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1967 Astronomical Equipment, Luton, 6-inch Newtonian reflector

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#26 Joe Cepleur

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Posted 18 February 2024 - 09:25 PM

Thank you, Richard;

I'm grateful for your annotated image, although it does not label the part I wondered about.

This picture of the old catalog:

https://www.cloudyni...03817-catalogue

shows what looked to be a large worm on the RA axis facing in the wrong direction, but this actual photograph:

https://www.cloudyni...-1708215790.jpg

shows that what I had thought appeared to be an over-sized worm to actually be... what? a compressed spring?

Still interesting. What is it, and what is it for?

I'm glad that you lugged the scope outside for even a brief view. Having used it since its reconditioning somehow makes it more authentic. It is now officially not just an artwork, but a proven telescope!

Edited by Joe Cepleur, 18 February 2024 - 09:44 PM.


#27 Richard Francis

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Posted 19 February 2024 - 07:00 AM

Ah, now I understand. In the image it does look like a worm. But it is actually a spring. Here's another picture showing the two axes from another angle

 

Axes Annotated

 

The two axes are unconstrained in their two bearings (the "plumber blocks" I showed in the second of the pictures you referenced). In the catalogue they are referred to as "accurate sintered bronze self-aligning bearings". To prevent the axes just lifting out they are secured by a locking collar, which pushes a bearing (containing regular ball-bearings) up against the plumber block via a spring. These are pretty strong -- when I was reassembling it I had to use mechanical assistance (a couple of clamps) to get them compressed. On the other side of the plumber block is what appears to be some kind of fibre washer -- I'm not sure why it's not another bearing, but I did know at the time I rebuilt it.

 

By the way, I didn't refurbish it recently -- it was in 2001/2002. And I used it quite a few times since, but it's nowhere near as convenient as the permanently-mounted, driven scopes I have in the 2 observatories in the garden, so it's more for the thrill of reusing something which I used incessantly as a teenager which makes me bring it out.

 

Another thing which might be obvious: I took the photo which opened this thread with the scope in the location of this picture, but the background in our entry hallway is a bit "busy". It's a 300 year old farmhouse after all. So I hung a curtain up behind the scope, then used Photoshop to pick it out from the background and made a completely synthetic background in the same style as the original catalogue picture. Photos like that were always very heavily retouched and I wanted to replicate the feel of it.

 

I only retouched the scope itself in one main area: the primary mirror was reflecting the yellow curtain, so I carefully masked everything else and reduced its colour saturation significantly.



#28 Joe Cepleur

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Posted 19 February 2024 - 07:10 AM

Thank you, Richard.

What is the advantage of having the spring? It appears to be compressed, so that the weight of the telescope rides on the spring rather than the ball bearings. Perhaps this allows them to roll more easily?

#29 Richard Francis

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Posted 19 February 2024 - 10:56 AM

I don't know the definitive answer as I wasn't the designer ! But my guess is that it's too difficult to get the locking collar tightly up against the bearing to ensure it all stays together. The bearing isn't one of those modern types which you can handle as a single object -- it's two metal end-plates and a centre one with holes for the balls, and nothing holding it together.

 

It appears to be compressed, so that the weight of the telescope rides on the spring rather than the ball bearings.

To me it looks more like the weight rides on the upper plumber block of the RA axis. But I'm not a mechanical engineer so could be wrong.

 

Cheers,

Richard



#30 Joe Cepleur

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Posted 19 February 2024 - 11:21 AM

I'm not an engineer either, but here's how I see it:

If the weight rode on the plumber block, then the friction against the fibre washer would bind the RA axis. The spring may be there to push the ball bearing upward so that it would carry the weight as intended. It may be hard to find an exact location for the locking nut where the bearing would work at any weight loaded upon the telescope (such as various eyepieces, cameras, or finders), but a firm upward pressure may sufficiently carry the weight so that the ball bearings would prevent too much pressure from binding against the fibre washer. It would, of course still be necessary to compress the spring to adequate pressure before tightening its locking nut.

It has been over forty years since I was a student in London. Nice to need to spell "fiber" as "fibre" again!

