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

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#26 Thomas_M44

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Posted 22 December 2020 - 01:31 PM

I admire the fact that you are being so thorough in prepping and properly priming *before* painting waytogo.gif

 

The prepping is where all the hard work is in repainting. So often people get impatient and cut corners in the prep --and the endresults are usually less than stellar

 

Your little restored Astrola is going to be a real gem.

 

On RKE's:

 

About the best you can get for planetary and double-stars, bar none. And with RA drive, 50-degrees AFOV is ample at high powers.

 

TeleVue Eyepieces:  Yeah, a couple of Panoptics or Naglers in the 19mm to 35mm range perhaps? wink.gif


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#27 Dave Cook

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Posted 23 December 2020 - 10:02 PM

Furiously busy with the project the last couple of days.  Let's start with paint-stripping on most of the black parts.  They got a dose of the Citristrip and covered over with some 4-mil plastic dropcloth and left overnight.  Something I found that works oddly well is to slather one larger face of the part with the stripper, and then plop it face down onto the plastic.  A few hours later the stripper/paint glomp will often transfer right to the plastic with no work.
 
Various parts with Citristrip, covered in plastic
 
After getting the paint off, I had a good look at the mirror cell base plate.  $%#!!  Rough grind marks all over it and some really deep gouges (0.5mm+).  I had already planned to face-mill it, but today I felt the need to do something about the edges...didn't want to scan the contour for a re-profiling on the mill, so I tried sanding with a coarse ~100 grit drum on the trusty Dremel.
 
Mirror cell base before edge cleanup
 
The Dremel sanding operation actually was a big success.  In under an hour I had all but the deepest grinder gouges out, smoothed out the curve radii and chamfered all the edges for good measure.  Next picture shows the result.  I still need to go back and sand off the casting roughness on the inner circle.
 
Mirror cell base after edge cleanup
 
Here's a bunch of small parts getting their 2nd coat of stripper.  Somehow there are always places that don't get enough.  Getting the dissolved paint off is a messy process involving mass quantities of shop towels, gloves (the stripper destroys nitrile gloves fairly fast), plastic dropcloth that gets sticky and wraps itself around everything, and relentlessly bad language.  I really need to find a local machine shop with a media blast cabinet, this would have been so much less trouble with glass bead blasting.
 
Small parts, second round of stripping
 
Today was also epoxy primer day for the legs and tube.  The tube got an all-over sanding first, and then everything got about 3 coats of primer with 5-minute flash-off in between.
Tube and legs after primer
 
The filled-in holes have completely disappeared.
 
Even more things got done that I don't have photos for.  I did some measuring and figured out that I can counterbore the holes for the spring-loaded cell adjusters to about 0.120 deep with a 3/8 end mill and use some #10 low profile SHCS to bolt it down to a plate for the face milling.  So I went to the hardware store and got the screws.
 
I also went down to Industrial Metal Supply (the go-to place in San Diego) and picked up a couple of 1/2"x4x12 6061 plates to use for that operation, and a chunk of 3.5" round stock to make a new dec shaft interface for a flat OTA mounting plate.  I need to give it more engagement length with the dec shaft, and have more diameter for a bolt ring.
 
It also occurred to me that I can address the issue of balance issues from immovable rotating tube rings (along the tube axis) by putting a ~16" Losmandy rail on the outer rotating rings (11.75" OD for the radius blocks) and a matching saddle on the base plate.  That will let me shift the tube +/- 4" for balance and should pretty much get rid of the need to add/remove tube counterweights, though it looks like there will still have to be some.

 


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#28 jcruse64

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Posted 24 December 2020 - 12:51 PM

Nice work!!!


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#29 Dave Cook

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Posted 24 December 2020 - 08:47 PM

I sanded the high-build 2k epoxy primer on the legs today, but it was every so slightly mushy...very sandable but felt just a tad soft under the sandpaper.  Comparison with the tube (same batch sprayed at the same time) showed that the primer on the tube was totally normal, so it's definitely the etching primer undercoat on the legs.  I gave it two days to dry - must not have been quite enough.  Not a serious problem but I'm going to let everything settle down before spraying the color coat.

