In the past I have used commercially available secondary holders for Newtonian secondary mirrors. I am particularly impressed with the Protostar design and with Gary Wolanski's design. For my Dall-Kirkham project I need both a secondary and tertiary holder, and ideally they would have a very similar design. Both sets of vanes should line up to avoid extra spikes, and a common design would help achieve good alignment.

I decided to make my own secondary and tertiary holders because the specifications were a bit off of what I could buy easily. The basic spider design would follow Wolanski's. The pieces were machined from 1/4 inch delrin. For the secondary holder I asked around and decided to use a simple "spring compression" design outlined on Jack Schmidling's page. Instead of a spring I used a flexible piece of plastic, in this case a self-adhesive vinyl furniture pad available at my local hardware store. This rubber compression design was modeled after Mike Spooner's plan.

Construction of the holders required drilling holes in 1/4 inch Al stock (6061) cut into circles. I used a milling machine as a fancy drill press, but it could be accomplished using simpler tools. The top plate holds the bolts and the holes are larger than necessary to accommodate some twisting of the bolts during alignment. The piece of Al that will hold the mirror was drilled and tapped, either with 6-32 or 8-32 holes. The upper plate was mounted on a 5/16 stainless steel rod threaded for an 8-32 bolt. A button cap SS screw holds the plate to the rod and provides a contact surface for the vinyl pad. The tertiary mirror holder was cut on a lathe and then drilled out using the milling machine and tapped. I painted all the outer Al parts with Barbecue Spray paint, which goes on metal well and is quite black and a bit flat. It is also good to 1000 degrees F in case the telescope is left out in the sun too long. The finished secondary and tertiary mirror holders are shown below.