Ignoramus6705 wrote:
I ran my mill for 16 minutes at 3,000 RPM (I get email when my CNC
jobs complete). It was machining a mold prototype for a kids toy. We
will need to cast 18 of them that in wax, and the mold will be made
from Aluminum. But I digress.

After I finished running for 16 minutes, I measured a few temps:

*) Inside the shop - 86 degrees
*) On the variable speed transmission on top -- 105 degrees

The varispeed runs hot, because the belts rub. That is normal, that's
why they have air vents in the housing.
*) On the low part of spindle (at the QC-30 collar) 115 degrees. I am
not sure if I fully believe this last measurement. The bottom of the
spindle feels warm to the touch, I can hold it indefinitely, but it is
not comfortable.

Would you consider this temp rise to be excessive?

Yes. This temp rise in only 16 minutes at 3000 RPM does sound
excessive. But, this is a series 2 machine, with 3 HP motor?
(I'm trying to remember.) They usually have sealed, grease-packed
bearings, which run a lot hotter at
high speed than the oil-drip bearings used in many of the Series-I
machines. This kind of heating is going to cause
spindle growth, for instance, making it hard to hold fine tolerances on Z.

(I see in your reply to Gunner that it is a sealed-bearing unit.) One
possible problem is somebody repacked the bearings with too much or the
wrong kind of grease, or that coolant and swarf has gotten up in there.
The oil-lubed Bridgeports depend on oil dripping down to flush
contaminants out of the bearings. If your bearing seals are shot,
contaminants could easily work up into the bearings (gulp). I think it
is fairly easy to drop the spindle cartridge out of the quill. There is
a setscrew that locks the bearing cap. You remove the setscrew and
unscrew the cap. The entire bearing/spindle assembly may just drop out
the bottom from its own weight, so be ready to support it. This should
allow you to examine the seals, at the least, and the cleanliness of the
inside of the bearing region. If filled with crap, you know you need to
flush and relube, at the least. The bearings need to be filled with a
known quantity of lube to avoid overfilling. If you have to replace the
bearings, they may be a bit expensive. I know the bearing sets for the
Series-I are quite expensive.

When reassembling, you use the dimple made for the setscrew to put the
bearing cover back in the rght position, and then GENTLY tighen the
setscrew to avoid warping the quill.

If you decide to take the bearing assembly apart, ask for advice, it is
a bit tricky, and I don't know the sealed bearing version. The bearings
need to be aligned a certain way and fitted with matched spacers. I
know there are couple guys on here that know the procedures well.

Jon