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1972 Cave custom built 6" Cassegrainian/Newtonian

classic mount equipment
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#1 allenawilson

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Posted 23 March 2020 - 09:51 PM

     I have been the proud owner of the following telescope since 1988.  I was living nearby the original owner when I saw it for sale.  I used it a lot for about the next 5 or 6 years, and eventually used it to guide my Celestron 5.5" Schmidt camera, which I piggybacked on top of it.  After about 20 years of not being involved in the hobby of astronomy, I have decided to dip my toes in the pool again.  I have, in the past couple of days, begun dismantling the scope, mainly for the purpose of cleaning.  Although I have taken reasonable care of it, after many moves and lots of time in a storage building, it's pretty dirty.  And so, as you might guess, I have lots of questions.

     Question 1: The ascension axis bearings are very sticky.  To clean, do you remove them or clean them in the housing?  After cleaning, do you use white lithium grease?  (No grease on the bronze gears, right?) 

     Question 2: The ascension axis fine control shaft (is that the right word?)  has a very small rolled pin that holds the worm gear in place that allows a slight bit of play in the movement.  Is there a way to tighten that or do you replace the rolled pin?  

     Question 3:  And this is the big one.  Should I just get the scope going again or is this the type of scope that one should completely rebuild to "like new"?  Is it an important Thomas Cave telescope or just "so-so"?  

     I'll provide any pictures any one requests, but keep in mind I have it in pieces right now.  

 

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Edited by allenawilson, 23 March 2020 - 10:18 PM.

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#2 CHASLX200

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Posted 24 March 2020 - 05:43 AM

Rare bird fir sure.



#3 davidmcgo

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Posted 24 March 2020 - 08:47 AM

Wow, that looks like a keeper and worth making all shiny again!  I’m a sucker for oddball scopes and think the endorsement from John Gregory adds a lot to it.

 

Dave


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#4 clamchip

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Posted 24 March 2020 - 09:38 AM

That's really nice.

Its the only Cave convertible I've ever seen or heard about.

Wow.

 

Robert


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#5 tim53

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Posted 24 March 2020 - 09:53 AM

That's really nice.

Its the only Cave convertible I've ever seen or heard about.

Wow.

 

Robert

They do exist.  I've never seen one smaller than an 8", though.


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#6 mattyfatz

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Posted 24 March 2020 - 10:07 AM

For lubricants I suggest looking here. It's aerospace grade stuff. You'll only need a little, but the grease will provide the right amount of viscosity without causing and erosion.


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#7 Terra Nova

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Posted 24 March 2020 - 10:42 AM

That’s cool! I’m excited to see pictures when you get it up and running again! Welcome to Cloudy Nights and the Classics Forum.


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#8 macdonjh

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Posted 24 March 2020 - 11:36 AM

     I have been the proud owner of the following telescope since 1988.  I was living nearby the original owner when I saw it for sale.  I used it a lot for about the next 5 or 6 years, and eventually used it to guide my Celestron 5.5" Schmidt camera, which I piggybacked on top of it.  After about 20 years of not being involved in the hobby of astronomy, I have decided to dip my toes in the pool again.  I have, in the past couple of days, begun dismantling the scope, mainly for the purpose of cleaning.  Although I have taken reasonable care of it, after many moves and lots of time in a storage building, it's pretty dirty.  And so, as you might guess, I have lots of questions.

     Question 1: The ascension axis bearings are very sticky.  To clean, do you remove them or clean them in the housing?  After cleaning, do you use white lithium grease?  (No grease on the bronze gears, right?)  The goal is to remove all the old grease and anything else in the bearings.  If you can remove the bearings that task will be easier to accomplish.  If you can't remove the bearings, do the be you can with whatever tools you can improvise and solvents required.  The default recommendation for grease on Cloudy Nights is SuperLube, it's a silicone grease with PTFE (Teflon).  I don't recommend white lithium, it separates too easily and the oil runs and makes a mess.  I'll bet any bronze components have dried out if they were lubricated originally.

     Question 2: The ascension axis fine control shaft (is that the right word?)  has a very small rolled pin that holds the worm gear in place that allows a slight bit of play in the movement.  Is there a way to tighten that or do you replace the rolled pin?  

