A bridgepport is a great mill, but lacks the high speed required for
miniature CNC work and engraving. I'm thinking of attaching a high
speed spindle to my Bridgeport spindle with an Erickson 30 holder.
It would hang on a bracket similar to what Jon Elson shows on his web
site, but under the spindle.

http://www.pico-systems.com/wwspndl.html

Any preference for which electric tool is better for this application
(die grinders, trim routers and cut-out tools)?

So you don't have to look them up (using Dewalt as an example):

Tool type Speed HP or watts (if
listed) Current Collet weight

Trim Router: 30K rpm 7/8HP 5.6
AMP 1/4" collet 4.75 pounds
Rotary Saw: 30K rpm ?
5.0 AMP 1/8 & 1/4 collet 3.2 pounds
1-1/2" Die Grinder: 25K rpm 350W 3.0
AMP 1/8 & 1/4 collet 3.25 pounds
2" Die Grinder: 19K rpm 485W 5.0
AMP 1/8 & 1/4 collet 6.0 pounds

Even though I may have to create an 1/8" collet, I'm thinking the
trim router gives the most bang for the buck, but I'm interested in
your take on it.

Thanks again and regards,
Jeff