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|Ranger Alta-az Mount Prototypes
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Posted by Glen Warchol/">Glen Warchol on October 14, 1998 14:30:54 UTC
FYI for anyone seeking plans for a mount for a small refractor. I could not find any plans or even fotos of homemade refractor mounts on the Web, though I know they must be there somewhere.
I talked to several ATMers at the Salt Lake Astronomical Society and studied plans for Newtonian Dob mounts. I've built two working prototypes. My goals were: a) Only the cheapest materials. b) Minimal fabrication c) Minimum of power tools. (Why? 'Cause I'm broke, lazy, and someone ripped off my power tools.)
In both prototypes, I was able to avoid the engineering nightmare of hanging the refractor off the side of the mount with a counter weight on the opposite side. This is done to allow the scope to point vertically without bumping into the mount/tripod etc.
Prototype 1 (Dobsonian tradition): I slid the Ranger into a 5" double-T ABS pipe fitting (my cradle). The fitting is basically an x with openings every 90*. I drilled a hole in the ABS at the scope's balance point and secured it with a 3-pod screw. The two 5" diameter flanges on either side of the scope act as the alt. bearings. I built a dob-like box out of 3/4" plywood, cutting two semicircles in the 9" wide tops of the sides for the above alt. bearings to ride in. I left a little room for nylon furniture sliders. This box was tall enough (just under a foot) to allow the eyepiece end to swing into the box/cradle when I go verticle. I rigged a so-so azimuth bearing out of some teflon furniture sliders and plastic discs.
It works great, but it's ugly and bulky, swallowing up my little Ranger.
Prototype 2 (Small Dob meets T.V. Upswing): At Home Depot, I bought one U-spaped versions of those galvanized patio deck-construction hangers. On each of its sides I screwed and glued on a 4" PVC pipe cap. These are the alt bushings. I attached the scope to the floor of the galvinized "U" with a tripod screw. (The pre-drilled holes worked perfectly.) I made a cradle similar to the one above, but only 5" wide. Again, it is tall enough to allow the eyepiece end of the scope to swing inside when zenith pointed.
I'm still experimenting with teflon vs. nylon pads and exact placement. The beauty of #2 is that it attaches in seconds and packs in a small gym bag.
At their worst, both mounts are better than a camera tripod. After an hour or two of refinement, they work damn good, indeed.
Tools: Hand saw, coping saw, rasp, sandpaper, carp. square, old ruler (to drawn circles), screw driver, cordless electric drill. Approximate material cost: Both mounts for less than $25. Time investment: 1/4 of a Saturday.
More details for the asking.
Glen Warchol Salt Lake City
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