Cello Guitar . Model Z9.1

I was given a broken 3/4 size guitar (children guitar) , and I wanted to avoid to drop it into the trash.

Unfortunately, to repair this guitar, I had to sand a lot, and the acoustic table became very thin and very fragile to such an extent that it was impossible to stick a bridge on it because the acoustic table could not have supported the string strength.

So I decided to turn this guitar into a cello, just for fun.

For the body : A 3/4 size guitar

For the neck : PVC tube diametre 8cm and a piece of wood 50cmx8cmx2cm

For the bridge : wood + hard sheet thickness 5mm (I used a bottle recycled plastic sheet)

For the tail piece : PVC tube diametre 8cm

For the foot : hardwood (to be turned on a wood lathe) + M10 threated rod

Tools: band saw, wood lathe, hot gun, hand saw, files, glue, screwdriver, etc...

Imagine: the bridge was unstuck, the acoustic table was cracked, and the varnish was in a terrible state.

I sanded the bad varnish, I glued the acoustic table, and there is the result.

It looks fine, but as you cannot see on the picture, on sanding, I was forced to eliminate a big quantity of wood, so that the acoustic table has become very very very fragile.

It means that I will have to reinforce the acoustic table later, in order to support the strength of the strings. This specific point will be explained later.

The principle of this cello guitar is to keep the guitar body, but to raise the strings over the acoustic table, in order to be playable with a bow.

The best is to have a look to the overall drawing

The neck of this cello guitar starts thin and gets higher as higher notes are played....

Three parts are glued together :

• an intermediate flat support for the PVC tube, and
• a cut PVC tube D=8cm
• a flat and triangular wooden part, (otherwise the bow touches the body of the guitar)

1 - The intermediate flat support for the PVC tube

This is a flat, hard 2mm sheet of hard material, having the same dimension as the wooden triangular part

You can use a flat aluminum profile or PVC but not HDPE because HDPE is difficult to glue, even with epoxy glue.

In my case, I used FR4 epoxy strips for PCBs I had on the shelves. Thickness = 2,4mm.

2- The curved PVC guitar neck

This is the hardest part of this project.

For more precaution, cut a PVC tube 30mm longer than the fingerboard. (30mm because we need 15 mm for the neck saddle, and 15mm as precaution).

At the end of the machining , this part must be symmetrical on its axis, and perfectly flat.

Draw an axis lengthwise and symmetrically draw the small fingerboard width (in my case 46mm) at one end and the large fingerboard width (in my case 60mm) at the other end of the tube. Cut out. In my case, I used a bandsaw.

Lay a sheet of sandpaper on a table, then sand the piece of tubing you just cut on in order to flatten it

Glue a piece of tube 15mm wide on the small width and cut it so that it is flush with the tube

 3- Triangular piece of wood

Cut a piece of wood (in my case 15mm thick, but check that you don't need more in your case) 15mm longer than the fingerboard of the guitar

Cut this piece of wood into a triangle (0mm at the start and 15mm at the end), so that the neck of this cello guitar starts thin and gets wider at the end

4- assembly

It is the flat support of the PVC tube which must be maintained on the nut of the neck of the guitar, and the PVC tube which must pass above

First, glue the PVC tube on the tube support with epoxy glue with an offset of 15 mm (neck saddle witdh).

Do not glue immediatly this assembly on the triangular wooden piece because you have to verify that the cello guitar is playable before gluing

Even without gluing, you can see if the assembly suits to the neck , and you can cut allready  this set to the size according to your guitar

As I said in introduction, the sound table was very very very thin. I decided to reinforce it with a fir plank. (thickness= 5mm. Decoration = Pyrography)

This plank supports the bridge (in my case 2 machined wooden pieces comming from a cupboard door) and the saddle.

The saddle itself has been done with a recycled plastic sheet I did melting transparent plastic bottles at 260°C. Thickness about 5mm. This part is very hard. It is possible to have a good result with hard wood (I did it in a previous prototype) .

The position of the saddle depends on the distance you measure between the neck saddle and the 12th fret (diapason distance) . Double this distance, and you have the position of the bridge saddle regarding to the neck saddle

The high of the saddle depends on the high of the neck . At he end, the strings must be 2mm higher than the neck at the 12th fret level

The Tailpiece :

I did it from a PVC tube D= 80mm .

The tube is heated with a hot gun in order to be shaped

It is flat on the the back of the guitar, and slighly round near the bridge saddle

The foot

Total length= 300mm

Turned wood = boxwood + Pyrography

Threated rod = M10

I had no idea about what kind of strings I had to mount

So I used D G B E metallic string guitar I had on my shelf.

I tuned the strings... in D G B E... like a guitar having only 4 tuning pegs!

I was later told that a cello isn't tuned like that, but I don't care as long as I can have fun with it!

In fact: Tune as you want!

File the notches at the neck saddle with a fine file. Since there are no frets, the height should be 0.2 mm near the neck saddle, and then , file and adjust the bridge saddle to have a height of 2mm at the distance of the tuning fork

File the notches at the neck saddle with a fine file. Since there are no frets, the height should be about 0.3 or 04mm 

Then , adjust the bridge saddle to have a height of 2mm at the distance of the tuning fork

Buy a bow (first price about 10 Euros on your favorite webstore) and rosin resin (first price about 1 Euro) and play!

The bow must be able to touch each string without touching neither the string nearbyn and neither the acoustic table

If it is not the case , rectify the triangular plank, or the shape of the bridge saddle

Note that as I don't play a cello, I drew dummy frets on the neck to get some reference points.

After checking that the cello guitar is playable (the bow can play all 4 strings), the triangular plank can be glued and then screwed onto the fingerboard

In my case, I counter-drilled two holes in the curved fretboard: one between the 4th and 5th fret, and another between the 16th and 17th fret (be careful not to drill too deep to go through the fretboard). guitar!), to pass 2 wood screws L=15mm inside the curved neck of the cello guitar, just placed on the intermediate flat support for the PVC tube (put a washer if possible)

Miracle!!!!! I have created the most beautiful in the world, unique and personal cello, playing the most wonderful music I ever heard! Admire my magnificent philharmonic concert costume, and.... Ouch! be careful with your ears!

https://youtu.be/vt0qBlkvAQs

Hem, Hem, Hem....To be honest, must admit that it doesn't sound really as good as a Stradivarius and that the instrument isn't exactly easy to play because of the thickness of the neck...

But it does not matter , because I achived my two goals wich were to  have fun creating an original music instrument and saving this broken guitar out of the trash, too.

Anyway, now, as bonus, it makes a wonderful decoration in my bedroom!

I hope you enjoyed reading this instructable!

Greetings from France!

Bruno