Re: ATM ALT bearing question

["Ed Erbeck Jr." <ed@crazyedoptical.com>]

> Jim Miller  asked:
> 
> I'm designing the support for the ALT bearings on my DOB.  The separation of
> the bearings is 70 degrees and the length of each of the four bearing pieces
> of Teflon is 1.25" resulting in a nominal of load of 15psi as suggested by
> Kriege and Berry.
> 
> The rocker diameter is 12" which results in a fairly shallow arc for the
> teflon.  I'm thinking about how to simply support this and am considering
> just making the supports flat (tangent to the rockers), gluing the teflon to
> them and creating their mating radius by temporarily fixing a some 400 grit
> carbide paper to the rockers and wearing in the bearings to the proper
> radius.  Of course this would all be done prior to mounting the mirror!
> 
> Thoughts, suggestions?
> 
> tnx
> jtm

     Personally I've never found anything "magic" about the 15psi number. By
changing the position of the Teflon you can change the startup stiction.
I've used .6" X 1.00" Teflon Pads on a 17.5" Coulter (~120 pound Load) and
it worked fine.
     If you are going to Glue Teflon it will need to be etched first (you
can buy it that way - it's called Skived), but you will be commited to the
position and thus movement you end up with. IMHO you will be better off
cutting the Radius and screw/nail (I've never been fond of nails as they
have a knack of working out and tearing up the Elevation bearings) mounting
the Teflon which will allow you to "tune" the movement. Once "tuned" the
Scope will move at 45 degrees using equal force.
-- 
         Crazy Ed