 

Just one photo today:  a rotating ring (inner part) after having the black paint removed.  It's beautiful - great surface finish from the original machining, looks like it was made yesterday.  A world above any other mechanical part I've pulled off the instrument yet.  I'm going to leave them as shiny aluminum on the finished telescope - feels like it would be a crime to paint them again.

 

Happy holidays everyone!

 

btw thanks for all the encouragement - it's a great bunch here.

 

Rotating ring after paint removal

 

 


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#30 Dave Cook

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Posted 27 December 2020 - 02:07 AM

Boxing Day update!!  Marching along during my 2 weeks off work over the holidays.
 
Sanded the epoxy primer on the tube and hit a few dings with spot putty (no photo, sorry). Note to self - need more putty.
 
Took a clue from another thread, got some Mother's Mag and Aluminum Polish at O'Reilly's and tested it out.  Good stuff.  As things stand I'll be polishing the tube end rings and the rotating rings in their entirety.
 
I was looking over the 8x50 finder, turns out it has the "AvA" maker's mark, which indicates Takahashi.  It is indeed razor sharp...the only flaw is that the threaded focus only has a couple mm of travel and won't come out far enough to let me use it without glasses - I need +4 diopters of correction so this comes up kinda often.
 
The Vixen bar and 125mm rings arrived from ADM today.  They look super nice and well packaged too.  Too bad every single aux/guide scope that made my shortlist is out of stock!
 
Face milling the primary cell back plate.  The casting was way more warped than I thought...it's basically level on both sides now; still needs to get a single finish pass with the giant Suburban Tool fly cutter.
Face milling the primary cell back plate
 
The legs got a final sanding (the primer turned out OK) and their color coat today - KlassKote dark gull grey epoxy.  This actually completes work on the stand (pier/legs/levelers).  After the paint cures for a couple of days I'll get the EQ head up on the stand for disassembly.
Legs painted

Edited by Dave Cook, 27 December 2020 - 02:16 AM.

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#31 Dave Cook

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Posted 28 December 2020 - 08:07 PM

After some consideration, I painted the tube white.  Many other things are being changed so I decided to keep this bit in character.  Plus I just always liked the observatory white look. It's at last back to something resembling actual white, and it's not going to fade now.  Before repainting the faded gelcoat was more the color of the Swiss Coffee wall in the background.  I got the paint on just ahead of the incoming SoCal rainstorm (and darkness) yesterday afternoon.  I mixed about 8 oz of paint and sprayed in a very old Craftsman 1-qt gun at 40 psi, going up and down with the wet edge vertical.  You have to not guess too low on the amount since this paint requires a 30-40 minute induction period before you spray it; you can't just run back and mix some more on the spot like you can with the 2k primer.
 
I'm hoping that the fairly tough paint combined with the fiberglass patches will prevent the stress cracks in the old gelcoat from propagating and re-appearing in the new paint, but I can't swear that won't happen.
 
Tube painted, 2k epoxy white

 

Other than that I've been doing mostly non-photogenic stuff like cleanup stripping and smoothing on the various cast aluminum parts.  I got the second inner tube rotator ring fully cleaned of paint and it's just as beautiful as the first.  After a good sanding on the inside surface to ease sliding them onto the tube, and a go with the Mother's mag polish they should be ready to re-install in their new location.  No paint for those babies anymore, they'll match the tube end rings as polished aluminum.

 

The outer rings need some surface work; there are tool marks on the sides to eliminate.

 

Last night I did some research looking into replacement shafts and found that Misumi will make semi-custom shafts in whatever length you want with one or both ends tapped (and/or setscrew flats), in 304 stainless.  I'm thinking of getting a dec shaft with both ends tapped and a setscrew flat at the top so I can add a thread-in counterweight safety ring at the bottom.

 

The 3 steel shaft collars have some rust and need to go into the Evapo-Rust for a day or two along with their grub screws.  It also looks like the rings had some kind of plating that is now partially gone; I think I'll need to touch them with the lathe to clean all that off and get rid of some pitting before repainting them.


Edited by Dave Cook, 28 December 2020 - 08:17 PM.

