Telescope Reviews: Again with the shutter problems!

I opened up my dome a couple of times yesterday without any problems. Russ had used the rest of the EPDM pitch pocket filler to seal around the inside base of the dome last week, and so we needed to put the tiles back down again. (Not finished with water sealing yet - but this looks to be a good improvement.) While doing this, I opened and closed the dome a couple of times without any problems.

So imagine my surprise as I open the dome last night to do some observing, to find that the front shutter of the dome pops out of it's track, rearing up backwards instead of smoothly opening.

This is pretty easy to remedy - you just climb up a tall ladder and pop it back in track. It's super annoying to have to fetch the ladder (If I wanted a ladder in my observatory, I 'd have a roll off and a big dob!), and it's a little stressful to see it malfunction, but no big deal. I fix it and go on to have a successful night of observing.

So today I try to reproduce the failure, and of course I can't. But in the course of watching the shutter open and close a half-dozen times, I am struck by how much force is pulling DOWN on the shutter, pulling it against the rear cover of the dome.

I examine things, and I notice that the tension on the shutter cables on the western side of the shutter is quite a bit higher than on the east side, and much, much higher when the front / top shutters near the zenith of the dome, which is where it seems to hang up, than when the shutter is closed. At the zenith, the cables on the west side are almost guitar string taut. When closed, they have a small amount of give.

So Bob, my brother-in-law, and I, try loosening the west cable a tiny bit. This helps - the cable is no longer completely taut when the shutter is raised. So we sand the rear slot and the front tab on the shutter (it was catching a bit on the slot), and we found the shutter to work much, much more smoothly than it ever has before.

I opened and closed it at least 8 times, and it just worked flawlessly. The motor strain sound when the dome closes is gone. The shutter parts seem to smoothly glide over one another while the dome opens, just as they should.

I may need to periodically sand the slots and tabs a bit, and I may not have the tension quite right (although it seems pretty even between the east and west cables now), but so far, so good.

If this turns out to fix the problem permanently, it would be a lot of grief caused by maybe 1/8" of adjustment to a cable.