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The Wilmington 16" Cassegrain Cave / Restore

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#51 orion61

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Posted 22 October 2014 - 01:05 PM

I doubt it will need more than a re-coating. I'll bet the figure is fine just the baffle and Spacing will do..

THIS IS GOING TO BE A MONSTER THREAD!! As always.... nothing but the best from Turk..

Duane



#52 DAVIDG

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Posted 22 October 2014 - 01:33 PM

Tom,
Your dealing with almost exactly what I was dealing with. Here is a picture of the school's observatory on the roof of the school building. The last time our scope was apart was 1962 and while it didn't have as much bird dropping as yours we also had that issue. It's going to be easier and safer to take the scope apart, carry the smaller piece down then to try the lower large pieces over the side. I would only do that as a last restort.
I don't believe the dome is doubled wall but only a single wall construction. I know our is only single walled. In our case it didn't take much to get it out of round. If yours is the same then if you warp it, by trying to hang any weight off of it, it will be difficult to get back into shape and if not, it will not rotate freely.

- Dave
aidupontobservatory2.JPG

Edited by DAVIDG, 22 October 2014 - 01:47 PM.


#53 turk123

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Posted 22 October 2014 - 01:34 PM

I wonder what bird poop has done to the mirror. You may be in for a re-grind but if the reputation for bad optics holds it will need one anyway. None the less that scope is a dream of mine -good luck!

 

 

I talked to a re-coater and he said the poop probably protected the surface over the years.  Bird droppings are uric acid and alkaline matter.  He told me it should not bother glass at all.



#54 turk123

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Posted 22 October 2014 - 01:40 PM

Tom,
Your dealing with almost exactly what I was dealing with. Here is a picture of the school's observatory on the roof of the school building. The last time our scope was apart was 1962 and while it didn't have as much bird dropping as yours we also had that issue. It's going to be easier and safer to take the scope apart, carry the smaller piece down then to try the lower large pieces over the side. I would only do that as a last restort.

- Dave
attachicon.gifaidupontobservatory2.JPG

 

 

I agree with you Dave!   But I just wanted to get the tube and some of the parts lowered using a sling.   I'm guessing I could rig the tube so that the line runs over the cradle allowing me to help lower it.  

 

I called Observa-dome just now and they remember the dome.  It is a 16.375' dome.   It may be double walled.  The owner will be back in an hour and will call me.  I emailed them some images of the dome.  To buy and install that dome today would be $132,000.   That's crazy!     



#55 DAVIDG

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Posted 22 October 2014 - 02:31 PM

Acid is no problem to Pyrex and won't touch it, alkaline in different story and will etch glass easily. That is why you never use Lye or any basic materials that contain sodium hydroxide to strip an old coating since it will attack the optical polish under it. You can also use most inorganic acids on crown optical glass to remove antireflective coating but not on the flints since both acids and bases will etch them as well. Another problem is aluminum parts around the glass since the metal will react with water to form basic materials and if that is allowed to sit on the glass it will etch it as well.
So hopefully the birds were eating an acidic diet. Your dome is the same size as ours.

- Dave

#56 turk123

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Posted 22 October 2014 - 02:42 PM

I just had a conversation with Jeff Decker at Majestic coatings.  He said there is a chance the bird droppings could damage the surface and explained why.  The Poop is alkaline.  That is a base.  Most people think coaters use acid to remove the aluminum.  They don't.  They use a base.   If the Poop mixes with the aluminum and is left on too long, the reaction with the aluminum can etch the surface of the glass.  It just depends on the environment.

 

Guess we will have to wait and see.

 

The good news is that Jeff has offered to do all the stripping and coating on the 16" Cave primary, and both secondaries for free. He's coming on board to help make this restoration a success.   Thanks Jeff!

 

Hmmm . .   maybe we should come up with a name for this project.  "Terleski's folly"!


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#57 DAVIDG

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Posted 22 October 2014 - 03:38 PM

Tom,
I would strip the coating myself. All it takes is a little ferric chloride which will not harm the glass. I'm really surprise that Majestic uses base since no matter what, it will degrade an optical polish. As a chemist I can tell you that is fact no matter what a coater states. I will never allow the coater to strip the old coating off of my optics since I'm not sure how they do it. The one time they did one of them they sleeked up one of my mirrors and also a good friends mirror that were sent separately. Never again !

- Dave

Edited by DAVIDG, 22 October 2014 - 04:51 PM.


#58 turk123

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Posted 22 October 2014 - 03:50 PM

Tom,
I would strip the coating myself. All it takes is a little ferric chloride which will not harm the glass. I'm really surprise that Majestic uses base since no matter what, it will degrade an optical polish. As a chemist I can tell you that is fact no matter what a coater states. I will never allow the coater to strip the old coating off of my optics since I'm not sure how they do it. The one time they did one of them sleeked up one of my mirrors and also a good friends mirror that were sent separately. Never again !

- Dave

 

Hi Dave

 

I'm looking at several suppliers.  Some require large min amount.  Supplier?

