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Cave-Astrola 8" f/7 Model B Deluxe restoration / upgrade

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#76 macdonjh

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Posted 23 March 2021 - 03:52 PM

Here's the inside of my 1979 Cave 8 inch f/7 Lightweight Deluxe.

I've never seen anything like it, marvelous.

I'm sure a boat builder's bad hair day.

That's our kitchen where I'm working on itcool.gif

Robert

 

attachicon.gifpost-50896-0-44565700-1483327357_thumb.jpg

That looks exactly like the inside of my Parks 10" HIT, which makes sense.  Unfortunately, I don't have any good photos of the inside of that scope.  I painted it with Rustoleum camoflage black, which is pretty flat.


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#77 Thomas_M44

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Posted 24 March 2021 - 01:33 PM

It's just a bottle of medium thick paint in a typical artist's paint squirt container.  I brushed it straight out of the bottle; coverage is pretty decent - I got the whole inside of the 9.5" x 60" tube done with one bottle.

 

I actually coated my tube with the 2.0 first and then the 3.0.  The inside of the tube originally was the fiberglass mat of the Parks tube that had been painted black with some unknown product back when it was made.  The roughness of the mat -- and it was seriously ratty on the inside -- meant I had to pay attention to get full coverage.  I ended up trimming or sanding off a bunch of glass strands to make things easier.  The 2.0/3.0 black doesn't seem super fragile after application.

 

I did look at various ways of killing reflections in addition to the paint...for example you can get even less reflection by attaching black velvet to the inside of the tube, but that brings up all kinds of issues with sticking it down, deterioration, shedding fibers, insects, etc.  Finally decided that a good black paint was the best way of getting it black enough without too much hassle.

Thanks for the rundown.

 

Yes, the elegance of the paint solution is appealing.

 

With flocking, I have concerns about: the potential for moisture retention and mold issues;  possible out-gassing from adhesives causing residue on mirror surfaces;  flocking material degradation with time and fibers/particles release, etc...

 

I'm liking the super-black paint Idea


Edited by Thomas_M44, 24 March 2021 - 01:34 PM.

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#78 Dave Cook

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Posted 24 March 2021 - 03:06 PM

I'm sure a boat builder's bad hair day.

That's our kitchen where I'm working on itcool.gif

Hah boat builder's bad hair day!!  I would love it if someone would post about how Parks made their tubes (or perhaps it's already up here somewhere).  It looks like they started with a sheet of some flat but rollable plastic material, slathered it with a heavy coat of black gelcoat, then pressed a bunch of random direction glass mat into it, rolled it up and dropped it into a tube to cure.  Lots of the fibers popped up along the way on the inside because of compression from rolling it up.  That's probably why they didn't use glass cloth...the wrinkles from rolling would have been even more objectionable.

 

And how do you remain un-murdered after using the kitchen?!?


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#79 YourNotSirius

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Posted 24 March 2021 - 03:29 PM

smarty.gif

Hah boat builder's bad hair day!!  I would love it if someone would post about how Parks made their tubes (or perhaps it's already up here somewhere).  It looks like they started with a sheet of some flat but rollable plastic material, slathered it with a heavy coat of black gelcoat, then pressed a bunch of random direction glass mat into it, rolled it up and dropped it into a tube to cure.  Lots of the fibers popped up along the way on the inside because of compression from rolling it up.  That's probably why they didn't use glass cloth...the wrinkles from rolling would have been even more objectionable.

 

And how do you remain un-murdered after using the kitchen?!?

Isn't the kitchen the best place to "cook up" some new concoction, be it half baked or totally toast? smarty.gif  

 

It's not a problem here because the old man is in charge of the kitchen! biggrin.png

 

Q


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#80 Dave Cook

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Posted 02 April 2021 - 07:53 PM

Time for some more photos - OTA physical configuration is done.  Had a serious timeout in the last few days to diagnose and replace a blown Z servo in the mill.  DMM put a new servo in my hands 3 days after order; impressive considering it came over the border from Canada.  There are just a couple of items to finish up on the OTA - anodize a few parts and repaint the finder tube, which is pretty scratched up and has a couple of dents, and get tube covers so I can put the optics in.
 
Here it is set up in the two different configs that I envisioned:  one with the 80mm secondary in rings on the tube up toward the eyepiece for visual use, and the other with a refractor on a saddle mounted directly to the outer frame of the rotating rings, which put the eyepiece very low but will be a lot more rigid for imaging.  In the 2nd config I'd be more likely to have a larger and longer EFL scope on there since the shorty 80 will probably have some field obstruction from the main tube.
 
OTA configuration with on-tube rail for secondary scope
 
OTA configuration with on-rings saddle for secondary scope

Edited by Dave Cook, 02 April 2021 - 07:56 PM.

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#81 Dave Cook

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Posted 06 April 2021 - 05:33 AM

Onwards!  Finder tube before and after stripping.  It needed #600 sanding to take care of some dings.  I was a bit surprised to find it was aluminum - no rust like there was on the Meade guidescope.  It will get primer, a bit of spot putty and baked epoxy paint.
 
Finder tube before stripping
Finder tube sanded
 
Boring the dec shaft interface on the mill with the baby Criterion boring head.
 
Boring the new dec shaft interface
 
The result:  the shaft bore is 1.5003" versus my design target of 1.5005".  The shaft spec is 1.5000 +0 -.0006 so we ought to have a really good location fit.  The setscrew flat on the shaft will prevent air pressure issues due to the very close fit.
 
Shaft bore size near perfect, 1.5003

 


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#82 mpsteidle

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Posted 08 April 2021 - 02:34 PM

This is an elegant solution to the wife problem.  Need to get rid of some telescopes?  Combine them into one giant one!


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#83 Dave Cook

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Posted 09 April 2021 - 10:01 AM

Top side of the dec shaft interface is done...counterbored for 5/8" bolt, tapped mounting holes for the ADM saddle, CNC chamfers, and a bit of sanding to get rid of small dings before anodizing.  Final step coming: drill for and install the ez-loks in thru the side for the setscrews.
 
Top side of new dec shaft interface

 


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#84 Dave Cook

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Posted 16 April 2021 - 07:32 PM

The dec shaft interface machining is done and it's ready for anodizing.  I'll have to make sure the bore does not get anodized as there's no dimensional margin for that.
 
Earlier this week I ordered the new stainless 30" dec shaft from Misumi...it's maybe 10 days away now.
 
This afternoon I dealt with longstanding focuser frustration in the old William Optics Crayford.  The locking thumbscrew seemed to be stuck and you couldn't adjust the tension enough to stop it from moving with a camera attached.  It turned out the aluminum locking thumbscrew was indeed jammed, and in a position where it prevented the setscrew from increasing the tension beyond a fairly modest point.  It was jammed badly enough that the aluminum screw broke when I tried to remove it.  My best guess is that I cross-threaded it in the elder days.  To make matters more interesting (ahem), the broken-off part prevented the unit from being disassembled, so I had to get out a small endmill and mill down the screw remnant until I could pull out the small aluminum contour block it was screwed into.  Then I had to drill out the screw and re-tap the hole, finally installing a new brass thumbscrew.
 
All's well now with adjustability restored, at the price of some cosmetic rash, and it didn't actually take as long as it sounds.  I am interested in eventually putting on a dual-speed focuser; TS-Optics has a pretty nice looking one with a selection of base plates for Newtonians, which is not so common anymore.  But this one should be fine for now.
 
Focuser teardown and fix

 




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