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1899 4" f/16 Cooke Photovisual Apo refractor

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#276 macdonjh

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Posted 25 October 2020 - 02:39 PM

 

Clearly the tube was not intended to slide in the rings to achieve fine balance. After stripping the old worn paint I found that the one of the rings actually has to be forced in place.

After you've measured the OD of the OTA at the position of the ring, as well as the ID of the ring, I wonder if a small amount of fine sanding would make the ring fit better without the risk of bending it outward?



#277 Peter Ceravolo

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Posted 25 October 2020 - 05:17 PM

After you've measured the OD of the OTA at the position of the ring, as well as the ID of the ring, I wonder if a small amount of fine sanding would make the ring fit better without the risk of bending it outward?

Perhaps. I expect to line the ID with something to prevent damage to the tube finish.

Prior to finishing/painting the components I plan to do a full up assembly of mount and OTA, looking for unforeseen problems that might cause damage to finish.


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#278 oldmanastro

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Posted 25 October 2020 - 05:43 PM

This project is coming out just fine.  Superb job on those parts that have been cleaned. I think your approach to the project is the right one. It will look old but wonderful.


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#279 RichA

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Posted 25 October 2020 - 11:38 PM

I like the scouring pads, they remove most of the corrosion without making the part obnoxiously shiny.

Here are the turret eyepiece holders.

 

attachicon.gifIMG_9512.JPG

 

The steel parts are another story. Here we have the screw that adjusts the mounts polar axis elevation. The screw pivots on the spherical section as the polar axis is adjusted.

It's one of the most corroded parts, second to the drives worm. There's not much to do here other than buff up the mangled metal and apply some grease to preserve whats left. I would not entertain using the lathe to shave off the war wounds.

 

attachicon.gifIMG_2667.JPG

Reminds me of something they'd take out of a ship sunk around 1700. 



#280 RichA

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Posted 25 October 2020 - 11:40 PM

I'm back at the Cooke, striping the telescope's tube of the paint. I use an automotive chemical paint stripper that is also used on aircraft. Although it does a good job, on some areas I have to apply the stripper several times to get all the paint off.

 

attachicon.gifIMG_2691.JPG

 

I use a scrapping tool whose leading edge is periodically sanded to remove sharp edges that can scratch the brass surface.

 

attachicon.gifIMG_2695.JPG

 

The bare brass reveals the blotchy original finish. It's interesting to note a visual illusion I experienced while stripping the tube. The tube as painted black always seemed small in diameter, as the paint came off the tube seemed to look bigger in diameter for some reason....

 

attachicon.gifIMG_2701.JPG

 

I have not decided if I will repaint the tube, or sand and polish it for the classic bare brass finish. The latter is a lot of work and will require making a tube "lathe". The clean up work I did on a Tele Vue Renaissance;

 

https://www.cloudyni...naissance-1778/

 

gave me a taste of what would be involved... yikes!

I wonder if a cheap wood lathe would hold it?  They're generally made for longer pieces on average than metal lathes.



#281 Peter Ceravolo

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Posted 26 October 2020 - 09:53 PM

The 7 lb clamp on counterweight fits the 4" OD telescope brass tube with precision. Given it's construction, I suspect this accessory was probably made around the same time as the telescope.

I wonder if it's a Cooke item. The telescopes original owner, Dr. Hugh Walsham of London, had an interest in solar physics. Was this weight used to counterbalance a spectroscope?

 

This Cooke refractor is my first foray into antique instruments so I had never seen such a clamping tube counterweight. Neither it seems have the members of the Antique Telescope Society. One ATS member did mention that Unitron used this kind of counterweight. If anyone reading this has seen this type of counterweight on other instruments please chime in.

 

As illustrated in previous posts, I used it to balance the OTA on modern mounts when doing visual observing and imaging.

 

IMG_2748.JPG

 

IMG_2747.JPG

 

The "bottom" side of the weight has a flat spot that I assume is for clearance issues. When the telescope arrived I never did try the counterweight out prior to disassembly. When I have the scope together again for fit testing prior to painting I plan to try the counterweight out to see how it works with the OTA and it's other parts.

