Re: [ATM] roller bearing vs Slider bearings

[Jan Bentz <jbentz@inreach.com>]

Many years ago I was curious about just this thing.  As a line of attack 
I looked up the specifics of the Rockwell Hardness Test.  It involves 
pressing a carbide ball into the steel in question and then measuring 
the diameter of the dent with a microscope.  The bigger the dent the 
softer the steel.  I then applied this principle to the semi-circular 
rectangular trough formed on the surface of a large round polar disc 
against which the rollers bore.  All it involves then is the geometry of 
the thing and a knowledge of the Rockwell hardness to see whether the 
"dents" would be visible at the eyepiece.   This presents a worst case 
scenario and assumes the yield point is exceeded.

Jan Bentz


Arjan te Marvelde wrote:

>Some thoughts about contact deformation.
>
>The contact "singularity" does not exist in reality, but is depending on the
>excerted force and the strain/stress curve (i.e. Youngs' modulus, E). The
>contacting surfaces will deform until the contact area is large enough to
>establish an equilibrium. As long as you stay away from the yield strength
>of the material the surface shape will restore itself.
>
>As Don suggests you might want to go for a hard, high-E material and get
>little deformation for a certain pressure. This implies that the contact
>pressure will be large and a high yield strength is required. This is the
>steel on steel route, which will indeed serve well as a stone cruncher.
>
>As an aternative, you can go for a low-E material, such as rubber. You get a
>lot of deformation but also a low contact pressure. Therefore the
>requirements on yield strength are relaxed . No stone crushing either, but
>as a consequence less positioning accuracy.
>
>Some design issues:
>What would be the accuracy required in an azimuth bearing?
>How much will the contact forces vary?
>What is the amount of deformation related to bearing diameter?
>
>Cheers,
>   Arjan
>
>  
>
>>Even hard-anodizing is only a few mils thick and does not always stand up
>>    
>>
>to
>  
>
>>extreme stress of the line or point contact "singularity" of a roller
>>bearing. I prefer to use hardened stainless steel strip bonded to aluminum
>>    
>>
>
>_______________________________________________
>ATM mailing list http://www.atmlist.net/
>
>
>  
>

_______________________________________________
ATM mailing list http://www.atmlist.net/