The Mirror Cell
Making a 4.25 Inch Dobsonian
Reflector Telescope
Purpose
The cell holds the mirror and allows
it's attachment to the telescope tube.
For smaller mirrors it functions merely as a bracket. For larger, especially thin mirrors, it provides
structural support so that the mirror will not bend under it's weight. While you might think that the mirror is
fairly solid, but consider that the surface is accurate to a few millionths of
an inch. How you get that structural
supports can be creative. I've tried
foam backing, but I've heard bubble wrap works well.
You can buy your cell or make your
own. The design I used was based on
an aluminum cell found in my first 6" Edmund Scientific telescope. Building it out of wood required the use of
a router with a circle jig. There are
two circular wooden pieces. The piece
that attaches to the tube much fit fairly closely. The smaller piece that is attached to the mirror is held in
place with three long screws, adjusted with wing nuts. The circles are held apart by small
springs. These can be obtained in a
hardware store with a good selection.
Below are some additional views.
The part of the cell that holds the
mirror was routed out first, and then cut out. After cutting the two circles, the large holes were drilled in
order to reduce weight and allow air circulation. The finished mirror was glued into the smaller circle with
silicon caulk.
Side View
Bottom View
Un-Assembled Parts View