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| At the upper end of the optical tube is this secondary cage assembly. Two aluminum rings 1/8" thick are held in place by 4 tubes 6" long. The tubes have threaded inserts in each end, as do the bottom ends of the truss tubes.
For attaching the spider I used shelf brackets and chrome acorn nuts. I punched out the pin in the bracket. The finder is a modified Daisy Dot gun scope attached to a Ruger dovetail plate I got from a gun shop. The rack and pinion focuser shown here with a Celestron Ultima 30mm eyepiece, came from the original Parks equatorial scope. It has since been replaced with a JMI MotoFocus unit. I used .020 styrene plastic for the black baffle material. |
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| Here you see the consequences of a couple of design errors. On the left you see the gap I had to provide for the mirror box to clear the azimuth encoder when the optical tube assembly rotates in altitude. I miscalculated the height of the rocker box risers by 1/8".
On the right, you see the counterbalance spring I'm using to overcome an imbalance in the optical tube assembly. Tom Krajci, with his article in Sky & Telescope, November, 1999 describes this approach. The altitude bearing arc segments started out as MDF 12 x 5/8" circles from Home Depot. I glued 2 of them together for 1-14" thickness, then used the router to make a ring. After applying the ebony star formica, I cut the ring to make the 2 arc segments, painted them with a metallic spray paint & installed them on the scope. |
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