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Balancing a Dob


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Just recently, Lee Valley, the Canadian tool purveyor, made the Beall Tool digital inclinometer called the "Tilt Box II" available at a special price. I bought one to help me get declination angles more easily on my 8" Orion dob.

The unit is a bit heavy when considering the fine balance of a dobson mount. For this reason, I'm a bit unsure about the best location to attach it to the ota. My first inclination was to put it near the telrad using velcro to attach it, but the telrad and finder and especially heavy ep's require a shot bag ballast using velcro along the spline over the pivot center of the ota. Because the vlecro strip on the ota is about a foot long (300-350 mm), I can vary the position of the small bag of shot that I use to counterbalance the weight at the opening end.

Has anyone here attached a digital inclinometer (Wixey, Beall, or other) to a dob satisfactorily? Is this a fool's errand? Should I abandon the hope of more accurate declination's using technology.

TIA

Bob

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Try placing it on the OTA's centre of gravity, where the azimuth bearings are. In theory this shouldn't affect balance. Placing it at the focuser end will mean a counter weight at the the other end. I use a large magnet covered in self adhesive felt to prevent scratching and move it around until balance is achieved.

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Thanks for the suggestion, John.

On re-reading my op, I realize that I didn't ask my question very well at all. You understood despite my inadequacy of expression. I'll try again to clarify my question, although I think your answer is probably spot on.

I already have a velcro strip down the top center of my ota that covers the center of the azimuth bearings and extends both up and down the tube. In combination with a bag of shot that has the opposite velcro piece attached, I have the means to counterbalance any weight added at the outer end. The weight of a wide-angle Meade ep and low sky viewing generated the need for the solution in hand.

I intend to add a velcro strip to the bottom of the Beall gauge and attach it to the ota at the pivot point above the azimuth bearing. This should have near neutral impact on the ota balance yet provide the benefit of the angle reading.

My question was to learn if this plan has any negative consequences which I should consider. If positioned carefully, there should be little, if any, affect on the ota balance and I should still be able to use the bag of shot for counter weight.

From your response, I take it that I'm on the right 'track' (sorry for the awful pun!).

Thank you again!

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  • 2 weeks later...

Hi Rabbit, If you have a metal tube, you might try using magnets for balancing. I bought 4 bucking magnets that weight about a pound each and wrapped them in duct tape to protect the tube and they work great. I use 3 of them to balance the meade 30mm uwa. They stick to the tube like glue and are easily removed or replaced as you need them. They were 3 or 4 dollars each shipped from an electronics store in Wisconson. I would have to look it up if you were interested.

Eric

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I also have a wixey, and a digital angle gauge which both go up by the focuser, but as John mentioned a substantial magnet wrapped it duct tape and the self adhesive felt works fine. I found that the weight of the magnet caused it to slip on dewy nights, so I stuck some butyl rubber pond liner under it, that keeps it safe.

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