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Overhaul of a Cave 8" Lightweight Deluxe

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#1 Datapanic

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Posted 28 November 2009 - 05:59 PM

I am the original owner of this '75 Cave and have used it a lot. It has moved around and been from Virginia, New York, England, New Mexico and now Arizona. It has held up well over the years without any damage. In the 80's, I set it up for astrophotography with a custom made RA/DEC slow motion control box, a Tangent Arm DEC motor mount, tube weights, guide scope with a finder and a low profile 2" helical focuser. It has had two paint jobs in the past and this time around, I decided to take the telescope back to it's pre-photographic mode, but keep the focuser and tube weights. I did not take any photos during this overhaul. Here's the Before Picture. It had a lot of weight on the tube, but gave some great pictures as long as there was no wind. It also had setting circle lights and a flimsy latitude adjustment toggle bolt.

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#2 Lew Chilton

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Posted 28 November 2009 - 06:06 PM

Panic,

A beauty and a true classic. Let's see the "after" pictures!

#3 tim53

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Posted 28 November 2009 - 06:08 PM

That would be an awesome planetary scope!

-Tim.

#4 Datapanic

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Posted 28 November 2009 - 06:08 PM

After about 2 months a lot of work, I am really pleased with it. The telescope was =completely= disassembled, sanded, cleaned, lubed and more before putting it back together again. All the zinc-plated fasteners were replaced with stainless steel or hardened steel allen-head fasteners. The tubes were painted satin black while attaching hardware to the tube and finder along with the black paint on the mount were painted a textured black. The stand column and legs were painted silver.

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#5 Datapanic

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Posted 28 November 2009 - 06:14 PM

The business end view shows a very black inside tube, I used some ultra-flat black spray paint and just sprayed it on, reaching inside from either end. Loose paint, mostly towards the middle of the tube was brushed out and as you can see, it's really dark in there!

The 4-vain spider hardware was replaced with stainless allen head fasteners and stainless acorn nuts.

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#6 Lew Chilton

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Posted 28 November 2009 - 06:14 PM

A beauty, indeed! You did a terrific job. (I'm in the middle of a resto on one of my old 8-inch Newts.) Are the optics pretty good in yours?

#7 Datapanic

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Posted 28 November 2009 - 06:18 PM

Here is a view of the stand and mount. When the telescope was setup for photography, I moved the DEC circle to the lower end of the DEC shaft, to make room for the Tangent Arm motor assembly. Notice in the first picture that I had to offset the RA Housing mount to the stand head so that the Clockdrive Housing and DEC circle could clear the stand. Now, the DEC circle is back in the original position, which was the norm for the Cave Lightweight series. While the shafts were removed, I polished them up although they never really had much rust.

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#8 Datapanic

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Posted 28 November 2009 - 06:21 PM

The original setting circles are a little rough, I have been thinking about replacing them, but it would only be for cosmetics. From this view, you can see my new and improved lattitude adjustment toggle. A closeup of that comes later.

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#9 Datapanic

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Posted 28 November 2009 - 06:28 PM

The latitude adjustment system was rather expensive to make, but the end result is a very sturdy toggle. The two forks are 1/2" sailboat toggle forks while the adjustment shaft and rod ends are from a high performance automotive pulley system made by March Performance. The pins in this picture that hold the rod ends to the forks are going to be replaced with Kwik Lok pins.

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#10 Datapanic

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Posted 28 November 2009 - 06:32 PM

The backplate of the clockdrive housing was cleaned up by replacing the brass knurl nut bolts with allen head sockets and plugging the drill-through holes used for the clock drive motor mount. In order to get to the guts, the latitude adjustment screw is released.

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#11 Datapanic

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Posted 28 November 2009 - 06:38 PM

The primary cell was also given a face lift with new stainless hardware and paint. The phillips head set screws in the center have acorn nuts on the end so they have good contact with the base without digging into the metal. That is the original 8" f/7 mirror. I added flat washers on either end of the adjustment screw springs.

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#12 Datapanic

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Posted 28 November 2009 - 06:51 PM

I just love this focuser - I don't remember who made it, that was at least 25 years ago. It is designed to allow a large range of focus distances. It can be as low as 1 1/8" to more than 5" from the outside of the tube. Shown is a 2" spacer with a 2" 38mm SWA Garrett eyepiece that was 1 lb 5 oz.

I followed Robert E. Cox's November '58 article, "Balancing the Tube of a Reflecting Telescope" to find the best position for the tube weights. On this telescope, there are two sets on either side of the rotating ring. I found that unless only one eyepiece is always used, the angle the tube weights are dynamic and change based on the weight and distance they eyepiece is from the tube. But, the end result is a tube that is balanced quite well and swings any way you want to with just the slightest push. Friction on the RA axis is only enough to keep the clock drive clutch engaged and only enough on the DEC axis to keep the wind from moving it now.

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#13 Datapanic

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Posted 28 November 2009 - 06:55 PM

Out in the field, I always set the telescope up for use of the setting circles. The mount head to column bolts are usually removed so I can adjust the azimuth and then lock it down with the thumbscrew. A nut was welded to the column to facilitate that.

