52 replies to this topic

[mfoose]

Hope everyone had a great Thanksgiving!

 

I was trying to take the secondary mirror and spider out of the tube to clean them, but I cannot seem to get them out. I tried removing the nut for the secondary mirror to slide the bolt with it out of the hub, but even after the removing the nut, the bolt remained stationary. I noticed there was a set screw with an allen head, but after removing that the bolt remained there (I left the nut at the end of the threads in case it did slide out. I did not want the secondary mirror to slam into the ground). It would slightly rotate, but would not slide out of the secondary hub. I also removed the nuts that tighten the spider to the tube, but could not remove the spider.

 

How should I proceed? I do not want to break anything.

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Edited by mfoose, 29 November 2024 - 05:02 PM.

[oldmanastro]

Congratulations on this very nice find. I rescued one many years ago. Coincidentally it is also from 1974, at least according to the date on the clock drive motor. The RV6 has been with me for 31 years now. About three years ago it underwent a refurbish and mirrors recoat. The optics are really good. It has never disappointed me and the clock drive still works as good as new. When I refurbished mine the spider was left in place. I just took the secondary mirror holder out. 

[Cavs56]

The three screws that adjust collimation release the secondary. Once removed check that the foam behind the mirror isn’t deteriorated allowing the mirror to move. I would not do it that way. Working with the mirror on its side. Or with the primary removed put two nuts together on the threaded shaft that holds the secondary. Tighten them together. Use the top nut to spin the shaft out. Use some oil . I believe there is a nut under the spider on that shaft also make sure it is loose.

[YourNotSirius]

Call me silly but, doesn't that threaded rod just unscrew? Don't make me dig through our collection of stuff to find out. Since that's the old man's stuff I'm not certain but, the machinist's instincts say that by looking at it, the mirror holder is threaded into that part of the spider and that is used for final position adjustment of the mirror. Provided, of course, that is what you meant.

 

Q

[DAVIDG]

 As stated by others the center 1/4-20 bolt is threaded into the metal center hub of the spider. So once you take the set screws out the center hub you can unscrew the secondary assembly from the spider.

   To get the spider out  of the tube you need to turn the nuts on the inside the tube on the 1/4-20 bolts all the way against the spider vanes.  Then you need to carefully twist the whole spider so the vanes bend into arcs and the bolts pull free from the tubes . 

 

                - Dave 

Edited by DAVIDG, 30 November 2024 - 10:33 AM.

[deSitter]

Call me silly but, doesn't that threaded rod just unscrew? Don't make me dig through our collection of stuff to find out. Since that's the old man's stuff I'm not certain but, the machinist's instincts say that by looking at it, the mirror holder is threaded into that part of the spider and that is used for final position adjustment of the mirror. Provided, of course, that is what you meant.

 

Q

The 1/4-20 threads in the hub are very tight and the slightest dimple from the set screw on the threaded stalk will make it stick in the hub. I ditched that system when I rebuilt mine and used a jam nut arrangement.

 

I see the vanes on the OP's scope are also mangled. I had to replace my vanes. I used the blue steel bands that came with a refrigerator carton. The vanes are held in with a pin. There is a little circular bay. You fold over one end of the new vane, shove it into the bay, then drive a thin finishing nail (a very hard one!) into the folded over part to make it expand into the bay. Very secure and the new vanes were a huge improvement.

 

A third improvement is to make little divots on the back plate of the secondary cell to receive the adjusters. I then sharpened the adjustment screws to fit into the dimples. This system kept collimation for at least 10 years, until I donated the scope to friends.

 

-drl

[YourNotSirius]

The 1/4-20 threads in the hub are very tight and the slightest dimple from the set screw on the threaded stalk will make it stick in the hub. I ditched that system when I rebuilt mine and used a jam nut arrangement.

 

I see the vanes on the OP's scope are also mangled. I had to replace my vanes. I used the blue steel bands that came with a refrigerator carton. The vanes are held in with a pin. There is a little circular bay. You fold over one end of the new vane, shove it into the bay, then drive a thin finishing nail (a very hard one!) into the folded over part to make it expand into the bay. Very secure and the new vanes were a huge improvement.

