I decided to design my own mirror cell rather than purchase a prebuilt model. There are several makes and models to choose from but I've not found any mid-range mirror cells that I liked. Most are either not substantial enough for imaging or are too expensive. Besides, making my own is more fun.

I will say up front that there is very little in the way of science or proven methodology in this design. I simply tried to use my own sense of weight and rigidity such that the latter would not be compromised. Six spaces were removed in the upper plate to save on weight leaving six spokes that measure 0.5" thick. In theory the spokes will still be plenty rigid while allowing some throughput for air circulation to the base of the primary.

TurboCAD 14 was used to draw each half of the mirror cell. This design assumes 6061 aluminum for the material at a thickness of 0.25". Royce's conical mirrors offer a particular appeal for use in imaging telescopes in that they are cast with a mounting bolt protruding from the base's center. This bolt is intended to be passed through a compatible mirror cell and then locked in place using a washer and nut. Royce's design illiminates the need to epoxy the primary in place. The 8" F/5 mirror uses a standard 3/8-16 bolt so I have placed a mounting hole in the upper plate accordingly.

After a great deal of research and waffling over pointless details I decided on 1/4-28 collimation bolts. This will allow for seven threads to be engaged in the 0.25" cross-section rather than just five threads with say, 1/4-20 for example.

The center hole in the lower plate measures a somewhat arbitrary 3.125" in diameter. This is to allow easy access to the mounting hole for tightening down the locknut as well as allowing air flow to the base of the primary. At some point I may mount an 80mm fan over this hole to aid in faster equalization before beginning an imaging session.