A Wire Spider for a Small Telescope: List of Components

Four of the main components. The fender washers have been drilled as described. Three unneeded holes are in the front fender washer (right side) because I originally intended to have the set screws pass through it, an idea which I abandoned because it was too hard to align the fender washers well enough to keep the set screws from binding.

The following is a list of the main components in my wire spider.

Stainless steel wire. I used 0.016" diameter wire, part number SWX-3016-01 from Small Parts, Inc. There are two separate pieces of wire in the spider; each wire starts at the end of the center hub closest to the top of the tube, passes through an eye bolt in the tube, and back to the bottom end of the hub. Then the wire passes through a hole in the hub, then back to another eye bolt in the tube, and finally ends back at the top end of the center hub. Each wire forms two "vanes" of the spider.
1/4 x 20 threaded rod, which forms the "backbone" of the hub.
Four 1/4" fender washers with a 1 1/4" outer diameter. Starting at the top end:
- The top fender washer has two holes drilled in it for the wires to pass through, and four holes for the tiny #4 screws to secure each end of each wire.
- The next two fender washers provide threads for the three set screws to pass through. If you have access to a tap, just use a single washer and tap the holes directly in the washer. Not wanting to invest in a tap and dye set, I used three #8-32 screws sandwiched between two fender washers. I did try attaching the screws to a single fender washer with JB Weld, but the epoxy kept coming loose.
- Finally, one fender washer is adjustable relative to the hub. It is attached to the dowel with three wood screws, and the mirror is glued to the dowel. Three set screws press this fender washer downward, while a tiny spring hidden inside the dowel presses the fender washer upward.
A very short spring (the shortest you can find) that fits around the 1/4"x20 threaded rod. This goes in a hole in the dowel so pressure is applied against the three set screws. I happened to have a perfect spring laying around. McMaster-Carr would be a good place to look for one, since they have a wide selection of springs.
Three short lengths of #8-32 threaded rod. These are the three set screws used to align the secondary mirror.
Knobs to go on the #8-32 threaded rods. I used some black plumbing gaskets sandwiched between #8 washers and nuts, which worked well.
1 3/8" diameter dowel, cut at a 45 degree angle. This kind of a dowel is used for closet rods. I used a table saw to accurately cut it at a 45 degree angle.
#4 screws, nuts, and washers, to secure the four ends of the two wires to the top fender washer.
Four eye bolts, and nuts for them. Lock nuts with nylon inserts might be a good choice. These eye bolts pass through holes in the web tube ring.
Silicone sealer to glue the secondary mirror to the dowel. This is in the same section as caulk in the hardware store. Get the "window and door" style, not "kitchen and bath." It sticks great to wood and glass. If you ever have to remove the mirror, all you need is an exacto knife.