 

A third improvement is to make little divots on the back plate of the secondary cell to receive the adjusters. I then sharpened the adjustment screws to fit into the dimples. This system kept collimation for at least 10 years, until I donated the scope to friends.

 

-drl

So, I was correct. Far out, man! lol

 

Getting those vanes out was a bugger. Getting them back in is even worse. I do like the idea of steel strapping. We get plenty of that every day at the shop so that an easy acquisition.

 

Instead of a nail I would use drill rod. It's made of stainless and will never rust plus, it's very smooth and stronger than a nail. A personal preference since we have that stuff everywhere. lol

 

Making "dimples" for the ends of the adjusting screws should have been something that was done at the factory. Apparently, they weren't as smart as everyone thinks they were. That one is a no brains required thing.

 

 

Q

[mfoose]

I removed the secondary mirror by loosening the 3 collimation bolts. I tried to spin the center bolt out of the secondary hub, but it would only spin a quarter turn or so and stop turning. I will work on that when I take the spider out. 

 

The secondary is in decent shape. Very dusty when I first came out, but it cleaned up nicely.

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[mfoose]

I am surprised that the collimation bolts can have no stop or plate to push against. They can just push up through the foam and put pressure on the secondary mirror. Has anyone experienced this? Seems like a small disc directly between the foam and the heads of the collimation bolts should fix that issue.

 

Only one small area where the coatings have worn away. 

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Edited by mfoose, 01 December 2024 - 03:15 PM.

[deSitter]

Something is WAY off here. Mine had a plate that the shell was screwed to in 3 places. Behind the plate was a wad of foam.

 

Well, you need to 3D print a plate here. Maybe even just print a cylindrical 45 degree prism and attach the secondary with 2-sided tape.

 

edit: I am completely confused. There are 2 plates correct? One is threaded for the adjusters, the other is just supposed to pivot on the stalk. Just put everything out in the open please.

 

-drl

Edited by deSitter, 01 December 2024 - 03:36 PM.

[mfoose]

Something is WAY off here. Mine had a plate that the shell was screwed to in 3 places. Behind the plate was a wad of foam.

 

Well, you need to 3D print a plate here. Maybe even just print a cylindrical 45 degree prism and attach the secondary with 2-sided tape.

 

edit: I am completely confused. There are 2 plates correct? One is threaded for the adjusters, the other is just supposed to pivot on the stalk. Just put everything out in the open please.

 

-drl

Sorry for the confusion.

 

Circled in red is the part I am talking about. It's the plate where the 3 collimation bolts enter into NOT where the heads for the bolts are. That plate is screwed into the shell in three places. The issue is that there is nothing inside of the secondary mirror holder, but the mirror and foam. So, the three collimation bolts are free to impede into the foam and hit the backside of the secondary mirror.

 

Notice the 3 indentations of the collimation bolts in the foam in the 2nd picture below. 

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Edited by mfoose, 01 December 2024 - 05:10 PM.

[deSitter]

Circled in red is the part I am talking about. It's the plate where the 3 collimation bolts enter into NOT where the heads for the bolts are. That plate is screwed into the shell in three places. The issue is that there is nothing inside of it but foam and the three bolts are free to impede into the foam and hit the backside of the secondary mirror.

So the screws here should be freely rotating in the holes in the outer plate, and PULLING the cell plate back against the free end of the stalk

 

This doesn't match my memory at all. Maybe I only remember the rebuilt version. I know there was a lot of room for improvement, and afterward it was much easier to collimate and kept collimation for many years.

 

-drl

[Cavs56]

The center stalk keeps the screws from reaching the mirror as one is loosened and another tightened it changes collimation. The center stalk rides in a recess- pivot point.

[apfever]

Don't panic. It is all correct. I'll go through some of these later today. 

Yes,  the collimation  screws pull the glass holder up against the center bolt. The top plate is fairly rigid. The mirror holder pivots on the main bolt. 

In theory, the collimation bolts would bind in the holder as the holder pivots but the amount of movement needed is very small.  Most likely I'll also try a spring loaded system on one of these, and other thoughts. 

