Shaft misalignment 1

[ihopeitworks]

I have a 2" dia shaft that has two ball bearings on both ends at about 20" apart. I have been trying to find what sort of misalignment I can get away with, but fail to find anything concrete. The bearing mfr does not give misalignment allowance so I'm wondering what standard practice is?

 

[JJPellin]

What type of ball bearing? Please be specific to configuration, cage design, cage material, metal shields, rubber seals, etc. What fits are you using to the shaft and housings? What type of loads will the bearings see? What are your reliability expectations for this machine?

Johnny Pellin

 

[ihopeitworks]

Thanks JJPellin,

https://us.misumi-ec.com/vona2/detail/110300107830/?HissuCode=B6804DDU

We're sort of stuck with these due to size constraints in the assembly. Each bearing would only see about 75 lbf max during operation at ~250 RPM.

We haven't spec'd in the sort of fits, but I believe we can get away with a loose or slightly press fit.

Reliability of 90%

 

[EngineerTex]

What type of misalignment - angular or offset? What sort of housing will it go into? How will the housing be machined?

Bearings will handle all kinds of misalignment. Just understand that if you have to use a hammer to assemble the system, misalignment simply increases loading. The bearings will have a reduced life while the shaft and housing will experience a higher amplitude of cyclic loading. Put together plots of stress on the shaft and housing vs. amount of misalignment and then pick a number that you're happy with and don't exceed that misalignment.

Engineering is not the science behind building. It is the science behind not building.

 

[GregLocock]

If you switch to self aligning bearings then you won't have to worry so much. Or pick up the awfully heavy phone and ask them for their design guide.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[electricpete]

Here is NSK's take for NSK bearings

https://www.nskeurope.com/prevent-bearing-misalignment-1168.htm

"A general acceptable alignment is better than 0.003 radian (10 arcminutes) for ball bearings..."

I assume they are referring to deep groove ball bearings.

Figure 2 gives an interesting interpretation in reduction in fatigue life as a function of angle misalignment for 6200 series deep groove bearing (the life curve decreases sharply in the vicinity of 0.004 to 0.006 rads). I assume below that angle you could tilt the bearings with relatively little effort and above that angle you encounter more resistance as the parts are firmly in contact. The exact angle where the sharp decrease occurs depends on operating internal clearance... higher clearance allows more tilting.

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(2B)+(2B)' ?

 

[Jboggs]

You said you have "two ball bearings on both ends". We all assumed you one bearing on each end, but is that the case? How many total bearings, 2 or 4?


As far as misalignment, there are many bearings made to accept angular misalignment. Unfortunately these are not among them. You need to specifically look for "self-aligning bearings". They're not expensive. That way you can estimate how much misalignment you anticipate and then get the right bearings.

 

[Tmoose]

Way more detail ( words, pictures and drawings) is needed about your application for good answers from the helpful folks on Eng-tips or the bearing tech support department.

regards,

Dan T

 

[CWB1]

You need to perform a stackup based upon the bearing class and dimensions provided.