View Full Version : advice on floating bearing - outer ting rotating
I've never used a floating bearing arrangement before and so wanted to check if anyone else knows anything about it. I have a housing which is a slide fit for a ball bearing, with the ball bearing 'floating' inside, it needs enough clearance to move up / down, but be held from side movements. Because of this, there's no retention for the outer ring and so the outer ring rotates with the rest of the bearing. Sometimes it gets a bit more friction from the side walls of the housing and it stops, but most of the time it just rotates as a whole inside the housing. This will cause wear over time and introduce more side play.
Is there anything that can be done about this? one solution is to use a roller bearing rather than a ball bearing and clamp the outer ring down as the inner ring is free to move vertically.
15-11-2013, 11:39 AM
Can i assume this is off an electric motor ?
The motor on my lathe has a conical washer that bears on the outer bearing ring, when the rotor shaft increases in length from expansion the washer will compress, as a rule the exerted pressure should stop the outer ring from rotating.
If i have this wrong i am sure someone will correct me.
Thanks for the reply Mike. It's not exactly a motor, but it's a similar arrangement. I was thinking of a crinkle washer under / above the bearing, but surely that will put load on the outer ring, thus pre-loading the bearing and I'm pretty sure ball bearings shouldn't be preloaded.
A crinkle washer may be enough to stop movement, and shouldn't cause any issues.
Standard bearings can take some axial load without issue, but you'd have to search for the exact figures. From memory I'm thinking it's somewhere around 10% of radial load rating, but that's pretty much a total guess!
Cheers m_c, looking at the data sheet for the bearing which is SKF6205, single row ball bearing, I can only see basic static (7.8kN) and dynamic (14.8kN) load ratings, not much about axial load though. Following your suggestion of 10% that would be around 0.8kN static, whatever that relates to in spring / compression force.
I've found some suggestions on Practical Machinist for using an o-ring as retention. One needs to machine a groove in the housing to fit and compress an o-ring and this should be enough to hold the outer ring in place. As this is a low speed application (max 300RPM) it might actually work.
O-ring should work. All you're needing is to create enough friction that the bearing won't turn.
Even an o-ring clamped onto the outer would likely be enough without worrying about machining grooves.
Axial loading details can be found at Axial load carrying capacity - SKF.com/Products (http://www.skf.com/group/products/bearings-units-housings/ball-bearings/deep-groove-ball-bearings/single-row-deep-groove-ball-bearings/axial-load-carrying-capacity/index.html)
So for the 6205, in theory you're good for 3.9kN of axial load, which would take one very strong crinkle washer to acheive!
Cheers m_c, I will give the o-ring a try.
Those axial load ratings are not what I was expecting, I might be able to ditch the top double row angular contact bearing and go with two 6205s instead.
I'd personally still keep the angular contacts, as they're more suitable for adjusting to a tight tolerance, however given the loading, you could probably get away with one single row angular contact that takes the main thrust load coupled to a standard deep groove bearing.
As I already paid a few quid for the double row angular contact bearing I will stick with it, but it's good to know 6205s would do reasonably as well.
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