It will be a few hours as I deal with getting the house painted during a freak warm spell and tight time frame. 

 

I'll clean these up and do two side by side with mods on one.  I'll do one stock first and line up some mods that might take an Ace Hardware run for parts. 

 

Imagine the 3 collimation bolts extending above the top plate and springs between the head of the bolt and the top plate. This would let each collimation bolt be done independently and eliminate the need to synchronize tightening one and loosening the other. The bolts can have a friendlier top than a straight slot,  what a pain! Just a philips would help.  The right type head might make finger work of a spring system along with the independent use of each bolt.    Make sense?  The worst part would be finger room...hmmmm.....super stupid long collimation bolts that extend above the spider collar for easy finger reach, then a spacer tube and springs against washers....I know somebody is going to 'see' this idea?  

 

The fun part is the super goofy RandR of the spider from the tube.  Bow two vanes rotate one way then the other...more later. First, I think it easier to build the assembly. Easier to install and remove the whole unit instead of working with the mirror assembly independent. 

 

Bolts that seem stuck in the spider hub are usually due to galls and ridges in the bolt caused by the set screw. This just has to be wiggled and pushed out. Try small wiggle and more push so you don't scratch the ridges in the bolt around the inside of the spider hub.

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Edited by apfever, 01 December 2024 - 06:01 PM.

[apfever]

HA!!  INSANE!  Absolutely insane. I have discovered more SAE threads that take a metric wrench or tool for the fastener. The RV-6 is the first I encountered with two of them taking a metric allen wrench to remove 1/4-20 thread set screws (motor back plate to housing).  I've now found the spider assembly has 1/4-20 main center bolt but the nuts holding the top collimation plate (and acorn nut) take a 10mm wrench!.  I now checked three spider assemblies - all the same.

 

The nuts on each side of the top collimation plate (and top acorn nut) are too small for 7/16" wrench, too big for 3/8, and just right for 10mm wrench. A 13/32" wrench might work but will be sloppy (bigger than 10mm) and I can't even find a 13/32 in an oversized ignition set.  Go figure.  This will be a bit ongoing.      

 

I now realize that I have never taken one of these apart over the decades I've worked with them. They will lock in collimation rock solid but not convenient to do with a straight slot screwdriver, it's more complicated than necessary.  Pictured are 4 standard 1/4-20 nuts. The top two are normal SAE that take a 7/16 wrench. The bottom two are the acorn and regular nut on the RV center bolt and they take a 10mm but the threads ARE 1/4-20 SAE.

 

The RV-6 also has over a dozen other metric and even discontinued JIS threads. JIS is "Japan Industrial Standard" metric that had a lot of sizes discontinued shortly after WW II.  This has delayed me a bit discovering what is on the spider. More to come. The other JIS metrics are in the motor drive box, and the finder set screws - so far.

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Edited by apfever, Yesterday, 12:17 AM.

[mfoose]

I understand how the original design works. I am just surprised they made it that way. Upon closer inspection of my secondary mirror, I see a small chip on the backside where one of the collimation bolts would have made contact with it. I am not sure how much more damage it could have done if an unsuspecting amateur kept tightening it. Certainly it would have put pressure on the backside of the mirror and pinched the optics. 

 

In other news, I removed the spider, the focuser, and the finder bracket. Plan to work on the focuser tomorrow.

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[deSitter]

I understand how the original design works. I am just surprised they made it that way. Upon closer inspection of my secondary mirror, I see a small chip on the backside where one of the collimation bolts would have made contact with it. I am not sure how much more damage it could have done if an unsuspecting amateur kept tightening it. Certainly it would have put pressure on the backside of the mirror and pinched the optics. 

 

In other news, I removed the spider, the focuser, and the finder bracket. Plan to work on the focuser tomorrow.

That brings back not exactly warm memories More like smelly ones - the brass would make my fingers smell like metal.

 

-drl

[apfever]

DON'T lose the finder set screws! They are archaic JIS M4X.75 and getting Very hard to find, especially original thumb heads.

