On 2010-07-29, Jon Elson wrote:
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?

It is an Interact mill, it is not really a Series II equivalent.

It has a 2 HP motor that says "good for 3 HP for 30 minutes".

(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.

Yes, sealed bearings.

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, I think that for now, I will file your advice but will refrain
from taking the head apart. It is just too risky. Just one stupid
thing and bye bye CNC mill.

i