#31 starman876

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Posted 19 February 2024 - 11:34 AM

Is the diagonal a prism or a mirror?



#32 Joe Cepleur

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Posted 19 February 2024 - 11:54 AM

Is the diagonal a prism or a mirror?


Tapping (clicking) on the picture in the first post opens or at a higher resolution. There, you can zoom in to see that the diagonal is an eliptical flat.

#33 starman876

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Posted 19 February 2024 - 12:34 PM

I had a similar scope that was a 10" F12.   It used a prism.  I finally gave up trying to use it because I did not have the proper mount to use it.    It was a beast. I still have the primary and the prism secondary. 



#34 Richard Francis

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Posted 19 February 2024 - 05:19 PM

If the weight rode on the plumber block, then the friction against the fibre washer would bind the RA axis

I completely agree with that, and it's why I said that I don't remember the rationale for using this, since the apparently obvious thing would be put a bearing on the other side too. The original designer (the late Rob Hysom) did not, and I'm confident he knew what he was doing. Like I said, when I disassembled it, it was probably clear to me why it was built like that and so I did not introduce another bearing.

 

But it's more than 20 years ago and short of disassembling it again (which seems a bit extreme) I'm not sure I can add more.

 

It has been over forty years since I was a student in London. Nice to need to spell "fiber" as "fibre" again!

Nice! -- I've lived in France for the last 10 years (30 years in NL before that) and here, like the Brits, they spell it "fibre" (especially in connection with network connections), but of course the pronunciation is as it's spelled.



#35 Richard Francis

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Posted 19 February 2024 - 05:30 PM

Is the diagonal a prism or a mirror?

As Joe points out it's an elliptical flat. At that time I'm not aware of any amateur scope that used a prism, and probably many would have been scared off by the potential extra light absorption in the glass of a prism, not to mention the square obstruction to the light path with associated diffraction spikes, and its inevitably larger cross-section.

 

Unless it was a prism with a an elliptical reflecting surface and therefore circular cross-section. But that would likely have been quite expensive to build. 



#36 PETER DREW

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Posted 21 February 2024 - 04:43 PM

I think I can throw a little light on to this topic.  I was closely associated with AE in the 1970's and a friend/colleague of Jim Hysom until his passing. AE began in Harpenden, Hertfordshire, moving later to Luton, Bedfordshire and finally to Cambridshire.  Luton, at the time was somewhat of a Mecca for astronomical companies, as well as AE there was Astrosystems run by Rob Miller of which I was also a founder director and my own company Bedford Astronomical Supplies.

Staff at AE as far as my memory provides were Jim Hysom (chief optician), Rob Hysom (engineer/designer), Cliff Shuttlewood (draftsman), John Mathers, Jim Muirden, Es Reid and Jon Owen (opticians).  In addition, the legendary Horace Dall was just a mile up the road.

AE made four standard mounts classified as A,B,C and D,  The first three were German style equatorials of increasing size and the D was a large fork equatorial.  The fibre washer that has been queried was in fact a clutch plate, the pressure of which was governed by the compression of the spring, the compression being adjusted by the position of the collar below it.       


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#37 Richard Francis

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Posted 21 February 2024 - 04:55 PM

Thanks Peter for this very useful insight.

 

I don't suppose you have any information on the appropriate force to be applied via the spring for this clutch to operate optimally?

 

I know it's a long shot, but you never know.

 

Thanks,

Richard



#38 PETER DREW

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Posted 21 February 2024 - 06:03 PM

Thanks Peter for this very useful insight.

 

I don't suppose you have any information on the appropriate force to be applied via the spring for this clutch to operate optimally?

 

I know it's a long shot, but you never know.

 

Thanks,

Richard

As far as I know there was no specific figure, I think the pressure was left to the owner and varied depending on the load carried.


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#39 Joe Cepleur

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Posted 22 February 2024 - 06:48 AM

"Clutch plate" meaning what? Was it part of a locking mechanism, or did this allow the axis to turn smoothly while allowing the amount of force required to turn it to be adjusted?


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