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Moving the RA wormwheel to the bottom of the PA shaft was seriously considered and finally rejected. I could have overcome the serious clearance problems but decided it was really only a cosmetic issue.
The sheer scale and weight of the finished mounting has to be experienced to be believed: Just lifting the Declination shaft [with saddle attached] and inserting it into the Dec housing bearings is quite a struggle. The image shows the dimensions in cm.
The bearing housings are 15cm or 6" square in cross section.
Total Declination length = 115cm = 45.25"
Height from under base plate to tip of saddle = 110cm = 43".
The PA housing is 70cm long = 27.5"
The saddle is 70cm long x 10cm wide = 27.5" x 4".
The RA wormwheel is over 11" in diameter.
The Dec wormwheel Ø = 8.5".
The axes shafts are solid stainless steel and 50mm in diameter or just under 2".
The heavy, cast iron, bearing flanges are 143mm or 5.6" square.
The four, corner, tension studs inside the bearing boxes are 16mm in diameter = 0.63".
As is the altitude pivot stud.
The cast iron counterweights are 23cm or 9" in diameter.
I should have called it the Compression Mounting had I thought of it earlier. The axes flange bearings compress the bearing housing plates with the four 16mm corner studs and domed brass nuts. The heavy stud's stiffness in tension is the resistance against which the cross studs and plates are retained. The multiple cross studs compress the 10mm thick plates of the axes bearing boxes against the tensioned corner studs. The cross studs employ furniture, flanged nuts. These have a long thread length for greater strength in tension and the flanges help to spread the compression loads evenly. The Dec axis housing is directly compressed to the large [7" Ø] cylinder.
The Tollok bushes are compressed strongly onto the heavy shafts by opposed, polished steel cones. The same Tollok bushes simultaneously expand outwards into their respective housings. The saddle bush utilizes a very heavy wall brass sleeve to contain the Tollok bush. Which is tensioned and located to the saddle by its 10 x 8mm fixing bolts. While the PA bush sits inside the 7" diameter cylinder. The two are secured together with additional 8mm stainless steel studs. To fix the Declination housing immovably to the large cylinder. The Tollok bush is simultaneously bolted to the nearest 10mm plate by its 10 x 8mm [SS] screws on a large pitch circle. Stainless steel washers spread the clamping load to the maximum possible extent. A far stiffer arrangement than a single large nut, bolt and washer.
These nominal 50mm shaft size, Tollok bushes were deliberately chosen to have the maximum flange size of 90mm. Simultaneously they offer the greatest, compressive sleeve length to resist any chance of rocking on the heavy axis shafts. Once the opposed cones are compressed together, within their enclosing metalwork, they behave as effectively a solid mass of metal attached to the shaft. The major advantage is that they are easily removable by releasing their 10 compression screws. These steel bushes are commonly used in industry for attaching large drive pulleys and sprockets. Spinning such heavy loads at high speeds while driving machinery is a far greater torsion and lateral load than on an [almost] static, telescope mounting.
The heavy, altitude pivot stud compresses the PA housing from either side using the massive 20mm thick x 20cm [3/4"+ x 8"] fork blades. The stiffness of any structure is dependent on its moment. Here, the bearing housings are not just constructed of heavy 10mm aluminium plate to a large cross section but reinforced by the internal, heavily tensioned, steel studs. [Aka.Threaded rods or all threads.] It would take a lateral force of several tons to bend these large, tensioned studs or housings.
This is not remotely a lightweight [portable] mounting as it was never intended to be one. A "Belt and braces" approach has been used throughout its construction. I was aiming for maximum stiffness and strength regardless of total weight, but not ignoring it, by using adequate cross sections of aluminium where possible. The mounting has no need of portability since it will be sited exclusively on a raised observing platform 8' above the ground. There is no other way to gain sufficient all-sky access within my garden.
Mass has the advantage of requiring considerable force to begin moving. So exciting a heavy mass into vibration is more difficult. High mass and high compliance tends towards low frequency vibrations. The disadvantage is that the mass keeps moving once under way. Avoiding vibration is best achieved by a massive or well damped support structure. Or complete isolation from the supporting platform. Timber is naturally self-damping. While steel is prone to vibration.
