Sorbothane Side Bearings

Alt Bearing Pic

Note the side bearings are not "cut out" below the top edge of the mirror box.

This is to accomodate 1/8" thick Sorbothane sheet compressed between the bearing and the box.

Though settle time was okay before, it dropped to nearly zero after installation of the Sorbothane.

In fact, it worked so well, I placed some scraps between the ground board and feet (don't know if that did any good at all).


There are several grades, styles and thicknesses of Sorbothane, but I suspect just about any of them will work. I also think the 1/16" thickness might work just as well as 1/8" in this application, but I needed a little more thickness to make the sidebearings sit flush to the edges of the rocker box...


I calculated where the balance point should be and tried to build the rocker so it would be at the top of the box. I missed by about an inch... so the sidebearings are offset up to put the center of rotation at the center of mass (with an average eyepiece).
    Determining the center of mass was easy -- the strut tubes were originally over 1-1/2 feet longer, so I could find the focal distance of the assembly and "hang" the entire scope from a dowel to find the balance point (and boy was I annoyed to find out I screwed it up -- but being able to do this made the final configuration much easier).
    The other problem is "assymetric" weight; any imbalance from across the bisector of the long axis of the scope. In this case, it amounts to the Telrad since the focuser is only "raised" ten degrees (but that's enough!)
    This slight imbalance is more than compensated for by the stiction of the large bearings.

The Finish

There is no aesthetic reason to use the "stone" finish paint here; I simply botched the original stain so it was easier to paint over the mistake.

However, it may have been serendipitous, since I also have a problem with how to finish the aluminum poles, and I think I'll end up using the same stone paint. However, I have to leave the bottoms and tops bare to fit the clamps, and another eight inches or so below the upper cage clamps for the shorter "binoview" configuration.

I'm thinking about leather...

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