If I was looking for a vertical mill for my home shop or small gunsmithing business I'd not get hung-up on the Bridgeport name brand. ...
I'd not let the fact that a nice mill I was looking at had one of the CAT tapers instead of R8, unless I already had a bunch of R8 tool holders. And thinking of tool holding, I'll opt for a tool holder over a collet any day. A lot of the CNC mills have CAT40-50 taper. They won't have if there was something 'wrong' with CAT tapers.
I agree with everything you've said here. The issue for some people will be the size and mass of a mill that uses CAT 40 or 50 spindle tapers; They're usually beefy machines. I'd expect most any machine with a Cat 40 spindle to weigh at least 4,000 lbs. For someone who has the room and the floor capable of holding the weight, a mill that uses Cat 50 tooling will often be cheaper (and the tooling cheaper) than the Cat 40 stuff, at least from my experience browsing in used machine tooling shops. No one seems to want those machines any more.
The R-8 collet system really is pretty weak stuff - it isn't able to transmit the full 2HP of a typical Bridgeport-style mill to the cutter held in a R-8 collet all that well. The reason why we see CNC machines use the Cat 40's and 50's is that a Cat (NMTB) style collet can transmit real power into the tool - like upwards of 20 HP worth of power. R8's have long since started slipping at 5 HP. Bridgeport-style mills are just not that rigid a machine. I like the Sharp version of the Bridgeport-style mill - they're a tad better built and they're more solid in how you can lock up the head's pivot functions.
Also agree about not getting hung up on the Bridgeport name. I'm unsure how much people would want me to prattle on about machine tool makes and quirks, so I just stuck to answering the question. Gorton mills aren't shown much love in the hobby market, so their prices tend to give excellent bang:buck. Same deal with K&T mills, my favorite in beefy horizontal/vertical mills. One day, in my new shop, I'll have a K&T #2 or #3 mill added to my collection. My wife isn't looking forward to the day I die and she has to figure out how to get all this metal back off the property...
For folks who have never seen a "real" mill go to work: You should make some time to snoop around Youtube and look for videos showing a horizontal mill (with optional vertical head attachment) and look at how much those mills can hog off in one pass. That takes rigidity as well as power. Bridgeport-style mills don't have that kind of rigidity, but in gunsmithing, we're rarely taking heavy cuts. Rigidity also gives you better surface finishes - surface finish is a function of tool sharpness, speed, feed, and then the mass/rigidity of the machine. Small, "floppy" machines like a Bridgeport have to take light cuts due to their R8 spindle and lack of mass. Sadly, those monster mills get tossed into the scrap pile at $0.30/pound all too often. If you have the room and desire to learn how to operate a "real mill," you can get screaming bargains on these monsters from the WWII era if you can haul them away. NB that you might be picking up a machine that weighs 6,000 to 12,000 pounds to get this bargain, however.
