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Construction I | Construction II | Construction III | Construction IV ]
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Construction III


Secondary Cage

The secondary cage rings are 1-7/8" wide, routered out of 3/4" plywood. The inner diameter is 24". I used my router jig that I built for the bearings and rocker box to do the cage rings.

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rocker thumb rocker thumb

I had seen several people online opt to make plywood struts instead of using the traditional aluminum poles. The folks at Astrosystems also recommended this, as they have seen aluminum pole struts flex enough to loosen up spider vanes. So I decided to try; it saved me having to powder coat a set of strut poles. :-) My struts are laminations of two pieces of 3/4" plywood, so they are 1.5" x 1.5" struts. The spider vanes pull parallel to the plys.

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I have always used both a finder and a Telrad. When I was first starting in astronomy, one of my buddies who was teaching me (Robin Barnes) advised me to get the largest finder I could afford. It was good advice, and I've never deviated from it. For Mariner I got a Stellarvue F80 RACI (I've never had a RACI before). I also got my beloved Telrad (modded with a pulser for the reticle, which many shops carry, like Astronomics). Of all the existing reflex finders on the market, the Telrad has always been my favorite. Iknow people think it is bulky, but I never am afraid that I'm going to break it -- it is TOUGH! I also think its reticle projection works the best of any I've seen. I also added a green laser to this setup; I got the bracket from Lumicon.

My focuser is from Moonlite with their gold anodization. It is a 2" Newtonian Crayford (Model CR), with a compression ring drawtube (1.75" of travel), and an 8:1 reduction knob for fine focus. I use one of their 1/4" spacers under the base.

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rocker thumb rocker thumb rocker thumb

My spider and secondary holder came from AstroSystems. I mounted it a bit farther down in the cage than is conventional (based on Kriege and Berry), as I usually do. This allows me to put my Telrad well forward of the focuser, and to have a bit of excess baffling provided by the extended cage. Even though it is BIG, there does not appear to be enough room for me to sit at prime focus.

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My secondary cages are all lined with Formica (909-58 Matte Finish in this case) rather than the recommended Kydex plastic. It is very tough and durable, and does not warp in the heat the way Kydex does. I line my secondary cage with flocking paper from Protostar.

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Side Bearings

I knew my side bearings were going to have to be larger than they were on Equinox. The establishing element of the design I stumbled on reading about Fiske Miles and his 22" scope; he sold me on the idea that I could raise the pivot point by using gigantic bearings and balance out the scope, I also needed the bearings to be removable (also an idea from Fiske) so I could put the scope in the back of my Tundra.

Each bearing was a layer of 3 pieces of birch plywood -- 1/2" + 5/8" + 1/2". The bearings are crescent shaped, with an overall diameter of 43.75". The outside radius was cut on a 22" radius; the pivot for the upper edge of the crescent was moved 22" and a 30" radius curve was cut. In order to get the pieces identical I laid out a jig on my table that captured each piece along a flat edge, then routered out all six layers before changing the router radius.

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When I put the pieces down, I screwed them down so they wouldn't shift during the routering process. The trick was to put the screwholes in a location that would go away after I made the cutouts.

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I always liked the 3 hole motif I used on Equinox, so I did a version of that here too. I routered out each of the holes using a small jig I made for the router. The cutouts are each 6" in diameter.

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The layers were glued and clamped together, and the small edge deviations evened out with a router. The test fit against the rocker sides, and also clamping to the mirror box, showed it was all going to work out okay!

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The mounting points for the bearings had to be located on the bearing, then transferred to the mirror box. The bearings are removable, mounted using socket cap screws that pass through the bearing and into tee nuts mounted in the mirror box.

bearing thumb bearing thumb bearing thumb
bearing thumb bearing thumb bearing thumb

The bearing surfaces are pieces of Formica 909-42 Sparkle Finish, just like the azimuth bearing. They are contact cemented down. I always make my bearings slightly larger than 180 degrees; this gives me space on the ends to put a screw through the Formica. This keeps the bearing surface from becoming detached when it invariably hooks on things during the normal transport of the scope.

bearing thumb bearing thumb bearing thumb
bearing thumb bearing thumb bearing thumb


[ Mariner Home | Introduction | Optics | Plans | Final |
Construction I | Construction II | Construction III | Construction IV ]
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Last Updated: 25 September 2012