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Sterope project - design and build a compact 16" binoscope

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#151 Oberon

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Posted 10 September 2020 - 03:10 AM

I love that deburring bit! Mine always create a slight hexagonal pattern when I apply pressure. I'll have to look for one like that. 

You’ll love it and never go back. I had to buy from eBay as not found in typical hardware stores. Like here.


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#152 Chopin

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Posted 10 September 2020 - 09:47 AM

You’ll love it and never go back. I had to buy from eBay as not found in typical hardware stores. Like here.

 

Excellent. Thanks for the link Jonathan.  


Edited by Chopin, 10 September 2020 - 09:48 AM.


#153 Oberon

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Posted 12 September 2020 - 03:14 AM

Actually I'm not so sure about those titanium coated units now...I just bought a set to replace my worn set I've had for years and I reckon the new ones are already more worn than the old ones! Suggest look around for same thing but better quality.

 


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#154 Oberon

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Posted 12 September 2020 - 03:26 AM

Going potty...

 

The adjustable secondary support plate will be held by 3 adjustable screws with a 10mm M4 polished steel ball potted into the plate.

The balls are readily available and low cost on line as they are used extensively in 3D printers. WD40 Teflon serves as lube and mould release, is simply sprayed on and wiped off before potting.  

A short section of 1/4" or 6mm aluminium tube is cut and placed over the screw, ensuring that epoxy stays clear of the thread, and that there is space to move once all is cured. It also enables the ball to be "locked" into place with the nut at a distance to keep clearance. For added security a short length of heat shrink is also applied. This will be cut away later, and the screws replaced with longer ones.

 

 

gallery_217007_4999_167343.jpg

 

A few dabs of hot melt glue help hold all together at the right angles and depth.

 

gallery_217007_4999_488.jpg


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#155 Oberon

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Posted 16 September 2020 - 05:22 AM

FB tells me this 1/8 model is a 7 yr old memory...

Attached Thumbnails

  • 9CDE130F-192B-43C4-869B-BB6A3D202725.jpeg

Edited by Oberon, 16 September 2020 - 05:29 AM.

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#156 Bob4BVM

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Posted 16 September 2020 - 01:15 PM

FB tells me this 1/8 model is a 7 yr old memory...

 

Great to see your progress Jonathan.

 

Mine has been slow due to other priorities and now the smoke too thick to be out in the shop,( but thankful i still have a shop, many here not so lucky )

 

 

7 years, wow.  But you did complete Merope in that time...

 

Mine is only a 2 1/2 year memory, thanks for making me feel better !

 

Cheers

Bob

 

binoscp-18 mockup3.jpg



#157 David Stevenson

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Posted 17 September 2020 - 08:39 AM

Thank you. I watched the video. I liked what I saw.

I'm not sure that router steps could ever cut the gradients as smoothly as a sweeping blade, but...well, it might be good enough that the difference can be sorted out with sanding. I hope so.

 

What attracts me most about the CNC method is that my shapes are getting more complex. Look at the shapes proposed for my UTA for example in these posts here and here, and in particular the focuser detail in this...

gallery_217007_4999_71254.png

 

While each of those were generated with my present routing setup in mind, it was going to be VERY fiddly. Now it should be a doddle. And now I'll be able to generate and cut oval sections, not just circular sections.

Oberon,

I understand you went another route here, but I was thinking about negative effects of the two top circular mirror  holders, having a vane curved certainly removes the spikes, but that big would't compromise contrast? Does that area sum to the central obstruction contrastwise?

 

Thanks



#158 Bob4BVM

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Posted 17 September 2020 - 02:37 PM

Oberon,

I understand you went another route here, but I was thinking about negative effects of the two top circular mirror  holders, having a vane curved certainly removes the spikes, but that big would't compromise contrast? Does that area sum to the central obstruction contrastwise?

 

Thanks

Jonathan

I was wondering the same thing David is. Seems like alot of obstructed area,  You have a full top ring, so why did you decide to not use a standard or wire spider ?  My design has no UTA ring structure, so i am stuck with a similar one-sided vane arrangement, but would prefer a spider for my heavy secondaries, For me it's  a tradeoff that allows my mono-frame design, But you have UTA rings...  just wondering.

CS

Bob


Edited by Bob4BVM, 17 September 2020 - 02:38 PM.


