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The
10mm plates of both bearing housings are under heavy, lengthways
compression by the large studs [US.all threads] These heavy studs have
been deliberately fitted tightly into the corners of each box housing.
Once under tension these same studs resist the inward pressure on the
plates by the 8mm studs and their furniture nuts. The smaller studs are
deliberately fitted almost touching the large studs to resist inward
pressure by further means. The large studs act as shoulders against
which the plates can firmly rest.The outer bearing housing plates cannot move inwards because of the sandwiched plates between them. The sandwiched plates press inwards against the large longitudinal studs. Which, being tensioned, cannot possibly move sideways under the constraints of the massive, iron bearing flanges.
These heavy flanges, being under the tension from the large studs, deny the plates any ability to go 'lozenge' shaped. Meanwhile the plates themselves deny the flanges any freedom to tilt by their own square ends and their huge 'stiffness' in their own plane. Even a 10mm thick plate may be bent given enough force but making one "go lozenge shaped" requires absolutely huge forces measured in many tons.
The image alongside shows the front plate removed for clarity of the stud arrangement inside the PA bearing housing. With the positions of the larger and smaller, M8 cross studs clearly visible. The front to back M8 studs are not visible because they have been temporarily removed for the picture. These would normally apply inward pressure on the sandwiched plates. Pressing them against the heavy studs.
A simple box casting of similar dimensions would have to rely entirely on the tensile strength of the cast aluminium material to avoid distortion or even catastrophic breakage. Here, the large steel studs act rather like pre-tensioned, re-bar steel in a form of highly pre-stressed reinforcement of the aluminium box. Similar methods are used to reinforce concrete beams.
I decided to use this unusual method of construction to avoid drilling and tapping the relatively thin 10mm aluminium plates for lots of much smaller screws. This allowed me to use the much sturdier 8mm [5/16"] cross studs. Which would have seriously weakened the 10mm plates had I drilled and tapped the edges in this size. Since weight was never a serious issue I was happy to use larger studs than strictly necessary. These cross studs could be duplicated in any desired number if it was thought desirable. I have used many more on the declination axis bearing housing. Which does not enjoy mutual reinforcement from the compressing fork blades and its tensioned, altitude, pivot stud.
I cannot fit the 10mm worm housing support plates yet until I know what size to make them. That must wait until I have the worm drive, pulley systems to measure against. I was promised mid December delivery but that deadline has already passed. It seems I must now wait until the New Year for my drive system. This follows waiting for months for the worms and wormwheels from another British supplier. Then having to accept an incorrect bore size, at the second attempt, or play a third round of their fixed lottery! Meanwhile the prices had rocketed from the years-old and long unchanged, website price list!
Did I mention the mess they made of the tooth cutting where they joined on the opposite side to the starting point? The so-called "accuracy" probably means that the drive speed will be dependent on the position of the wormwheels relative to the worm. With two completely different pitches from start to finish. That is, if the journal bearings don't fall out of their housings!
I am beginning to see a clear pattern emerging amongst small, British astro equipment suppliers. There were serious problems with another British supplier which I won't go into here. BTW: I am British myself, so this is not overt racism. I wonder how many other customers have been left hanging over the years thanks to completely unrealistic promises of delivery. No doubt these small companies imagine they are doing the customer such a huge favour, by providing rather unique items, that all public criticism is unwarranted.
Click on any image for an enlargement.
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