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#32 Dave Cook

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Posted 02 January 2021 - 02:09 AM

Sanding sanding sanding...I've almost completed the rough sand/grind with #150 on the OTA parts.  Very time consuming, there are a lot of casting pits and tool marks; I've probably spent 30+ hours since Christmas on this task.  Would have been drastically faster with a good belt sander.  Just for fun, here's a machinist-drool-worthy one I came across while looking around: https://tradesmangri...belt-48-tmb-48/

 

But the end rings and rotating rings are gonna look good.  I'm down to the last few rosette knobs.  Despite being painted, they had really heavy oxidization underneath as if it had been a really long time between when they were cast and when they were painted.  Hopefully all the finer grits won't take as long as we'll just be smoothing out the texture from the previous grit.  Planned sequence is 150 -> 320 -> 600 -> 1000 -> 1500 (maybe?) -> Mother's polish.

 

Meanwhile I ordered some BLCK 2.0 and 3.0 from Culture Hustle to experiment with on the inside of the tube since I'm about ready to start reassembling the OTA and need to get it blackened first.



#33 Dave Cook

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Posted 02 January 2021 - 08:31 PM

Here's what I've been dealing with on some of the aluminum parts.  This rosette knob underside shows tool marks on the right and rough casting texture on the left.  It's about 1/3 of the way done at this point.  Ultimately I went down to #100 on some of these knobs to go a little faster.
 
The little sanding fixture is just a chunk of the always handy 1x2 with a 3/8 bolt.
 
Rosette knob in sanding fixture showing tool marks and casting texture


#34 Dave Cook

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Posted 03 January 2021 - 07:49 PM

Last day of my vacation frown.gif so progress will slow down some.

 

Here's the main counterweight after wire-brushing.  It remains very dark rather than shiny - I imagine it's cast iron.

 

Counterweight after wire brush
 
Same counterweight after getting a coat of the self-etch primer.  To paint it I put it on a 1" dowel between two chairs.  I had to do some indoor/outdoor gyrations to keep the parts and paint can above the recommended 65˚ F temperature since outdoor temps have barely cracked 60˚ the last several days.  Kept paint and parts inside, set up fixturing outdoors, went outdoors and quickly painted it, then brought everything back inside.
 
Main counterweight primer on
 
Here's the fixturing I came up with for the shaft collars, re-using the old 1/4-20 leveling leg screws and the tube counterweights.  I dunno why but the CN gallery sometimes takes photos that the iPhone, Finder and every other Mac app says are horizontal and turns them vertical.
 
Shaft collar paint fixturing

 

Lastly some bling - here are the inner rotating rings.  The right one has been polished with the Mother's Mag, looks fantastic and didn't actually take too long.

 

Inner rotating rings, one polished

 


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#35 Dave Cook

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Posted 05 January 2021 - 12:40 AM

I did get a bit done today...fly cutting the base of one of the tube counterweight brackets.  Perfect fit afterwards...I might have had to relieve the center a little if they were on top of one of the tube undulations, but everything was good right off the bat.  Setup was a bit of Haimer measurement plus calibrated eyeballs since there are no accurate reference surfaces anywhere on these little guys.
 
9.6" diameter cut on a PM-30MV, I'm pretty stoked !! I think there's an 11.7" diameter flycut coming up (OD of the outer rotating ring) but now it totally looks like it should work.
 
Fly cutting a tube counterweight bracket
 
Tube counterweight bracket perfect fit

 


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#36 Dave Cook

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Posted 11 January 2021 - 04:32 AM

Paint work this weekend.  Here's a string of knobs after getting the self-etch primer.
 
Stringer of knobs primered
 
After a couple of tries I got the VHT wrinkle black paint working pretty nicely.  You have to put on a *lot* of paint to get it to wrinkle...more than I thought, you need 3-4 coats with a short flash time of 5-7 minutes in between. It feels like you're hovering on the edge of having it run.  With just one heavy coat it will turn out gloss black with zero wrinkles.
 
Finder bracket with VHT wrinkle paint

 

Checking out the new position of the now polished rotating rings.  I put the mount on top of the newly complete pier assembly and measured clearance for the bottom of the tube at the zenith position.  With the rings moved forward 3" I still have the back end of the tube 4.5" above the ground, with the levelers retracted fully.  Seems OK, it will still go a bit past the meridian.