 

Also Dave.  Could you outline the process?  I have two mirrors I would like to send out now.  I think I would like to try this.  How much do I need?  (2 - 10" mirrors)



#59 albert1

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Posted 22 October 2014 - 04:00 PM

Oh man, talk about projects being on an upwards trajectory, Tom - the next one is bigger then the last. It's quite something watching you work - good for you, Classics and us :waytogo: .

 

Really is too bad no one thought to cover that beauty before leaving it. I can't understand that. No biggie. With your expertise, It'll clean up fine I'm sure.

 

Good luck!



#60 kansas skies

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Posted 22 October 2014 - 04:34 PM

Oh man, talk about projects being on an upwards trajectory, Tom - the next one is bigger then the last. It's quite something watching you work - good for you, Classics and us :waytogo: .

 

Really is too bad no one thought to cover that beauty before leaving it. I can't understand that. No biggie. With your expertise, It'll clean up fine I'm sure.

 

Good luck!

I'm waiting for the post where he rescues the Hubble from a decaying orbit... :)

 

Bill


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#61 DAVIDG

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Posted 22 October 2014 - 04:46 PM

Tom,
Ferric chloride solution was/is sold by Radio Shack to etch copper circuit boards. I have been using the same 24 oz for years. Here is a link to the Radio Shack website that still lists it http://www.radioshac...g solution&sr=1
There are two methods I have used. The first is to just make a dam around the mirror with masking tape and pour the solution on it so it just covers the surface. In about 15 to 20 minutes the coating will be gone and I just pour the liquid back into the bottle to reuse it
The other method is to cover the mirror with a paper towel. Pour some solution on the towel so the towel is soaked and the glass surface is covered with the saturated towel. Put some plastic food wrap over the towel and again wait about 30 minutes and the coating is gone or just leave it over night and the next day it will be stripped. Unlike any type of basic solution which will etch the surface, the ferric chloride solution won't touch the optical surface.
If you want to speed up the process warm up the mirror and also the ferric chloride solution.
Here is a picture of a couple of mirrors being stripped at the Delmarva mirror making class I help teach each year.

- Dave
03_MMM10.jpg

Edited by DAVIDG, 22 October 2014 - 04:52 PM.


#62 CHASLX200

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Posted 22 October 2014 - 06:00 PM

The OTA with otpics and rings has to be around 170lbs so that is something 2 guys can handle.  I sure as heck would not try to remove it from the mount by myself.  The EQ head without weights is a easy 2 man job.  Again not something i would wanna carry by myself with my bad back.  I would just love to get a chance to get up there and get my hands dirty.  I love them old Cave Observatory mounts.

 

Chas


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#63 roscoe

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Posted 22 October 2014 - 06:17 PM

Is there a way to get some staging in the dome? Eeither standard construction stuff or the narrower version used indoors by painters and drywallers??  having something solid to stand on, or even taller and tall enough to rig a winch onto would make life easier and safer.  Or, perhaps you could build a big tripod or quadpod out of doubled-up 2x4's and hang a winch from the top.  It doesn't have to be super-rugged, you'll be lifting less than 200 pounds at a time - and you can test it by setting it up and hanging from it, if it'll hold you, it'll hold the scope parts.

 

I agree with those who suggest not using the dome as a skyhook.


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#64 turk123

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Posted 22 October 2014 - 07:12 PM

Is there a way to get some staging in the dome? Eeither standard construction stuff or the narrower version used indoors by painters and drywallers??  having something solid to stand on, or even taller and tall enough to rig a winch onto would make life easier and safer.  Or, perhaps you could build a big tripod or quadpod out of doubled-up 2x4's and hang a winch from the top.  It doesn't have to be super-rugged, you'll be lifting less than 200 pounds at a time - and you can test it by setting it up and hanging from it, if it'll hold you, it'll hold the scope parts.

 

I agree with those who suggest not using the dome as a skyhook.

 

I'm not going to attempt this by myself.  That would be foolish.   The skyhook idea to me seems to be the safest method.  I'm not so worried about the mount parts, just the big OTA.  It's got to be 175 lbs with just the large rings and no real grab points.  Scaffolding would be hard to get over it but could provide a safer footing.  I own all the equipment to do all this if it were on the ground.  I won't have any problem moving it when it gets home.

 

Pictured is my 416C Caterpillar Backhoe with 17' shovel.

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#65 turk123

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Posted 22 October 2014 - 07:15 PM

The OTA with otpics and rings has to be around 170lbs so that is something 2 guys can handle.  I sure as heck would not try to remove it from the mount by myself.  The EQ head without weights is a easy 2 man job.  Again not something i would wanna carry by myself with my bad back.  I would just love to get a chance to get up there and get my hands dirty.  I love them old Cave Observatory mounts.

 

Chas

 

The rings have to come off the OTA before it is moved.  Remember the only stairs I have to get it down are spiral!  I probably will tie a rope to it and lower down the building (without rings).



#66 CHASLX200

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Posted 22 October 2014 - 08:15 PM

 

The OTA with otpics and rings has to be around 170lbs so that is something 2 guys can handle.  I sure as heck would not try to remove it from the mount by myself.  The EQ head without weights is a easy 2 man job.  Again not something i would wanna carry by myself with my bad back.  I would just love to get a chance to get up there and get my hands dirty.  I love them old Cave Observatory mounts.

