5" Secondary Holder
Well, since the size of the secondary mirror in the Cassegrain
increased
from 4.25" to 5", the secondary holder had to increase in size too.
The
3/8" rod and attached plate with adjusting screws was just fine, but
the
plate and the piece of thin sheet aluminum that surrounded the mirror
and
held it in place had to be changed.
I found a piece of 3/4" baltic birch that was slightly over 5" by 5".
I
roughed the circle out with a jigsaw, and made a quick jig to sand the
shape
to that of a true, round circle, slightly over 5" in diameter. A
nail
was driven through a hole in the center of the wood disk, and sanding
was
performed by turning the disk by hand into the rotating sanding drum in
the
drill press. Worked like a charm.
Three holes were drilled to accept T-nuts which would be engaged by the
three
adjustment screws. This accomplished, the plate was attached to
the
rod/aluminum plate assembly.
Finally, I bought some sheet aluminum (about 0.025" thick) and cut a
piece
to surround the new secondary. I bent the lip down to retain the
mirror
and bent it around the circle, and attached it with some small screws.
Voila,
a new secondary holder. Now it will be given a coat of paint by
Mr.
Conron in his "paint shop/optical shop/car storage facility".
Next stop, a coated secondary mirror.