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Mr Magoo's Cave

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#76 Mr Magoo

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Posted 03 December 2018 - 10:28 PM

Congratulations on the great find!  I have a '75 Cave 12.5" which I am planning to restore...and the identical weight, also frozen hard on the declination shaft...will be interested to see how you get the two separated!

 

John

Do you happen to know what that thing weighs John? I don't have a scale to weigh it, but it is seriously heavy and awkward. I am very tempted to take it to work and cut in to two pieces when I get it off. 



#77 Mr Magoo

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Posted 03 December 2018 - 10:40 PM

Some progress today in the short time I had to work on it. Sorry no pictures today. 

 

After soaking the weight and the shaft collar in PB Blaster I was able to remove the collar and the shaft from the Dec housing. I was happy to discover that both ends of the Dec shaft housing have needle roller bearings. The grease on the shaft and the bearings as sticky as fly paper. This also allowed me to separate the housing from the RA shaft.

 

I notice that the Dec housing had a lot of play in it and that is because the bolt holding it on to the RA shaft was partially backed out. Kind of scary with that massive weight hanging out there. 

 

Some good news with the weight too. I now have fluid bleeding out of one side of the weight. It still won't budge though. Someone painted the exposed parts of the shaft so I need to get that stripped off. 

 

Regarding the shafts Cave used, does anyone know what the material is? Is it actually hardened shaft steel or plain old polished mild steel? Has anyone replaced theirs with a stainless shaft? I have a piece of 1.5" 316L stainless long enough to do it. 



#78 Mr Magoo

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Posted 03 December 2018 - 10:59 PM

Put a "cheater" on the long end of a L shaped Allen Wrench .........More Leverage waytogo.gif wink.gif ..... IF you round out the socket set screw , split the " Stop Collar " on one or both sides of the set screw with a die grinder . Buy a new Stop Collar , they're CHEAP and look Good new and Shiny lol.gif waytogo.gif

I used these clamp on collars from McMaster on my Criterions and I really like them. Not original I know, but they don't mess up the shafts. https://www.mcmaster.com/6435k43


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#79 John Higbee

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Posted 04 December 2018 - 12:20 AM

Do you happen to know what that thing weighs John? I don't have a scale to weigh it, but it is seriously heavy and awkward. I am very tempted to take it to work and cut in to two pieces when I get it off. 

Ken - at least 50 pounds...and could be heavier. Like your suggestion to turn it into two weights down the road.

The mount was installed on a pier on the observing deck of a college science building for around 25 years, with only a tarp for protection...and the tarp was in very bad condition when I bought it.  The mount looked like "10 miles of bad road".

The RA and Dec shafts rotate...but the shafts are both rusty; I may replace both shafts with stainless replacements once I disassemble the mount for restoration this spring, and get that monstrous counterweight freed up!.

The paint on the mount is extremely deteriorated, and the aluminum setting circles (10" diameter) both have a lot of surface deterioration (blotchy, dark spots). Haven't even checked out the Dec and RA drives yet (the dec drive is a nice 360 degree gear drive...not the tangent drive that my '79 uses).

The OTA was stored in a waterproof, gasketed box (also on the observing deck), so it and the finder and guide scopes are in very good condition.

I highly recommend Jeff and Majestic...had him recoat the primary and secondary mirrors for my '79 Cave 12.5" f/6 Model D...they came back in flawless condition!


Edited by John Higbee, 04 December 2018 - 12:26 AM.


#80 Don Hall

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Posted 04 December 2018 - 01:55 AM

Ken,  I did replace the shafts on my '69  Cave 10" F7 with stainless about 7 years ago and they are in perfect condition today.  Since I was in the metals business the stainless I used was cold drawn and centerless ground to bearing tolerances for 1-1/2" ID bearings.   Is your 316L bar cold drawn (would have very smooth surface and very straight)?   CD tolerances are general good for bearing applications.

Don



#81 Geo31

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Posted 04 December 2018 - 06:45 AM

Tom Terleski (Turk on CN, and Cave-Astrola.com owner) used precision ground shafts in his restorations.


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#82 DAVIDG

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Posted 04 December 2018 - 10:28 AM

 Before you go out and  spend the money to have the mirror recoated, test it. There have been a number of Cave mirrors that have been duds. I have posted test images of them. Ask Steve Swayzes as well since he has refigured a number of them. Just because the mirror is Cervit doesn't mean that it s figured any better then one made out of Pyrex or even plate. It is the skill of the optician that counts not the the material the mirror is made of.