 

Checking new position of rotating rings
 
Dry fit of the ADM Vixen rail.  It seems like a good length to allow flexible position of the guidescope/secondary 80mm - if only I could get one smile.gif. The C8 radius blocks fit the Parks tube perfectly.  It won't actually sit at this location; it'll be several inches away from the rotating rings toward the fore end of the tube.
 
Dry fitting the ADM Vixen rail
 
Stability test selfie!  I'm sitting on the complete pier / legs / levelers subsystem.  There's no detectable wobble even if I try to scoot it across the floor.  That's probably 250% of actual load so I think we're good there.
 
Pier stability test selfie!

 

 


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#37 Dave Cook

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Posted 15 January 2021 - 01:08 AM

Photo of the day - a cookie sheet full of the wrinkle finish OTA parts ready for baking (200˚F for an hour).  Yummy!
 
Wrinkle parts baked

 

I checked out the behavior of the axis gears and clutches while I still have the mount assembled on the pier.  RA seems OK, no great backlash in the worm gear interface and the clutch is even still fairly smooth.  The dec axis is much worse; as I remembered, there is really huge backlash in the worm gear, and the clutch really sticks.  The latter should be easily cured with some lube and adjustment.  The worm is another story...the fixed-position worm block does not have the worm close enough to the rim of the worm gear, i.e. not there is not enough engagement.  That's basically a manufacturing error, and it's going to require modification of the worm mounting to make the engagement adjustable and maybe spring-loaded.  Losmandy has a good video about how to set up and adjust theirs that gave me a couple of ideas.

 

The motors are definitely getting changed out since the original AC sync motors are now unobtainium, and I want to increase the system capability anyway.  SiTech and Explore Scientific systems could both work.  I do like the idea of open source software, since processor hardware goes obsolete on a predictable cadence, and when the controller board inevitably dies you have to get a new and probably different one.  ES seems to think steppers are better than servos and I'd like to understand why.


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#38 YourNotSirius

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Posted 15 January 2021 - 08:16 AM

 

Photo of the day - a cookie sheet full of the wrinkle finish OTA parts ready for baking (200˚F for an hour).  Yummy!
 
 

 

I checked out the behavior of the axis gears and clutches while I still have the mount assembled on the pier.  RA seems OK, no great backlash in the worm gear interface and the clutch is even still fairly smooth.  The dec axis is much worse; as I remembered, there is really huge backlash in the worm gear, and the clutch really sticks.  The latter should be easily cured with some lube and adjustment.  The worm is another story...the fixed-position worm block does not have the worm close enough to the rim of the worm gear, i.e. not there is not enough engagement.  That's basically a manufacturing error, and it's going to require modification of the worm mounting to make the engagement adjustable and maybe spring-loaded.  Losmandy has a good video about how to set up and adjust theirs that gave me a couple of ideas.

 

The motors are definitely getting changed out since the original AC sync motors are now unobtainium, and I want to increase the system capability anyway.  SiTech and Explore Scientific systems could both work.  I do like the idea of open source software, since processor hardware goes obsolete on a predictable cadence, and when the controller board inevitably dies you have to get a new and probably different one.  ES seems to think steppers are better than servos and I'd like to understand why.

 

If you still have the old motors I think I can make them work. Hit me up with a PM. Actually, if ANYONE has those old Saybrook Model 447 drives then let me know. I just resurrected one for the Cave 8" f/7 Deluxe B that I have restored.

 

Q



#39 apfever

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Posted 15 January 2021 - 03:50 PM

I'll have to check mine. I have two Caves but the 1958 was made using proto type parts Cave had shelved. I don't know what motor that one has. It could be interesting so I'll check when I can.



#40 Dave Cook

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Posted 15 January 2021 - 07:07 PM

Sorry if I gave the wrong impression - my motors probably work, but I'm planning to upgrade to a goto system so they'll go into my box of original parts that I'm preserving along with the instrument.  I should know this weekend; I've gotta check out the condition of the wiring before I plug in the 120VAC.



#41 YourNotSirius

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Posted 18 January 2021 - 11:31 PM

As long as the motors are the model 447 I believe I can resurrect them. At least, I can try to do so. It's easier to know when I have them in my hands and can run tests upon them.

