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Restoration of Criterion RV-4 Deluxe

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#1 DAVIDG

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Posted 28 June 2019 - 01:02 PM

 I picked up a RV-4 Deluxe a couple of weeks ago. The scope is in  very good shape and looks like it was hardly used. So a few nights ago I started the restoration process. I plugged the drive in and the scope didn't move. Off with the cover for the clock drive to see what is going on. The first thing I noticed was the drive had never worked since there was the original glob of grease on the worm and rest of gearing was free of grease. That told me the motor had never rotated the worm. I took the worm assembly off the scope and plugged the motor back in. Still no movement so I took the motor off the worm assembly. The shaft on the motor spun freely, not good. The motor is a fairly common 1/10 rpm pear shape unit but the output shaft is special in that has a slotted end. That part could be made fairly easily but I decide to dig into the motor to see what was wrong and if it could be easily fixed. So out comes the antique high wattage soldering iron to try to unsolder the motor case and get into the gear box. It took awhile of heating the solder and scraping it away but after about 30 minutes I had the case open. It only took another minute to find the problem. The gear that drives the output shaft had come loose. It is  a press fit on the shaft and the knurling on the shaft was too short to really grab the gear.  So I carefully pressed the gear back onto the shaft so it was square to the axis of rotation. The mechanical bond was too weak to firmly hold the gear in place so I used one drop of super glue at the joint and let it cure over night. The next morning it was firmly in place but for safe measures I added a little of JB Weld epoxy around the joint and let that cure while  I was at work. When I got home last night the gear was very firmly attached. 

 I reassembled the motor and plugged it in. The output shaft turned smoothly and timed the rotation to be sure  nothing was slipping. All looked good so I soldered the case shut in two places 

   The next step was to mount the motor and adjust all the parts of the drive. The first was the worm assembly. It didn't turn perfect smoothly. I took it apart and  lightly sanded the end of the brass take up assembly. That fix the slight hang up I was feeling. I then carefully tighten the brass take up screw on the end of the worm shaft until there was no slide  to slide movement of the worm in it's housing but it still rotated freely and easily. Then I tighten down the locking  nut. Next step  was to reattach the motor. I found the holes in the motor brackets and those on the  worm assembly were a little off and could cause the motor to bind. A small file was used to enlarge the holes on the motor and now the motor dropped into place. 

   I then powered up the motor and put a piece of tape sticking off the worm so I could see the motion of the worm. It ran smoothly.  Next I loosen the clutch on the main drive gear. Now the scope was free to move in RA and positioned the counter weight  on the RA shaft  so the  scope was  balanced. This results in the least amount the torque needed to have the  scope track and the least  amount of wear on the motor.  Next I reinstalled the worm/motor assembly back into the clock drive housing  and adjusted the worm so it squarely meet up with the main drive gear. I tighten the clutch and rocked the scope back and forth in RA to see how much play there was between the main gear and the worm. I adjusted the worm assembly to just remove any play making sure it wasn't too tight so the worm wasn't jammed against the main gear.

  Took the scope out and looked at Jupiter. Scope was tracking,  most likely for the first  time ever.  The next step in the restoration is to straighten out the problem with the diagonal mirror/focuser issues since the diagonal is out of alignment but glued to the metal stalk that is part off the focuser.

   Here are a couple of pictures  showing the motor being repaired.

 

             - Dave 

 

     RV-4 Deluxe.jpg                   

     RV-4 opened motor.jpg   

     RV-4 reapired gear.jpg

     RV-4 motor mounts.jpg     

 

 

 


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#2 TOM KIEHL

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Posted 28 June 2019 - 01:15 PM

Nice Save Dave , Welcome to the club lol.gif

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#3 dgreyson

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Posted 28 June 2019 - 02:16 PM

Nice save. When working with clock movements, use a long piece of broom straw attached to amplify the motion. You can easily see the end of the straw sweeping smoothly and any irregular motion in the gear train becomes readily and obviously apparent.