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#14 Datapanic

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Posted 28 November 2009 - 07:11 PM

This was a fun project!

One of my goals was to reduce the number of tools needed to make adjustments on it in the field. Before, a crescent wrench, set of allen wrenches, large and small standard screwdrivers and a phillips screwdriver were needed to co anything. Now, just a crescent wrench and a set of allen wrenches are all that's needed.

The mirrors are actually in good shape for having never been recoated, however I plan on sending them off soon just because the technology now is a lot better than it was back when Pancro first coated them.

Last night I set it up in front of the house for testing, the DEC circle was set as well as the latitude and it worked great as always.

Something that is kind of disappointing, because this is, after all a Cave, is that almost every hole drilled at the factory seems to have been eyeballed. For example, the three bolt holes for the stand column to the mount base are not 120-degrees apart and can only line up one way. Same thing for the mirror cell to the tube, the clock drive clutch plate and more. Even the cradle is a little off, and has a north - south end and if the tube is put on the cradle 'backwards', it will be about 1 degree off from parallel to the RA axis. But, all this can be adjusted off and doesn't affect the end performance at all.

I live in Arizona and we go camping out in the desert quite often, I can't wait 'till the next trip! Out there, you can see your shadow from the milky way!

#15 Datapanic

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Posted 28 November 2009 - 07:26 PM

A beauty, indeed! You did a terrific job. (I'm in the middle of a resto on one of my old 8-inch Newts.) Are the optics pretty good in yours?


Thank you! The optics have always been great. The telescope has always been stored inside and the tube ends plugged to keep dust off. I have only cleaned the mirrors about 10 times in all these years. There are no scratches, but there are some specs of light that come through when holding the mirror up to a bright light. Last night, after dialing in the mount, I tested it on the double cluster and was really pleased with the detail, even though the moon was out.

#16 deSitter

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Posted 29 November 2009 - 07:34 PM

Nice work - remember not to tighten that turnbuckle too much, or you may crack the cast aluminum drive housing!

-drl

#17 Datapanic

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Posted 29 November 2009 - 08:10 PM

A new DEC setting circle pointer was made out of plexiglass. The old one was short and the index line did not even reach the lines on the circle. The original RA setting circle pointer face was sanded down, then a narrow groove was cut with a jeweler's saw and the surface was painted. Then a sliver of white plastic was laid in the groove and then the face was painted with a clear satin finish.

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#18 Datapanic

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Posted 29 November 2009 - 08:15 PM

Nice work - remember not to tighten that turnbuckle too much, or you may crack the cast aluminum drive housing!

-drl


Thank you! It is always scary to me working with aluminum, because it's so easy to strip the threads or just break it. For the turnbuckle that mounts to the drive housing, I used a jam nut and flat washers on either side of the housing to spread out the load a little bit and only tightened them enough to be snug and not swivel without a lot of force.

#19 Jae

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Posted 30 November 2009 - 10:14 PM

Very impressive work and restoration over the years. Great stuff !

It's great to see the original owner put such care and love into a beauty of a scope. I always wanted a Cave, esp. an 8 inch but settled for an RV-6 back then.

#20 EddWen

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Posted 01 December 2009 - 11:25 AM

Good job !! Now you can enjoy it for another 40 years.

#21 Datapanic

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Posted 02 December 2009 - 02:12 AM

Good job !! Now you can enjoy it for another 40 years.


Thank you! If I live that long, I am sure I will drive my son and daughters nuts by then! :lol:

#22 Datapanic

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Posted 05 December 2009 - 04:14 PM

The Kwik Lok pins arrived the other day, here's a shot of them on the latitude adjustment toggle setup. They are kind of big, but I like them better than a Clevis pin because they're easier to handle.

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#23 tim53

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Posted 05 December 2009 - 04:28 PM

Dan:

Did yours have the Dec pointer mounted on the dec housing? And was it a simple L-bracket looking thing?

My mound doesn't seem to have any mounting holes in the castings for a pointer, so I'm wondering where it might have been.

-Tim.

#24 Datapanic

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Posted 05 December 2009 - 04:41 PM

Here's a closeup of the Dec circle pointer and mount. It is about 1/4" thick and 3/4" wide made of aluminum. #6 x 32 bolts hold it to the Dec axis housing and a #6 x 32 holds the pointer to the mount. Originally, it had #6 x 32 round head standard slotted bolts holding it on. It is about 2" long with a #6 flat washer spacer between the plexiglass pointer and the mount's end.

The plexiglass pointer is not the original, but the beveled edges are about the same as the original.

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#25 tim53

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Posted 05 December 2009 - 04:44 PM

Okay, so that looks like something I could fabricate without too much trouble. So yours must be mounted just above the Dec lock knob? Funny my mount doesn't have any holes drilled in that area or on the other end (counterweight end) at all. Makes me wonder if it ever had a pointer! :ooo:

-Tim.






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