Mak127 piggyback on a C8, how?

[LondonNeil]

I've a Mak127 and a celestron C8 and it might be useful to occasionally have the 2 piggyback.  Key word there is 'might'.  The main use case is to have a second EP pointing exactly at the same view as the other so when my kids are out with me there is less fighting over a view and that means less stress for me. 

Currently both scopes have vixen/skywatcher dovetails on them and the c8 is just in a celestron evolution mount.   The mount has 11.5kg of capacity so should manage the 2 ota fine (there's roughly 2kg of headroom but the additional hardware to mount the 2nd ota will reduce that a bit)

I'm trying to work out the easiest way to mount the 2 in order to try it.   I'm Currently thinking it would need me to drill and tap holes in the c8 and to attach another dovetail bar to its top (which would mean careful disassembly and reassembly). Drill and tap the dovetail to attach a vixen mount to it,  and the mak127 would then mount into that. Alignment of the 2 scopes would require a bit of adjustment of that vixen mount attached to the c8 dovetail. 

Does that seem the easiest and best way?  I can think of a couple of alternatives but I think the above is cheap,  neat, robust, although a little faffy to do initially due to needing to disassemble and reassemble the c8 to drill and tap screw holes for the extra dovetail. 

I could avoid that by using tubes rings on the c8, mounting the 2 dovetails (the one to mount in the evolution and the one to piggyback the mak127) to the rings, and a vixen mount to the extra dovetail as above.... less faff but extra cosy of tube rings.

What would you do? Am I missing an easier method?

Thanks

 

[Cosmic Geoff]

I wouldn't go drilling holes in a C8 OTA or dismantle it if it were my scope.  If piggy-backed, the eyepieces will be relatively close together. I suggest you go for some other solutions.

[michael.h.f.wilkinson]

On an EQ mount, you might use a dual mount bar, but I do not think this would be practical on the AZ mount you have, unless you use some kind of L-bracket used for big binoculars. The problem with that (and the piggy-back solution) would be that although the total weight might be OK, the torque on the mounting would be rather high, because the centre of mass would be far from the mount's dovetail clamp. These "single-armed fork mounts" tend not to like this. A full fork mount would not work either, as the two OTAs would not fit.

[LondonNeil]

I'd piggy the mak127 on the top of the c8 so the torque on its evolution mount would be just the extra weight acting at the same moment arm.   I might even have it nearer.  If you picture the c8's dovetail mounting it to the evolution at 9 o'clock as viewed from the rear the mak127 would be at 12, or 1045.  I've weighed the c8 at 4756g bare ota, so about 5500g with diagonal,  EP and dew shield.   I don't seem to have a weight noted down for the mak,  I'll put it on the scales later,  but i've read the ota is 3200g,  <4000g ish with diagonal, ep and dew shield.   The total before any extra mount hardware is therefore about 9500g, so about 9800g with an extra dovetail and mount to piggy the 127.

Compare that to the 11.5kg capacity celestron state and it ought to be fine.   Compare also it to the c9.25 that also uses the evolution mount, celestron quote 9070g which will include diagonal, ep and dew shield.  The torque on the mount is (very very roughly... and in the odd graminches unit) 9070x9.25/2=41949.  The c8 with mak mounted at 12 o'clock would be 9800x8/2=39200, ie less.  Hence why I'm fairly confident the mount won't struggle to do this occasionally.   As for 2 eps close together,  it's one turned to oneside (2 to 4 oclock) and the other above by about 7 inches and turned to the otherside (8 to 10 o'clock) so both usable I think but I do appreciate avoiding head clashes may need a bit of care!  If balance allows I suspect the 127 would be a little forward of the c8 too.

I don't mind drilling and taping extra holes.   This is a 40+ year old c8 that originally was on a fork so it's been drilled for a dovetail once before.   I just thought....I could I perhaps just rebolt one of the fork mount attachments and add a vixen shoe/ mount to that.... but the mak127 would then be carried by just the primary cell on the c8 rather than spreading some load to the collector assembly.... not ideal but then a single fork mount attachment could carry half a c8 ok so it's not a ridiculous option to consider for a quick trial perhaps. Hmm.

 

 

[RT65CB-SWL]

 

3 hours ago, LondonNeil said:

…

What would you do? Am I missing an easier method?

I would go for a dual-mount bar or a ‘T’-mount as shown in my image shown below.

If you go with a dual-mount bar, then balance is critical. With one ‘scope on top of another, it is going to be top heavy and unstable.

[LondonNeil]

Hmm, yes I hadn't considered it could get top heavy.   A T mount though is way beyond financial possibility for some occasional use with the kids unfortunately.

[Cosmic Geoff]

If it's for occasional use, why not have two scopes and mounts side by side? No modifications required.

[LondonNeil]

I was/ am exploring ways to not have to jump 2 tripods and mounts to the park which is my viewing area. 

[Gfamily]

13 hours ago, LondonNeil said:

Hmm, yes I hadn't considered it could get top heavy.   A T mount though is way beyond financial possibility for some occasional use with the kids unfortunately.

How about using the Mak as part of the counterweight? I'll let you work out the practicalities of mounting and collimating the two optical axes.

[LondonNeil]

The evolution is an alt az mount,  there is no counterweight,  so unfortunately that idea doesn't fly.  Otherwise it's a fine idea. 

[LondonNeil]

I found this. 

https://www.rothervalleyoptics.co.uk/geoptik-vixen-style-piggyback-bracket-for-sct-telescopes.html

I could likely mount that to the c8 using existing tapped holes that were for the fork mount attachments.  I'd just have to drill that bracket for the correct bolt spacing.  So £59 to try it and see how the evolution copes.   Watch the classifieds for a used piggy bracket going cheap if it doesn't work!