[CS900]

I posted this in my build thread as well, but I think it's a relevant topic for most mills so I decided to make a separate thread for it.

background info:
I have a cnc'd PM45M that I'm finally getting around to doing a pulley conversion on. I've installed the typical 7206 and 7207 bearings that almost everyone who does this seems to use and I'm trying to test the pre-load of the bearings by running the spindle in my lathe. I originally started out with a special high speed NLGI.5 lithium grease but due to my issue I have switched to a thicker NLGI 2 lithium based grease.


that brings us to "The issue":
As I start running the bearings all the grease gets pulled thru the bearing leaving the races dry-ish after about a minuet or so. It's to the point where I can hear the difference in the bearing. It's much more noticeable on the upper bearing, but after removing the dust cap the bottom bearing also seems to have this issue to a smaller extent.

So has anyone else noticed this happening? I know a lot of people use kluber isoflex nbu 15 when doing this conversion, but i'm not shelling out that kind of money until I can get the grease to stay in the bearing. I've been tossing around the idea of removing the bearing and making a shield to instal under the bearing, but I'm lazy and I don't want to jump to removing the bearings if I don't have to quite yet.

[engnerdan]

Bearings can't stay loaded full of grease at the speeds a spindle turns. If the bearing was full of this grease it would cause heat to build up in the bearing and a significant amount of drag. In fact too much grease will cause premature bearing failure. All that is needed in the bearing is a very light film while it is running.

-Dan

[CS900]

Hi Dan,
You're very correct. However currently I'm running the spindle no faster than 800 RPM at room temp. According to the dN of the grease I've been using I'm well within the capability of the grease (i won't be at 8000rpm though!), so even if I were to over-pack it, at these speeds it shouldn't cause too much of an issue I wouldn't think?

The more I read up on it, the more I'm thinking about doing a controlled oil drip or mist system for these speeds. CNCcookbook has a pretty good read on the subject as well.