#4 DAVIDG

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Posted 28 June 2019 - 02:32 PM

Nice save. When working with clock movements, use a long piece of broom straw attached to amplify the motion. You can easily see the end of the straw sweeping smoothly and any irregular motion in the gear train becomes readily and obviously apparent.

 I didn't use a long piece of straw on the motor when I had it out but I used about 6" of solder since I happened to have the roll on the bench, and used that  to verify the output motion of the motor was smooth and also at 10 minutes per rev.   Also been restoring clocks for years as telescope for many years.

 

                  - Dave 


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#5 steve t

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Posted 29 June 2019 - 07:27 AM

Dave, 

That is a very nice looking scope. I'll be interested in hearing on what you think of the optics.

Steve T 


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#6 DAVIDG

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Posted 29 June 2019 - 11:19 AM

 I had RV- 4 out to check out the image. I was using a vintage Galoc 16.3mm and 7mm eyepieces.  A check of the collimation before I started  and it showed the diagonal was off.  I could tell that the diagonal was glued onto the metal stalk upside down since the 45 degree bevel on one the sides was at the top instead of the bottom and it was off to one side. I was able to loosen the focuser and shim it enough to get things close enough to test things out. 

   So out into the back yard to check out a couple of objects. First was Jupiter. The image wasn't  bad and the there was some detail visible. Most would say the images was very good. I then switched to  the 7mm and things started to look a little weird. It was like I had two images of Jupiter on top of each other that were slightly out of register. Still most I bet would say the image was very good and it was seeing that night.

   Now onto Vega to do a star test.  To do a star test correctly  you need to use an eyepiece with  a focal length that is  around the F-ratio of the scope. This one is  around f/11 so the 7mm was fine. I looked at the slightly defocused image of Vega on both the inside and outside  of focus to see what the correction was like. Right from the start I could see that was something wrong and it wasn't just from the misalignment. The diffraction pattern were asymmetrical  and looked like blops.  That indicated  some optical problem.

   It was been my experience that almost all of these small reflects have good primaries but the secondaries are junk. So back into the shop to see what is going on with the secondary. The diagonal is glued  to the thick metal stalk with epoxy and that could be distorting the  surface of the diagonal. So out comes the heat gun and heated the diagonal to soften the glue and the diagonal pulled off with no problems.

    So I let the diagonal cool back down to room temperature for about two hours so I knew that the diagonal wasn't  being distorted by being hot. Then got out a precision flat that is good to around a 1/10 wave and has partially reflective coating. The coating increases the reflectivity of reference surface so it is  a closer match to fully coated diagonal and allows one to see the interference pattern much easier. So I set up the monochrome light and tested the diagonal. The picture attached shows the problem. The diagonal has astigmatism. So once again the odds are pretty high that the  diagonal in these scopes are junk and if you want to improve the image get a good diagonal and test it to be sure it is good.

   So the plan is to cast a small pitch lap, press it against one of my Master flats and use that to refigure this diagonal to flatten it out.

So my advice continues to be if your going to spend the time and money to mechanically restore a vintage scope, take the time to test your optics so know what you have. A telescope should be just as good to look through as it is to look at.

 

                       - Dave

 

 

 

         

 

 

 

 

 

 

RV-4 diagoanl focuser.jpg

RV-4 diagonal.jpg

 


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#7 steve t

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Posted 29 June 2019 - 12:25 PM

Hi Dave,

I'm looking forward to following your thread. 

 

For sometime I've been trying to isolate the source of a very slight astigmatism in the system of my 4" Newtonian that only shows up during star test. Individually the optics have tested okay and I've started looking at the mechanics as the source of the problem.  

 

Steve   



#8 DAVIDG

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Posted 29 June 2019 - 05:48 PM

 Steve,

   How are you testing your optics to be sure there is no astigmatism in them ?