     Question 3:  And this is the big one.  Should I just get the scope going again or is this the type of scope that one should completely rebuild to "like new"?  Is it an important Thomas Cave telescope or just "so-so"?  

     I'll provide any pictures any one requests, but keep in mind I have it in pieces right now.  There are two general schools of thought: "leave your classic scope as original as possible" (think of it as an historical antique), and "go crazy and modify as much as you want".  You'll have to decide which school you belong to. I'm in the restore to new camp.  I would try cleaning to the best of my ability (perhaps repainting in the original color(s) ), restoring function to your mount (again, perhaps repainting and/ or polishing) and replacing any missing parts.  If the mirror coatings have deteriorated I would get the mirrors recoated.  Since, to me, a telescope is also a tool which should be used, if I sent the mirrors off for coating, I'd have them evaluated and refigured if they could be improved.  No sense in having a scope that's good to look at but not through. 

Welcome to Cloudy Nights.  I also have a convertible scope, a Parks 10" HIT (hybrid integrated telescope).  I've always wanted the Takahashi CN-212 as well.  

 

I don't know if your read the Terms of Service, but now that you've posted you are obligated to post photos.  Obligated.

 

Actually, a picture or two of your RA slow motion control would likely help those who know about your mount advise you about repair.


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#9 macdonjh

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Posted 24 March 2020 - 11:57 AM

One of my favorite restoration threads:

https://www.cloudyni...ore/?hl=tinsley



#10 allenawilson

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Posted 24 March 2020 - 01:05 PM

Wow!  Thanks for all the help.  One of the bearings on the polar axis is a sealed bearing.  Is that original or should it be replaced with one like it has on the other end?  The sealed bearing needs replacing anyway.  It's very rough feeling.  

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#11 macdonjh

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Posted 24 March 2020 - 02:32 PM

Wow!  Thanks for all the help.  One of the bearings on the polar axis is a sealed bearing.  Is that original or should it be replaced with one like it has on the other end?  The sealed bearing needs replacing anyway.  It's very rough feeling.  

I have no idea if the bearing in your photo is original or not.  If it's rough, it should probably be replaced. 

 

I participated in a fairly long thread here about lubricating bearings.  I learned a lot even if I didn't follow all the recommendations offered.  At the time, I was working on an old EQ-6/ Atlas mount owned by the club I belong to.  The shaft bearings of the mount were quite rough.  They were sealed (rubbery guard, if the guard is metal the bearing is considered shielded).  It was recommended I not remove the seals, clean and relubricate the bearings.  I had already done all that, though.  The reason behind the recommendation is if the bearing is rough it's already damaged and needs replacing.  I found the mount operation to be much improved even though I put the original bearings back (cleaned and regreased).  My theory is the bearings were simply dirty, not damaged.  

 

Later, when I was working one of my mounts I found the shaft bearings to be silky smooth and left the seals alone.  That mount is so smooth I actually had a hard time balancing it.  Any little bit of imbalance was noticed.

 

Another recommendation was don't try to remove a metal shield.  It will likely be damaged and unusable. 

 

Good luck with your project and keep those photos coming.


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#12 allenawilson

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Posted 24 March 2020 - 02:51 PM

Here is a photo of the other end.  Bearing is completely clogged up with old, congealed grease.  I'm thinking this one can be cleaned and greased.

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#13 macdonjh

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Posted 24 March 2020 - 03:09 PM

Seems reasonable.  Looks like it will be easy to get a toothbrush in there to work out the dried up grease.  The more old grease you remove, the more the rollers will turn and the more grease you'll get out from the "back side" of the rollers.  It'll take some time, but it's not hard work.


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#14 photoracer18

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Posted 24 March 2020 - 03:41 PM

They do exist.  I've never seen one smaller than an 8", though.

I have an unrestored 12.5" convertible.


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#15 allenawilson

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Posted 24 March 2020 - 04:40 PM

I have no idea if the bearing in your photo is original or not.  If it's rough, it should probably be replaced. 

 

I participated in a fairly long thread here about lubricating bearings.  I learned a lot even if I didn't follow all the recommendations offered.  At the time, I was working on an old EQ-6/ Atlas mount owned by the club I belong to.  The shaft bearings of the mount were quite rough.  They were sealed (rubbery guard, if the guard is metal the bearing is considered shielded).  It was recommended I not remove the seals, clean and relubricate the bearings.  I had already done all that, though.  The reason behind the recommendation is if the bearing is rough it's already damaged and needs replacing.  I found the mount operation to be much improved even though I put the original bearings back (cleaned and regreased).  My theory is the bearings were simply dirty, not damaged.  

