I really wanted an ATC for my machine. I looked and researched and tried just about everything for around 2 years. I made the tormach style changer (Mock up for feasibility) using a head stock from a lathe, a MT2 1/2" collet, and homemade draw bar, actually worked pretty well. Until I tried to run it past 5000 rpm. then the vibration was pretty scary. We build spindles at the company I work for (large ones, 120mm is the smallest). I showed my design to the engineers who design the spindles. They said it was defiantly do-able. The issue was that you would need to do high precision machining and balancing, which are expensive. To make a prototype I would be looking at a few thousand.

So it's not that it can't be done, it's just that to get what we need it's expensive. In the end I dropped around $2k for a used columbo, and a new Delta VFD. and another $300 on tool holders (Got lucky got 12 used for $300). I would do this again in a second. I see used ones come up on eBay every once in awhile, just need patience.

One other thing I looked at was using a router, and actually swapping out routers. This would be the cheapest method, but take the most space. You can buy porter cable routers on eBay for less than $100. Or make your Y axis extra long and put 2 or 3 routers on the same set of rails with different drives, for Y1, Y2, Y3 etc. I know routers aren't the best spindles, but changing brushes and bearings is actually pretty easy.