Tool changing

I'm interested in the possibilty of fitting an automatic tool change
mechanisim to my R8 CNC converted drill mill. My thoughts were to use a
pneumatically activated 20 mm R8 collet that picked up tools (mainly drills
and small slot mills ) each mounted in 20 mm diameter holders. These would
be in a dispenser at one end of the mill table. The holders would have a
flange of some sort at the collet end to fix the position when the collet
was closed. Means I could only use tools up to a shank diameter of say 16
mm but that would be enough for many jobs. All activated by a modified
TurboCNC.

Has anyone done this sort of thing. Ive looked around the web quite a bit
but so far haven't found too much detail on how automatic tool changing on
commercial CNC machines is accomplished. Any leads would be appreciated.

I don't really have to have this feature BUT what a nice toy!

Alan Matheson