#159 Oberon

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Posted 17 September 2020 - 03:21 PM

Good question. That design arose from our findings in this thread where Maskulator was used to compare the effectiveness of different design concepts. The objective was to find the best alternative to straight vaned spiders to prevent apparent flicker as the brain argues within. That design quickly emerged half way through the thread as very effectively minimising total diffractive energy, but by the end of the thread it was also demonstrated to suffer more loss of contract than the minimum obstruction, and so abandoned. 

 

https://www.cloudyni...o-what-to-avoid

 

It was a really educational experiment that produced interesting results - the thread is well worth reading - but ultimately it proved a dead end.



#160 Oberon

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Posted 17 September 2020 - 03:23 PM

Jonathan

I was wondering the same thing David is. Seems like alot of obstructed area,  You have a full top ring, so why did you decide to not use a standard or wire spider ?  My design has no UTA ring structure, so i am stuck with a similar one-sided vane arrangement, but would prefer a spider for my heavy secondaries, For me it's  a tradeoff that allows my mono-frame design, But you have UTA rings...  just wondering.

CS

Bob

At that point the ring structure was really only there to support baffling. The reason not to use wire or standard vanes is to avoid spikes that flicker.



#161 Bob4BVM

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Posted 17 September 2020 - 05:52 PM

At that point the ring structure was really only there to support baffling. The reason not to use wire or standard vanes is to avoid spikes that flicker.

My understanding is there is no flicker if vanes are perfectly aligned L/R, give an 'in phase' image.



#162 Oberon

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Posted 18 September 2020 - 12:12 AM

My understanding is there is no flicker if vanes are perfectly aligned L/R, give an 'in phase' image.

As I will be rotating my UTA’s to provide IPD adjustment then my vanes will not remain aligned.



#163 a__l

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Posted 20 September 2020 - 05:29 PM

Good question. That design arose from our findings in this thread where Maskulator was used to compare the effectiveness of different design concepts. The objective was to find the best alternative to straight vaned spiders to prevent apparent flicker as the brain argues within. That design quickly emerged half way through the thread as very effectively minimising total diffractive energy, but by the end of the thread it was also demonstrated to suffer more loss of contract than the minimum obstruction, and so abandoned. 

 

https://www.cloudyni...o-what-to-avoid

 

These conclusions are most likely not true. Not the result of diffraction, but artifacts of digital analysis

Details here

https://astronomy.ru...166577.460.html


Edited by a__l, 20 September 2020 - 05:45 PM.


#164 Oberon

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Posted 21 September 2020 - 04:09 AM

Which conclusions?

There was considerable discussion of the artifacts of digital analysis, and I believe it was adequately dealt with and taken account of by the end of the thread.

In any case this is not the thread to discuss Maskulator, aside from noting its part in the design development of Sterope.

What is remarkable is that a 5 year journey leaving no stone unturned whilst searching for the best possible curved spider from both a diffraction pov and a structural pov ended up settling on the classic 3 vane curved spider in both cases...albeit with thicker vanes than I would have liked!


Edited by Oberon, 21 September 2020 - 04:12 AM.

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#165 eroyer

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Posted 21 September 2020 - 12:05 PM

 The reason not to use wire or standard vanes is to avoid spikes that flicker.

Is it really a problem. On my binoscope, I never thought about it. I've used it for 10 years and brought it at may star parties throughout those years. No one  ever complained or even said something about spikes flickering.

Have you tried that yourself ? Take a pair of ordinary binoculars, add some vanes in front of the objectives (without aligning them) and look at bright stars. Does the diffraction from the vanes bother you ?
 


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#166 clivemilne

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Posted 23 September 2020 - 05:11 PM

Is it really a problem?. On my binoscope, I never thought about it. 

 

 

Same here... the spikes are really unobtrusive 

You just don't notice unless you purposely look for them.

 

I have never seen them sparkle.

 

The degradation of the view induced by the wire spiders is of such magnitude 

that the time I have spent giving consideration to curved spiders is precisely zero.

 

best

~c


Edited by clivemilne, 23 September 2020 - 05:15 PM.

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#167 Bob4BVM

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Posted 23 September 2020 - 11:17 PM

Thanks Clive & Eric,

Great to hear from guys like you who have long experience building and actually using binoscopes.  Your comments remove one more thing i was worried about. Glad to hear it is much less of an issue than i have been lead to believe by popular opinion !