 

Mr. Cook: If you find that they do not work then let me know. If you wish to send them over for an attempt at revival I'd be happy to help.

 

Q

 

PS. Please note that I get on this site randomly. It depends upon work loads and other obligations. Heck! I don't even get to check my normal email sometimes for days on end. (Why does that sound like it's not a bad thing? lol)

 

Thanks,

 

Q


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#42 Dave Cook

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Posted 19 January 2021 - 01:05 AM

Some action from the weekend.  Here are the mirror cell clips as I started work on stripping them.
 
Mirror cell clips before stripping
 
I knew they were a little rough.  How rough, I had no idea.  Cleaned up they look like abstract art with 3 ghostly figures.  They are not even all the same size, the slots are irregular, and there's not a square edge to be found.  Heavy grinder marks on all surfaces.  I'm thinking about just milling the slots straight and cleaning up the rest by hand with a file and Dremel sanding drums.
 
Mirror cell clips
 
The dec drive assembly.  Completely standard I believe.  Worm pinned to the shaft, single-piece aluminum bracket, worm bearings retained by a single SHCS on the rim, metal motor shaft coupler, nothing is adjustable.  Everything looks to be in good condition though.  I'm planning to modify it to make the engagement adjustable, lap the worm to the gear, and probably change to a Sitech style DC motor and a no-backlash flex motor coupler.
 
In the dec stack there is a set of open-frame ball bearings between the motor mount plate and the clutch assembly (not visible in this photo).  I'm curious about how this interacts with the clutch with regard to thrust load.
 
Declination drive
 
And finally, a fun delivery from Australia post - some reaaaally black stuff for the inside of the tube, spider and mirror clips.  I painted a test patch with the 2.0 (at right) and it looks great.  The plan is to put a base coat of the 2.0 on the entire inside of the tube and then come down from the top with the 3.0 until I run out of it.
 
Really black paint

 


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#43 ccwemyss

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Posted 19 January 2021 - 09:46 AM

I was just looking at these paints for adding some baffles to a refractor. I notice they say it's not meant for outside use, or durable to wear. I'm really looking forward to hearing how they work in a telescope interior, which is sort of an inside space under outdoor conditions, and not exposed to wear, except perhaps at the end of a tube/dew shield. 

 

Chip W. 



#44 Dave Cook

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Posted 19 January 2021 - 04:41 PM

I think (hope?) the über-black paints should be OK, at least for my case where the instrument will live indoors most of the time, rarely see condensing humidity, and won't ever be exposed to extreme cold as long as I stay in SD.  And the UV exposure that kills paints outdoors won't be happening either.  I'm hoping for noticeable benefits; the inside of the tube is going to be orders of magnitude less reflective than it was before.



#45 Dave Cook

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Posted 20 January 2021 - 09:57 PM

Totally annoyed with the ultra sloppy cell clips...measured the slots and they are an average of .020 to .025 too wide for the #10 screws. So I drew them up in OnShape and made some new blanks from 2 x 2 x 0.125 aluminum angle.  Now they are the same size and reasonably square even though I just sliced them with the Fein coldsaw.  The main reason I made the CAD drawing was to get a file I can throw into CamBam to cut the slot with a 3/16 endmill.
 
If anyone is interested, the drawing is public on OnShape at https://cad.onshape....f7ac3642d89bc15
 
mirror cell clip cad
Old clips and new blanks
 
Cutting setup using a slitting saw to trim off the short side.  Bandsaw would have been quicker to use, but my garage lacks that.
 
Cutting with slitting saw

 


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#46 Dave Cook

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Posted 21 January 2021 - 02:29 PM

Hmm I just noticed that the first photo in my post of the 19th is oddly distorted.  Here is the correct version (too late to edit the original post).  [Edit: Investigated and I'm pretty sure this happened after doing a rotation in the forum software...I won't do that anymore!]
 
Mirror cell clips before stripping

Edited by Dave Cook, 21 January 2021 - 02:34 PM.

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#47 Thomas_M44

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Posted 22 January 2021 - 05:27 PM

I've had pretty good luck with that VHT brand spray crinkle finish.

