Arturo,
This wasn't touted as a replacement for Brian's tool changer but more for a conversion of a centre lathe to CNC.
This also answer Bloy's question in the same post, these are off the shelf units, made in Italy to quite a high standard and available in a number of ratio's.
As an idea these cost about 80 UKP each, new.
You couldn't make one for the price given hardened worm, bronze wheel and 4 bearings. I have had one of Brian's tool changers in pieces and they are crudely made.
There is tons of backlash in the worm and wheel, in fact it's a gear not a worm, and it relies heavily on being driven backwards against the pawl
My idea was to take one of these, fit a stepper and a large top hatted disk, the smaller diameter to fit inside the final drive worm and the larger diameter disk to carry 6 or 8 tools.
On the rear of the disk would be machined 6 or 8 ratchet teeth for a pawl to lock into.