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Restoring a Criterion Dynascope Deluxe Mount

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110 replies to this topic

#26 Geo31

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Posted 11 December 2018 - 02:48 PM

If you're not going to powdercoat them, there is nothing wrong with using some JB Weld.  If want to see some real art work with JB Weld, search for Robert's (Clampchip) thread restoring what I thought was an unrestorable Tinsley Saturn.  Wow.



#27 Geo31

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Posted 11 December 2018 - 02:53 PM

It seems to me this mount took a fall. You stated part of a crack is raised relative to the rest so I'd think a side shock from a fall. Since the mount has been modified anyway, it would be easy for an owner to take it apart and shim a bearing after a fall.  Criterion may have been starting to hurt at that time but I don't see them installing shims on a major crack to send it out the door.  I could see factory shims being used but not on known damage like that. 

From what I've seen restoring the RV-6 mount, I'd just guess, as Dave did, that something wasn't quite machined right.  I kind of doubt it would crack in a fall.  I suppose if there was already some internal stress in the casting, maybe.  The bearings were probably pressed in, causing the cracking.  The one with the shim was probably bored a little too large.  In fact, it wouldn't surprise me if Criterion actually machined the bores with a drill press.  The bores they did were not exactly tight tolerance work, what with the peening they did to the outside of the bores to tighten them up sometimes.  My RV-6 mount is definitely sloppy.  The misalignment Dave describes is part of why I didn't try over-boring the castings on my RV-6 to insert Oilite bearings.


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#28 clamchip

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Posted 11 December 2018 - 03:33 PM

If you're not going to powdercoat them, there is nothing wrong with using some JB Weld.  If want to see some real art work with JB Weld, search for Robert's (Clampchip) thread restoring what I thought was an unrestorable Tinsley Saturn.  Wow.

My tinsley was missing a piece out of it's cell so I made a dam and filled it with JB weld, it wasn't

structural just a cosmetic repair. The difficult part of the repair was cutting the threads in the JB on

the inside of the cell for the screw in lens cover, just in case I ever find one! 

I think with your Dynascope cracks I would strip the paint, clean all the crud out of the cracks, clean

the bearings and dry assemble the mount and see how everything feels.

If the mount seems to operate okay take it apart and drill tiny holes at the ends of the cracks to keep

them from growing and leave them alone, and paint the mount.

If a bearing is loose in it's bore tighten it to a light push fit with the brass shim stock you have there.

Robert

 

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#29 DAVIDG

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Posted 11 December 2018 - 04:05 PM

 Very nice repair on the lens cell. ! Just to point out the obvious that the repair to the cell isn't under any stress but  fills in missing material. I used the same method to repair a Unitron 114 cell. 

   In the case of the Criterion mount, the casting and the repair will be  under the  load of the weight of the telescope and counter weight, along the metal being under stress if the bearing is a tight fit in the bore.  While JB Weld is pretty tough stuff it doesn't have the same strength as if the part was TIG welded or brazed to make the repair which under these condition would be a more  permanent. 

 

            - Dave 

 

repaired unitron cell.jpg

painted unitron cell.jpg


Edited by DAVIDG, 11 December 2018 - 06:00 PM.

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#30 mfoose

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Posted 11 December 2018 - 04:13 PM

Good call guys. I am not sure how they bored this, but the top and bottom are not straight. The top is the first picture and the bottom is the second. Looks like I will be buying some more of that brass shim material. 

 

My thoughts now are to strip and clean all of the paint and grease from this, drop it off at a friend's who is a welder, put the rod in and then slide the needle bearings into place using shims to align the bearings, then disassemble and paint it. 

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#31 mfoose

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Posted 12 December 2018 - 04:49 PM

Another parts question: where could I find replacements for these plastic/rubber washers that were on the 1.5" shafts? They are 1.5" ID, 2.2" OD and about .075" thick.

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#32 bremms

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Posted 12 December 2018 - 07:58 PM

https://www.mcmaster...roller-bearings

 

While you could certainly weld up the crack, you could probably get away with JB Weld also (if you're careful).

