Thrust bearing destruction - need lube?

[jsheerin]

Hi all,
I just destroyed the thrust bearings on the Y axis of my router. It took maybe 10 hours - probably less. Only 3 hours of that (or less) was actually cutting. The rest was just moving around getting my machine working. The thrust loads would be cutting loads plus acceleration of moving about 20 pounds - just my z axis and associated bearings. Cutting loads were about 25 pounds or less (that's the max force the stepper could produce at the speed I was cutting at according to the torque-speed curve). Bearings were as recommended by cncrouterparts - 03380904 needle roller thrust bearings plus washers from MSC. There's no load rating on them that I see. A similar looking and priced bearing at McMaster, 5909K31 is rated for 1920lbs of dynamic load and max rpm of 13000. I was running at 250rpm max while cutting, maybe 750 max ever.

Web page is here: http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=60416987

What happened to the bearings was (I think) the rollers wore down until the cage that holds them started rubbing against the washers on either side. I think they locked up at that point and started wearing against my radial bearing blocks and cutting a groove into my mild steel acme screws. There was a little pile of black dust under each bearing. There was no evidence of contamination in the bearings - it's not like they were full of sawdust.

I did not lube these bearings. Should I have? It wasn't mentioned anywhere, but now I'm thinking that might have been a good thing.

If lube is the problem, I'll buy some more of these and have another go. If not, I'm looking at other heavier duty bearings, but they're $16 a pop versus about $5 for what I just tore up.

Any thoughts or experience appreciated.

Thanks,
John

[jsheerin]

After doing some reading and some helpful suggestions from other people, I found that yes, I do need grease or oil in my thrust bearings.

However, on further examination today, my thrust bearings look okay. What was happening was the washer that does not turn with the leadscrew was carving a groove in my lead screw. That's what the black dust was from. My working hypothesis is that the washer ID is a tad too tight on the screw and due to the washer being hardened, the lead screw not being hardened, and the relative motion, a groove was cut. I think then what might have happened is the washer fell into the groove and started moving with the screw some times, but other times not depending on the thrust loads applied. When it was pressed against the block it rides against, it would stop turning with the screw and carve some more out of it.

So I think what I will try is to relieve the ID of the washer slightly and then tack it to the block it rides against with something - super glue maybe for starters. I think a more ideal solution would be to have the larger ID washer and machine a counterbore into the block to locate the washer radially. Maybe I'll eventually do that.

[abomb55076]

Yea, that sounds like a good start, make sure you dont forget that grease this time, it will make them run alot better. Good Luck!