I started trawling TradeMe (New Zealand's too small for Ebay to bother) and ran into a problem. New Zealand seems to be going through a Ukulele renaissance at the moment and second hand ukuleles are going for hundreds of dollars while guitars are going for tens.
Would it be possible to take 2 strings off a guitar and call it a ukulele?
Step 1: Find the Right Scale Toy Guitar
Since you can't pick up and strum instruments online, it's always a gamble, but at least you can find out whether it would be possible to string it as a ukulele.
Here are some typical ukulele lengths. I know I found them online somewhere but I can't remember where. Scale Length (SL) is the distance of the strings, from nut to bridge (see photos). Overall Length (OL) isn't as important as scale length but it is more likely to be in the description.
Soprano Uke - SL = 13"/33cm OL = 21"/53cm
Concert Uke - SL = 15"/38cm OL = 23"/58cm
Tenor Uke - SL = 17"/43cm OL = 26"/66cm
Baritone Uke - SL = 19"/48cm OL = 30"/76cm
The toy guitar I found was:
SL = 49cm OL = 74cm so I was confident it would be OK for a baritone uke. It also had two missing tuning pegs which didn't bother me but is probably why it went for only $10.
Step 2: Convert the Nut and Bridge From 6 to 4 Strings
I thought my $10 guitar wasn't worth a new nut and bridge so I decided to mangle the original ones.
For the nut, I used a mini hack saw for the two new grooves. I used a regular sized hack saw blade to widen the grooves.
For the bridge, I used an extra long 2mm drill bit and drilled from the end until it showed in the groove.
You can probably see that I could have done a better job of the hole drilling. I drilled holes in between the old holes but I should have drilled the holes closer to the center. The gap in the middle strings ended up larger than others.
Step 3: Set Up the String Action
You can change the action by the depth of the grooves in the nut and by height of the bridge. I adjusted the nut by holding down the 5th fret and cutting the groove until the string was within half of the diameter of the string to the first fret. Then I started shaving off the plastic bridge but it was still too high so I had to take off the strings and plane down the wooden bridge base to give more adjustment. The bridge base was black and you can see the part I planed off.
I kept shaving off the plastic bridge until I thought that any lower and it would start to rattle.
I put some ukulele strings on it and I haven't looked back!