OO Dob Mount + Skywatcher OTA

[Carbon Brush]

Looking for suggestions, or maybe advice from someone who has done something similar.

I have an Orion Optics (UK) dob mount, intended for their 10" offering and wish to fit a Skywatcher 10" tube.
I already have both items so the cost to me is fitting effort & parts.
The scope gives good views and the OO mount is superior to the Skywatcher 'MFI' mount that I don't have anyway.

The Skywatcher 250 tube has the standard rings, intended to fit to the dovetail.

The OO tube rings are quite thin and bent to the diameter of their tube, which is a bit smaller than a Skywatcher tube.

One choice is to slightly straighten the OO rings, fit a spacer to extend the hinge and a longer clamp screw.
This solution also involves machining a couple of millimetres off the OO spacer blocks as the assembly will be just a bit too wide for the frame.

Another choice is to mill the SW rings flat in the region of the fixings and drill more holes to match thee OO block.
Possibly thinning down (milling) the OO blocks as well.

The above options mean that the OTA can be moved in the rings for balance.

If I drill the OTA for the OO blocks and add a shim, that would work.
That means fitting a balance mechanism. Adjusting either weight or location to suit different eyepieces from 1.25" plossl up to 2" jam jar types.

I will try to get some photos of the bits later today, or tomorrow.

Suggestions and ideas please......

David.

 

 

[Alan White]

I think someone on here has such a hybrid scope already, @AdeKing if I am correct.
One thing to consider is the whole SW tube is larger than the OOUK ones,
so you may not have enough clearance to do what you wish in the OOUK Dob mount you have.
Good luck with this.

[AdeKing]

Yes, @Alan White is correct, I have an 8" Skywatcher dob OTA which I use on an OOUK 8" Dob Mount which I was fortunate to pick up used from @DRT a while ago.

If you contact OO they will make you rings and blocks to fit, but I found their price quite high so I used the Skywatcher rings for an 8" OTA, and then used washers as shims on the bolts keeping the base together to get the clearances right and ensure nothing rubbed when rotating the OTA on the bearings. 

Using the washers as shims on the base allowed me to add a few mm to the width of the base and allow the bearings to sit flush with the sides if the base as intended. 

If I remember correctly I might have also needed to put a washer or two between the side bearings and the tube rings as I seem to remember the squared off part of the SW tube ring fouling on the mount somewhere. 

It was a bit of a fiddle and took a few attempts to get it right but I got there eventually. 

The OO solution also provides slightly larger blocks which provide the threads that the side panels fit to. My solution isn't as tidy but does the same thing but for just the cost of some longer bolts and a few washers and most importantly no DIY skills, which I sadly lack. 

The Dob is buried at the back of the summerhouse at the moment but if I can get to it without too much trouble I'll post some photos or maybe draw a diagram in a bit if the above is unclear. 

[Carbon Brush]

Thanks for your comments. And apologies for not replying earlier. For some reason I missed the daily notifications.

Ade's suggestion about washers has set me thinking.
If I use some ali bar to space the entire side frame out, and use longer fixing screws, then I can make a frame to suit the (chunky) SW rings.

Balance can be set initially by sliding the OTA in the rings. Or if Want to do the job properly, fasten a bolt on the rear ring to add a weight.

I will look again armed with the measuring kit then report back.

Thanks, David.

[AdeKing]

29 minutes ago, Carbon Brush said:

Thanks for your comments. And apologies for not replying earlier. For some reason I missed the daily notifications.

Ade's suggestion about washers has set me thinking.
If I use some ali bar to space the entire side frame out, and use longer fixing screws, then I can make a frame to suit the (chunky) SW rings.

Balance can be set initially by sliding the OTA in the rings. Or if Want to do the job properly, fasten a bolt on the rear ring to add a weight.

I will look again armed with the measuring kit then report back.

Thanks, David.

Apologies for the lack of photos but it's still buried in the summerhouse.

I Will get around to clearing the furniture out of the Summerhouse to sell soon then I'll take a look to see exactly what I did.