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Aluminum tube replacement for Skyview extension

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#1 hudson_yak

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Posted 07 June 2009 - 12:41 PM

I mentioned in another recent thread that I was ordering this to replace the heavy steel tube the extension is made from. The intent was to lessen the weight and with a shorter length hopefully mitigate the rather bad jiggle resonance the original extension has with my particular combo of equipment.

The length ordered was 8", cost was very reasonable. I was a bit concerned when it arrived in a package not much bigger than the tubing itself, but it survived shipping without being crushed out-of-round, fortunately. The tubing wall thickness is 1/8". The ends were cut square, I just had to drill screw holes, a bit fussy but not super-difficult job. This is industrial tubing so would need a bit of sprucing-up to give a more finished appearance.

Certainly the weight issue was much improved, weight, including the end caps, went from 12-13 lbs to 3.5lbs.

The 8" length was good since I like to use my tripod with legs extended to get the eyepiece tray and lower homebuilt tray at a more comfortable height.

Unfortunately, the jiggle problem, though certainly better than the original extension, will not go away with my scope. I've tried many things, including smoothing the tripod top surface for flatter contact with the bottom of the extension. Have tried differing numbers of counterweights in different locations on the bar. I've tried it with the tripod legs fully-retracted. Nothing makes much difference. The jiggling takes longer to dampen out and does this weird 90-degree direction change partway through it is decays. It makes focusing a chore, even with a fine-focus knob.

So, up into the attic it goes until some other part of the puzzle, scope, mount, or tripod, changes. If you are having no such issues with the original extension it seems likely you'll be fine with something like this too though.

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Mike

#2 johnfdean

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Posted 07 June 2009 - 10:16 PM

Have you considered going to a local woodworker for longer tripod legs?

#3 hudson_yak

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Posted 08 June 2009 - 08:55 AM

I've considered making some myself, occasionally. And yes, if I were to do that I'd make them long enough to not need an extension on top, so it would sort of make the whole extension jiggle issue moot.

I'm quite happy with the tripod's performance and convenience as long as the mount head is directly on top of it. I bought the original extension after a number of people had spoken highly of it, in hopes of not needing to drag out my chair every time. I tend to think my best option, as far as my lower back goes, remains to just use the chair. Even with the extension I needed the chair for objects directly overhead anyway.

Another issue I have to consider here, if the scope is perched too high my wife can't look through it easily.

Mike

#4 JimK

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Posted 09 June 2009 - 01:29 PM

What about using a Hargreaves strut? Some ( link-scope and link-parts ) find it provides better stability, especially with long refractors.

#5 hudson_yak

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Posted 09 June 2009 - 03:11 PM

Interesting, I'm pretty sure I'd seen that thread before but forgot. Might learn something about my particular setup by trying that, thanks.

Although I probably didn't make it clear enough in my OP, this wasn't really meant to be just a cry for help, it was mostly just to show an alternative solution for anyone who hoped the Orion extension didn't weigh so much. It's come up in a few other threads recently. Similar aluminum tube replacements have been shown, but they were of the "my buddy who works at a machine shop made this for me" variety. I wanted to show it could be accomplished by anyone without the special buddy requirement.

Mike

#6 deezdrama

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Posted 09 June 2009 - 04:35 PM

hmmm- Im using a SW 120ed Pro on a cg5 tripod with the skyview extension and a WO ez touch mount head and have no jiggle. But the first time I set it up I noticed a little jiggle, I went back with an allen wrench and really locked the 6 bolts down that are on the extension and it solved the problem. Might give it a try

#7 hudson_yak

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Posted 09 June 2009 - 04:59 PM

I've spent hours on this issue and have tried all sorts of stuff like that. I'm pretty sure it's just an unfortunate resonance from the particular combination of components I have. Almost no one else seems to see the same problem, but there's always something different in the setup compared to mine. Bigger scopes actually seem to help avoid it, that's one pattern that seems to hold true.

Another person did have the same issue, also with SVP and 100mm class scope (don't know the focal length though). They described the behavior as a "tuning fork" which is about right.

Mike

#8 Mittag56

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Posted 09 July 2009 - 07:33 AM

If its a machine resonance problem, you may get some sof it out by intentionally offset of the components. What we used to do to high speed metal presses when i was an industrial mechanic..adding a small wieght on the shafts and components of the press would change the resonance of the equipment and really not change ballance...maybe try a small 1/2 pound weight taped above and below where scope is attached, i also have to hang about 5 pounds under my spreader bars..this moves center of gravity a little lower and less wiggle up top..just a thought ;)






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