The Mirror Cell
Making a 4.25 Inch Dobsonian Reflector Telescope
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.
Un-Assembled Parts View