 

                               - Dave 


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#9 steve t

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Posted 29 June 2019 - 09:26 PM

 Steve,

   How are you testing your optics to be sure there is no astigmatism in them ?

 

                               - Dave 

Hi Dave,

 

I didn't personally test the primary, but had it tested twice by two experienced mirror makers and both pronounced the primary to be very good. I know first used a Foucault test, but not sure what  method was used by the second.

 

The quartz diagonal came with a datasheet, from the  manufacturer, that claimed it to be about 1/10 on the wavefront.  Since my 6" newtonian has the same size diagonal mirror and type of diagonal holder (Novak). I tried swapping them between the two scopes and the astigmatism didn't follow the diagonal.  

 

I was wondering if I could have missed something mechanical in the system that could introduce astigmatism. 

 

Thanks

 

Steve T 



#10 DAVIDG

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Posted 30 June 2019 - 09:36 AM

 Steve,

     If you are using  a Foucault test with a  knife edge, it difficult to detect small amounts of astigmatism. It is better to use a Ronchi screen. You adjust the screen use the pattern is perfectly vertical on one side of focal plane, then move the grating the other side of  the focal plane. If you detect any rotation of the pattern then you have astigmatism.

    As for the diagonal flat, I don't trust what a test report states. I have seen too many that state "1/10" wave flat and look worse then the picture of the Criterion one I just posted when I test it against one of Master flats.

   If you assume that the optics are not the issue then it is alignment issue. It just takes a tiny misalignment of the tilt or centering of the diagonal to introduce astigmatism. I use  laser collimators with a built in target so I can get the return beam perfectly aligned. By the way I have couple of laser collimators and a majority of them were not correctly aligned. I chucked them in a lathe and projected the beam about 10 feet away then slowing rotated the chuck.  Instead of the  spot staying stationary, it was making a 4" to 6:" diameter circle, that  showed the laser wasn't aligned with the outside diameter of the collimator.  There are three screws that you can adjust to correctly align the device so it will give you correct then correctly align your optics.

   So again I 'll say, double check everything to be sure it was what it suppose to be. 

 

 

                       - Dave 


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#11 steve t

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Posted 30 June 2019 - 10:30 AM

Dave,

Thanks for the reply. I'll keep working on the collimation.

 

From experience,  I've learned not to trust manufacturer claims smile.gif   

 

On a side question,  in the past, when I did a final check of the collimation I've used an auto collimator to make sure the primary center dots reflections are stacked on each other. Would a laser collimator be more accurate?

 

I've always thought the 4" Criterion was the nicest looking scope in that size. I'll be looking forward to following your restoration. 

 

Regards 

Steve T 



#12 DAVIDG

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Posted 30 June 2019 - 11:26 AM

 Beautiful day down here in Delaware so before I get busy with other tasks around the house I wanted to keep the RV-4  restoration moving.  Removed the counter weight, and finder bracket and already had the focuser off so I finished disassembling it. I washed them using a toothbrush to get all the dust and dirt out the wrinkled paint and let them dry. The wrinkled paint is still  the well  adhered to the  parts but a bit dull  after 60 years  so to freshen them up  I gave them a light spraying of gloss back. 

   I hope to do more of the mount this evening  and cast a pitch lap to refigure the secondary with.  More to come as  the project continues. Now off to the house project of painting molding. 

 

                   - Dave 

 

 

RV4 pianting parts.jpg


Edited by DAVIDG, 30 June 2019 - 11:27 AM.

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#13 DAVIDG

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Posted 30 June 2019 - 11:34 AM

Dave,

Thanks for the reply. I'll keep working on the collimation.

 

From experience,  I've learned not to trust manufacturer claims smile.gif   

 

On a side question,  in the past, when I did a final check of the collimation I've used an auto collimator to make sure the primary center dots reflections are stacked on each other. Would a laser collimator be more accurate?

 

I've always thought the 4" Criterion was the nicest looking scope in that size. I'll be looking forward to following your restoration. 