I have often been tempted to try a flotation isolation system for a mounting using liquid containers. Though it would need to be immune to hard winter frosts to avoid the liquid icing solid. Some observatory domes have relied on a flotation ring in a circular trough of liquid for friction free support. Sealed polystyrene floats would provide nearly 60lbs of lift per cu ft. Bulk and guaranteed stability are the main problems. As is complete isolation between the floats, their troughs and the supporting structure. It would be very easy to produce an unstable raft structure which turned Topsy-turvey. Few amateur raft builders seem to have the slightest clue about stability. Pond skaters are the real experts.
The cast iron counterweights are 23cm or 9" in diameter.
I should have called it the Compression Mounting had I thought of it earlier. The axes flange bearings compress the bearing housing plates with the four 16mm corner studs and domed brass nuts. The heavy stud's stiffness in tension is the resistance against which the cross studs and plates are retained. The multiple cross studs compress the 10mm thick plates of the axes bearing boxes against the tensioned corner studs. The cross studs employ furniture, flanged nuts. These have a long thread length for greater strength in tension and the flanges help to spread the compression loads evenly. The Dec axis housing is directly compressed to the large [7" Ø] cylinder.
The Tollok bushes are compressed strongly onto the heavy shafts by opposed, polished steel cones. The same Tollok bushes simultaneously expand outwards into their respective housings. The saddle bush utilizes a very heavy wall brass sleeve to contain the Tollok bush. Which is tensioned and located to the saddle by its 10 x 8mm fixing bolts. While the PA bush sits inside the 7" diameter cylinder. The two are secured together with additional 8mm stainless steel studs. To fix the Declination housing immovably to the large cylinder. The Tollok bush is simultaneously bolted to the nearest 10mm plate by its 10 x 8mm [SS] screws on a large pitch circle. Stainless steel washers spread the clamping load to the maximum possible extent. A far stiffer arrangement than a single large nut, bolt and washer.
These nominal 50mm shaft size, Tollok bushes were deliberately chosen to have the maximum flange size of 90mm. Simultaneously they offer the greatest, compressive sleeve length to resist any chance of rocking on the heavy axis shafts. Once the opposed cones are compressed together, within their enclosing metalwork, they behave as effectively a solid mass of metal attached to the shaft. The major advantage is that they are easily removable by releasing their 10 compression screws. These steel bushes are commonly used in industry for attaching large drive pulleys and sprockets. Spinning such heavy loads at high speeds while driving machinery is a far greater torsion and lateral load than on an [almost] static, telescope mounting.
The heavy, altitude pivot stud compresses the PA housing from either side using the massive 20mm thick x 20cm [3/4"+ x 8"] fork blades. The stiffness of any structure is dependent on its moment. Here, the bearing housings are not just constructed of heavy 10mm aluminium plate to a large cross section but reinforced by the internal, heavily tensioned, steel studs. [Aka.Threaded rods or all threads.] It would take a lateral force of several tons to bend these large, tensioned studs or housings.
This is not remotely a lightweight [portable] mounting as it was never intended to be one. A "Belt and braces" approach has been used throughout its construction. I was aiming for maximum stiffness and strength regardless of total weight, but not ignoring it, by using adequate cross sections of aluminium where possible. The mounting has no need of portability since it will be sited exclusively on a raised observing platform 8' above the ground. There is no other way to gain sufficient all-sky access within my garden.
Mass has the advantage of requiring considerable force to begin moving. So exciting a heavy mass into vibration is more difficult. High mass and high compliance tends towards low frequency vibrations. The disadvantage is that the mass keeps moving once under way. Avoiding vibration is best achieved by a massive or well damped support structure. Or complete isolation from the supporting platform. Timber is naturally self-damping. While steel is prone to vibration.
I have often been tempted to try a flotation isolation system for a mounting using liquid containers. Though it would need to be immune to hard winter frosts to avoid the liquid icing solid. Some observatory domes have relied on a flotation ring in a circular trough of liquid for friction free support. Sealed polystyrene floats would provide nearly 60lbs of lift per cu ft. Bulk and guaranteed stability are the main problems. As is complete isolation between the floats, their troughs and the supporting structure. It would be very easy to produce an unstable raft structure which turned Topsy-turvey. Few amateur raft builders seem to have the slightest clue about stability. Pond skaters are the real experts.
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