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Zeiss Coudé telescope rebfurbish

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#1 Peter Ceravolo

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Posted 14 January 2019 - 10:25 PM

Last spring I acquired, via Cloudy Nights classified, a classic Zeiss Coudé telescope with a 150mm f/15 objective for a princely sum.

The telescope is interesting in that the converging beam is folded with two flats to a fixed focus at the south end of the polar axis. What is not obvious in the image below is that the telescope is huge. The polar axis is almost twice the diameter of the objective!

 

I had no real reason to acquire the instrument, it seemed like an interesting telescope to play with. I conned my wife Debra into letting me buy it by suggesting that it would be her solar telescope. :-)

 

Zeisscoude.jpg

 

The telescope has an interesting history, it was purchased by the MacMilan planetarium in Vancouver, Canada in the early '80's I believe. I spoke with Ken Hewitt-White, noted Canadian astronomy writer, who was on staff at the time. He and the other younger staff were not happy with the very expensive purchase, they wanted a bigger reflector that could better punch through the light pollution.

 

Zeiss telescope small.jpg

 

The telescope left the Vancouver planetarium in 1990 and wound up in East Point Solar Observatory in the Boston area in 1995.

 

I am not sure when the telescope was fabricated, but almost all the parts have the numeral "10" stamped on them. The telescope is quite weathered. A close look at the above image reveals that the bolts were rusty. At some point extra layers of paint were applied to spruce it up. Examining the instrument I realized that it would be best to do a complete refurb. What I didn't know yet is that the instruments RA bearings had potentially fatal damage.


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#2 Peter Ceravolo

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Posted 14 January 2019 - 10:50 PM

Buying a huge telescope is easy, transporting it is another issue.

 

I actually purchased the whole East Point Solar Observatory, essentially the scope and a 3 meter dome.

 

epso.jpg

 

And it took a big truck to get it to me on the other side of the continent.

 

Observatory on truck 1s.jpg

 

There is other stuff on the truck but the dome, dome base and the telescope crate dominated the ride.

 

Of course you have to get the big heavy items off the transport so you hire a crane truck...

 

The telescope's tall pedestal is wrapped in white plastic. The telescope crate is just behind the transports cab.

 

crane.JPG

 

 


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#3 Peter Ceravolo

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Posted 14 January 2019 - 10:59 PM

We used the shipping crate as a work bench to disassemble the telescope.

 

IMG_2328.JPG

 

My buddy Ed, a retired air force aviation mechanic, helped me take the instrument apart.

 

IMG_2367.JPG

 

When the instrument was in pieces I was careful to bag all the fasteners and keep them with the relevant parts.

 

Shop.jpg


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#4 Peter Ceravolo

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Posted 14 January 2019 - 11:11 PM

The Zeiss is a complex classic instrument with lots of gears and small parts.

 

IMG_2395.JPG

 

IMG_2419.JPG

 

The focuser is huge and non conventional. The big hand wheel drives planetary gears that moves the big draw tube via long threaded rods.

 

IMG_2388.JPG

 

The RA drive is a complex set of gears that allows manual and motor driven motion.

 

drive.jpg


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#5 petert913

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Posted 14 January 2019 - 11:48 PM

Wow! That is such an interesting project. Thank you for sharing. 


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#6 Peter Ceravolo

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Posted 15 January 2019 - 12:16 AM

The big, nasty, surprise came when we extracted the massive and hollow RA shaft and spun the main bearing.

 

IMG_2468.JPG

 

IMG_2470.JPG

 

There was a lot clunking happening as the bearing rotated. You could feel it when rotating the outer race by hand slowly.

The bearing was easily disassembled to reveal the problem.

 

IMG_2473.JPG

 

IMG_2477.JPG

 

The Zeiss Coudé telescope uses wire race bearings in the RA axis. The balls roll on wire pressed into the shaft and outer race.

 

IMG_8922.JPG

 

The problem with this telescope was that at some point, most likely in transport, the mount was subjected to vibration that caused the balls to dent the wire affecting the smoothness of rotation.

