*
A wooden pier made from 4" square pressure treated timber can be bolted together. Wood naturally damps vibrations and needs no maintenance. Those with deep pockets can choose green or even seasoned oak and pretend they have a Great Dorpat Refractor. We have a local timber yard which offers large sections of oak to feed the half-timbered, thatched houses market. Curved braces to copy the Dorpat refractor may even be available. For the height needed [about 6'-7' or 2m] the cost is a fraction of wimpy, commercial, metal offerings which never attempt such pier altitudes anyway. And could never support a heavy, classical refractor in the first place. The height in the SketchUp drawing is truncated.
A four legged pier is far more stable than any tripod or other three-legged arrangement. Only on concrete will an infinitely stiff four legged structure rock. A wooden pier is not infinitely stiff and has easily enough mass to avoid any tendency to rock. On a lawn or gravel it will sink slowly under the combined weight until the pressure under the feet is more or less equalized. If it should list over time then it can be lifted back to vertical with a lever or crowbar and packed under the sunken foot.
A wooden pier offers advantages which a large steel pipe does not, except perhaps, cosmetic appearance. Stability from a large footprint is no hindrance except for viewing directly overhead. The large area of the top of the four posts avoids the necessity for mounting spindly mounting adapters. It provides an excellent match for the intended triangular pyramidal base I am planning to use. Adding heavy timber bracing to the heavy mounting is simply a matter of cutting suitable sections and bolting into place. Galvanized threaded rod [studding] is probably cheaper than long coach bolts in the likely lengths needed. If necessary the whole thing can be literally taken apart with a single spanner [wrench] and rebuilt elsewhere. The image above shows the compliment of the 55° PA altitude angle does not
suit the triangulating props at 35°. I need to add channel sections first. Then
bolt the props to those to bring the props far more upright. First buy
a 16mm drill! I keep thinking that an adjustable height pier would be incredibly useful. Not least for mounting and dismounting a long and heavy OTA. I have looked at counter-weighted, parallel-paired, parallelograms but a counter-weighted see-saw arrangement might be easier to achieve and use in practice. Moving the heavy counter-weight between observing sessions might be quite a hurdle unless it could be easily spun on a threaded rod. Not impossible as large stud sizes are readily available in timber merchants. The counterweights could also be duplicated to halve the immediate workload.
A long reflector and classical refractor have such extreme opposites in their needs for pier height that they almost preclude each other. It is difficult to see how the [very heavy] mounting can be easily and quickly moved between piers of only two feet high and well over six feet. The sheer weight of the mounting does not make the task appealing. Perhaps the mounting could be attached to a sled which rises and falls under the control of a block and tackle along a sloping pier?
Oddly, the two instruments are very similar in both length and breadth. Except hat one is viewed from up near the top and the other from the bottom. The arrangement shown is simple to achieve but has a massive overhang requiring equally massive counter-weighting. Having each instrument at the opposite ends of the declination axis means they would balance each other at not much extra weight.
Parallel mounting of two such instruments on the same pier makes little or no sense. Even though the reflector could be heavily top-balanced to allow a tall pier, the mass required could hold a lot of heat. Which is likely to be released into the light path for literally hours. The alternative is [perhaps] to arrange a mid-height pier but allow large differences in observer viewing height. A platform or stepladder for the reflector and an adjustable height seat for the refractor?
A more serious arrangement might be a car port to protect the instruments and refit the optics for observing sessions. Though I'd much prefer the instruments to be permanently set up ON TOP of the carport as a raised platform. Then all I need is an observatory to protect the very exposed instruments from storms and the elements. And, all on top of a very tall pier? Better, I think, to have a cross-axis mounting supported independently of the platform.The observatory would have to be highly wind proof. It must also ensure against any chance of the observer falling from a great height when using a stepladder while observing with the 10" f/8 reflector. This is all getting very expensive and cumbersome and requires an awful lot of heavy woodwork before building the raised observatory is even considered.
I keep thinking a miniature "Nissen hut" could roll back on rails over the roof of my existing, pitched roof workshop. Such, tunnel shaped structures are readily available in all sizes for protecting farm animals. Or, a semi-cylindrical, roll back roof could protect the instruments with them both permanently mounted on a tall [long] cross axis. This would leave walls of a suitable height to protect me from the almost incessant wind. The degree of roof roll back could be adjusted to provide reasonable protection from the overhead projection of the 'barrel' roof. A semicircular, southern gable end could be folded down with a hinge at side wall height.
A much cheaper alternative would be a cross-axis mounting built onto a triangular timber 'trolley' with large, free running wheels. This could be wheeled out from under a protective cover and moved to clear sky. Not ideal from a number of standpoints. Not least rapid polar alignment and a lack of shelter. Then there's the matter of providing power and cables for computers for imaging and power for the drives. Never buy a garden with the house along the southern border!
Click on any image for an enlargement.
*
No comments:
Post a Comment