   Also when it comes the zero expansion glass, while the figure doesn't change with temperature, that doesn't mean that  you can use the scope any faster. The optics need to come to equilibrium, if not they are giving off heat, that causes tube currents and that distorts the image. A big thick piece of Cervit is going to take longer to cool down then a thin piece of plate glass. 

 

               - Dave 


Edited by DAVIDG, 04 December 2018 - 01:47 PM.

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#83 Mr Magoo

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Posted 04 December 2018 - 05:01 PM

 Before you go out and  spend the money to have the mirror recoated, test it. There have been a number of Cave mirrors that have been duds. I have posted test images of them. Ask Steve Swayzes as well since he has refigured a number of them. Just because the mirror is Cervit doesn't mean that it s figured any better then one made out of Pyrex or even plate. It is the skill of the optician that counts not the the material the mirror is made of.

   Also when it comes the zero expansion glass, while the figure doesn't change with temperature, that doesn't mean that  you can use the scope any faster. The optics need to come to equilibrium, if not they are giving off heat, that causes tube currents and that distorts the image. A big thick piece of Cervit is going to take longer to cool down then a thin piece of plate glass. 

 

               - Dave 

So what advantage is there to using Cer-vit vs. regular Pyrex?



#84 DAVIDG

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Posted 04 December 2018 - 06:12 PM

 For making flats Cervit or Zerodur is the substrate of choice since you can figure and test without waiting and of course to won't change shape. If you make a flat out of other materials with a  larger Coeff. of thermal expansion, you can wait hours before it settles down to know it's real shape.  If you have a super precise surface like a true 1/30 wave flat and you need to maintain that surface, then you want to use Zerodur or Cervit because the expansion of the other materials will not hold that need accuracy.

    When it comes to other optics  it has the advantage that of course it not changing shape so again you can  test, then get right back to figuring. For certain designs like a Cassegrain with a secondary with a high amplification,  a small change in the figure can make a large amount of image shift. So that is another application were it has an advantage.  But again if you have this big chuck of Cervit and it is at 70°F and you take it outside on a 30° night, the image won't be any good until it cools off, since your still going to have heat currents coming off the optics.  Look at  Mak optics like a Questar, the front meniscus is BK7 optical glass  which a larger CTE then Pyrex. So if the primary  mirror is Cervit even thou it isn't changing shape as it cools  the meniscus is. So again until the scope fully cools you won't get the best image.  Questar 7 are famous for taking hours to cool down and they usual have quartz, Cervit or Zerodur primaries. 

   If you look at major observatories like Keck were the mirror segments are all made of Zerodur, they still air condition the dome so the optics are close to what the night time temperature will be.  

  So it all depending on the application of the optics. 

 

                          - Dave 


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#85 CHASLX200

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Posted 04 December 2018 - 06:50 PM

So what advantage is there to using Cer-vit vs. regular Pyrex?

You can take it outside from a warm house to cold outside and start viewing much sooner vs other types of glass.  But i never view on cold nites and don't need to worry.


Edited by CHASLX200, 04 December 2018 - 06:52 PM.


#86 Geo31

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Posted 04 December 2018 - 07:55 PM

Perhaps  you should spend those cold nights reading the post above yours?  ;)


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#87 CHASLX200

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Posted 04 December 2018 - 07:57 PM

Well that may be a while as it sure don't get cold like it used to be.



#88 clamchip

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Posted 04 December 2018 - 09:35 PM

Here's a little something on ceramic mirrors:

http://www.rfroyce.com/pyrex.htm

I once owned a 10 inch f/6 with a Astro-Sital primary and I found it would not give up it's heat

very easily. If I brought it outside it would never acclimate, if I left the scope outside it was great.

 

Robert


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#89 CHASLX200

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Posted 05 December 2018 - 06:12 AM

Here's a little something on ceramic mirrors:

http://www.rfroyce.com/pyrex.htm

I once owned a 10 inch f/6 with a Astro-Sital primary and I found it would not give up it's heat

very easily. If I brought it outside it would never acclimate, if I left the scope outside it was great.

 

Robert

I am lucky i don't have to deal with big temp drops. 



