Easiest DIY mod ever - an AZ3 mod, now so easy to use!

[mental4astro (Alexander)]

Hi all,

I recently picked up a 4" achro with an AZ3 mount. Nice scope, terrible mount! Terrible only because it put the scope, and its centre of gravity SO high up that it was impossible to point the scope up anywhere over 30deg without way over tightening the altitude nut, or else the scope's weight would just over load the mount and the whole altitude motion just tipped back on its own. Not safe for scope, mount or user.

The solution was the easiest DIY mod I've ever done. One 15mm plywood off-cut, two 1/4" bolts, two wing nuts, four washers and drilling four 6.5mm holes. The plywood was cantileavered off the mount head using the 1/4" bolts. The wing nuts make for very quick and easy removal from the head. The scope's rings were then attached on the underside the ply using the nuts that came with the rings, and the scope just hangs underneath. This brought the centre of gravity more in line with the pivot of the mount head, and now the tension nut of the altitude action is only firmly tightened, rather waaayyyy over tight, and the scope can be easily pointed up to any angle without tipping back!

Only 10min work and the solution was soooo easy to now have such a user friendly scope and mount combo! Woohoo!

It's not perfect - I could move the OTA further forward for perfect balance, but this would require a larger piece of ply. I don't see the benefit to the added work.

Thing is, ALL AZ3 mounts have this exact same problem of placing the centre of gravity of the scope way too high above the pivot of the alt bearing. This bugger all cost mod makes the AZ3 mount a very user friendly mount, without risking your precious gear. Can't ask for more with DIY, can we,

Mental.

[Wavytone]

Aah... Now you're learning the value of an isostatic mount most of the time my scopes are un-clamped, just the bearing friction is enough to keep them in place ...

If the plank was a bit longer you could have another scope on the other side to balance it ... Great for outreach nights as one can have the eyepiece low down for the littlies, the other scope with its eyepiece higher for yourself and the taller kids.

[mental4astro (Alexander)]

I like the idea of the longer plank & mounting 2 scopes. Scopes I'm not short on, There's a star viewing night at a high school next month, this longer plank could be just the thing.

"Isostatic", so that's what it's called. Known of the principle & used it for a long time, but didn't know it had a name. Thanks.

[alistairsam]

ah now I get it. took me a lil while to understand, so by fixing the ota's horizontal centre almost parallel to the mount's pivot point, the COG still stays very close to the pivot point when you point upward as opposed to it inscribing a large circle further away from the mount's centre. sorry layman's terms but yeah I get it.
nice mod.
I had this issue with a homebrew AZ mount for my ST80 and was wondering why on earth it kept falling off when above 30deg. time to revisit.
Thanks Alex.

[alistairsam]

one example for dual scopes

http://www.buytelescopes.com/images/thumbs/0049672.jpeg

found some math here. overhead transmission for me.
http://www2.warwick.ac.uk/fac/sci/ma...aticmount8.pdf

[Damienandwendy (Damien)]

I have a slightly younger version of the same scope/mount combo and suffered from exactly the same problem as you have discussed - movement in altitude because the CoG is out. As my other scope is an EQ3 mount with some counterweights hanging off the front, I found some scrap ally flat bar and a 1kg weight and attached that to the mount. Works a treat.

The Townsville Astronomy Group have started approaching local schools to do some astro presentations/viewings. The isostatic mount idea looks perfect to get more people to view things at the same time. Will have to investigate that as well.

cheers