[zephyr9900]

Just Gary, thanks for the feedback. The collet is proud of the nut when finger-tightened with the "lozenge wrench"), and also seems to be proud when just finger-tight, so that is encouraging. I just found a few PCB mills with distance rings I bought years ago at a model railroad show, so I can do some testing.

I have been buying my tiny endmills from Bits & Bits, and they're not quite as free as your dentist-originated bits.

I recently replaced the nose bearing on my Proxxon with a hybrid ceramic bearing from Proxxon World in Australia, which seems to have a better feel than the stock metal bearing did. It is a single bearing, but spring-loaded upwards against a stop on the spindle. With the light milling passes I'm hoping (and it seems so) that the mill doesn't pull down against the spring enough to deflect it (well, I realize that everything has deflection, but relatively not here...)

thackman, the Machinist Mate software I use to calculate feeds and speeds (not being knowledgeable enough to do it in my head ) says for a 2mm 2-flute endmill in aluminum 29krpm and 16ipm feed. So at 5krpm the feed would be 2.75 ipm--I've had good success ratioing the feedrate from the rpm, assuming I'm using coolant. The .020" endmills I've been using want 76krpm and 10.7ipm in brass, and I'm not breaking any lately going 2.8ipm at the Proxxon's (assumed) top speed of 20k.

herbert, the distance rings I'm talking about are the ones pressed onto the endmill itself. I know the term is used for various purposes (I've seen it used for lens spacer rings too). But your bearing distance rings (for preloaded pairs, right?) sound very nice. I'd like to hear about your experience doing that, if you don't mind telling.

Randy