[ATM] Rotating secondary

[artbianconi@blast.net]

Hi!

In my design efforts up until now, I've used a 2.6" diagonal in 
making the calculations for the OTA for the 15" f-4.4 mirror I am 
polishing.

A complete 2.6" assembly is already part of my existing 3D model 
database. Upgrading that to a 3" is not a major undertaking, not in 
the engineering model and not in the real world, so I paid little 
attention to it.

However, while in Smyrna, Delaware at the Mirror Making Event, 
someone suggested that I might be better off using a diagonal with a 
3 inch minor axis.

While "toying" with the change, it occurred to me that there is an 
awful lot of room in the shadow ABOVE the secondary in which to mount 
a ground shaft and a pair of tapered roller bearings (the kind made 
for precision instruments) to the spider. 

With a little effort, I might be able to make a device that allows me 
to rotate the entire secondary and focuser 360 degrees about the 
sight axis of the OTA, without having to rotate the entire tube!

The spider itself is to be made of carbon fiber and pretty damn 
rigid. It should be able to handle the slight bending moment and 
maintain collimation, provided I keep the weight of the focuser to a 
minimum.

"This is too obvious" I thought "Someone must have tried this 
already!"

Does any of this sound familiar to any of you?

Thanks

Art

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