 

Chas

 

The rings have to come off the OTA before it is moved.  Remember the only stairs I have to get it down are spiral!  I probably will tie a rope to it and lower down the building (without rings).

 

It sure won't be a easy fish to bring in.

 

Chas



#67 Geo31

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Posted 22 October 2014 - 08:17 PM

You know, for the amount of screwing around to rig something up to get it ti the ground, it may make sense just to completely disassemble the OTA in place and carry each part down by itself. May even be faster, not to mention safer.

I'd be inclined to build a box (or boxes) for the optics for transport down.
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#68 TOM KIEHL

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Posted 22 October 2014 - 09:06 PM

You just might want to rent one of these for a day......http://www.reevesequ...og/hoisting.htm



#69 terraclarke

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Posted 22 October 2014 - 11:05 PM

Moving large, ungainly, heavy objects down wide linear flights of stairs separated by landings wouldn't be so bad, especially when broken down into individual units each weighing 100 pounds or less. Especially with a pair of stout fellows and a nice hand truck. Even narrow stairs going down a straight corridor would be fairly doable. Like taking a water heater or a washing machine in or out of a basement. But the thing that  scares me about this particular job is that spiral staircase! I wonder what was used in the past to move large heavy lights, fresnel lenses, and rotational mounts up and down light houses. Find that out and we and might have a plan. It is certainly a similar problem.


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#70 Datapanic

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Posted 23 October 2014 - 12:11 AM

If the spiral staircase could be temporarily removed, it might be easier to lower the parts down the hole.  That's what I'd do :)  In my past life, I was a rigger at a major shipyard.  Lots of crane experience.


Edited by Datapanic, 23 October 2014 - 12:12 AM.

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#71 Jeff B1

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Posted 23 October 2014 - 07:16 AM

Hey, this should be made into a great movie; "The Turk Legacy."  :)



#72 roscoe

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Posted 23 October 2014 - 07:29 AM

All the large stuff for lighthouses (including the granite blocks they were built with) was moved up the outside of the structure using jib boom cranes - an earlier, smaller wooden version of the modern cranes atop every tall building under construction. 

Is there access from the dome to the roof?  How did they get that desk in there? that's gotta be at least as bulky and heavy as the scope parts.....

 

I haven't seen a layout of the floor plan, but depending where the spiral is, if you had a tripod over the scope, the same block-and-tackle used to lift the scope parts could be used to take the weight as items were lowered down the staircase, all a person would need to do is provide sideways pull and guidance as the item traveled down.  I've built timber-framed barns, it's pretty surprising what two people and some pulleys can move and lift.

 

For ungainly things like the OTA, perhaps you could pick up one of those webbing net covers that are sold to cover loads in a pickup truck - or a small surplus military cargo net - and put the tube into that.  That would support it, and give lots of places to hold on while moving it.


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#73 DAVIDG

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Posted 23 October 2014 - 09:14 AM

I have a couple of old Cave catalogs and while the 16" Cass is the ONLY one they don't list the weight for, they do list it for a 16" f/6 Newtonian on the same mount but a heavier pier. That weight is 800 lbs so the Cass is most likely 100-200lbs lighter. While not light, the scope will break down into parts that are moveable without cranes and hoists.
Just keep in mind that if the story is correct that Tom Cave drove the scope out there, and somehow he and whoever set it up.

- Dave

#74 Datapanic

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Posted 23 October 2014 - 08:49 PM

Tom, after we talked on the phone.  I checked out the Observa-Dome website and found Structural Analysis for the 5m dome, very informative stuff.  These domes are built tough and can withstand a lot of weight on top.  Go here and scroll down to the bottom for the PDF:  http://www.observa-d...lintegrity.html  Anyway, after looking at Observa-Dome's website, I found that when the shutter doors are open, the is about 27" or so of space past zenith.  That means, a crane could drop a hook down and center on the scope and then the major parts could be pulled up and out.  The inside lift point can probably handle the load as well and they mention in the analysis something about the dome structure is more stronger towards the top because of the sections joining up there.  I hope you can get more info from the engineer at Observa-Dome!


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#75 turk123

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Posted 23 October 2014 - 09:13 PM

Tom, after we talked on the phone.  I checked out the Observa-Dome website and found Structural Analysis for the 5m dome, very informative stuff.  These domes are built tough and can withstand a lot of weight on top.  Go here and scroll down to the bottom for the PDF:  http://www.observa-d...lintegrity.html  Anyway, after looking at Observa-Dome's website, I found that when the shutter doors are open, the is about 27" or so of space past zenith.  That means, a crane could drop a hook down and center on the scope and then the major parts could be pulled up and out.  The inside lift point can probably handle the load as well and they mention in the analysis something about the dome structure is more stronger towards the top because of the sections joining up there.  I hope you can get more info from the engineer at Observa-Dome!

 

 

Great work Dan!  Now that is a report!    I did not reach him today.  I will try tomorrow.




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