Sunday, January 7, 2018

Baby Reflector

I thought replacing the chipped diagonal  would have me ready to go.   I think it was just sheer blind luck that had the chipped diagonal close enough to square with the main mirror to collimate.  After putting the new diagonal mirror on to the holder and  reassembling it was clear that the diagonal needed to rotate about 15 degrees into the optical axis to have any hope of the laser beam to hit the mirror center.  My revised design lacked enough access to the screws to adjust, even if there had been enough room to do so.  

I have given up on trying to reuse the existing spider hardware.  I have decided to start from scratch.  I can reuse the round part with the three 8-32 screws enlarging the 1/4 through hole with a 3/8-16 bolt.  Instead of using a spring to tension the diagonal holder against the spider, I will use a 3/8-16 bolt to position it in the right location up and down the tube to get it under the eyepiece  and turn the diagonal to be directly under the eyepiece.  This might not be ideal,  but at worst, getting the diagonal under the eyepiece focuser is only going to be 1/16th of an inch too far from or too close to the primary. 

The next step is building a spider to hold the diagonal.  I will make four legs from hacksaw blades.  These are springy enough and thin enough to make minimal interference optically.   Bends at the ends will mate to the diagonal holder and the interior of the tube.  I was hoping to reuse the existing spider holes but that may or may not be practical.

After deep thought while falling asleep, I figured out that I could reuse the existing spider by enlarging the 1/4" through hole to a 3/8"-16 threaded hole.  Much less work.  I did have to remove the spider from the tube to enlarge and tap the hole.  Looking at it, it looks like something I hacked together from an existing spider; not pretty, nut functional.

The mirror holder is still on a 1/4"-20 screw so I will make a 1/4"-20 to 3/8"-16 adapter to join the mirror holder to the spider.

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