2" shaft mounting Pt 12: Curvy alternatives?

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Yet another interesting idea has cropped up on CN. Instead of aiming for a traditional but boxy GEM I should consider curved forms. Building a mounting this way can avoid the serious cantilevering of the Declination axis, telescope and counterweights via a single flange and shaft socket. A large C-shape can provide polar altitude adjustment while neatly splitting the declination loads on the polar axis into two. 

Provided the curve is given an adequate cross sectional area it can be as stiff as aluminium. The image shows the basic idea. Thinner plywood strips are laminated over a former and clamped tight while the glue sets. Normally there is a degree of spring and the radius of the final result may increase. The flange bearings can be placed inside or outside the "arms". A bolt, fitted with load spreading washers or plates will clamp the curve securely to a suitably curved base.

The next step is to be equally adventurous with the design of the declination axis and saddle.

Here a similar, but tighter curve is nested within the polar axis curve to provide twin declination bearing supports. The downside of this arrangement is the severe obstruction of the telescope tube on either side of the mounting. To point at the Pole the telescope must lie alongside the mounting rather than above it. 

Since the two axes shafts cannot physically cross each other it is not possible to have the declination shaft perpendicular to the polar axis in the usual sense. [As shown by the red arrow] This would require a stub shaft and plate bearing impaled on the red arrow. A separate Declination counterweight shaft could be attached via a clamp but this adds bulk and complication. The telescope tube needs to clear the polar axis and large wormwheel. So the declination overhang/saddle must be extended considerably in the direction of the arrow.

The declination shaft could be offset slightly to the east or west of the PA shaft but this would introduce an offset force which must be counterbalanced. The offset force would also change with telescope weight so would need adjustable counter-weighting which is best voided. Just swapping a heavy eyepiece and star diagonal for a much lighter one might require re-balancing. Though a sliding counterweight could be fitted to the opposite side of declination shaft, from the offset, for rapid changes of lateral balance.

The lower image shows a circular declination assembly with a superimposed T-shaped box. All made form plywood laminations. The head of the 'T' provides the declination shaft housing and enough offset to avoid collisions between the OTA and mounting. The advantage here is that the declination assembly lies between the PA bearings and is evenly supported by flanges. So no stress raising cantilevering for the Polar Axis. The saddle is cantilevered but has a plate bearing formed by the wormwheel.

Click on any image for an enlargement.

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