Spindle Bearing Oil for Toolpost Grinders

Bill, I just sent a unit back to Dumore for overhaul, as the shaft and bearing assembly is pretty special and is balanced at the factory. At least my grinder is sealed and no lubrication is required. My bill was around $350 all in. I didn't think that was too bad. I'm not sure this is a lot of help, but more, I don't know. Perhaps calling them on the phone would be useful, they were very friendly and helpful when I spoke with them Steve

Thanks Steve, I didn't notice any Dumore models that weren't serviceable (in looking thru their various models), but I did see their recommendation to return their motors for servicing.

These grinder's parts would need to be made up of specialized parts for the speeds they operate at, and I'd suppose that many used ones don't operate as well as they were intended to.

Bill, If the spindle assembly is not up to snuff, you see harmonic patterns in the finish. I think it's cheaper to leave it to the experts to sort out. My last experience was with a small unit that I bought used. It looked like new, but when I tested it, there was an inperceptable vibration and this could be seen in the finish. When I sent it back, I was told that there had been an engineering change in the design, which they applied to my unit at the same time. If I had had not sent it back, I would not of known. It now works perfectly. Steve

At those speeds, most bearings will be running with air/oil misting and a very light turbine oil such as DTE Light

Cavitation becomes a real problem at high speeds in oil baths, as does the fact that oil isnt a compressible and too much tends to make the balls in the race ride up and over the oil droplets, slamming back down on the other side.

The same effect that makes potholes on the back side of speed bumps.

Gunner

"They couldn't hit an elephant at this dist..." Maj. Gen. John Sedgewick, killed by a sniper in 1864 at the battle of Spotsylvania

A $6 6001 (12 x 28mm) bearing is rated for 26KRPM grease lubed and 32K in oil. Oil mist or oil spot lube will probably push that to 45K. But the devil is in the details of the spindle's construction at those speeds. What you get with a $200 bearing is not necessarily higher speed, but closer tolerances on the bearing's dimensions and running accuracy.

Thanks for the suggestion. As most things, there appear to be various grades of Mobile's DTE oils, and I'll spend some time looking into Light and the others.

Yep, the balls want to hydroplane, but there's nowhere to go.

Thanks for the technical info, Ned. Those numbers help to put things into perspective.

I think those numbers were intended to apply to quality bearings, and not many varieties of the dirt-cheap versions.

I suppose that a portion of the $200 bearing price would be for individual human inspection and selection of the bearing assemblies, and possibly related to a certain number of rejects that don't make the grade.

Thanks again, Steve. Yep, I would expect any slight problem to relate directly to the performance and the overall quality of the finish.

I was reading the earlier posts on balancing, and was surprised to learn of the number of effects of balancing for different characteristics, and the effects of those procedures on different speed ranges.

I don't know if I'll use these grinders on lathes, or maybe just apply them to dedicated small parts grinding setups.

I don't do any machine operations that require any level of high precision, but if I were to do some tooling grinding it may involve finishing of an arbor taper, cutter sharpening or resizing small hardened parts.

The numbers come from SKF. I didn't check, but I imagine recommendations from other major mfrs would be similar. The $6 I mentioned will get you an SKF, NSK, etc., bearing. A remarkable bargain all things considered. But, yeah, I'd be reluctant to install no-name bearings in any critical app to save $2.

I'm sure that's a big part of the price. That $6 bearing is quite likely to come very close to, or even meet, the specs of the $200 bearing. But it doesn't come with the guarantee that it will.