Wire tuner are a quite good compromise between function, working effort and price. However, they can not hold too much tension. So for Ukuleles, they are definitely perfect. Also, for guitar nylon strings everything is all right, but steel strings might not work well.
How to make wire tuners:
First, find some good wire. It must be strong enough to hold the string’s tension, but at the same time still stay bendable, so you can work on them. 2-3mm wire should be a good calibre. Fence wire, wire from cloth horses, wire from giant sparklers… you will find something.
It’s good to sand the ends of the wire before. The bending itself is pretty easy: take some pliers and bend your wire. It may take a few tries, before you get a consistent style, if this is important for you. That’s it in the most basic form. Wanna do the fast edition? Take a powerful cordless driller and attach the top of the wire from the side. Then slowly let the driller pull the wire.
The straight end, should go around 2cm deep in the neck. Predrill the hole. If you are not sure about the required drilling diameter, try it first with a left over of the same wood and see, if the tuner sits in tightly. If you don’t have the right driller diameter, you can also just take a piece of the wire, make it pointy and use it in the electric driller.
In case the tuner ever gets loose, take it out and give a bit of wood glue to the sides of the hole. Let it dry and bring the tuner back.