 

IMG_2751.JPG

 

I'd like to paint the weight the same color as the mount, but I'm having a devil of a time popping the pin out of the pivot. Both sides are roughly the same diameter so it does not appear to be tapered. As it was the pin face was nearly perfectly flush with the side of the counterweight, as if the surface was ground after assembly. An ATS member suggested the pin ends may have been flared to prevent the halves of the counterweight from coming apart and I may have to drill it out. But I'm inclined to not do anything destructive. It may wind up on the shelf unpainted as I don't expect to mount a spectroscope on the focuser.

 

IMG_2744c.JPG


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#282 luxo II

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Posted 26 October 2020 - 11:35 PM

I'd like to paint the weight the same color as the mount, but I'm having a devil of a time popping the pin out of the pivot. Both sides are roughly the same diameter so it does not appear to be tapered.

 

Peter I've seen examples of these old pinned joints before. Looking at your photo, there is a faint cross in the centre of the pic and I suspect this was where it was previously struck with a punch and a hammer - this will cause the end of the pin to expand slightly, locking it firmly in place.

 

The pins usually are tapered ever so slightly and they have to be carefully punched out with a steel bar with a flat end slightly smaller than the pin. Typically, put your finger over one end, then place the punch on the opposite end and tap with a hammer. If you feel the pin move ever so slightly you probably have chosen the right end to hit. a few more taps and it should loosen enough to be pulled out with pliers. If it doesn't move, swap ends and retry.

 

Whatever you do, do not use a punch with a pointed end on the pin as this will swell the end of the pin.

 

Otherwise it has to be drilled out and a new pin made to fit.

 

PS I doubt the weight was supplied with the scope - Cook would have taken pride in ensuring the complete OTA could be balanced without something so crude. My guess is that it was a part adapted from some other piece of machinery.


Edited by luxo II, 26 October 2020 - 11:51 PM.

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#283 astro140

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Posted 27 October 2020 - 08:15 AM

The 7 lb clamp on counterweight fits the 4" OD telescope brass tube with precision. Given it's construction, I suspect this accessory was probably made around the same time as the telescope.

I wonder if it's a Cooke item. The telescopes original owner, Dr. Hugh Walsham of London, had an interest in solar physics. Was this weight used to counterbalance a spectroscope?

 

This Cooke refractor is my first foray into antique instruments so I had never seen such a clamping tube counterweight. Neither it seems have the members of the Antique Telescope Society. One ATS member did mention that Unitron used this kind of counterweight. If anyone reading this has seen this type of counterweight on other instruments please chime in.

 

Takahashi used such a clamp to balance their TOA-150 refractor.  Here pictured with optional handle.

Attached Thumbnails

  • Takahashi Counterweight.jpg

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#284 RichA

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Posted 29 October 2020 - 12:52 AM

Peter I've seen examples of these old pinned joints before. Looking at your photo, there is a faint cross in the centre of the pic and I suspect this was where it was previously struck with a punch and a hammer - this will cause the end of the pin to expand slightly, locking it firmly in place.

 

The pins usually are tapered ever so slightly and they have to be carefully punched out with a steel bar with a flat end slightly smaller than the pin. Typically, put your finger over one end, then place the punch on the opposite end and tap with a hammer. If you feel the pin move ever so slightly you probably have chosen the right end to hit. a few more taps and it should loosen enough to be pulled out with pliers. If it doesn't move, swap ends and retry.

 

Whatever you do, do not use a punch with a pointed end on the pin as this will swell the end of the pin.

 

Otherwise it has to be drilled out and a new pin made to fit.

 

PS I doubt the weight was supplied with the scope - Cook would have taken pride in ensuring the complete OTA could be balanced without something so crude. My guess is that it was a part adapted from some other piece of machinery.

It might need hammer raps to punch it out, or a 1000-5000psi press using a stainless steel pin the same diameter of the pin might work. You would also need a cylindrical stainless or tool steel piece for the other side. 



#285 Peter Ceravolo

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Posted 31 October 2020 - 01:42 AM

Well it turns out that the pin is not tapered, but it is ( um... was ) flared on both ends to give the assembly a very clean look.

I applied heat to the weight via a hot plate, and then hammered the pin out.

 

IMG_2753.JPG

 

Unfortunately there was some collateral damage to the thinner sections of what looks like cast iron. They were not the result of a direct blow from the hammer, but likely stress fractures from vibration, I think.