 

Regards 

Steve T 

 Steve,

   I would check the alignment with  a laser collimator. A  couple of years ago I displayed a Celestar 4 at Stellafane that I refigured the optics. In the optical judging it tied for second but I knew the primary was dead on the money but I could  detect a tiny bit of astigmatism that  the judges  saw also. When I got back home I put a laser collimator on it and sure enough  the diagonal was a little off. It was difficult to see visually but the laser showed it. Aligned it and now no astigmatism.  

  Something is causing what you see so you just have to go step by step and check everything to find the source. Like I said  don't assume the quality and accuracy of the parts including your laser collimator. Confirm everything and then you'll be able to find the source instead of it being a mystery. 

 

  I agree a RV-4 Deluxe is great looking scope and from using it  a little a great working scope as well. The rotating tube and the slow motion in Dec makes it a cut above many 4" reflectors. Once I get  the optics straighten out and I'll have the scope that will perform better then 90% of the 4" aperture stuff out there.

 

                  - Dave 


Edited by DAVIDG, 30 June 2019 - 06:43 PM.

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#14 steve t

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Posted 30 June 2019 - 12:58 PM

Thanks Dave, I'll start shopping for a laser collimator.

 

Regards 

Steve T 



#15 DAVIDG

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Posted 01 July 2019 - 11:20 AM

 More progress on the restoration. I took the tripod apart and lightly sprayed the hub assembly gloss black. That really makes the wrinkled finish stand out.  The oak legs were in good shape so just a light sanding and sprayed the legs with semi-gloss polyurethane.  The yard is calling my name so off to work on that. 

 

                    - Dave 

RV-4 Tripod hub.jpg

 

RV-4 legs.jpg


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#16 DAVIDG

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Posted 01 July 2019 - 08:23 PM

 More progress. I pulled the primary and tested it  via a Foucault test. It measures out to be F11.5 so a  long focal length. At 4" aperture at this focal length and aperture a clean sphere would be a true 1/8 wave system. That would give an excellent image when teamed with a good diagonal. When I tested the mirror I was very pleased to see that this mirror has perfect edge and very smooth with no zones. The best is that is it an excellent parabola. So the wave front is better than 1/8 wave ! 

   The parabolic shadows on these small aperture long focal length mirrors are faint. So if the mirror looks like it has parabolic shadows like you see in a book or photo then the mirror is very much over corrected. So it is difficult photographic them but you can see them visually.  I measured the inner to the out zone and it comes out what theory shows it should be. So my hat is  off to Criterion for getting this one right. 

    Here is  a picture of the mirror. The bright  edge on both side indicates no turned edge and you see a smooth figure with no sharp shadows indicates no zones. 

 

                               - Dave 

 

RV-4 Mirror.jpg


Edited by DAVIDG, 01 July 2019 - 08:32 PM.

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#17 steve t

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Posted 01 July 2019 - 08:54 PM

Hi Dave,

I was just curious as to what size diagonal did Criterion use? 

Steve T 



#18 Mr Magoo

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Posted 01 July 2019 - 09:24 PM

Really cool Dave. I have a very short list of scopes I would still be looking for and a Deluxe is high up there. I really love the 4" ones. I wonder how many of these were sold? You just don't see them come up for sale hardly ever compared to others. 



#19 DAVIDG

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Posted 02 July 2019 - 09:56 AM

Hi Dave,

I was just curious as to what size diagonal did Criterion use? 

Steve T 

 Steve ,

    The diagonal measures out to 1" x  7/8"  

 

                  - Dave 


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#20 Don Hall

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Posted 05 July 2019 - 11:42 AM

Dave,  nice report on your test of the RV 4.  I had a 4" Deluxe with eq mount which was received as a Christmas gift in 1954 I think.  Keep it until I was in my 40's.  Always thought it performed well.  I, too,  have tried to find another but they are hard to locate.   When you make additional changes to the RV4  would be interested in what you did. 



