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As a conscientious objector to limited imagination I really had to try the rubber bands on the pier. I managed to find 16 punctured inner tubes and hooked those over the top of the octagon's support posts.
The pier was made into four parallel, vertical posts without any splay at the base. I did not want any 'tripod effect' to alter its natural behaviour. With the 16 "rubber bands" fitted the pier proved to have a settling time of about 2.5 seconds regardless of how hard I tugged on it. Hitting the pier with my fist had no obvious effect. Adding the few hundred pounds of mounting and OTAs would have increased mass resistance to disturbance. Whether this would provide a serious means of support for a high power telescope is quite another matter.
The pier was made into four parallel, vertical posts without any splay at the base. I did not want any 'tripod effect' to alter its natural behaviour. With the 16 "rubber bands" fitted the pier proved to have a settling time of about 2.5 seconds regardless of how hard I tugged on it. Hitting the pier with my fist had no obvious effect. Adding the few hundred pounds of mounting and OTAs would have increased mass resistance to disturbance. Whether this would provide a serious means of support for a high power telescope is quite another matter.
So I have now returned to the tall, pyramidal pier of previous blog and forum posts. I think I am on much safer ground with this. Triangular sides and inherently stiff, 4"x4" posts will provide plenty of stiffness. The base can be reinforced with timber to ensure a lack of distortion. Cross bracing is easily arranged. As is sheathing or cladding the pyramid.
I set up a first trial with roughly 4' sides to the base. The posts are presently too tall because i did not want to have to replace them all if one of mynutty ambitious plans failed to succeed.
The image shows the pyramidal pier propped in place. The splayed posts are surprisingly easy to walk through and around. The trick would be to avoid closing the lower area with braces which would impede normal foot traffic.
Leaving the floor smooth, perhaps with a buried base frame of 4"x4s" could be concealed below a plywood or boarded floor of modest height. Or suitable gravel could be used, to provide a solid foundation beneath the base frame, to avoid sinking or listing over time. The ground should remain bone dry under the building.
I planned to use the same concrete footings as before to provide fine adjustment in individual post height. This does not preclude using packed sand & gravel under the base frame to provide a firmer foundation. Perhaps offering a structure less prone to 'ringing.'
The legs will probably want some cross bracing to prevent them vibrating like a struck bar. They may be thick and relatively dead timber but their considerable length could be prone to individual, flexure and vibration. Arranging the cross bracing above head height or providing a through 'corridor' to plywood cladding is easy enough.
I set up a first trial with roughly 4' sides to the base. The posts are presently too tall because i did not want to have to replace them all if one of my
Leaving the floor smooth, perhaps with a buried base frame of 4"x4s" could be concealed below a plywood or boarded floor of modest height. Or suitable gravel could be used, to provide a solid foundation beneath the base frame, to avoid sinking or listing over time. The ground should remain bone dry under the building.
I planned to use the same concrete footings as before to provide fine adjustment in individual post height. This does not preclude using packed sand & gravel under the base frame to provide a firmer foundation. Perhaps offering a structure less prone to 'ringing.'
The legs will probably want some cross bracing to prevent them vibrating like a struck bar. They may be thick and relatively dead timber but their considerable length could be prone to individual, flexure and vibration. Arranging the cross bracing above head height or providing a through 'corridor' to plywood cladding is easy enough.
Click on any image for an enlargement.
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