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The 1.7mm, elastic, fishing line leader turned up in the post. Sadly it proved to have too much friction despite the silicone grease I used for lubrication. The line was amazingly soft and flexible. It fitted the etalon housing grooves nicely. But, it still made the etalon slightly too stiff for the Skywatcher motor to turn reliably. The timing belt was slipping on the 16T motor drive pulley.
UPDATE: I have used a combination of the fishing leader and a length of sleeved copper wire. One arc in each groove. This provided a nice balance between friction and floppiness of the drive band. The motor now happily drives the etalon tuning from end to end. Thinking that there might be a problem, I had dismantled the etalon assembly. Just to check the foam rubber ring wasn't hardened. There were none of the rubber pads added to some etalons shown online. I'll assume as is now well with the etalon unless I discover otherwise.
This has become an expensive exercise by the time I have added up all the different, monofilament strimmer lines and O-rings I have bought online, plus postage. One expert told me that the original PST O-rings were 1.7mm Ø but that does not match my own experience. While I could easily modify the etalon shell in the lathe, that was not the idea. I wanted to find a readily available, O-ring size, or replacement material, for others to copy. To provide a guaranteed, freer moving, etalon tuning band than the original.
Without sufficient freedom the timing belt cannot turn the textured, etalon tuning ring by friction alone. The little motor and gearbox are easily powerful enough to slide the timing belt over the etalon band if the etalon is not free enough. No amount of tightening of the drive belt seems to help.
The friction of my original PST etalon and its O-rings is far too high even for normal, manual use. No lubricant tried so far makes it otherwise. I have no reason to believe that anybody changed the O-rings before I bought this PST secondhand. That would have required the paper security label over the etalon drive, screw head was broken. It wasn't until I pierced it myself to dismantle the etalon shell for the first time. It was not stiffening of the foam rubber ring which surrounds the etalon itself. It is [probably] a machining tolerance issue causing too much friction between the original O-rings and the thin metal shell which supports the textured rubber, drive band.
After I received the PST I actually believed that my pressing the etalon band wrongly was causing the high friction. So that I would wrap my fingers around the band not to apply local pressure when tuning. I was completely mistaken! My PST etalon housing was just badly made. Or, somebody arbitrarily changed the O-ring dimensions at the factory for some reason. Perhaps they simply ran out of the usual O-rings and substituted what was locally available? Perhaps until they could restock with the correct O-rings?
The known, slapdash manufacture of the PSTs, in a Mexican factory, must be responsible for the wide range of image quality experienced by PST buyers. The way the thread locker was applied suggests the lowest imaginable standard of worker or zero work experience. Presumably an attempt by Meade to save even more money than typical Mexican worker's average pay compared to the USA.
There was the debacle over the "rusting" of the original, PST objective coatings. Then the same with the internal ITFs. It all added to the doubtful quality of these very expensive little telescopes. The same also seems to be holding true of some other, solar telescope manufacturing "labels."
The Daystar Quark has an unenviable reputation for variation in image quality and general unreliability. With endless returns to the dealer or manufacturer for replacement and/or repair. These items are far too expensive to be messing paying customers around like this!
Hopefully a far better item will soon become available. One which does not require a compressor and very long waiting times every single time the tuning is adjusted! However tempted I might be I certainly shan't invest in such a quirky unknown!
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