 

Later, when I was working one of my mounts I found the shaft bearings to be silky smooth and left the seals alone.  That mount is so smooth I actually had a hard time balancing it.  Any little bit of imbalance was noticed.

 

Another recommendation was don't try to remove a metal shield.  It will likely be damaged and unusable. 

 

Good luck with your project and keep those photos coming.

Okay.  I was told by my bearing people that the replacement for the bearing (that looks sealed) will not fit inside.  The replacement is ever so slightly larger.  Plus, I'd rather not try to take it out.  And it looks sealed, but it IS shielded.  How would one go about removing that shield so I can clean and lube that bearing and just leave it in place?  



#16 Stevegeo

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Posted 24 March 2020 - 06:08 PM

You can remove the shield and probably relube the bearing... to remove the shield you will need a very small screwdriver flat headed, and a pick  and a right angle pick.

On the outside edge where the shield meets the bearing, carefully with a pick (straight) pry the shield up, then using a screwdriver and the right angle pick get under it and pull the shield up. Mind you you may bend the shield,  it can easily be bent back and popped back in when done.

Once the metal shield is out using  the straight pick pull the seal back on the inside surface, a drop or two of WD 40 on the seal will soften the rubber enough to facilitate  this.   A needle greaser / oiler used for sewing machines works well for this and for lubricating the bearing itself..  once lubricated with light oil like 3 in one... rotate the bearing back and forth with pressure on the bearing this will force lubricant to the opposite side of the bearing ... then inject a tiny amount of clear grease.  Some here say super grease is best and though I agree. If you are not using the scope in extreme temperatures,  a good lithium or silicone base CREAM grease will work... do not use wheel bearing grease with fillers, .

Work a bit into the bearing  and spin it , this will fill the minute scratches  and voids in the bearing making it spin easier.

Remember  it does not have to spin fast or that easy. IT JUST HAS TO SPIN SMOOTH..  pressure on the bearing  from the weight of scope will do this.   Assemble and check, a full rotation a few times should result in better performance. 

Hope I have helped .

Stevegeo 


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#17 Stevegeo

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Posted 24 March 2020 - 06:22 PM

Here is a photo of the other end.  Bearing is completely clogged up with old, congealed grease.  I'm thinking this one can be cleaned and greased.

Yes this bearing can be cleaned and regreased...  remember LIKE EATS LIKE ,  a simple thing to consider. Bearings are oil and emollients usually moly, and lithium. To dissolve the hardened grease ,  any light oil such as WD 40 worked into the grease may rejuvenate the grease ,  but a removal and replacement with a better grade is best.. a toothpick, Q tips will help clean then a washout with light oil,  sometimes brake cleaner blast to wash out  the sludge , let dry  then a repack with a good grade lithium cream grease packed into the bearing journal by hand.

 

Stevegeo..... yes I am a machinist, fabricator, builder , fabricator, welder and inventor... 


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#18 macdonjh

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Posted 24 March 2020 - 07:49 PM

allenawilson and Stevegeo,

 

I typically use mineral spirits to dissolve old grease and clean up the innards of mounts I work on.  I typically don't try to rejuvenate old grease since I have no idea what kind is in there, or how much grit is in the bearing.  Once I have a clean bearing, and housing, I'll relubricate the bearing and go on. 

 

With that EQ-6/ Atlas I rebuilt, I damaged about half the seals taking them off the bearings.  I cleaned and regreased the bearings and simply left the damaged seals off.  I figured when the mount gets dirty on the inside again, I'll rebuild it again.  No big deal.

 

I am not advocating anyone consider this best practice, but it's what I did.


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#19 macdonjh

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Posted 24 March 2020 - 07:52 PM

Okay.  I was told by my bearing people that the replacement for the bearing (that looks sealed) will not fit inside.  The replacement is ever so slightly larger.  Plus, I'd rather not try to take it out.  And it looks sealed, but it IS shielded.  How would one go about removing that shield so I can clean and lube that bearing and just leave it in place?  

