Chriske

Forgot to mention. In the most upper (printed) part there's room for a laserpointer to align the unit to the north.
In that part the hole for the major (M16) bolt and the hole for the laser are printed in one piece, so I can set it up very accurately.
The laser is adjusted in a lathe.

Some progress ...

Mount not finished yet

Upper polar axis, threaded rod M16

Lower polar axis, brass axis 12mm

Movement...

Still... drive unit + motor to be installed.

Today the secondary mirror will be installed
It has a diameter of 800mm, Also gold coated.

The mirrors are a bit deformed because we have tilted the complete set 15° forward.

When the mirrors will be relocated to it's final destination all will be installed perfectly vertical and the deformations will disappear.

Btw the curly boy in the mirror's reflection holding the camera is me. In real I am not that curly...😁

This is the 'final' product, the first version is just 4.2m high because the room were it is stored during our open door is only that high.
After open door it will be relocated to our planetarium were the full height will be installed. 6.5m

A few more changes.
The two red axis are both fixed.  They will be connected by a GT2 belt or maybe a set of gears don't know yet.
The cycloidal drive has a reduction of 15x
For quick adjusting the polaraxis I'll add a green laser parallel to the upper polar threaded rod.

To be more flexible I'll drop the bevel gears and replace it with a stepper and a Cycloidal Drive.

Not yet started building.
A few changes have been applied, has to do with the tracking speed.
Instead of bevel gears I'll be using a Worm/wormwheel set.

I already made a  JWST scale model 1:7...😉

Just now, Dr_Ju_ju said:

My one suggestion would be to cross-grain the timbers to reduce the amount of wooden flex in differing temperatures etc....

👍

Change of plan : Plan 'C' is to buy sheets of acrylic that has a 'standard' glossy gold finish on it's surface.

A long time ago I saw something similar.I kept working on it and came up with this solution to track the stars with a Dob.
I added a tracking system based on a few cardan couplings and a thick threaded rod.
In the thick wooden beams I added a few rods @51°(polar axis), both in the vertical as well in the horizontal beams. All will be supported by ball bearings.
These bearings are all sitting in a printed blocks.
Tracking is done with a small motor and two bevel gears.
Running time of the unit is about 90minutes.

Next week I'll start building one.

On 12/06/2024 at 12:55, Owmuchonomy said:

We have an animation which resolves into a full scale image of the JWST primary and secondary mirror onto the dome.  This usually creates some gasps across the audience when they grasp the unfolded size.

Wooow...! Nice idea...!👍

First test were very disappointing.
Using 3mm plywood resulted in very bad  surface quality, Even after applying a few coats of varnish.
The idea was (after varnishing and sanding) to add a layer of (high)glossy gold vinyl.

So now plan 'B' is to use sheets of acryl. Acryl has a very flat surface. Did already a small test and it looks promising.

Just started building a full scale model of JWST's mirror.
It will be the show-piece of our next open door at our observatory mid September.
Yep, that thing is 6.5m high...

Now that I come to think of it, I should not use the word 'scale' but rather 'copy'...😄

I did replace that blue filter and made a very big difference. The old one became somewhat foggy.
In my case it was a Lunt.

We often shared files, Gina and myself
Gina's giant clock was one of here favourite projects. She printed it on here 'Giant printer'.
She sent a copy of here clock(she drew it her self..!!) to me. If I'm not mistaken it has a diameter of nearly 500mm
It used a small stepper...

You're going to enjoy this big bino. Observing with these large binos has many advantages. Simply said, you see much more compared to a 'singles scope'. I've built a few binos myself...😉

To me, as a mechanical engineer, there's a high drooling factor involved in what you construct...👍

Thanks John,

Nice tool..!

David,

I'll be using that 'Plossl' in combination with a 150mm refractor f15.7.
So primary image of the Sun will be about 24mm. I'll project the image of the sun on a white screen. I'll be refocusing until I have a very large sun on that screen.

So if the combined FL of that Plossl is 90mm it has no effect on the projected image. Visual observing would indeed give me a very low magnification. But I will not use it for visual observing at all.

The most important reason why I use these large lenses, and as a Plossl combination, is to avoid heating up that eyepiece while projecting the sun.

Thanks for the input. Still have to learn about these self-made eyepieces...;-)

Did not know where to post, so I also posted in the eyepiece section.

Hi,

Just finished building an eyepiece and I was surprised it worked, and it worked rather good as a matter of fact. It was a quick test using a refactor with a 1 1/4 focuser, handhelding that eyepiece. So I could not see the entire FOV.

From what I've read the acromats should be placed as near as possible, front lenses pointing to each other, so I did.

I made a holder in which I could change the spacing between the two. Observed a large post at about 300m distance : in both occasions, lenses very near and also at about 60mm apart the result is just the same.

How is that possible...?

Lenses 50mm diameter(was a binocular) F=180mm

Thanks...

Just finished building an eyepiece and I was surprised it worked, and it worked rather good as a matter of fact. It was a quick test using a refactor with a 1 1/4 focuser, handhelding that eyepiece. So I could not see the entire FOV.

From what I've read the acromats should be placed as near as possible, front lenses pointing to each other, so I did.

I made a holder in which I could change the spacing between the two. Observed a large post at about 300m distance : in both occasions, lenses very near and also at about 60mm apart the result is just the same.

How is that possible...?

Lenses 50mm diameter(was a binocular) F=180mm

Thanks...

Done and ready to use it in two ways...

This position is to observe..

and this is the 'other' position...😀

Optically it performs rather good, as a matter of fact I was a bit surprised.
To be clear it is not a optical masterpeace, I made 'a few' better mirrors in my lifetime.
Visitors at our open door will not see the difference between a perfect 'bottle' and mine...😉

Problem during polishing and figuring a square @ f/4 (about) there's no ideal way of polishing a square mirror on a circular lap. Or is it...?...😄