Since I was very young I've always wanted an upright bass, but I am too poor to afford one (they are VERY expensive!) so I decided to try and make as close an approximation as possible.

Presenting: A fretless archtop upright bass made from a wheelbarrow!!

neck-thru (cigar box style) made from a solid mahogany door frame. Wheel left on for portability.
Technical specifications:

Aluminium wheelbarrow body
67 inches tall (1.7 metres / 5.58ft)
3 strings (weedwackers) tuning: EAD
Scale length 41 inches (104.14cm) w/ adjustable bridge
Action 0.5 inches
Neck width 3.5 inches (8.89cm)
1.75" diameter body-coloured foam bumpers
Sound post and f-holes
Bridge piezo pickup

Can have saddle bags attached to carry other instruments (mandolin, guitar, etc)

Supplies

Aluminium wheelbarrow,
For the neck: Hardwood length (approx 2M long)
For the bridge: Softwood (pine is best)
For the face: Plywood board (5mm thick)
Pencil & Jigsaw
Cordless Drill

Step 1: Prep Wheelbarrow & Cut Neck Holes

Disassemble the wheelbarrow and cut the handles off just below the point where they meet the bottom. This will make crude 'feet' on which the wheelbarrow can stand vertically (pictured)

Using the drill, I cut holes in each end of the wheelbarrow under the lip right in the centre. Symmetry is very important throughout this process as I need the bass to be well balanced when it is standing up to be played.

After cutting out some pilot holes, I used the jigsaw to cut out a rectangular hole at both the top and the bottom, being sure to keep the 'lip' of the wheelbarrow intact.

It's important that the neck goes all the way through the body (cigarbox-style) as this will support the massive string tension when the bass is finished.

Step 2: Push Neck Through

Since the holes I just cut are only the same size as the neck, I had to really *force* it through. Tight-fitting is desirable, ensure it goes all the way through. The 'wheel end' of the wheelbarrow is the 'top' where the neck protrudes and the 'handle end' is the bottom where there should be a quarter-to-half-inch of the neck sticking out which will later be used to screw a threaded bolt that will support the tailpiece.

Notice from the picture above that I left the 'lip' of the wheelbarrow intact - this is very important.

Make sure the neck is straight (touching both lips) so that it is parallel with the top of the wheelbarrow. When it is standing up, the neck should point straight up at 90 degrees.

Step 3: Shape Neck, Make a Heel

I removed 2.5 inches of thickness from the neck with a jigsaw, then I used a rounded file and various grits of sandpaper to make a heel. This stage took many days. I end up with a very long smooth neck approx 4 inches thick at the heel and 2 inches thick for the remainder of the length.

Step 4: Sound Post

The sound post will transfer vibrations from the face plate (not fitted yet) to the aluminium wheelbarrow body. It is cut with the jigsaw from a (roughly) 20mm diameter broom handle which sits in a hole drilled in a block of pine and then mounted using spray-adhesive and a screw.

Mounting point for a second sound post can be seen in the picture but I later found just the one to be more than sufficient for volume.

Note that at no point can the sound post ever be allowed to touch the neck. This will be important later.

Step 5: Face Plate, F-Holes, Fingerboard Test

F-Holes are very important for hollow-body instruments. I looked for an internet image, scaled it up and drew on the face-plate (5mm ply slightly bigger than the wheelbarrow top) using a sharpie. The F-Holes will later be jigsawed out of the face-plate.

Next I cut a test piece of wood the same width and thickness as my fingerboard will be. This was temporarily screwed on to the neck at the top and some small blocks were used to raise the bottom end so that it 'floats' (image 4) - the resulting V-shaped 'gap' will be filled with a wedge of hardwood that was trimmed off the neck width earlier.

I marked the location of the F-Holes and where the nut will be, in my case this gave me the desired scale-length of 41.5 inches.

I then cut off any remaining length of neck above the nut. Here's the headless result (pics 5 and 6)

Step 6: Tuners & Peg Box

I never originally intended for the headstock to be a separate piece, but I found these massive tuning pegs on eBay and instantly fell in love with them which necessitated building a peg box for them.

The peg box is approx 1 foot long and glued and screwed together. I used a pillar drill to cut large holes for the tuning posts.

Step 7: Putting It All Together

I mounted the peg box on top of the neck and because of the 'wedge' that was made in an earlier step, the peg box does not sit flush with the angle of the neck but rather that of the fingerboard, which is approx 10 degrees sloping backwards (pic 4 shows the back of the peg box flush with the neck, the angle difference is clearly visible)

Pic 3 shows a profile view.

Pics 1 and 2 show how much glue and screws I used (taking no chances!) I used spray-adhesive, waited for that to dry, then kept adding 'stronger than wood glue' for a few days until I was sure it had filled every gap. I used white spirit and a scouring pad to remove all the excess glue after it had dried (4 to 5 days)

Step 8: Archtop & Ribs

The face plate (sound board) cannot contact the neck piece or else the acoustic properties of the instrument will be ruined, so I used a band saw to cut some 'ribs' from hardwood with notches in them that allow them to fit over the neck piece but without contacting it.

The sound board is then screwed directly to these ribs which forces it into a curve. I mentioned in an earlier step that the ply must be slightly larger than the wheelbarrow. This is the reason for that.

I sprayed the inside of the wheelbarrow and the ribs with black paint to emphasise the F-Holes when the soundboard is fitted.

Step 9: Nut & Bridge

The bridge is a simple block of wood with two legs and some grooves to carry the strings. The nut is some more broom handle (grooves in the same place on both)

Step 10: Tailpiece

The tailpiece is made from mahogany, approx 2/3rds of a foot long with holes drilled for the strings, plus a larger decorational hole at the bottom. Two small holes were also drilled at the bottom through which I attached a U-Bolt which hooks over a 'tapcon' masonry screw approx 2ft long and straight into the bottom of the neck (pictured in image 2) - This allows for intonation to be adjusted, and since the bridge is adjustable too, the scale length can be changed (between 40 and 42 inches)

Step 11: FINISHED!

For the strings I used 'weed wackers' bought from a music store. I bent the metal lip of the wheelbarrow over the sound board and hammered it down ( this is to ensure that sound can only escape via the f-holes) then I concealed the ugly edges with water-pipe foam insulation. The 'body-coloured bumpers' give it a whimsical appearance.

Because I plan on using this for recording sometimes, I attached a piezo-pickup to the bridge, although this is undoubtedly unnecessary since this instrument is very LOUD acoustically as that was its primary design brief.

I am making small saddle bags and a removable metal cage which will attach to the bass and be used to transport smaller instruments (ukulele, mandolin, washboard, etc) as well as tobacco, food, whatever else.

When converted into 'wheelbarrow mode' by gently tipping, the bass has an all-terrain tyre.
tuning is E1, A1, D2 - same as the lowest 3 strings of a 'traditional' upright bass
Technically it is not a double bass but a contrabass balailaika (barrowlaika!)