CS

Bob


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#168 Oberon

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Posted 25 September 2020 - 07:15 PM

Is it really a problem. On my binoscope, I never thought about it. I've used it for 10 years and brought it at may star parties throughout those years. No one  ever complained or even said something about spikes flickering.
Have you tried that yourself ? Take a pair of ordinary binoculars, add some vanes in front of the objectives (without aligning them) and look at bright stars. Does the diffraction from the vanes bother you ?


Same here... the spikes are really unobtrusive 
You just don't notice unless you purposely look for them.
 
I have never seen them sparkle.


Thank you Eric and Clive for chipping in here. At present I have zero experience looking through a binoscope, so am only working from what I am told.

The flicker problem was mentioned to me whilst discussing my project with someone at Bintel one day, as in "what are you going to do to manage the flicker effect?" owtte. As I'd not heard of it before then I asked and received an explanation...which set me on a long and arduous course of ensuring I eliminated the risk without loss of secondary stability. And despite have 0.4mm thin wire spiders on Merope, spikes are immediately noticeable on bright objects like planets (and planets are my favourite targets). Of course, with its large secondary mirrors I appreciate Sterope is not optimised for planets, but still, I didn't want to find myself avoiding them. I agree that once the brightest objects are out of the field then spikes not longer exist, and for that matter believe I can improve on Merope's 8 x 0.4mm wires either with 0.2mm brass sheet or 0.3mm SS cable ties, either of which should reduce diffraction further whilst improving rigidity.

 

Anyway, the point is you've stopped me at a very critical juncture just as I was about to infuse a new set of carbon curved spiders. Fortunately I'm not totally committed at this point and my design can easily accomodate changes; and I would very much welcome going back to straight spider vanes if I can be fully persuaded that there will not be a flicker problem.

 

I'll do the binocular test when the skies clear...
 


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#169 clivemilne

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Posted 26 September 2020 - 05:45 AM

Hey Jon,

 

Yeah, it's definitely worth doing some experimentation. 

 

The spikes associated with bright objects which most people attribute to diffraction

have a component (due to thermal effects) which is poorly understood.

 

Essentially, the spider vanes will radiate heat to space and reach thermal equilibrium

1 to 2 degrees below ambient (I have measured this with a FLIR camera so it is genuine)

 

The air jacket surrounding the vanes will have a thermal gradient which acts as a lens.

The effect on the star image looks very much like a diffraction spike.

 

The minimum condition (for thermally induced spider 'spikes')  will be a function of

lowering the surface area of the spider vanes and selecting a material with low emissivity.

 

The lowest surface area possible in a spider vane would be achieved by employing carbon filament.

 

The lowest emissivity would probably be achieved by using polished aluminium wire...  0.9mm Aluminium MIG wire is off the shelf at Bunnings.

 

It would be interesting to see which parameter dominates?

 

Anyhoo....There goes the white rabbit.

 

the fun is in the doing.   wink.gif


Edited by clivemilne, 26 September 2020 - 05:52 AM.


#170 Oberon

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Posted 04 October 2020 - 05:27 AM

Going potty...

 

The adjustable secondary support plate will be held by 3 adjustable screws with a 10mm M4 polished steel ball potted into the plate.

The balls are readily available and low cost on line as they are used extensively in 3D printers. WD40 Teflon serves as lube and mould release, is simply sprayed on and wiped off before potting.  

A short section of 1/4" or 6mm aluminium tube is cut and placed over the screw, ensuring that epoxy stays clear of the thread, and that there is space to move once all is cured. It also enables the ball to be "locked" into place with the nut at a distance to keep clearance. For added security a short length of heat shrink is also applied. This will be cut away later, and the screws replaced with longer ones.

 

 

gallery_217007_4999_167343.jpg

 

A few dabs of hot melt glue help hold all together at the right angles and depth.

 

gallery_217007_4999_488.jpg

Unfortunately this operation failed...mainly because I tested it before the epoxy had properly hardened. Basically the 4 joints in the thinner section all fell out.

gallery_217007_4999_325395.jpg
 

Time for Plan B



#171 Oberon

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Posted 04 October 2020 - 05:43 AM

Plan B is to pot new bearings within a short section of 16mm aluminium tube (CF would be better but I have aluminium in stock so will make do), and then pot the potted bearing into the mirror plate.

 

In the end this works well. Here is the result...

 
gallery_217007_4999_105577.jpg


gallery_217007_4999_182640.jpg
 



#172 Oberon

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Posted 04 October 2020 - 05:56 AM

However this is a construct thread. That means I show what techniques works and what fails. So in the next few posts I'll walk through the construct details in case anyone wants to do something similar.

