23" f4.75 Newtonian for Don  in Geneva, IL.:

This 23" f4.75 Newtonian is an interesting hybrid of a "mirror box and upper tube assembly" made by DobSTUFF.  Rather than a strut OTA design, however, this telescope will be a "truss" design. Given the size and weight of the telescope, the traditional truss configuration insures a stable and rigid OTA.

The owner, Don, contacted me in June 2009 asking if I could make the wood components for his large telescope project. At first, I didn't think that the ultra-lite design would work for a scope this large, but I later realized that the design is quite sound. I just needed to make the wood thicker, adding strength and structural integrity to the project.  All of the wood components are made from furniture grade 13-ply Baltic birch. The mirror box components have been laminated to 1.25" thick -- including the altitude bearings. 

These components were completed in July 2009.


The scope is set up and ready to use. Notice the "truss" design as opposed to the parallel strut design of smaller scopes.  You can check out the general of "truss" vs "strut" design and rigidity here.
Inside diameter of rings: 25"
Outside diameter of rings: 29"
Height of mirror box: 14"
Height of upper tube assembly: 12"
Mirror cell: 18-point flotation
Diameter of mirror: 23" f4.75 -- 3.85" thick (weight 60#)

Don in Geneva, Illinois along side his 23" f4.75.

View of the scope from the front.

The 18-point mirror cell is visible in this picture. The mirror is made from 3.85-inch thick Corning ULE glass and weighs 60#.

The 23" rocker box/ mirror box, altitude bearings and mirror cover after varnish has been applied. The struts used in this part of the telescope are 1.5" in diameter.

Here's a picture of the 23" mirror installed in the mirror box.
The top of the mirror box and its "ring" during lamination. Total thickness is 1.25" composed of a 3/4" and 1/2" thickness of 13-ply Baltic birch plywood.
The 30" diameter altitude bearings during lamination. The total thickness is 1.25"
Here's a completed rocker box, altitude bearings and mirror box.
Detail of the 18-point flotation cell underside.
The ground board is also 1.25" thick. Three large holes have been routed into the wood to reduce weight.
The only component that is not 1.25" thick is the upper tube assembly I made for Don's telescope. These rings are 1/2" thick. The focuser board is 3/4" and the 12" long struts are 1.25" in diameter. The struts that compose the mirror box are 1.5" in diameter.

For more information about your requirements:
--Dennis Steele
--Tel: 650-315-6578 (anytime)
--Email: densteele@dobstuff.com

More of my photos here. 

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