From: "Tom Krajci" 
To: 
Reply-To: "Tom Krajci" 


From: Douglas Braun 

>Where we're on the subject:  I am thinking of building a
>cylindrical-bearing platform using roller skate bearings.

>Does anyone know how good the bearings have to be?
>I have seen skate bearings in grades ABEC 3, 5, and 7.

My first version of my equatorial platform (cylindrical bearing) used,
ahem, plastic furniture casters (the frame was metal, the wheels were hard,
injection molded plastic) that did not swivel, and had no ball bearings for
rotation of the wheels.  The cylindrical bearings were hardwood.  For
visual observing, this was adequate (the image did not deviate north/south
as high/low spots were encountered on the wood bearings or the hard plastic
wheels.)  My biggest gripe was friction. It had to use more current to the
stepper motor drive, and that tended to make vibration a problem.

Then I put sheet metal over the bearings, and walked into a local bearing
supply store (in the old part of town...junkyards, welding shops...an
ATM'ers dream.) and just bought some ball bearing units from their stock on
hand.  I don't know what ABEC rating they were.  Friction was much lower
this way, and for me that was the biggest improvement.

>There are also miracle ceramic and titanium bearings
>for the serious skater fanatics, but I think that
>would be overkill :-)

These bearings are probably meant to handle higher shock/transient loads
that skaters generate.  Or perhaps handle wear or dirt in the races.
Fortunately we don't treat out mounts that way, so I think we can skip
these kind of bearings.  ;-)

Tom Krajci
Tashkent, Uzbekistan


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