 

I've found it best to have the metal to be painted slightly warm --same with the paint can itself.

 

It definitely takes a bit of practice to get the knack of applying the right thickness of coat.

 

It's easy to apply a bit to much, or a bit too little.


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#48 D_talley

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Posted 23 January 2021 - 06:55 PM

To go back to the subject of the motors, I refurbished my 10 inch Cave last year. I was worried about the motors since my scope was outside for 15 years.  However I discovered that I did not need to worry about replacing the motors since they are available everywhere.  I got replacement motors on eBay.  If your motor is electrically burned out, be it a Hurst or a Bristol Saybrook, but the gears in the motor are still working, then you can go to eBay and purchase the same series of motor and be back in business.  How?  The electrical part of the motor is interchangeable.  It is the gearing that determines the speed. So lets say your 1 rpm motor is electrically dead.  Go to eBay and pick up a similar motor, chances are it will not be a 1 rpm version. I got a 1/5 rpm one and then swapped the electrical part with the dead one I have and I was working again.  The Bristol motors are not screwed together and come apart without effort.  The Hurst motors will have to be pried apart carefully at the bottom where you see the three indentions holding it together. When I started this journey to fix the Cave I have, I worried about the motors being bad. Well, no worries now. There are plenty of motor parts to get your mount going as long as the gears are not broken, however the gears are very tough. I now have two motors in reserve just for future failures.



#49 Dave Cook

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Posted 24 January 2021 - 03:14 AM

I'm actually not super concerned about my AC motors.  I think they still work, and I'm heading for DC motors anyway so I can have some decent speed control.  Good point about the gear subassembly being interchangeable.

 

The last couple of weekends I've been back to working on the tube finish.  The first #600 wet sanding with the orbital revealed a bunch of noticeable hills n' valleys and led to places where the paint on the hills was thin.  The tube is really not very round compared to what the color-sanding will reveal.

 

Of course the car restoration attack on that would be to slather Bondo on absolutely everything and get rid of the undulations.  Not wanting to do quite that much work, I opted to spray another couple of coats of paint and then put a soft foam interface pad on the sander so it wouldn't be so aggressive on the hills.  That seems to have worked decently...the photo shows the tube after sanding 600, 1000, 1500 with the soft pad.  It's starting to show a glossy sheen.

 

Tube ready for polishing after 1500 wet sand
 
Today the polishing goodies showed up.  I got sampler packs of the Chemical Guys polishing compounds and their foam polishing pads.  They actually have 7 different levels of firmness on the pads (overkill anybody??) but I figure the 3 pads in the smaller sampler pack should be fine.  The pads have standard hook-and-loop on the back.
 
Chemical Guys polishing sampler packs

 

Also today I took a deep breath and removed the saddle from the dec shaft by taking out the single 1/2-13 bolt.  I was not disappointed [insert evil grin here].  The engagement length is just about 1.0" not counting the chamfer on the shaft (first photo below), and the bore in the saddle is so oversize that there is a ton of wobble if the bolt is not holding the saddle and shaft together.  Measurement showed the shaft is 1.497", and the saddle bore is 1.501".

 

Dec shaft with saddle off
 
The saddle bore is also really rough; you can see it pretty well in this photo.
 
Dec shaft to saddle interface
 
The saddle could be improved a fair bit by boring it out for a bronze bushing that would be a press fit into the saddle and a much closer slip fit on the shaft, and by adding one or two set screws through the side to help fix it more rigidly in place.  But the saddle has other issues...the radius of the cradle is so much smaller than that of the rotating rings that the contact patches are tiny and were digging into the rings before I rounded off the cradle tips long ago.  For extra confoundery, there doesn't look to be enough material in the casting to allow it to be machined enough to really correct this.  So I'm going to focus first on making a new and larger interface block with more engagement length and a top face large enough to support interchangeable bolt-on mounting plates for single and dual Losmandy saddles.

 


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#50 Terra Nova

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  • Loc: 39.07°N, 229m AMSL, USA

Posted 24 January 2021 - 11:25 AM

Looking good! Really nice work you’re doing to give the old girl new life. 


  • Dave Cook likes this


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