WARNING For Those Using Spaceage Ceramic Thrust Bearings

[George]

I've been using the ceramic guides for over a year, and find them a superior way of controlling the blade when cutting wet wood. Bought the thrust "bearings" a couple of months ago, and have been satisfied with them - until today.

The directions say that "harmless" sparks may be produced, and so they seemed until I saw smoke curling up from under the insert today. I had cut some spalted beech earlier, without the vacuum attachment, and the sparks ignited some of the punky dust which had collected in the little pocket formed by the guide holders and thrust bearing. Don't know if the vacuum would have prevented or exacerbated the problem, but I'm seriously contemplating a return to the steel bearings, at least below, where dust might create a tinder situation.

You're warned.

[Duane Bozarth]

What causes the sparks?

And I think sparks are never "harmless" in a wood shop...

[George]

The ceramic (flint) and the blade (steel).

I'm fussy about sawdust near the grinding wheel myself, and won't use my belt/disk sander for sharpening because of possible dust, but I'm sure most folks regard the sparks as events with so little fuel in the form of filing that they can't ignite something else.

[Duane Bozarth]

But if they're adjusted properly they shouldn't be against a tooth edge??? That's where I'm confused about the manufacturer saying there're to be some...

Most of the time that's true...it's the once that's a potential problem if the chunk (of ceramic in this case) just happens to be large enough to hold enough energy and the fuel is just close enough to the ignition point...

[George]

Think a moment. As the back of the blade is pressed occasionally against the thrust bearings (what we're discussing), it peens the edges a bit, like turning the edge on a scraper. Since it flexes and such, pieces apparently develop a case of stickout, smacking the ceramics as steel on flint.

If you were ever a scout, you remember that sparks ignite tinder, which is used to ignite kindling, etc.

The normally self-extinguishing dust - because it's got poor access to oxygen - can ignite a chip or coarse piece of dust which burns hotter because there's oxygen to more surface area, which can ....

[Duane Bozarth]

...

Hmmm...as you can tell I've never used the ceramic guides nor bearings...if they behave as you say (and I've no reason to say otherwise) I'll agree...don't seem like a good idea at all. I've never really seen a problem w/ the roller bearings on mine...

[George]

You will, eventually. Though the upper is normally mounted on an eccentric on the Delta and clones, the lower is not, and doesn't always rotate under pressure from the blade. Cut enough wet wood for turning, seize the bearing, and sparks will fly, bearings will score.

[Steve Knight]

I have been using them for 4 years or so with no problems. almost a year without a dc. I never had any problems with them. but maybes it is the blades I use. I had ruined two sets of roller guides with ipe dust. it would clog them up.

[Duane Bozarth]

...

Under those circumstances, no, I won't... :) (I don't work green wood and so far haven't done any turning since high school although I would like to get a lathe eventually).