Resurrecting an old friend

[25585]

I have found my 12 inch Dark Star dob's main mirror. On the back it says FL 58.7" so 1490.98mm.

Somewhere still to find is its original spider and flat in a holder. However that was for a 1.25 in focuser. 

For a 2 inch focuser to be fitted, what size flat do I need, and presumably holder assembly to go with it? The tube pipe is strong plastic with thickish walls. Is there a round hole cutting tool I could use to enlarge the existing one for a 2 inch focuser?

Last requirement is a new cel, strong, light with easy collimation nuts etc. Orion's prices are high. Where else could I buy a new cel, spider and flat holder which have adjustable fixings to cater for different tube wall thickness. Then "Cap" can come out of the ice!

[ronin]

Cannot see why you would need a bigger flat for a 2" focuser, the present one should deflect all the light to the present focuser, so a bigger one would not deflect any more. A 2" focuser may sit further out but present day focusers are 1.25" and 2" combined.

Hole cutting may not be simple as you have nothing to keep the hole cutting bit central.

Mirror Cell try TS they do a selection. https://www.teleskop-express.de/shop/index.php/cat/c64_Telescope-Making-----mechanical-parts.html

However they seem a fair cost. If you have the tools you could make your own from plywood disks and assorted bits. Try the Stellar site: https://stellafane.org/

Somewhere in the list of links there will be plans or ideas.

[25585]

3 minutes ago, ronin said:

Cannot see why you would need a bigger flat for a 2" focuser, the present one should deflect all the light to the present focuser, so a bigger one would not deflect any more. A 2" focuser may sit further out but present day focusers are 1.25" and 2" combined.

Hole cutting may not be simple as you have nothing to keep the hole cutting bit central.

Mirror Cell try TS they do a selection. https://www.teleskop-express.de/shop/index.php/cat/c64_Telescope-Making-----mechanical-parts.html

However they seem a fair cost. If you have the tools you could make your own from plywood disks and assorted bits. Try the Stellar site: https://stellafane.org/

Somewhere in the list of links there will be plans or ideas.

I will try the original flat first. The TS cels look user friendly, but are pricey as you say! 

[John]

My 12" F/5.3 (FL 1590mm) Orion Optics tube assembly has a 63mm minor axis secondary which seems to fully illuminate my widest 2" eyepieces without any problems. Your scope is around F/4.9 which is very similar to the chinese 12" F/5's and they use secondaries of 68mm minor axis approx.

Others with more DIY knowledge will advise on enlarging the focuser hole in the tube no doubt.

The DIY section on here is probably the best place to ask about componants such as mirror cells, secondary supports etc. Telescope Services in Germany list some but they are not exactly cheap either:

https://www.teleskop-express.de/shop/index.php/cat/c64_Telescope-Making-----mechanical-parts.html

 

[Ricochet]

2 hours ago, 25585 said:

For a 2 inch focuser to be fitted, what size flat do I need, and presumably holder assembly to go with it?

See the following article for a discussion on secondary sizing http://garyseronik.com/sizing-up-the-newtonian-secondary/

2 hours ago, 25585 said:

The tube pipe is strong plastic with thickish walls. Is there a round hole cutting tool I could use to enlarge the existing one for a 2 inch focuser?

If the existing hole is a standard hole saw size then you can use a hole saw enlarging adaptor to nest a smaller hole saw that matches your existing hole inside a hole saw of the size you need for the larger focuser.