Secondary mirror holder

These are the first useful parts made on the lathe. This will become the secondary mirror holder on the Newtonian telescope we are making. The secondary mirror is elliptical with a minor axis of 50 mm, so these parts are 50 mm in diameter. There is a spring-loaded M6 bolt that pulls the mirror holder upwards, while three M4 adjustment-screws placed 120 degrees apart push down on the holder. The 45-degree cut turned out surprisingly well straight from the metal band-saw, and I'm not going to sand or polish it since there is going to be plenty of silicone glue between the holder and the mirror anyway. The plan is to use three or four M3 threaded rods for 'the spider' which attaches this holder to the telscope tube.

2 Comments

  1. Its beautiful- let me ask- why did you use solid bar stock? 50 mm is about 2"- I guess you have to use solid to have something to thread into. The center bolt is not threaded in the actual mirror holder- right- only in the top disk- but the 3 bolts at 120 degrees apart are- since they do the pushing and pulling. Did you put springs in between the components on the bolt shafts? thanks!!

  2. admin

    February 11, 2018 at 10:28

    The 2" size comes from the design of the telescope which dictates the size of the secondary mirror.
    You are right, using solid bar for this part makes it unnecessarily heavy - some lighter material or construction would be better.
    If I remember correctly the center bolt goes through the disk (no threads) into threads on the mirror-holder.
    We would have needed a much stiffer spring to pull the mirror holder against the disc firmly.
    The adjustment bolts are threaded into the disc and only push against the mirror holder.

    In the end we used a commercial spider and mirror holder for our telescope build.

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