I finished mounting the dovetail plate on Big Bertha 2.0 yesterday, and did a sufficiently slapdash job on it that I decided to replace that one square aluminum tube with one with a 1/8" wall. This way it will be stiffer, and I can do a more precise job drilling the holes because it won't be attached to the rest of the telescope when I drill them.
Then, I decided to go ahead and put Big Bertha 2.0 on the CI-700 mount, which is the only one that I have with the weight rating for a 50 pound telescope. This soon led to a minor disaster for the following reasons:
1. A German equatorial mount is a balancing act. The counterweight shaft for a 50 pound telescope has to have 50 pounds of weights on it, or at least close to it. That means that when the telescope isn't on the mount, it is intrinsically unstable.
2. I had not removed an extension from the tripod that put the equatorial mount head twelve inches higher than it needed to be. Partly I didn't do this because it would have required me to drill two holes in the tripod to mount some of the CI-700 mount's electronics on it, and I was in a bit of a hurry.
3. I neglected to lock down the casters under the tripod before trying to mount the telescope, and so it was a little too willing to roll.
The net result was that when my wife and I tried to put Big Bertha 2.0 into the dovetail slot on the mount, the mount (but not the telescope) fell over, landing on the counterweight shaft, and narrowly missing the 5" refractor that I had just taken off this mount.
The head of most equatorial mounts (including the CI-700) are positioned in between two verticals, held in position by a bolt that squeezes the verticals tightly against the head. It isn't a great picture, but you can sort of see this (especially if you know what you are supposed to be seeing from the description above):
Click to enlarge
In the case of the CI-700, there is also a latitude adjuster bolt that goes in between the bolt and the verticals, and makes it easy to adjust the mount for your latitude. The latitude adjuster bolt moves a cylinder back and forth that presses against two sets of "ears" on the under side of the head. Here you can see the latitude adjuster bolt, and the cylinder that moves back and forth against those ears.
Click to enlarge
The counterweight shaft had enough force against it to break most the ears (the lobes?) off the under side of the head, and bend the latitude adjuster bolt. Here are the broken pieces of aluminum that were the ears:
Click to enlarge
The ears are an integral part of the head; replacing the head would cost many hundreds of dollars--if parts were available, which they aren't. It might be possible to have them welded back in position, although I am afraid of what that might cost. I'm quite sure that epoxy wouldn't have the strength for this bond.
The latitude adjuster bolt is a 3/8"-16 thread. I'm thinking of buying a bolt of the right length, turning down the end that isn't threaded, and then making a larger cylinder--large enough that it will work against the parts of the ears that weren't broken off. This means that the hole that I have to tap in it will be offset, instead of centered.
Any suggestions or hints for alternative strategies?
No comments:
Post a Comment