That is not a JB weld job. It needs to be properly welded.


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#33 charlesgeiger

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Posted 18 December 2018 - 01:19 AM

The first thing to do is take it to a welder.  I don't want to be negative, but this may not be able to be welded.  Those castings were not the best and the metal may be poor quality.  

I hope it does work out for you.  I used an 8" custom dynascope and it was a wonderful instrument rating with the top tier telescopes of the day..

Charlie



#34 Geo31

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Posted 18 December 2018 - 07:02 AM

That is not a JB weld job. It needs to be properly welded.

While I would always prefer welding, I want to question why JB Weld is a bad idea.  This is a legitimate, serious question, and not a "challenge" per se.

 

My reasons for thinking JB Weld would be fine are:

 

  1. The cracks are likely from internal stress in the casting that were opened up when the bearings were pressed in.
  2. The casting does not see any of the rotational force from the shaft as that is felt by the bearing, which is stationary in the casting.
  3. The bearing spreads the force from the weight over basically half the bore.
  4. Modern fillers/adhesives form pretty strong bonds.

 

Again, I'm asking because I'm trying to learn here.  Is JB Weld really a bad idea, or was it dismissed out of hand?  I'm just really curious here.



#35 apfever

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Posted 18 December 2018 - 10:24 AM

For starters, JB is good for full face contact fixes where both surfaces to bond are open and accessible for complete cleaning and drying. JB should be seriously worked into the grain of both faces to be fixed. If you want a serious bond, you need serious access to both faces.  The fractures presented here will not allow that kind of access for either cleaning or application of the glue. Spraying 100% evaporation electrical cleaner or brake cleaner through the crack isn't an ace cleaning. The JB will never get completely through the cracks, ESPECIALLY TO THE END OF THE CRACK WHICH IS THE SENSITIVE STRESS POINT.  For the most part, the glue would never get through the crack very well at all even if stressed open a little and never close to the end of the crack. Deepening a groove along the crack isn't a JB fix like it is for welding.  The posted situation is simply not a good JB fix.  I like JB for the right job, I have plenty here, I've fixed machinery with it, I've seen JB do impressive things, I've seen JB fail, and JB is NOT for this king of repair.  Placing JB Over the crack is a total failure in application. 

 

Brazing is a different story. Flux can clean and penetrate a crack and flow ahead of the brazing deep towards the ends. Brazing can be drawn completely through the crack by proper application with flux on steel, copper, brass, etc.  I don't know about aluminum in particular.  It would be easy to make some professional inquiry about such for aluminum.  This is a substantial scope with a substantial concern. I'd probably research brazing aluminum and give it a go myself but this is the sort of thing done off and on out in country in various ways (lots of other metals) so basic experience lives here. I'd suggest taking the part to a shop and ask for an opinion, not just a description with a phone conversation. A shop isn't going to charge for counter examination and quick analysis for this kind of repair, they've probably seen plenty like it. Shop your shops, pick one, get it LOOKED at and go from there,  Oh, then let us know here, thanks.

 

PS. I'd still put a clamp around it and make it look good, like the split clamps I showed in a previous post. I intend to clean and paint mine in Edmund grey for the 8" mount. I'll Clean off the shipping oils with spray cleaner, and then put the clamp in a metal prep etch (have the stuff here already), then probably won't even use a primer after the prep etch. 

 

There is no need to literally have to press in the bearings for this application. A 'zero' thumb push fit is plenty and a drop of light duty thread locker (such as Loctite Blue) should hole the outer race if there aren't other structural anomalies such as misaligned bores.  If the bores on each end aren't aligned, that should be addressed - boy I sure would.  Put the unit on a straight shaft of stock and support it on each end with single shim of stock (you can mic the shims for identical thickness).  A backlight will show a scissor gap of  even 0.001" easy and that much would be no big deal. 


Edited by apfever, 18 December 2018 - 10:27 AM.