#90 Mr Magoo

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Posted 05 December 2018 - 10:29 PM

Congratulations on the great find!  I have a '75 Cave 12.5" which I am planning to restore...and the identical weight, also frozen hard on the declination shaft...will be interested to see how you get the two separated!

 

John

John is this the same scope that is in your Gallery?



#91 Mr Magoo

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Posted 05 December 2018 - 10:47 PM

I took a closer look at my tube tonight and boy is it a mess. First off it is a 14" tube. It is fiberglass. Shows a seam running the length of it. The inside is really uneven the way the fiberglass was laid. I will have to try and get some pictures of it, but it is hard to show in a picture. The outside is just as bad. Really uneven and even has some sizable ridges and depressions. I don't know if it was damage or if the shimming of the rings could have caused it. The thing is that the gel coat is not cracked where it has these odd places. Can a fiberglass tube deform in the heat?

 

I am toying with the idea of rolling my own aluminum one. The trick to rolling something like this is to be able to roll it with no flat spot on the seam ends of the sheet. I know that probably won't make sense to anyone who has not done this before. It has to do with how the material enters the rolls. I work in the industrial section of my sheet metal shop and our rolls that are long enough to roll this have really big rolls. Not good for light gauge smaller diameters. We do have one with 9" diameter rolls that may do it, but it is really old and stressed out. I may do a test piece. 

 

I'm not kidding at all when I say that if someone had a 15" tube anywhere in the country I would make the drive to come and get it.


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#92 CHASLX200

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Posted 06 December 2018 - 06:15 AM

14" OD sure is odd for the OD if it is a Parks tube. Most times any 12.5" i have had was 16" OD.  They all seem to have a clean seam and the inside was always rough to help with light scatter.


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#93 Geo31

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Posted 06 December 2018 - 10:02 AM

The tube for the Gustavson Cave has the same seam, out-of-round condition. 


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#94 Mr Magoo

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Posted 06 December 2018 - 05:53 PM

14" OD sure is odd for the OD if it is a Parks tube. Most times any 12.5" i have had was 16" OD.  They all seem to have a clean seam and the inside was always rough to help with light scatter.

Cave catalogs said that the 12.5" had a 15" tube which would fit the rotating rings. I have not heard of one with a 16" tube. 



#95 CHASLX200

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Posted 06 December 2018 - 06:42 PM

Cave catalogs said that the 12.5" had a 15" tube which would fit the rotating rings. I have not heard of one with a 16" tube. 

I had Parks build a OTA around a 12.5" Mirror and it was 16" OD in 1990.  Maybe the size changed over the years.


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#96 Geo31

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Posted 06 December 2018 - 10:42 PM

Cave catalogs said that the 12.5" had a 15" tube which would fit the rotating rings. I have not heard of one with a 16" tube. 

 

My "Field Cave" had a 16" tube.


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#97 CHASLX200

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Posted 07 December 2018 - 06:17 AM

I think Parks changed the OD of their tubes over the years.  I remember two sizes of their tubes for a 10" mirror from older to newer.


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#98 Mikefp

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Posted 07 December 2018 - 09:27 AM

Cave catalogs said that the 12.5" had a 15" tube which would fit the rotating rings. I have not heard of one with a 16" tube.


16" on my latest of all documented cave scopes, March, 1980
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#99 John Higbee

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Posted 07 December 2018 - 09:48 AM

John is this the same scope that is in your Gallery?

Ken - no.  That is the Cave I got in 2012 from a fellow CNer in upstate New York.  It dates to March 1979...the optics are very good; the tube is a Sonotube, focuser is a 2"/1.25" Meade, the declination drive uses a segment arm, and the setting circles are Bakelite.  The mount and the pier are in excellent condition, and the legs are set up on casters...so I can roll it out of my garage on demand.

 

The Cave I've mentioned on your topic dates to mid-1975...was privately owned, then donated to a university from which I purchased it (they had used it for several decades).  Haven't star tested it yet.  The tube is a Parks product, focuser is 1.25" only, the dec drive uses a shaft mounted gear, and the setting circles are engraved aluminum.  It came without a pier or legs, but the university threw in three very large Edmund Scientific legs (probably from a '60's vintage 8" reflector that they no longer have). 

 

new Cave tube.JPG

 

John


Edited by John Higbee, 07 December 2018 - 10:43 AM.

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#100 pbealo

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Posted 07 December 2018 - 09:55 AM

From RIT??




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