This, of course, was potentially fatal to the scopes function. Imagine tracking on a planet and suddenly the image goes haywire because all the balls in the bearing fall into the dent.


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#7 halx

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Posted 15 January 2019 - 12:35 AM

Very cool! This is the favorite telescope of my childhood! I still remember the sound of its gravity-driven tracking and how we've been moving it to the roof of our club (3 story building) piece by piece using a DIY over the edge crane. The Sun's projection looks fantastic with it no doubt as well as planets...



#8 Steve Allison

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Posted 15 January 2019 - 01:26 AM

Wonderful thread!

 

For a refractor nut like me, it doesn't get any better than this.

 

And with Peter Ceravolo doing the refurb, the telescope should be spectacular when finished.

 

Peter, please keep the pictures and details coming!


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#9 Benach

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Posted 15 January 2019 - 01:49 AM

Well Peter, You know that we are doing almost the same thing at the other side of the world so thanks for your photos already and let's hope that yours will perform just as good as ours.



#10 Peter Ceravolo

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Posted 15 January 2019 - 02:11 AM

I had never heard of wire race bearings, but apparently it's the way to go when you need large diameters at a low price that fit in a tight space.

It's no surprise that the craftsmen that built these telescopes have either long retired or passed on, so it would seem that Zeiss is not able to support their classic instruments. I researched and called many companies that work with wire bearings to see if the mount was salvageable. A big problem was that the wire was pressed into the metal, it could not be easily replaced. This is curious because that is supposed to be be one of the advantages of a wire race bearing. Companies that have experience with wire bearings, from North America to the UK and EU could not help with this odd ball classic telescope's bearing problem.

 

If you look at the picture below you'll note that the wire race is not continuous, there is a gap. But even with the gap the bearing functioned well. When one ball fell into that one gap the other balls in the race supported the instrument resulting in smooth motion. The dents in the wire of course matched the original ball spacing. It finally dawned on me, if I could increase the number of balls in the race the telescope would be supported while the originally spaced balls fell into the dents.

 

IMG_2477.JPG

 

Fortunately the balls are widely spaced in the original bearing. The holes in the cage that keeps the balls from running into each other has plenty of room for more balls.

 

IMG_2475.JPG

 

I clamped the cage in a drill press and drilled some extra holes in between the original holes for the extra balls. Precise spacing was not necessary, in fact I randomly staggered the new hole spacing to ensure the new balls did not have the same spacing as the original balls.

 

IMG_9035.JPG

 

I reassembled the bearing, adding the extra 10mm diameter balls in the cage's new holes.

 

IMG_9038.JPG

 

It worked!

 

At least when spinning the bearing by hand I could not hear or feel the clunking of the original damaged bearing. I felt confident enough that the problem was solved that I could continue with the expensive restoration. Of course the ultimate test will be tracking the stars, but to be quite frank I do not expect to be able to take high res, long exposure, deep sky images with this instrument. I expect the tracking smoothness will be adversely affected by the many gears in the drive train. But deep sky imaging is not what this instrument is about. What is important is the high speed solar imaging that my wife Debra will do with the telescope... :-)


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#11 Peter Ceravolo

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Posted 15 January 2019 - 02:12 AM

Well Peter, You know that we are doing almost the same thing at the other side of the world so thanks for your photos already and let's hope that yours will perform just as good as ours.

I hope you do not have the same problems with the RA bearings!



#12 photomagica

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Posted 15 January 2019 - 03:01 AM

Peter,

Very clever how you solved the wire bearing problem. 

 

I was working for another Canadian planetarium at the time this was purchased. I forget the telescope's price, but it was enormous, and I wondered at the great expenditure for the relatively small aperture. The rationale I heard at the time was the fixed eyepiece was wanted for accessibility, even including wheel chairs. The original dome, which I last visited a couple of years ago, does have a ramp system for access to the floor near the telescope. The dome now houses a 20" Cassegrain telescope.