#21 Gil V

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Posted 06 July 2019 - 03:27 PM

Why not just buy an elliptical flat for a secondary?

Glad the primary is good! You’ll end up with a fine scope.

Edited by Gil V, 06 July 2019 - 03:29 PM.

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#22 DAVIDG

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Posted 06 July 2019 - 03:56 PM

Why not just buy an elliptical flat for a secondary?

Glad the primary is good! You’ll end up with a fine scope.

 Unfortunately it has been my experience that almost all the small ones  are junk when I test them.  In the time it would take to buy a handful and find good one I'll have this one right.  

   I just got done painting the mount. So the scope should be finished in a day or so. Only the tube cradle is left.  Here are two pictures of the finished tripod. A light coat of gloss black really brings the wrinkled finished back to life !

 

                    - Dave     

R4 finished tripod.jpg  

RV4 finished tripod hub.jpg


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#23 steve t

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Posted 06 July 2019 - 04:21 PM

Wow, very nice.

Steve T 



#24 DAVIDG

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Posted 09 July 2019 - 09:31 AM

 The scope is almost finished. I finished the mount over the weekend. Totally dissassembled, cleaned ,lubed and sprayed a light gloss black coating over the original wrinkled finish. I got the Dec slow motion working nicely now. I had a setback in that the drive stopped tracking. I took the motor back apart and found that the epoxy didn't hold, and the gear on the output shaft was just spinning free again. So this time I got medieval on it and took out the propane torch and soldered the gear to the shaft. The scope is back to tracking and hopefully fixed for good.

   I wimped out on refiguring the diagonal. I was digging around in my collection of parts and found an rectangular flat and when I  tested it. it was flat over the area that  would be active, it is good to around  a 1/16 wave.   So no guessing to it's quality and when teamed with the excellent primary which I know is good because I tested it, the combination will produce an image that is truly in the 1/8 to 1/10 wave range.

   The next step is to make a drawing of the focuser and the diagonal mount  as it sits on the tube to determine the position of the diagonal on the mounting stalk. The surface of the diagonal  needs to be in the correction position to intercepts the light cone from the primary and since it is mounted on a fixed stalk it has to be mounted correctly from the start. 

 

                        - Dave 

RV4 finished mount.jpg

RV-4 new diagonal.jpg


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#25 DAVIDG

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Posted 14 July 2019 - 08:48 AM

 The mechanics of the RV4 have all been restored. The only thing  left is to glue the new diagonal in place and start enjoying the scope or  so thou I thought. Before I glued the diagonal to the stalk that is part of the focuser I made a cardboard template to show were the surface of the diagonal needs to be so it would be centered in the focuser tube and centered on the optical axis of the primary.

   The ID of the tube is 4-1/2" so the reflected surface of the diagonal needs to 2-1/4"  from the ID of the tube.  I made the template 1.25" wide and the  end cut at 45 degrees so it would slip into the focuser tube.  I maked a line  showing  were the template needs to positioned in relationship to the ID of the tube.  As the attached picture shows, the template comes right up against the mounting surface of the diagonal ! So the focuser/diagonal mount doesn't take into account the thickness of the diagonal. Both the original diagonal and the replaced are 1/4" thick. So if I mounted the diagonal on the mounting plate,  the diagonal would be too close  to the focuser and too far forward. What this does is move the optical axis of the primary from the center of the focuser back toward the primary. So  what you see centered in the eyepiece is not the center of the field of view from the primary but the off axis image. The off axis image has coma. Also what is worse is to make the diagonal looked centered when you collimate it you would  have to either tilt the focuser or tilt the primary, both of which introduces astigmatism into the image. So I would never get the image quality that the excellent primary can deliver because of this flaw in the design the diagonal mount. 

   So I'm going to have to cut the mounting plate off and reattach it lower to compensate for the thickness of the diagonal and any glue and padding placed between the metal surface and the glass.

 

 

                          -Dave 

 

RV4 focuser.jpg


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