Primordial Light: Technical: Pier Modification
August 29 2009

When I designed my observatory my main telescope was an 8" Meade on a fork mount. Proper dome geometry required the telescope pier to be 15 cm (six inches) south of the center of the dome, and that's the way I built it. When I put my Meade on a German Equatorial Mount (GEM), proper geometry required the telescope pier to be in the center of the dome. I did nothing about it, and the discrepancy had no visible effect whatsoever.

More recently, however, I have obtained a Takahashi TOA-150 refractor, which is much longer than any telescope that I had previously used in my small (2-meter dome) observatory. In some attitudes of the mount there was insufficient clearance between the telescope focuser and the wall of the observatory to permit mounting a camera. Since the pier and its 725 kg (1600 lb.) concrete base could not be moved 15 cm northward in any circumstance, and the observatory building could be moved 15 cm southward only with the greatest of difficulty, I decided to bolt a 2 cm (3/4") steel plate to the existing pier top, with the new plate extending 15 cm northward. Such an arrangement is called a cantilever. It allowed me to move the GEM 15 cm northward without making any other changes. The very excellent Circle Machine Shop in Glen Burnie, MD, fabricated the steel cantilever plate and drilled such holes as were necessary in the existing top plate and the new plate to accommodate the Astro-Physics 1200 GTO mount. I primed the original plate (second photo below) and the cantilever plate and I painted both plates with white high-gloss epoxy appliance enamel.
 
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The Pier, Stripped and Forlorn, Waiting for the Machine Shop to Finish its Work
 
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The Original Top Plate, Repainted Ready to Accept the Cantilevered Plate
The four socket-head cap screws are 3/4" x 13 threads-per-inch (tpi) hardened steel. Stainless steel would have been my first choice, but stainless bolts were unobtainable in this size, and they might not be quite as strong as hardened steel. Previously, the A-P 1200 Standard Pier Adapter was mounted on this plate.
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Equipment Stacked and Waiting for Re-Installation
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The two telescopes seen here are the TOA-150 and a Takahashi FSQ-106ED wide-field astrograph. The modular construction of the Astro-Physics mount is a real asset when assembling or disassembling the mount.
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The Cantilevered Plate Bolted in Place
North is to the right—the direction of the cantilever. The bolts received a thick coat of anti-seize compound before insertion. The compound, which is a type of grease, will also help prevent rust. The four holes at right will accept 1/4" x 20 tpi stainless-steel bolts that will fasten the A-P 1200 Standard Pier Adapter to the cantilevered plate. The A-P mount, in turn, bolts to this adapter, as seen in the next two photos.
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The A-P 1200 GTO Bolted to the Cantilever Plate
 
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Another View of the Mount Bolted in Place
The black dovetail atop the mount is the Astro-Physics 16" Easy-Balance Dovetail Saddle. The OTA rings are from Takahashi and the dovetail plate to which they are bolted is from BT Technologies.
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31 August: The Telescopes and Cameras Are In Place and Balanced.
Photographed from outside the dome on the south side. The A-P mount is in park position 3. The remainder of the photographs on this page show other views and other orientations, and show that there is now more than ample clearance between the cameras and the observatory walls.
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Park position 3 as seen from the east.
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The cameras now have plenty of clearance in park position 3.
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Photographed from the north. Counterweight east.
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Photographed from the north. Counterweight west.

Since I made these photos I have re-routed power and data cables as necessary,
added additional strain relief to cables, and generally dressed up the cabling.
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