Edited by apfever, Yesterday, 12:30 AM.

[apfever]

I'm working on it.  Three RV spiders, all showing the same parts and configuration.  Rebuilds will be tomorrow now. I'll probably re use the original parts because they are... originals.

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[mfoose]

That brings back not exactly warm memories More like smelly ones - the brass would make my fingers smell like metal.

 

-drl

I can smell them as I type with them. 

[mfoose]

DON'T lose the finder set screws! They are archaic JIS M4X.75 and getting Very hard to find, especially original thumb heads.

I have all 6 and tightened them all the way in the bracket so they won't wonder off. Now, if I lose the bracket I am sunk.

[apfever]

I probably have an extra bracket but I'm getting stingy. Don't lose your bracket. 

You probably worked with the nuts on the spider center bolt. How did you find your tools fit the nuts?

 

All you have to do is raise the back plate for collimating the secondary, if you want to keep it original. The back plate is supposed to be positioned so the collimation bolts will work and not go into the glass holder too far. 

Edited by apfever, Yesterday, 01:05 AM.

[apfever]

The set screw that holds the center bolt is standard 1/4-20 on all three spiders. Allen wrenches are shown in two of them.

Two of these take a standard 1/8" allen. One of them requires a 3mm allen. It's not a defect, they are made this way. I have found two sets of 3 (6 total) like this that hold the drive back plate to the RA housing, on two completely independent RV-6.  No, a 7/64" allen wrench doesn't cut it. SAE allens won't work on the freaks.

 

The center bolt is threaded into the spider hub. The set screw crushes the bolt threads which locks the bolt in. If you want to remove the center bolt, you will have to bite the bullet and force rotate the bolt while grinding the thread damage through the hub.  I didn't find it too bad so far. You might damage the spider hub threads if the bolt has been severely crushed by the set screw. 

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Edited by apfever, Yesterday, 01:54 AM.

[apfever]

Secondary collimation bolts can not be extended out the top of the spider because the shanks hit the vane hub. One collimation bolt is centered under a spider vane. 

 

Three point collimation can be done using only two bolts, namely the two that are not under a spider vane. Replacing those two with cap screws will allow you to insert two allen wrenches (long arms) that will extend above the spider. You can then have simultaneous adjustments with both hands, while the allens remain in place on their own.  This will beat the tar out of loosening/tightening one bolt at a time with a straight slot. 

 

The collimation bolt that can hit the glass is the one under a spider vane. This one can be safely set and left alone. 

Edited by apfever, Yesterday, 08:45 AM.

[deSitter]

Secondary collimation bolts can not be extended out the top of the spider because the shanks hit the vane hub. One collimation bolt is centered under a spider vane. 

 

Three point collimation can be done using only two bolts, namely the two that are not under a spider vane. Replacing those two with cap screws will allow you to insert two allen wrenches (long arms) that will extend above the spider. You can then have simultaneous adjustments with both hands, while the allens remain in place on their own.  This will beat the tar out of loosening/tightening one bolt at a time with a straight slot. 

 

The collimation bolt that can hit the glass is the one under a spider vane. This one can be safely set and left alone. 

I remember now what I did. I converted mine to a pusher arrangement with hex cap screws. The cell plate was captured with an acorn nut inside and the outer plate was threaded by tapping out the holes to the next higher size - probably 10-24. The cell plate was free to be pushed into place by the pushers. The natural position for all this was "almost collimated" already, so collimation was very easy and positive. No springs needed. I also ditched the stalk set screw, a terrible idea. I used a simple hand nut and washer to fix the stalk position.

 

The original configuration meant the longitudinal position of the secondary was variable when the adjusters were operated. This is why mfoose's screws were about to damage his mirror. In the rebuild, that cannot happen and the longitudinal position is determined by the stalk position alone.

 

I also remember thinking very hard about the entire problem of spiders and diagonals, and all that stuck with me these many years later. My current 10" flagship scope benefited from the experience, and never comes out of collimation. The Criterion spider is a baroque mess with too many parts and bad ideas!

 

-drl

Edited by deSitter, Yesterday, 09:57 AM.