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Cave Restoration

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#1 joerbiker

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Posted 21 October 2012 - 10:52 PM

About a month ago I purchased a rather unloved 10" F5 Cave off of Craigslist. I'm just able to now put some time into trying to get it back into working condition and could use some advice.

Pictures of the scope are here: Cave Restoration

A couple of questions for this group.

I'm having trouble bringing the optics into collimation. Could it be that the SonoTube is just so old and broken down that it's flimsy?

Along those lines, the exterior paint is in very bad shape. Would it be better to just start over with a fresh tube? I know that decreases the "collectible" value, but I'm not sure that there's a whole lot of "collectible" there to begin with at this point.

Any help, comments, and/or advice would be greatly appreciated.

Thanks in advance,

#2 Mirzam

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Posted 22 October 2012 - 06:54 AM

I doubt the problem is the tube. Possibly the secondary holder? I added a small spring to my RV-6 holder and it made a big improvment (simply by providing an opposing force against the adjustment screws).

There are folks here who can help you fix-up the tube. I don't think it will be hard to do.

JimC

#3 clintwhitman

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Posted 22 October 2012 - 08:05 AM

MyCave Page
Joe your secondary holder is setup funny the three screws are supposed to be pushing on the secondary holder, not threaded into it.
(aveman :smirk:

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#4 trainsktg

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Posted 22 October 2012 - 08:17 AM

That tube doesn't look so bad and its intact. Better to re-use it. Overall the kit looks like it'll be a fairly straight-forward restoration:) .

Keith

#5 tim53

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Posted 22 October 2012 - 09:29 AM

That secondary holder looks like the way Meade did it. Pivot the hub on an acorn nut and thread the adjustment screws into the hub. The screws go through the adjustment plate without threads.

That tube could be repaired. I would strip the paint off (should be easy to do) and use a liquid epoxy like Abatron (expensive, but worth it!) that'll wick into the porous cardboard, especially at the ends, and really harden it up. Then prime with a good primer (something Cave didn't do) and paint. Could be done with rattle cans if you're careful, and easiest if it's not full gloss. Alternatively, you could check with Parks to see if they have a fiberglass tube that size (I don't know if the cardboard tube is similar to the fiberglass in size). It won't be cheap, though.

This cave must date from the end of the line, based on the focuser and the cardboard tube. This lightweight 1" shaft mounted 10" must have been the inspiration for the Meade Starfinder 10" Equatorial.

-Tim.

#6 joerbiker

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Posted 23 October 2012 - 06:36 AM

Thanks Jim, Keith, Clint, and Tim.

I do have some doubts about the secondary holder. The mirror seems loose/able to move around easily. Also, the plate that the screws go through is bent up.

Clint, I've reviewed your pages several times, very well done! Do you have any close up photos of the secondary? From the side?

Anybody know where I can get a leg for the mount? I've looked into having one cast and it's very expensive. My current thoughts are to fabricate something out of aluminum channel that looks close.

Thanks again.

#7 dgreyson

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Posted 09 November 2012 - 12:24 PM

Joe
A common trick in high power rocketry is to wick adhesive into the tube edges and clamp till it sets with wax paper and clothespins on thick cardboard backer strips to stop fraying / delaminating. or just superglue/wax paper and pinch it together with your hand as you work around the rim. screw holes can be hardened in cardboard tubes with a thin wick of superglue. Let it dry before putting the screw back of course.

The missing leg looks like it was one piece cast at the top and bottom of the leg and the round inner stringer bars and curved mounting plate were welded on afterwards. Any competent welder should be able to weld up something closer looking out of bar and round stock cheaper than sand casting it. Nice cave scope!

#8 dgreyson

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Posted 09 November 2012 - 12:44 PM

Typical diagonal setup i've seen on 70's era spiders:

the diagonal holder has a central stalk threaded into the spider hub.

three long alignment screws should thread thru the spider and press against the back of the diagonal holder. A light compression spring should be slipped over each alignment screw in between the spider hub and the diagonal holder.

A stop nut on each alignment screw on the screw head side to lock the alignment screws down.

It would be unusual for the alignment screws to thread into the diagonal holder as they could hit the back of the diagonal mirror then and crack it if overtightened.

#9 dgreyson

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Posted 09 November 2012 - 11:18 PM

I need to repaint my Cave tube after patching holes and gouges so I pulled my spider to take a look. I think Tim is right, it isnt like my University optics spider, the screws are set up to pull instead of push. They made the mounting bracket smaller than the diagonal so the screws projecting into the diagonal cell are below the slant and miss the mirror. Neat.

Collimation: try this procedure Joe, if it still wont, describe whats wrong exactly. http://www.skyandtel...iy/3306876.html

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#10 joerbiker

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Posted 10 November 2012 - 11:56 PM

I'll be able to give it another shot tomorrow. We have been very busy at the shop, which is a good thing.

I'll pull the mirror cell to mark the center, and the secondary for photos.

Thanks!

#11 clintwhitman

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Posted 11 November 2012 - 09:11 AM

Tim is right it is like a Meade holder, should work fine. I have a set of legs but I would hate to break them up. Anyone else come up with a single leg? :confused:

#12 joerbiker

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Posted 22 November 2012 - 10:36 AM

Clint, thank you. I would never ask anyone to break up a complete set. I have a good friend that is a machinist, and I'm not to bad myself, so we should be able to come up with something passable until I find one "out there".

#13 joerbiker

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Posted 22 November 2012 - 11:03 AM

Hi all,

I've added some specific pictures of the secondary here: Cave Secondary

As you can see the foam that held the secondary tight to the lip of the holder has severely degraded. It powders when you touch it. Also, look at the swash plate. I think a lot of the problems came from the amount of disfigurement.

I've replaced the foam, and straightened/reinforced the swash plate. That should help. A question; would it be a benefit to add small springs between the head to the adjusting screw and the swash plate? I think it might. As it is right now, the secondary doesn't "float". I think that's how it got bent so much.

Once I get it into somewhat reasonable collimation I'll be able to see if I get any decent views. I'll then decide if it it worth the time to do a complete re-hab.

If it is, (And my guess/hope is that it will be!) I'll probably upgrade as I go. Stainless fasteners with allen heads as opposed to galvanized slotted head, that type of thing. Obviously a tube repair and repaint. Fix that leg.

I'm more interested in creating a good working scope than keeping it original. I'll keep the old parts in case someday someone wants to revert back.

Once again thank you all for your insightful comments and suggestions. This is a great group of folks.

Happy Thanksgiving!






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