Best way to triple stack telescope's?

[Nigella Bryant]

Hi all, what's the best way to stack my three solar scopes on my neq6 mount. I've seen a triple dovetail bar running at £400. Can I buy a long losmandy dovetail bar and fit vixen clamps to that? Each scope runs at 4kg so weight for the neq6 won't be an issue at 20kg. I'd probably be running at 14kg with three zwo camera's. Currently I'm running two scopes on a double dovetail bar. It's all mounted on a concrete piller so is very stable. 

Thanks for looking. 

[Rusted]

I have hung three refractors 180/150/90mm from my big DIY GEM but it needed very careful balancing.
Get it wrong and you introduce serious asymmetric imbalance [torque] with different sky pointing positions.
I'm not talking about simple balance around the Polar Axis or even the DEC axis. Though that needs to be correct.

I "wrap" my OTAs around the cradle to avoid adding too much moment.
Main OTA flat on the saddle. The other two each side of the saddle. Fortunately I have a channel shaped saddle.
You could try getting a suitable bit of channel to fit on your saddle if the idea appeals.

Worst case scenario is a series of OTAs stacked "in series" away from the saddle. Each OTA supporting the next.
It also loads the first OTA's tube rings because they must support all the other OTAs.

The Cog G of each complete OTA/camera/at focus ought to be individually balanced by sliding them through the tube rings.
Remember to tighten the rings afterwards. You'll need extra counterweights to balance the heavy load.

When you get close to balance you need complete freedom of the axes as you try pointing all over the sky.
The clutches can easily spoil the balance until it suddenly lies beyond a critical point.
I like to give the OTAs a very gentle shove as this is much more sensitive than static balance. You can better sense any bias in one direction.

Keep a tight hold on the set-up or you might get a rapid nosedive! I doubt you'll need the restraining ropes I use to avoid disaster.

[Rusted]

[Nigella Bryant]

Thanks Rusted, appreciate your input.

[skybadger]

I have a large asymmetric dual setup. While I can only echo rusted regarding a careful 3d balancing with the kit in place you use, I would recommend three side by side as you mention since they are all reasonably small and putting one on the central axis is the best place for it. 

The hardest part might be sourcing the long cross-dovetail for the vixen clamps. They come up to 14" typically, is that enough ? Also, how are you planning to co-align them ?

Edited April 8, 2021 by skybadger
Add photo

[Neil27]

A long time ago, in a galaxy far, far away when I had money ..... 😔

I had several bespoke clamps and plates made up, it can be done but needs careful balancing as Rusted mentioned.

Good luck sounds a great set up 👍 

[Rusted]

1 hour ago, Nigella Bryant said:

Thanks Rusted, appreciate your input.

I should have said more clearly that the balance problem is applied torsion around the DEC axis.
Some people add a weight on a stalk at right angles to the saddle and DEC axis.
I tried that but ended up calculating the moment of the OTAs around the Dec axis as if it were a simple see-saw.

[Nigella Bryant]

Thanks peps, I was thinking side by side with one in the centre. I align my double scopes with one currently in guiding rings the other in the clamp. I guess two scopes could be in guide rings and the other clamped directly. Pic added.

Edited April 8, 2021 by Nigella Bryant
Pic added

[Rusted]

23 minutes ago, skybadger said:

I have a large asymmetric dual setup. While I can only echo rusted regarding a careful 3d balancing with the kit in place you use, I would recommend three side by side as you mention since they are all reasonably small and putting one on the central axis is the best place for it. 

The hardest part might be sourcing the long cross-dovetail for the vixen clamps. They come up to 14" typically, is that enough ? Also, how are you planning to co-align them ?

Nice!

Ideally, you should weigh both [complete] OTAs and then space them away from the DEC axis.
To balance their moments just like a simple see-saw calculation. Mass x distance from the axis.

I used a crossbar on either end of the saddle. Then placed the heaviest 180mm OTA closest to the DEC axis.
The lighter 150mm was then spaced on the other side of the DEC axis spaced to balance the pair. It worked.

With three smaller OTAs you'd weigh all three. Place the heaviest in the middle of your two crossbars.
Then add the balanced OTAs. Carefully spaced on either side according to their calculated moments.

[globular]

Maybe something like this added to the middle of your existing dual mount?

https://www.altairastro.com/lightwave-refractor-finder-scope-bracket--rings-2511-p.asp

Not sure how you'd add it though, nor if it's big enough, maybe I'll just leave now.... 🚪

[Nigella Bryant]

1 hour ago, globular said:

Maybe something like this added to the middle of your existing dual mount?

https://www.altairastro.com/lightwave-refractor-finder-scope-bracket--rings-2511-p.asp

Not sure how you'd add it though, nor if it's big enough, maybe I'll just leave now.... 🚪

Probably not sturdy enough but thanks for the thought.

[skybadger]

It's easier than that. 

The scopes go wherever the dovetail clamps can be/need to be  located on the triple bar. Move the bar as a single unit to balance the whole setup . I let off the clamps a touch and use a long g clamp to move the triple bar in its dovetail the small distance required. Clamp up,  Spin to check balance and repeat.