14"/360mm truss dob

[Rustysplit]

To run alongside http://stargazerslou...e-mirror-grind

I thought I had better do an actual scope build thread too.

Having seen many of the build threads and the fantastic end results, I could not resist having a go any longer. A change in direction from imaging back to visual seemed a good time to start.

Having had a look through Si's (simonfromsusssex) 16'"LB, well that sealed the deal. I had a look at the space I have to store it and the vehicles to transport it, and 14" seemed a good compromise between aperture and useability. The other criteria is ease of assembly and weight. A stripped down truss tube design seemed the logical answer.

I have looked at as many travel dob designs as I can find, and the one that keeps coming back to me is the Sumerian Canopus. Simple, yet elegant. I hope to make a dob, heavily inspired by the Canopus, but not an all out copy.

This scope will be based around a 360mm/25mm thick plate glass mirror, hopefully ground by myself. It will be made of Birch ply of varying thicknesses, and have the usual ally truss tubes.

Right, here goes....

My first stage was to download the mirror cell software, plop, and sort out a suitable configuration. I was going to go the Kriege and Berry route of a metal tailgate, but loved the look of the rear end of the Canopus. The bit I don't like about it, is the way the collimation bolts are all near the centre . I wanted mine to be near the outer edges. Here is a mock up of what I am proposing to do...

The square board is the mirror box floor. This will carry the sling and edge pins with retaining clips, the blue pen marks. Behind this will go the actual mirror "cell", Floating on it's collimation bolts....

The actual parts will be much thicker than this, but in principle, do you think this will work?? Obviously the sling will not be hung off 2 woodscrews

[estwing]

good luck with the build Alan, i shall be watching this thread with great interest..sadly i wont be able to offer any "real" help,but wish you luck with the project,calv.

[Rustysplit]

I have made some progress with this now. No pics as yet, but will take camera to workshop tomorrow.

I have cut the ali triangles for the mirror cell, made up the mirror box, cut out the side bearings and cut out the rocker box rings and base board. I will post pics tomorrow hopefully.

[Rustysplit]

Here is a pic of the work so far...

It is all just rough cut. I have lots of cleaning and chamfering to do yet. The 2 rocker box rings will be separated and fixed together by thick round wooden dowels, not the screw boxes there at the moment. Although this may change, as I am not totally decided on this bit yet.

The alt bearings will have cut outs to save weight both physically and visually.

[estwing]

nice work there Alan,keep on,keepin' on.

[swamp thing]

Looking good Alan

I shall be watching your progress with interest.

[Rustysplit]

Thanks chaps. It is so nice to be able to think about building something else other than household furniture for a change. I am really enjoy this. Designing the 'scope and attempting the mirror grind are good for the soul

[steveb1977]

Nice work. Looks like this will be an impressive looking telescope.

[JamesF]

I'll be another who can't offer much in the way of advice but who will be following with interest I've not seen the wooden tailgate design before so it will be good to see how that pans out.

James

[trev27]

I gotta keep an eye on this one as well as I'm finishing my dob up at the moment ;-) That canopus design is gorgeous. Really nice work so far there Alan!

[Rustysplit]

I have not spent as much time on the actual OTA as I would have liked, due to getting on with the mirror grind. But I have been thinking about the secondary support and spider. This is what I have come up with for the secondary support....

The button head screws will be replaced with small plastic headed bolts for easy tool less collimation. I still need to add a thin metal disc to sit on top of the angled holder for the adjusting bolts to run against.

I have cut the arms for the spider out of 1mm ish, stainless steel. The plan is to attach the spider to the UTA cage by using bolts through the ali tube uprights, which screw into a stud connector on the end of each spider vane. Hopefully this will give me some lateral adjustment for lining up the secondary mirror. I should get some of that done tomorrow, so more pics then hopefully.

[estwing]

coming together nicely...

[Moonshane]

looking very nice indeed. I really like the secondary arrangement. you might want to screw an ali plate to the face of that to allow better adhesion of the silicone? I'd be nervous about silicone and wood but this might be unfounded.

[estwing]

orion optics told me to use clear silicone as the coloured stuff only lasts about 5yrs ..the clear lasts about 25yrs!!!!

[Moonshane]

that's interesting, not heard that. I have just done mine with black too. might redo it.

[estwing]

the chap said the colour breaks down the strength of the silicone..orion only use clear now he says

[Moonshane]

well that's good enough for me. I'll be changing mine sometime in the near future.

[Rustysplit]

It will all be stained and lacquered before the mirror goes on, so hopefully this will give the aquarium type sealant a good smooth base to adhere to.

[estwing]

well that's good enough for me. I'll be changing mine sometime in the near future.

..that's the first time i've told you somethin' useful Shane!

[SkyGibbon]

Used some construction strength silicone adhesive that dries clear. Unfortunately, I didn't realize how strong it was going to be. Would be difficult to cut through to get the mirrors off their holders. This stuff seems like it may last a trillion years. So be careful if you ever need to get your mirrors off.

Quality work going on here. That secondary looks great. What size secondary you putting on it?

[Rustysplit]

Thanks Skygibbon. I am going to use a 69mm MA flat. The focuser is a low profile one, so it should be fine.

Today I cut the stainless steel washer and trial fitted the vanes. I also made up the vane connectors.....

[SkyGibbon]

The focuser is a low profile one,

Which was going to be my next question, which should have been included with my earlier question.

Best of luck and can't wait for your 20" grind and build. You know it's only a matter of time.

[Rustysplit]

This weeeks progress has been to make the UTA and trial fit the spider assembly. I gotta say I am chuffed with the way it has worked. I have full adjustment and it is as solid as a rock.

[John]

Looks a wonderful piece of work. I've not seen a diagonal support and back cell made in wood before

[SimonfromSussex]

That's looking really good Alan! Beautiful work.

Cannot wait for the first light on this!!