Apologies first for posting this here as well as on a CNC forum. (It's been on almost a week and enough people have looked at it but not one reply or suggestion.)
I'm considering building an auto tool changer for my home built CNC mill (based on an Alexander engraving machine). I designed the spindle (perhaps short-sightedly) to take ER32 collets directly in the spindle. I did however put a 12mm hole right through the spindle with a drawbar in mind.
The taper on the ER32 is very similar to an R8 taper which is commonly used with the Tormach TTS toolholders. The TTS toolholders have a plain 3/4" spigot and an annular flange which is pulled up against the end of the spindle by the action of the collet pulling the toolholder into the spindle. This gives a repeatable tool height.
I am thinking of making a special collet with an 8 degree taper (as ER32) but with a plain section and 12mm thread for a drawbar which will be pulled up with Belleville washers.

I would make the collet out of a decent tool steel but don't contemplate hardening it as I don't have the facilities.
The spindle has a 3 step poly-v pulley arrangement and with a nominally 0.55KW 3-phase motor and VFD can run anywhere between 200 and 10,000 rpm.
Can anyone think of any good reason why this wouldn't work?
I don't particularly like the idea of a pneumatic actuator for depressing the drawbar as my compressor is deafeningly loud and it frightens the life out of me every time it starts. I've thought about linear actuators either acting directly on the top of the drawbar or through a lever system to amplify the force. I haven't tried to do any calculations but I'm thinking I will need a force of around 5,000N (roughly 1,200 lbf) to compress the Belleville washers. I'm not too worried about speed of operation as long as it only takes a few seconds rather than minutes to open the collet.
Another drawbar solution I've seen used is to use an electric impact wrench to tighten the drawbar but these are noisy and still need something pneumatic or motor driven to lower the impact wrench onto the drawbar hex.
Any other ideas?
Cheers.
Phil.