I got old computer table that was in bad shape, panels were moving and it needed some fixing. Someone before me was nailing it and doing all sorts of things. To make it stable so it was not looking good at all. I need some work bench but I live in small apartment which i rent so i did not want to screw foldable bench to wall. Also i like option that I could move it around depending of place where I need to work.
Problem with small folding tables is that if desk top is small there is not much place to fold legs.

Step 1: Cutting

I am not giving exact measurements because it depends of table you are using as base and/or how big table you would like to make at the end. I'll give just guidelines by which I made my cats.

Min leg panel length = desktop -panel width * 2 -1cm

In my case
75-1.8*2 -1 = 70.4cm

I made round cuts with radius of 8cm which was smallest I can make with saw-blade I had so for comfortable cut make it bit bigger.
You need desk top and to leg panels. Cut leg panels as on image. I made first middle cut and then from that cut 3 parts for legs.

Step 2: Connecting

To connect all parts you'll use 18 hinges. Left image shows outer side of leg and right inner side of it. After connect legs to desktop with 2 hinges each.

DONE!