 

First step is cutting some very short rings from the 16mm aluminium tube. My sections of tube want to be only 10mm deep, and this means the job is VERY likely to be caught up in the saw blade and flung about and damaged. So extra precautions must be taken to ensure the tube is controlled, and that the cut piece has no where to go once cut free from the mother tube.

I use...

 

1. a plate of plywood to ensure a flat surface

2. the saw is set to cut into the ply but not through the ply; this stops the job dropping down, tilting and grabbing

3. a section of 3mm aluminium angle to support the back; this minimises the gap

4. a section of 3mm aluminium flat under the ply to match the angle and support the ply

5. a sacrificial section of 20x40 pine to hold the job and keep my fingers clear

6. an aluminium cutting blade (of course!) on my drop saw

BEFORE the cut...

 

gallery_217007_4999_49172.jpg

 

AFTER the cut...

 

gallery_217007_4999_109174.jpg

 

Even better (but not shown) is to avoid cutting all the way through the 20x40 as this ensures that the job piece remains firmly held in place after the cut is complete. 


Edited by Oberon, 04 October 2020 - 05:59 AM.


#173 Oberon

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Posted 04 October 2020 - 06:14 AM

Meanwhile the balls are mounted on a piece of polypropylene board (epoxy doesn't stick to it) drilled with 4mm holes and countersunk. The balls sit in the counter-sunk holes and are held firm by screws from behind. The entire arrangement is then sprayed with Teflon WD40 lubricant and allowed to dry.

gallery_217007_4999_36881.jpg

 

IMPORTANT TIP. Note that I only need 4 new bearings but I make 8 of. When potting bearings always make more than you need, then choose the best.

 

The aluminium tubes are sat carefully in place and held with hot melt glue.

gallery_217007_4999_183334.jpg

 

And then with the aid of a syringe potted with a very fluid epoxy.

 

gallery_217007_4999_49382.jpg



#174 Oberon

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Posted 04 October 2020 - 06:33 AM

But there is a catch!

 

When I placed the first 5 tube sections I was worried about centering them neatly and used a conical rubber valve seal to hold them down whilst centered on the ball...and holding down firmly to ensure centering I then applied the hot melt glue. This worked really well and is DEFINITELY RECOMMENDED.

 

Why?

 

gallery_217007_4999_246334.jpg

 

Because it means that the tubes don't leak epoxy! Note the units closer and on the right...these I held only with my finger lightly as I dabbed the glue on and consequently they didn't seal hard against the board...and so the epoxy is leaking away!

 

It got worse...

 

gallery_217007_4999_217057.jpg

Epoxy keep leaking away and threatened the whole job. In desperation I decided to displace and hopefully block off the leaking epoxy with hot melt glue confident I could remelt it later with a heat gun. 

It worked. It looked terrible as a big glutinous blob, but all came good in the end and the potted bearings were all recovered.

Next time I shall probably apply a continuous bead of hot melt glue in the first place to ensure no leaks, or some other scheme, the important point being to take precautions one way or another.



#175 Oberon

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Posted 04 October 2020 - 06:52 AM

The plate itself has to be drilled out to accept the new larger bearings. Once again I've used a 16mm bit with a short (now 10mm) section of aluminium tube fitted on the pointy end to ensure neat centering in the original hole.

 

gallery_217007_4999_36021.jpg

 

Not shown I've also followed up with a conical bit both sides to ensure the aluminium stays clear of the carbon fibre to avoid corrosion.

 

Now shown potted into place...

 

gallery_217007_4999_111432.jpg

 

Beautiful!

 

At this point all should be well...or is it?

 

For my job the bearings must freely point the screw in any direction, but the ball must also spin freely...without any sense of being loose, without any hint of bistability. Unfortunately one of the bearings was a little tight, and if too tight would make it hard to adjust the secondary mirror smoothly without potentially upsetting something else.

So after trying to bed it in by hand and teflon lube without success I decided to use a drill and spun it for say half a minute or so. The bearing heated up so much that the epoxy melted and the ball fell out!!!!!!!

Failed again!!!!!!!!

 

gallery_217007_4999_289715.jpg

 

Fortunately it was simple enough to drill out and rebuild in situ, and this time worked perfectly from the get go. I think the trick is to be liberal with the teflon spray and don't wipe it off. Let it dry but don't wipe it at all.


Edited by Oberon, 04 October 2020 - 07:03 AM.

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