New, larger telescope mounts

["Merle W. Jephson-King" <mjking@wi.net>]

Please don't be dismayed by the prospect of making a larger mount for 
four larger TASS cameras.  Whether you want to point your 35mm camera 
or a 4-meter reflector at the heavens, the design principles are the 
same.  

I recommend that we use an equatorial mount similar to the English 
type.  You can make the mount out of steel tubing and off-the-shelf 
bearings.  The rule of thumb is that a hollow shaft is stiffer in 
bending than a solid shaft because you have a combination of tension, 
compression and shear stresses.  Also, I/c is larger which lowers the 
stress.  If you take a hollow shaft to the extreme and make the wall 
as thin as foil, you then have a cylindrical membrane which is subject 
to local buckling.  Fortunately, the mount doesn't need to fly and how 
much it weighs will only change its status from portable to fixed.

Use pillow block bearings.  The ball bearing grease type provides 
positive lubrication and is relatively cheap.  Pillow blocks are 
bolted to the rest of the structure.

You can hand calculate the stresses and deflections of all the parts 
and get good results.  Don't sneer.  The fore-runners of the box in 
front of you were designed with slide rules and analog calculators.  
Today's hand held calculators are _much_ more powerful than the 
calculators of 30 years ago.

"Roark's Formulas for Stress and Strain" by Warren C. Young contains 
enough formulas to completely analyze the TASS scope mount.  Also, the 
HP 48 calculator carries 12 significant figures in its calculations 
which is sufficient accuracy for TASS (many other things as well).  
What I'm trying to say is that a mount can be designed and built for 
TASS without doing a FEA (Finite Element Analysis) with a big number 
cruncher.

Keep the design simple and statically determinate and the results will 
be just fine.  Something you could write home about.

Merle King