Tube Assemblies
Here's a view of a completed optical tube assembly.
Building it in sections will make it more portable. The rear section
could have been made shorter, but the shorter it is the harder the alignment
problem gets. The box frame that will hold the rear tube sections
should still be small enough to fit in the trunk of a medium size car or
the rear seat of a small car.
The secondary cage was made from a 12
1/4" piece of 10" ID Sonotube. (Sonotube for the whole project
was donated by J&K Supply of Lafayette.) This section was
made almost entirely by Jim Sattler.
View from the top: The spider was made from
2 very short pieces of 4" aluminum pipe. The
curved spider vanes eliminate the diffraction
spikes caused by standard spider vanes.
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View from the bottom, showing the reflection
of the built-in Barlow in the 2.14" secondary.
The secondary holder was made from a piece
of black PVC pipe.
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Barlow, diagonal, and focuser: the Barlow tube acts
as an extension tube. The Barlow lens cell unscrews
from the Barlow tube for low power viewing.
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Jim machined the helical focuser from two pieces of spare aluminum.
The inner piece threads into the diagonal where the original eyepiece holder
tube was. The inner piece is threaded on the outside. The outer
piece then threads onto the inner piece for fine focusing. The upper
inside of the outer piece is not threaded, rather the original eyepiece
holder slides into it for coarse focusing. The outer piece has a
knurled grip ring.
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John Mahony took charge of the truss tube section,
with help from George Gourko and Jim Sattler. Once the tubes were
cut and drilled, the ends were beaten into submission with a vise and a
large hammer to fit them to the tube sections.
The lower tubes are also made of Sonotube, about
22.5" long. The mounting rings were made by George Gourko.
George Gourko also made the mirror cells.
Three sets of push screws and spring-loaded pull screws adjust the mirror.
The plates are wood with ventilation holes. The mirror is held to
the upper plate with 6 large drops of silicone rubber cement (aquarium
glue), three on the bottom and three through holes (not visible in the
image because they're filled with glue) in steel angle brackets that act
as a back-up support in case the bottom silicone comes loose. The
mirror was supported on coins on the upper plates until the glue dried,
so it rests on the glue rather than the wood.
Bottom view showing the ventilation holes.