Gregorian telescope 10" f/24 - MDL

[Rusted]

The problem with any beam begins when you rotate it on its axis.
Beams do not function well when the loads are across the minimum dimension.
An equatorially mounted beam OTA will soon find the weak dimension.

My twin profile beam was 4"x4" but hopelessly weak in torsion.
I could have put my whole weight on the centre of the beam when "upright."
Not having a laser handy I used a light but stiff crossbar.
This easily indicated the OTA's own twist as I moved it around on the GEM.
Square beams are not as stiff in torsion as round ones.

The absolute worst OTA I ever made was with eight, parallel 16mm dowels arranged around eight plywood rings.
It could not even support its own weight without sagging several inches at either end.

I hope your new OTA works simply as a result of increasing its dimensions.
Previously it had a very similar profile to a rainwater gutter.
Which must be the absolute worst possible profile for resisting torsion.
 

Edited September 9, 2019 by Rusted

[Chriske]

3 hours ago, Rusted said:

It could not even support its own weight without sagging several inches at either end.

Several inches...???

😱

I think you mean mm..??

[Rusted]

Nope! It was inches of sag.
2m long x 35 cm Ø circles carrying eight 16mm dowels.

 

[Chriske]

This is very sturdy...!!
That extra(fourth) tube(not present in this picture) did the job. The complete setup is very stiff now, and non of the bolts are set. Just the heavy friction between tubes and stiffening parts made it very stiff. There's no doubt in our minds that this thing will sag. We did use a rubber mallet to assemble this scope.
In the picture we were busy testing for COG. The stiffening parts are not at the correct location. They need to be relocated so they all are separated at the same distance + one on top of the secondary tube.

Weight of the scope 7.8kg

Edited September 19, 2019 by Chriske

[Rusted]

That is a pretty amazing OTA! Including the light weight. 

Can you explain the large object in the garage, please?

It looks like it wants to be a vertical panel saw but it has an odd round bit in the middle.

[Gina]

I think I know what that might be...

[Rusted]

10 minutes ago, Gina said:

I think I know what that might be...

Stop teasing!

It looks rather like a sander or polisher.

Or a very large table with a microscope in the middle.

Or a very large table with a mirror tester in the middle.

Or a... thingamajig? 

 

[Chriske]

The object in Marc's garage is a Maslow
and that 'thing' in the middle is a router.
 

[Rusted]

57 minutes ago, Chriske said:

The object in Marc's garage is a Maslow
and that 'thing' in the middle is a router.
 

Thanks. I would never have guessed a CNC router.

Getting back to your OTA: How does the additional tube pass through the mounting?
Doesn't it need to pass right through the dovetail?
If you extend the mounting arrangements, to compensate, then your OTA's moment increases dramatically.
Requiring far heavier counterbalance weights.
Doesn't it?

[Chriske]

The fourth pole arrangement stops at the dovetail. There's no need to add a additional fourth pole alongside the primary cage. That lower parts is stiff enough as it is.
What's more, when we were testing stability of the combination mount/scope, we were very surprised how stable it was. Hitting the scope very gently, it moved a little bit and stood still almost immediately. I would expected a scope this long to keep on moving for at least a few seconds or so.
We're very happy with the result...!
Last thing to do is polishing the secondary mirror and adding a shroud around the primary mirror. That shroud will be added only if stray light is hitting the PM.(or in case of damp weather).
And also a few surfaces needs to be blackened.

[Chriske]

This is how the primary baffle will be collimated.
At both ends of the primary cell-a are 3 slots in which 2x3 M6 nuts are inserted. In all nuts 6 grub-screws.
Around the primary baffle are glued 2 metal(brass) rings. Setting the grub screws the baffle can be pointed in all directions. Needles to say, when the baffle is mounted in it's cell only minor adjustments will be needed.

 

[Chriske]

Hi,

My best friend Marc passed away a few days ago.
In his honour I will continue and finish this(his) Gregorian. He was very eager to start using this scope.
Marc joined me building telescopes in '82. He was 20 back then. We never stopped grinding and building. We made 'a few' scopes together..!
Hard to believe he's gone...

Chris

[Rusted]

I am sorry to hear of your loss.

[Alan White]

Chris
Very sorry to read of Marc's passing and your loss, my condolences to all.
Your completing his scope is a very fitting tribute.
 

[Gina]

Very sad indeed.  The telescope is a grand tribute!

[Rob Sellent]

I don't know what to say. I'm just really sorry to read such tragic news. Condolences to you, Chris and all of Marc's friends and family. 

[Chriske]

Thanks to you all very much for all the kind remarks and messages.

Aside been very good friends we were a very close 'two men team'.
I did all the designing and drawing work, together we grinded our glass disks side by side, and Marc was the electronics man.

As a matter of fact, we spent many hours sitting in my workshop in front of our two 24" MoM's.

[Gina]

Magnificent machines Chris!!  Wonderful engineering!  I can practically feel your loss for your dear friend!!  My most sincere condolences for you and your family and Marc's wife and family, of course.  <<<HUGS>>>