spindle bearings overheating

[Andrew Wilding]

Waitroda,
How hot do your bearings get? I did not measure mine but I estimate over 60-70 deg C as I could not keep my fingers on the housing. Much higher and I think that the grease would start to smoke!

I have a plan of action on my spindle:

Bin the cheepo bearings and go for some middle of the road koyo bearings (still not expensive at 10 quid each). I could have gone with Timkens at twice the price but I think these should suffice.

Replace the rubber sealed lower with an aluminium labyrinth with a couple of thou clearance over the shaft.

Grease with short fibre grease (I cant afford the kluber grease and I think a decent bearing grease should suffice at the speeds that I am looking at)

Run it in a more managed way.

Possibly look at increasing the speed of the spindle up to 4500rpm in future if 3500 proves successful

I will update my build log to show the progress.

[Jonathan]

It might be worth pulling the seals off the existing bearings to see how much difference it makes? If there the same as the seals that were on my bearings then they do come off with some 'encouragement' and it does appear to make a big difference to the coefficient of rolling resistance. I removed the seals from these bearings in my wind turbine for this reason and covered up the bearing with a piece of steel machined to be a close fit.

I think submerging the bearings in oil is a good idea.

[wiatroda]

Waitroda,
How hot do your bearings get?
I will update my build log to show the progress.

I was running today machine non stop for 4 hours and after I couldn't keep fingers on spindle as well. I never paid too much attention to bearings temp until I read your post :) That's the DIY spindle filled nearly entirety with synthetic engine oil with a little air gap. When I mill next time I'll do the temp checks in some time periods.
I'm awaiting for your update

[BillTodd]

Are your bearings too tight? It's very easy to over tighten them when cold (BTDT), especially if the expansion tends to tighten them.

Try backing them off a bit.

Bill

[Ross77]

Hi Andrew, Not sure if you have solved this problem yet?

I hope I've understood you problem I I think it might be the seals ( as you suspect) and the oil!

firstly wheel bearing seals are designed to keep al sorts of nasties out but at relativly low speeds, once you put them in a spindle the extra friction is a problem, low or zero friction seals are a must in a spindle.

Secondly over greasing or over oiling is the worst thing you can do to a spindle with regards to heat, as the shearing action within the oil that allows the parts to move easily generates heat.

as Bill mentioned it is easy to over tighten the bearings, but it depends on the orientation of the bearings. if they are face to face then if I remember correctly you need to preload them so that as the shaft grows under heat the correct loaing is acheived as the extra length reduces the loading, BUT if they are back to back then any heat generated will add extra load on the bearings and in turn generate more heat.......visious circle ect.

This could be be your problem in that the original seals are generating a bit of heat(plus to much oil/grease) which in turn is putting load on the bearings, which is then generating heat and so on and so on.....

Im no expert but I have been looking in to this for my own spindle and it seems that spindles are suseptible to any small change,be it heat, vibration to over loading the tool.

sorry for the ramble, just ignore it i have got your problem it all wrong. Let me know how you get on tho

[Andrew Wilding]

Thanks all for the advice. I am still waiting for the new bearings so I have not made much progress on the problem yet. I have made a guard for the spidle belts and am making way covers. But when I get around to it I will post on my build thread.