Help near beaudesert with making a 8" truss dob?

[Jethro777 (Jethro)]

Feeling a little bit lost, I have a wonderful 8" f/8 mirror and most of the bits (secondary, focuser, tubes, clasps, shroud), but am stuck and really need a mentor.
I have never done this before and it's very daunting.
I need supervision and directions - books are not doing it for me. Is there anyone that might be able to help?

[doug mc]

If you can find instruction drawings to make it, a local men's shed may well be a good place to start.

[mura_gadi (Steve)]

https://www.youtube.com/watch?v=GxI1ijCoDqw

That's a fairly comprehensive video for truss style dob's.

[Jethro777 (Jethro)]

Thanks Guys,
I wonder if there is a simpler method. If I had a Skywatcher / Saxon 8" Dob, couldn't I simple exchange the mirrors and extend the poles?
Does anyone have a 8" Truss dob? What is the diameter of the poles?
It's an f/8, so it would make it longer, and I would probably have the weight the box section to compensate, hmm?

[Rod]

Hi Jethro

Can you tell us a bit more about what you are trying to achieve with the truss design? Im assuming it’s to fit a smaller space in the car? Is there room for a tube and a collapsible rocker?

I’ve made truss tube scopes and they can be great in larger sizes but as you suggest there can be simpler options for a smaller scope.

Rod.

[Jethro777 (Jethro)]

Well, I have come across a lovely mirror, an f/8 8" by Galaxy Optics. I want to use that mirror. I am prepared to do a build, and try and get it all working together - frankly, the bit that really worries me with these builds is the mirror cell, and the top of the truss scope.
I am thinking a much simpler method might be to get a Skywatcher 8" truss, and replace the tubes to bring it out to f/8, and then to weight the box. Optionally, if possible, I could replace the focuser as well, as I have a low profile one I would prefer. I do have a secondary mirror already, but let's see what the Skywatcher / Saxon one does before going silly.

[mura_gadi (Steve)]

Have you tried stellafane?

How to build a telescope - https://stellafane.org/tm/dob/index.html
and
Newt for the Web - https://stellafane.org/tm/newt-web/newt-web.html

newt for the web will help you work out if the SW tube might be viable.

Ps. telescopes can be square...

[Rod]

Hi Jethro

The mirror cell can be pretty simple for an 8 inch mirror. The stellafane design I’m sure works well. I like and recommend this one:

https://garyseronik.com/a-simple-dou...our-reflector/

I’ve used this design on four 8 inch telescopes and I find it holds collimation extremely well. The only thing I have changed is that I don’t like using silicone to attach mirrors. I made some simple supports with angle brackets and plastic bolts. If you are interested in the details let me know and I’ll post some pictures.

Buying the skywatcher truss seems a very expensive way to go, especially since you will then need to modify it for a longer focal length. If you go the truss route there are some simple ways to do it without all the fancy brackets. The most obvious is to make 4 pairs of truss tubes joined at the top like in the photos below. The bottom tubes can be attached via bolts and wing nuts through a hole in the mirror box.

Hope that helps.

Rod.

[mura_gadi (Steve)]

they're pretty much a snap apart from a few aesthetics* and Rod knows his stuff... Neither uses over the mirror clips which may introduce "optical pinch".

Flexiply and Optiply wood might help on the tube as well, I know Optiply is marine quality plywood and hardwood cores.

Though Gary Seronik clips are better positioned imo, I am assuming Stellafanes on uses silicon pads to stop the base of the mirror from touching the brackets.