2" shaft mounting Pt.40: PA/Dec Overhang.

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The large overhang beyond the top PA bearing was irritating me if I kept the RA wormwheel on top. A preference for this position required further thought.

The "painted" image [right] shows what happens if the wormwheel boss is removed. The boss provides a three point, adjustable, radial, nylon "clutch" to allow telescope movement independent of the wormwheel. As I already have a clutch in the form of a PTFE disk pressing down from just above the wormwheel the boss becomes irrelevant.

Its removal saves a useful 25mm [1"] of overhang. Sadly, its absence makes very little difference visually to the degree of cantilevering. So, I might as well just leave the boss in place. Or give up trying to place the wormwheel at the axes junction. Or, just ignore the overhang problem altogether. If only I could. As an obsessive mounting admirer, of over half a century, the overhang glares right back at me. Though a fork mounting would instantly introduce yards of overhang. Without anybody giving it a second thought. It's, really, all about appearance.

The Tollok bush's un-expanded sleeve diameter is 65mm so the wormwheel won't fit on that even if I spent hours and turned away a large section of the cylinder. The Tollok bush could be slightly shortened but not enough to make it worthwhile before the opposing cones risked losing their gripping power. Best not to go there. Though Tollok do make much shorter bushes I chose the one most likely to offer maximum support to the cylinder and Declination axis.

An alternative would be to add rollers for the cylinder to run on. Not easily achieved with the large wormwheel getting in the way of any natural upward extension from the existing polar housing. Using rather large rollers might do it. They would avoid an ugly, dog-leg support system for the rollers and simultaneously reduce friction.

I have tried adding counterweight to the bottom of extended PA shafts. This doesn't work well with the former plain bearing mountings on which I have done this. The problem of increased friction is very unlikely to arise with these huge flange bearings. Their load capacity greatly exceeds anything I could possibly imagine hanging on the end of 50mm [2"] mounting shafts. Perhaps if I bought a much longer PA shaft it would completely alter the visual scale? That would mean finding the materials for another, much longer, PA bearing housing. I have thought of borrowing the longer Dec shaft and bearing housing for the PA but discarded the idea. The shorter housing looked rather lost on top of the much taller PA housing. I'd also have serious problems adding enough counterweights to a short shaft.

As I have already discussed, the wormwheel might be difficult to house right at the bottom of the PA shaft. My 55° North situation leaves little room under this steep polar angle for an 11.5" disk. I'd also need a retaining collar to stop the wormwheel from literally falling off the end of the PA shaft. That aside I lose the greatly increased stability offered to the RA wormwheel by the cylinder and PTFE 'clutch' disk. There is also the matter of greatly increased complexity in arranging a slow motion control shaft back at the eyepiece for a "bottom dwelling" worm and wormwheel. A top mounted worm needs only a straight shaft provided the worm is placed on the side of the wheel.

Click on any image for an enlargement.

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