If you have a caliper, and can remove the bearing, you should be able to measure the ID, OD and thickness.  That should be enough information to find a replacement, if you so desire.  If you get asked by your bearing vendor of choice, I'm sure he will laugh when you tell him the design rotational speed is 1 revolution per day and design load is 200 lb.


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#20 allenawilson

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Posted 24 March 2020 - 10:05 PM

I did damage the seal (or shield) getting it off the bearing, but just cleaned and repacked the bearing with SuperLube, as suggested.  So far, so good.  And the bearings feel great!  Now to the clutches.  One of them appears to have a  teflon sleeve and one has two thin pieces of clear plastic.  I would guess the teflon has been replaced.  But I don't know what to lubricate them with.  The two small plastic circles are going to be trouble when it comes to reassembly.  And once again, I want to thank everyone for their help.  I think at some point a complete restoration might be in order, but right now I'm losing dark skies.  I won't be making photos or anything for a while, I just want it to track reasonably well.    



#21 macdonjh

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Posted 25 March 2020 - 07:21 AM

Clutches should not be lubricated.  The clutch depends on friction increasing as the adjustment bolts are tightened to transfer torque from your mount's motors to the axes shafts.  If you lubricate the clutch, friction will be reduced and it will slip.


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#22 allenawilson

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Posted 29 March 2020 - 10:31 PM

Does anyone know the thickness of the teflon strips used on the clutches?



#23 macdonjh

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Posted 30 March 2020 - 08:36 AM

Does anyone know the thickness of the teflon strips used on the clutches?

Does it matter?  Don't the clutch adjustment screws pull the clutch plates together, so a certain amount of variation in the thickness of the PTFE (between original and replacement) could be tolerated?  For example, if the current clutch pads are 10 mils thick, couldn't the design of the clutch tolerate 5 mil, or even 30 mil pads?


Edited by macdonjh, 30 March 2020 - 08:37 AM.

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#24 DAVIDG

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Posted 30 March 2020 - 09:31 AM

Does it matter?  Don't the clutch adjustment screws pull the clutch plates together, so a certain amount of variation in the thickness of the PTFE (between original and replacement) could be tolerated?  For example, if the current clutch pads are 10 mils thick, couldn't the design of the clutch tolerate 5 mil, or even 30 mil pads?

 The Teflon strip is not the friction pad in a Cave drive. It is thin strip a few thousands thick that goes between the ID of the 100 tooth drive gear and the raised rim of the plate it is riding one. In these drives it is a  metal to metal clutch surface. In the drives I have rebuilt I added a thin gasket of material so it wasn't metal on metal.. This greatly improved the feel of the movement and made it much easier to adjust the clutch pressure.  First of all the metal on metal surfaces are not dead smooth so the contact area is not even and with metal on metal there is  a very limited pressure range  that has the right feel to move the scope  yet stiff enough to track. Adding  the clutch material gives a much larger contact area and by doing so increases the range of pressure you can set to have the scope track and  have the right feel when you move it  ie  not too easy or too stiff.

 

                     - Dave 


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#25 allenawilson

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Posted 30 March 2020 - 12:42 PM

 The Teflon strip is not the friction pad in a Cave drive. It is thin strip a few thousands thick that goes between the ID of the 100 tooth drive gear and the raised rim of the plate it is riding one. In these drives it is a  metal to metal clutch surface. In the drives I have rebuilt I added a thin gasket of material so it wasn't metal on metal.. This greatly improved the feel of the movement and made it much easier to adjust the clutch pressure.  First of all the metal on metal surfaces are not dead smooth so the contact area is not even and with metal on metal there is  a very limited pressure range  that has the right feel to move the scope  yet stiff enough to track. Adding  the clutch material gives a much larger contact area and by doing so increases the range of pressure you can set to have the scope track and  have the right feel when you move it  ie  not too easy or too stiff.

 

                     - Dave 

Thanks Dave.  As I stated earlier in this thread, one of mine has been replaced with two pieces that seem to just be thin plastic.  I was just wondering about the thickness because I thought about replacing it.  But as it appears to move smoothly, I think I'll just leave it as is.  But now you've given me another idea.  I hadn't thought about adding a "gasket".  What material do you use?  I think this would really smooth up the motion when moving the scope manually.  




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