter would be interesting to try.
I recommend starting to cut on the smaller sides of the rectangle in the direction of the guitar neck because if you incorrectly guessed the location of where you should cut, you can still adjust it after sawing through on the sides to get a position indicator.
The best way I would to use the Dremmel was to spin up a little over halfway of the given speed settings, cut all the way into the body in one place and then slowly follow the line along the entire side in once clean cut.
Make sure to clean up after all that cutting, there will be a lot of dust!
Step 4: Hinge and Latch
Next you will need to add a small hinge and way to keep the door closed. I had access to a Makerbot Rep 2 so I just printed all of my components, but small hinges and latches are available at all hardware stores and will be cheap to boot. The files I used are attached below. Note that I had to cut smaller rectangles out of the door to help everything fit together nicely, you may have to do the same. I attached the plastic parts to the wood with super glue and it has been working fine for me, you may opt for screws if you want something a little sturdier.
Step 5: Adjustable Strap
Next we will make an adjustable strap for the guitar. If you have an old leather belt this works perfectly. Remove the buckle and find some twine. Make sure there are holes on either end of the guitar strap and tie one end of the twine to one of the holes. If you would rather just make two straps as I ended up doing about a year after using it feel free to skip this step.
To make the strap adjustable we will use what is called a 'line tensioner'. It is essentially a small rectangle with two holes that can be made out of any material. You can find them at your local hardware store, or in a badminton kit. See the picture below for how to tie it. simply make a loop at the other end of the rope and there you have it!
I've attached the file that I used to 3D print a line tensioner also.
Step 6: Strap Pins
Now if you guitar does not already have a place to attach your strap to the guitar I will show you how to add these as well. Originally I used a 3D printer to print some small plastic loops to attach to my guitar but any local music shop will carry guitar strap pins for very cheap or perhaps you can scavenge them off an old guitar. To increase the robustness I replaced these with heavy duty metal bolts and nylon, the thick blue straps seen in the images, which has worked wonderfully. Locate the areas you want the strap to mount on the body and drill two holes for mounting. Most guitar strap pins are press fits, but if not reach inside the sound hole of the guitar and fasten them with the appropriate screw. The files for the 3D printed strap pins are attached to this step.
Step 7: Stringing
The last step before you are ready to both rock and actually roll will be to restring the guitar. If you need help with this check out this wonderful instructable: https://www.instructables.com/id/How-To-String-a-Guitar-1/
Step 8: Adventure
Take your guitar to cool place while carrying awesome things. I use it for everyday tasks such as carrying books to class and running errands as well as fun things such as carrying picnic or hiking supplies. It's a good camping companion and then there's always a reason to play guitar! It's come on multiple flights and made the journey to San Francisco, Boston, Chicago, and many mountains. Make sure to learn some crowd pleaser songs because undoubtedly you will be asked to play.