 

I'm delighted you have obtained this instrument and wish you every success in the refurbishment.

Bill


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#13 Peter Ceravolo

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Posted 15 January 2019 - 03:04 AM

With the nasty bearing problem tamed, the next phase of the Zeiss project is to clean up the mount and make the telescope pretty again.

 

I hoped I could strip the paint off the many mechanical components, send them to a commercial painter and have them re-painted.

 

Simple.

 

IMG_9055.JPG

 

But the parts were not easy to strip chemically. There was more under the surface than I expected. The paint's tenacity exceeded my time budget, patience and skills. So I thought of simply handing over the job to a commercial paint shop.

 

But then the nightmares started. All these parts, large and small. Mostly small, could be misplaced... Lost... If that were to happen my desire to preserve this wonderful piece of history would be severely compromised.

 

Then I remembered my buddy and neighbor Mark. He did the extensive body work on my 1981 Corvette restoration. He worked on that fiberglass body with enthusiasm and finesse, maybe he would consider refinishing my Zeiss....

 

booth.jpg

 

Having a craftsman devoted to your project, one who is only a 2 minute drive away, is an incredible advantage.

 

The parts were stripped of the old paint and body filler to ensure the longevity of the modern materials to be applied.

 

IMG_1593.JPG

 

 

 

 


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#14 Peter Ceravolo

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Posted 15 January 2019 - 03:18 AM

To preserve the original appearance, modern body filler was used to smooth out the welds.

 

IMG_1597.JPG

 

Then painted and transported home to cure over the winter.

 

IMG_1604.JPG

 

repaint.jpg

 

IMG_20181123_160650283.jpg


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#15 Peter Ceravolo

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Posted 15 January 2019 - 03:21 AM

Peter,

Very clever how you solved the wire bearing problem. 

 

I was working for another Canadian planetarium at the time this was purchased. I forget the telescope's price, but it was enormous, and I wondered at the great expenditure for the relatively small aperture. The rationale I heard at the time was the fixed eyepiece was wanted for accessibility, even including wheel chairs. The original dome, which I last visited a couple of years ago, does have a ramp system for access to the floor near the telescope. The dome now houses a 20" Cassegrain telescope.

 

I'm delighted you have obtained this instrument and wish you every success in the refurbishment.

Bill

Thanks Bill, I just wish I could spell refurbish in the topic line right... :-)

Peter



#16 R Botero

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Posted 15 January 2019 - 03:29 AM

Peter
Magnificent project and even more so now you are documenting it. Clever yet simple solution for the ball bearing problem :waytogo: Can’t wait for the next instalment! :cool:
Roberto

Edited by R Botero, 15 January 2019 - 03:29 AM.


#17 Benach

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Posted 15 January 2019 - 04:59 AM

I hope you do not have the same problems with the RA bearings!

We'll see on that in a few months. But Peter, I wonder: those two short movies of the RA-axis you have send me, are they a "before" and "after" your tweaking of the wire race bearings? if so, the difference is indeed huge!



#18 Max Lattanzi

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Posted 15 January 2019 - 07:28 AM

I had never heard of wire race bearings, but apparently it's the way to go when you need large diameters at a low price that fit in a tight space.

It's no surprise that the craftsmen that built these telescopes have either long retired or passed on, so it would seem that Zeiss is not able to support their classic instruments. I researched and called many companies that work with wire bearings to see if the mount was salvageable. A big problem was that the wire was pressed into the metal, it could not be easily replaced. This is curious because that is supposed to be be one of the advantages of a wire race bearing. Companies that have experience with wire bearings, from North America to the UK and EU could not help with this odd ball classic telescope's bearing problem.

Peter, thank you so much for sharing this solution in such a detailed way and for the other info you gave me.

As I told you in pvt, I still have no clue on the state of my polar bearings.
What I know for sure is that, once I load them with the AS-200/3000 lens + extension tube + additional CWs, they will be loaded more than yours -- although that is foreseen in the Zeiss project (so bearings should be already well dimensioned).