 

IMG_2754.JPG

 

The flared pin really cleaned up the look of the hole in the casting. The damaged parts don't look too bad when the sections are joined.

 

IMG_2757.JPG

 

The whole point of separating the components is to be able to paint them properly. When the pin is reinserted the assembly will not be as clean. It remains to be seen if taking the weight apart was a wise thing to do...



#286 Kunama

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Posted 31 October 2020 - 03:05 AM

JB Weld will put those cast bits back like new, then paint ....


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#287 Kokatha man

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Posted 31 October 2020 - 06:56 AM

JB Weld will put those cast bits back like new, then paint ....

Brazing for cast iron - especially if they get a painted finish!



#288 Peter Ceravolo

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Posted 10 January 2022 - 09:45 PM

Hi gang, it's been a while!

 

I've not had the opportunity to continue restoration of the 4" Cooke Photo-Visual telescope, but I prepared a talk on the -

 

"Opto-Mechanical Analysis of a 1899 4" Taylor Photo-Visual Objective"

 

for last years Antique Telescope Society virtual convention. You can find mine as well as a host of other talks at this link:

 

https://vimeo.com/user161970464

 

Peter


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#289 deSitter

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Posted 11 January 2022 - 12:57 AM

I think it's very cool your calculator looks like it's older than your spherometer.

attachicon.gifhp41.jpg

 

I have it's cousin: an HP 15C and still use a 42S at work.  I wish HP still made reasonable calculators.

The 50g is in my top 5 prized possessions. I had the original 41C and then the 71B in college. But the 50g is a vast improvement on both. 50g's are harder and harder to find.

 

Now back to telescopes, sorry for the interruption :) This is a fun thread! The optical analysis was fascinating.

 

-drl



#290 TG

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Posted 11 January 2022 - 04:26 PM

Hi gang, it's been a while!

 

I've not had the opportunity to continue restoration of the 4" Cooke Photo-Visual telescope, but I prepared a talk on the -

 

"Opto-Mechanical Analysis of a 1899 4" Taylor Photo-Visual Objective"

 

for last years Antique Telescope Society virtual convention. You can find mine as well as a host of other talks at this link:

 

https://vimeo.com/user161970464

 

Peter

Loved the talk even though I had followed most of its content here.

 

TG



#291 Peter Ceravolo

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Posted 12 January 2022 - 12:28 AM

The post talk discussion was interesting, most everyone thought the plate that presses the objective lenses against the cell "cheeks" was not authentic Cooke, probably because the part does not look like it's made with the "finesse" one would expect from a Cooke instrument and the absurd amount of pressure the part imparts on the lenses. I don't agree, there are a few parts that I consider to be less than high finesse with the instrument - the tube rings for one, they are a lousy fit on the tube for some reason. They were pressed in place and painted over.

 

The other thing that confused me was the amount of wear on the pressure plate where the lenses contact. But then it recently occurred to me that during testing/polishing process, the lenses were in and out of the cell quite a number of times as the Cooke opticians figured the objective's 5th surface to compensate for all the errors in the previous surfaces. It would not take long to mar the plate's surface when repeatedly sliding the plate in and out of the cell.

 

The big take away from my analysis of this Photo-Visual objective (I may have mentioned this in an earlier post) is that the ideals that Taylor described in his book, figuring individual surfaces to be spherical, did not happen with this objective. And more importantly, the easy technique Taylor describes of sliding the cell off with pressure plate in place is actually dangerous with this particular objective. I did it that way the first time because I did not know any better. Every subsequent time I disassembled the objective I removed the plate first, with the help of needle nose pliers, gently extracting the plate until there was enough metal standing proud of the glass. Then I was able to extract the last of it with fingers, bending the plate even more to clear the glass.

 

IMG_1789.JPG


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#292 PawPaw

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Posted 12 January 2022 - 05:34 AM

Peter,

Thanks for sharing.......I came away from both your post and the presentation with a new appreciation of our past optical masters such as Cooke.  I highly recommend both but reading through the  post first gave me an leg up  for your vemo.

 

The one term that sticks in my mind that you mentioned is............."Optical Patina".  Fascinating!  

 

Cheers

 

Don 




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