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The advantages of a permanent pier are increased stability, better access to the telescope (no tripod legs to trip over), and facillitation of rapid setup (the telescope can be automatically polar aligned). This example illustrates my own pier, it is not (yet) inside an observatory and remains exposed to the elements year-round. On top of the pier is a Meade Super Wedge which is also normally left attached to the pier, however it is removable should I wish to transport the telescope to a dark site.
A diagram of the pier's construction is shown below:
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The pier foundation is a cylinder of concrete some 5 feet deep overall, whilst the pier itself is a steel tube 8" I.D. with a wall thickness of 3/8", it's 7' 6" long and weighs about 200lbs. At present, the telescope (a 10" LX200) is rather too high for comfortable viewing of ojects near the horizon, this is because I plan to enclose the pier within an observatory and I expect the surrounding floor level to be some 6-8" higher than it is now.
The first job (having selected the best site for the pier) is to dig a hole for the foundation. Note that for my pier there is actually more tube underground than there is above, this is a good plan but perhaps errs on the safe side. The exact dimension I used was governed by the length of tube I managed to aquire, there seemed little point in hacking a foot of the bottom. About a 3 foot depth below ground and about 3' to 3' 6" above ground level would be adequate for most installations - provided this got below the frost line (not a problem here in the UK). The hole was dug out with a shovel - no mean task I can assure you - but luckily the ground was good soil most of the way, only the bottom foot or so being clay. A 6" thick aggregate mix of concrete was put in the bottom of the hole first and allowed to set for a week, this acted as a sub-foundation to support the heavy pier and to seal the bottom. The steel tube was then lowered into the hole onto this sub-base and it was carefully levelled and held in place with wooden braces. The next layer of concrete was added to bring the level up to about 6" below the surrounding ground level, and was allowed a couple of days to set. The braces were then removed and a circular form made from hardboard and placed around the top edge of the hole, the top edge of this form was made level and would provide the final shape for the upper part of the base. More concrete was added to a level a couple of inches above the surrounding ground level (to the top of the harboard form), and immdediately it was poured three wood sticks were set at an angle into the top surface forming drainage channels to prevent the pooling of any standing water. It would have been a good idea at this point to use a length of 1" copper pipe and elbow fittings (plumbers supplies) to lay a cable duct under the surface of the concrete to reach the central pier. However, as my pier will eventually be inside an observatory with a higher surrounding floor level I didn't bother with this.
The concrete was covered with plastic sheeting and left another week to set completely, then the steel tube was filled with fine (dry!) sharp sand. Note that the tube had been painted all over with a thick coat of black Hammerite (c) paint beforehand. A fillet of silicone sealant was run around the joint between tube and concrete base to prevent water seeping into the gap - differential theremal expansion would likely make this a possibility. The sealant would offer protection from subsequent frost-cracking (although again, this is perhaps not of serious concern here in the UK).
The ends of my steel tube were flame-cut, and although reasonably true were quite rough. It would have been an extraordinarily difficult job making the top edge perfect so I just dressed it with an angle-grinder and painted it. The top-plate would therefore have to be supported by additional brackets, and adjustable so it could be levelled. The diagram below shows the arrangement for attaching three pairs of blocks (half inside and half outsite the tube walls) which support the top-plate:
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The blocks were machined from 1" aluminium, radiused to fit the inner and outer tube walls, and bolted through with 8mm stainless steel cap-head bolts. The inner block was threaded to accept the three 10mm bolts which hold the top-plate in place. The through-holes were slightly over-size to allow a little adjustment to get the top-plate perfectly horizontal, it didn't take much adjustment. The top-plate itself was an 8.75" disk of aluminium, machined all over, and attached to this was a machined replica of the standard Meade tripod-top (another aluminium disk, this time 6-1/2" diameter and 1-1/2" thick). This part had a central stainless steel stud (1/2" x 13 tpi) to accept the hand-knob, and three tapped holes to accept the wedge clamp bolts. A tangent arm was machined so the Super Wedge could be adjusted in the usual way.
 Pier top-plate showing replica tripod top and tangent arm. |
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 Two more views around the pier top-plate. |
A useful accessory is shown below, consisting of a shelf/table on a flexible arm which can be moved around the pier as required. I find this useful for a number of things - holding charts, bulky accessories etc., and because it's attached to the pier there's no chance of tripping over it in the dark. It is actaully one of the wall brackets for holding a TV, painted all over with Hammerite so it won't corrode, and bolted to the side of the pier.
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 The flexible shelf attached to the pier. |
The pier has proved to be very stable indeed, the only remaining flexure now lies within the LX200's fork mount and this is difficult to eradicate. As mentioned earlier, my SuperWedge normally remains on the pier, there is nothing to rust or corrode so the weather doesn't bother it. With the ledge attached to the SW's tilt-plate it is possible to remove and replace the telescope without having to polar align each time, I just bolt it in place, synch on a star, and off we go!
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