I find I'm spending a lot of time on the phone trying to teach my brother how to buy a mill. I thought I'd put together some fundamental principles and practices and send them to him. To remind everyone, he's looking for a manual (not CNC, sorry to disappoint those who advocated for it) vertical mill, probably a Bridgeport type.
Here's what I've thought of so far off the top of my head.
Bring a small powerful flashlight, a rag, and the list of BP serial numbers
Look very carefully for missing handles. Pull the powerfeed engage handle to the left - it should stay there. Crank the table all the way side to side and front to back. Note the resistance to cranking - it should be even end to end. Looser in the middle is bad. Check backlash on the table cranks - it should be under .015" on the dials. Tighten the table's X and Y locks and then try (gently) to move the table. If Bridgeport, date the machine by comparing the serial number to the table. (The serial number that matters is on the top front of the knee under the way guard.) Pull the one-shot oiler and see how it works - i.e. if it feels plugged up. Look for oil.
Run the spindle & listen. Should be quiet and smooth. Any bearing noise is bad. Run the table powerfeeds (if any) making sure the table isn't locked. Turn on the DRO (if any) and watch it as the table is fed. Run the spindle in both directions. Vary the spindle speed from lowest to highest, listening. Should stay quiet.
Anything else? Anyone have LA area machinery dealers to suggest?