Doing The Wrong Test, Bearings, A Let’s Build Resource

When doing a performance test you have to know what to test. Consider this video. It attempts to show how the German bearing is better than the Chinese bearing.

This came from Digg and I saw it first on Popular Mechanics.   Now it’s an interesting video, but unfortunately it doesn’t prove anything.  Now I have no doubt that the German bearing is probably better than the Chinese Bearing, but just sliding it on and spinning it doesn’t tell you anything other than the fact that the Chinese bearing has more grease on it than the German bearing does.  The real test of the bearing is life under load.  The real way you test a bearing is to press it either on to a shaft or into a hole, attach a motor and run it out.  Then you get the bearing curve from the manufacturer and see how long it’s supposed to last for the load and speeds that you are running.  If either bearing fails under those conditions, then that’s how you select the bearing.  Weapons grade means nothing.  What you want is to make sure that your bearing life exceeds your MTBF.  You do that by going to the manufacturers charts and  checking the load against the life.

Here’s some bearing stuff from manufacturers.

http://webtools3.skf.com/BearingCalc/selectProduct.action

http://www.nmbtc.com/bearings/engineering/load-life/

http://www.tribology-abc.com/calculators/l10.htm

http://www.timken.com/sites/newproducts/en-us/typee/Documents/Bearing_Life_Calculations.pdf

 

An article from machine design.

http://machinedesign.com/bearings/meaning-bearing-life

A bunch of different formulas for bearings on efunda.

http://www.efunda.com/designstandards/bearings/bearings_rotary_ld_life_data.cfm?search_string=bearing%20life

If you are working on your own project where the bearing comes from and how well it performs may not be that big an issue.  If you are doing a design, taking the time to figure out the loadings and correctly size your bearings will save you a ton of grief.  There are good online and book references to help you figure your loadings and spreadsheets available to help with the calculations.  The bearing manufacturers are willing to help as well.  It’s better to do it right than smell the burning bearing smell.

The Let’s Build Series.

https://theartsmechanical.wordpress.com/tag/lets-build/

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2 comments

  1. penneyvanderbilt · May 15, 2016

    Reblogged this on KCJones.

    Like

  2. roger · May 17, 2016

    I think the fact that China outsources the balls for pens to the Germans tells you everything you need to know about some classes of Chinese ball bearings.

    Like

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