Quote:
Originally Posted by AstroViking
Wow, that's an interesting tale of misadventure.
Would this be a manufacturing issue, or a previous owner??
Cheers,
V.
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Once I got inside, it became clear that it was meant to be this way right from the factory. It's not a bad idea. The front ring is also bonded to the tube so nothing can come loose and shift like it did on the big SCT I dealt with recently.
The OTA turned out to be very easy to dismantle although the primary mirror is larger than the clear aperture. The trick is to turn the primary 90 degrees, after pulling it off the central supporting tube, and getting it out sideways through the two cutouts provided in the corrector plate seating.
I turned another fixture and set up the primary assembly on the lathe to see what was causing the tilt. When I started spinning it, I was dismayed to see just how bad that piece of glass looked like. There were serious runouts on every surface - I mean millimeters. The metal hub was running true and yet the outside diameter of the mirror had a major runout meaning that the hole is not in the center of the mirror.
I also measured a wedge error, at the rim of the mirror, of 0.7mm.
Also there are very rough and uneven (eccentric) chamfers on the front of the mirror and the one around the perforation is particularly troublesome because it produces an uneven contact area against the rubber washer that is supposed to define its squareness on the hub.
I ended up replacing the rubber washer with a cork one and after a lot of mucking around I managed to get the front of the mirror running reasonably true.
After that I reassembled the OTA and set it up again on the lathe only to find that it was only a bit better than before. The primary was still wobbling quite a bit and after closer inspection I saw why: The central tube that the primary assembly slides on, is not square to the optical axis.
I dismantled the OTA again but I can't unscrew the central tube to see what the problem is.
So I'm a bit stuck at this time and need to sleep on it.
The back of the primary is covered in texter marks indicating that someone else has tried hard to fix this problem before me.
I can't see how this scope ever passed the QC at the factory.