Zeiss figures for the instruments are:

AS-150 with mount : 670 kg  (1.479 lbs)
AS-200 with mount : 810 kg  (1.788 lbs)

 

So, as you see, in due time I may need your help too wink.gif

 

Cheers.

-- Max



#19 starman876

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Posted 15 January 2019 - 09:00 AM

Simply amazing



#20 Peter Ceravolo

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Posted 15 January 2019 - 05:22 PM

As mentioned before, the Zeiss Coudé telescope is quite complex, and in some ways perhaps overly complex, for example the Declination axis counterweight system.

 

One removes a thick, heavy cover plate (already removed) to reveal an small counterweight that can be slid up and down a tube to finesse balance.

 

Dec counterweight 1.jpg

 

One uses a screw driver to engage pins that clamp the small weight in place. The screw that does the clamping is accessed through a central hole in the cover plate. I think that's how it works as I have not actually used this set up yet.

 

Dec counterweight 2.jpg

 

The weight slides up and down a tube within the main counterweight to finesse balance about the RA axis. I'm not sure how convenient moving the weight up and down this tube is in practice since you can't actually grab the thing.

 

Dec counterweight 3.jpg

 

The main counterweight is unbolted from a ring that is bolted to the Dec housing.

 

Dec counterweight 4.jpg

 

Unfortunately you have to remove all these heavy counterweight parts to get at the fold mirror in the Dec housing, as the port adjacent to the fold mirror (for accessing alignment screws) is too small to pass the mirror cell through. This makes mirror cleaning a big job with the telescope in the observatory.

 

Dec mirror.jpg

 

 


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#21 Peter Ceravolo

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Posted 15 January 2019 - 05:30 PM

Very cool! This is the favorite telescope of my childhood! I still remember the sound of its gravity-driven tracking and how we've been moving it to the roof of our club (3 story building) piece by piece using a DIY over the edge crane. The Sun's projection looks fantastic with it no doubt as well as planets...

Another cool fact; Mark, who is refinishing all the parts, actually looked through the telescope years ago as a child growing up in Vancouver!

 

Many people are happy to have the Zeiss telescope back in Canada, even the ones who didn't want it in the first place.. :-)


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#22 Jim Curry

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Posted 15 January 2019 - 09:26 PM

Great documentation Peter

 

Jim


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#23 halx

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Posted 16 January 2019 - 12:07 AM

Perhaps, you can fix the wire dent in place by polishing a welded over blob?



#24 Benach

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Posted 16 January 2019 - 06:28 AM

I'm not sure how convenient moving the weight up and down this tube is in practice since you can't actually grab the thing.

 

I really liked this counterweight. So simple, so elegant. And no, you do not need to rebalance this scope once it is balanced. The telescope mass is so high, no imagetrain or eyepiece will make any noticeable difference to the balance of the total telescope.

 

BTW Peter, do you have pictures of the declination axis assembly by any coincidence? Especially the region where the pinion from the polar axis goes into the "dogbone" part of the declination axis.

 

All the other images were highly appreciated yesterday by our project team. We were also impressed by the painting that was done. Probably we are going to paint our scope either the original colors or (off-)white. Rest via the e-mail.



#25 JohnH

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Posted 16 January 2019 - 09:42 AM

Peter, glad to see this historic instrument that I remember from the planetarium years ago has and it up someplace where it's going to undergo a major refit and end up back in service. Being a child who grew up in the bank near Vancouver in the seventies, I recall this telescope vaguely. Later, as a member of our RASC Vancouver I got a history lesson from Dan, the resident operator of the observatory there and its equipment, and often wondered what happened to this scope after they replaced it with the 6 inch regular refractor. One question I do have, is about the light path of the scope. There are a couple of folded refractors floating around Vancouver, a pair of them built by some friends using the same Optics from some European company, and both ending up being 6 in ff15 versions.
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