Oil Mist Lubrication Versus Sealed Greased Bearings

Woodworkers discuss lubrication systems and the pros and cons of machine modifications. June 28, 2013

Question
I have several old frequency pin routers with oil mist lubrication directly to the bearings. I've replaced one set of bearings on one machine with greased high speed spindle bearings. I've done this before with some success but I'm wondering if others have tried this?

Forum Responses
(Solid Wood Machining Forum)
From contributor H:
Would 20,000 to 25,000 rpm overheat the grease in sealed bearings? I think liquefied grease may not lubricate as well as an oil mist.

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From the original questioner:
Yes you're right, regular sealed bearings won't cut it at 22,000 RPM. The spindle bearings which I've installed are precision high-speed bearings which must be packed with special high RPM grease. They're fairly expensive and not too easy to replace. They also don't last forever.

As a rule, I don't like re-engineering stuff or "tweaking" stock tools or equipment to satisfy some ill-conceived notion but in this case it was necessary. I have another router motor however that is also in need of new bearings. I've been told that as long as the spindle rpm doesn't exceed the rpm rating of the greased bearings, I shouldn't have a problem.

I think though that I will probably just stick with the original oil mist system and stop trying to re-invent stuff. My old grandpa was good at re-inventing stuff until he had a whole workshop just chocked full of "special tools and equipment" (junk).

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From contributor D:
I don't know about reinventing stuff, but I'd prefer high speed sealed bearings over oil misted, and oil misted over babbet. I've just been through changing cheap stripped out brass nut inserts on a widebelt sander's jackscrew. Higher quality components like oil bath or greaseable inserts, or even higher quality ballscrew units usually found on heavier duty more expensive machines would have lasted longer than the pathetic 3 1/2 years this one did.

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From contributor F:
Is there a downside to oil mist bearings? I have open bearings in a shaper that the oil drips down into. I've been told by several people these were the best kind to have, and that sealed bearings would be down a notch. Would oil mist be about the same?

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From the original questioner:
I believe the old oil mist systems allowed for freer and quieter spindle rotation and therefore more hp where you need it. After switching the machine off, the oil misted spindle will continue to rotate much longer. My problem was that I needed to permanently invert the motor which made the oil mister inoperable (all the oil drained out).

I agree with Contributor D though that some equipment improvements or alterations can be made, but I always give it more than a second thought. Years ago, my grandpa took his old babbett bearing jointer and lathe (both circa 1880) and cut them up and added ball bearings and electric motors. Of course this was the logical solution at the time but (as far as I'm concerned) he ruined two vintage pieces of equipment. To his credit (and though he's long gone) his lathe still runs fine but I had to junk the old jointer which was a real shame. It was once a pretty piece of Victorian machinery before he started welding on it.