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#36 Geo31

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Posted 18 December 2018 - 11:31 AM

Many thanks for the thorough explanation.  Truly appreciated.



#37 Mr Magoo

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Posted 18 December 2018 - 07:38 PM

I thought I saw this mount for sale being parted out a few days ago. Can't find the ads now.


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#38 Geo31

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Posted 18 December 2018 - 09:20 PM

I thought I saw this mount for sale being parted out a few days ago. Can't find the ads now.

If this mount is being parted out (or one like it) I want the bloody settings circles (along with everyone else).


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#39 TOM KIEHL

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Posted 18 December 2018 - 10:17 PM

I thought I saw this mount for sale being parted out a few days ago. Can't find the ads now.

 

 

If this mount is being parted out (or one like it) I want the bloody settings circles (along with everyone else).

THIS 'IN ? https://www.cloudyni...h-mount-2-axis/


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#40 Mr Magoo

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Posted 18 December 2018 - 10:36 PM

Different mount than this one. Missed it by that much George!



#41 Geo31

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Posted 19 December 2018 - 12:16 AM

Different mount than this one. Missed it by that much George!

Actually, I think it's the original ad for the same mount.  Note the plastic handle knobs.

 

Glad this one is not being parted out.  Too nice.


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#42 rolo

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Posted 19 December 2018 - 08:02 AM

Looks like your mount has an RA assy for the declination? Never seen one like that before.

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#43 bremms

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Posted 19 December 2018 - 08:46 AM

While I would always prefer welding, I want to question why JB Weld is a bad idea.  This is a legitimate, serious question, and not a "challenge" per se.

 

My reasons for thinking JB Weld would be fine are:

 

  1. The cracks are likely from internal stress in the casting that were opened up when the bearings were pressed in.
  2. The casting does not see any of the rotational force from the shaft as that is felt by the bearing, which is stationary in the casting.
  3. The bearing spreads the force from the weight over basically half the bore.
  4. Modern fillers/adhesives form pretty strong bonds.

 

Again, I'm asking because I'm trying to learn here.  Is JB Weld really a bad idea, or was it dismissed out of hand?  I'm just really curious here.

It is a structural area where the bearings are inserted. It needs be welded and line bored and automotive shop can even do the boring for not too much.  Fix it correctly the fist time and save yourself the hassle.  The Epoxy might be ok for a while, but it is not a real fix. The casting would still need to be line bored so just get it properly welded.


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#44 astro140

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Posted 19 December 2018 - 10:51 AM

Looks like your mount has an RA assy for the declination? Never seen one like that before.

Rolo,

My deluxe 8" Dynascope has the same (exact same?) assembly on the Dec axis.

Steve

New Mexico

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#45 mfoose

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Posted 19 December 2018 - 11:37 AM

Actually, I think it's the original ad for the same mount.  Note the plastic handle knobs.

 

Glad this one is not being parted out.  Too nice.

That is indeed the mount. 


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#46 mfoose

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Posted 19 December 2018 - 11:41 AM

It is a structural area where the bearings are inserted. It needs be welded and line bored and automotive shop can even do the boring for not too much.  Fix it correctly the fist time and save yourself the hassle.  The Epoxy might be ok for a while, but it is not a real fix. The casting would still need to be line bored so just get it properly welded.

I am getting it welded, though I may use JB Weld for a cosmetic fix on the mount that isn't related to the cracks. I may also look into getting it bored. It may be straight, but based on the bored holes already it sure doesn't look like it.


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#47 mfoose

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Posted 19 December 2018 - 12:02 PM

Looks like your mount has an RA assy for the declination? Never seen one like that before.

Good eye Rolo. I noticed that too and I am unsure what the deal is. In all of the other pictures and advertisements for the Dynascope Deluxe 8 I have not seen another mount with an RA assembly box on the DEC. It has all same holes too. I think it came like this from the factory. The RA is on the left and DEC on the right. 

 

I also noticed something else while looking at pictures and advertisements for Dynascope Deluxe 8 mounts. For the 6" and 8" deluxe the equatorial heads are made of cast aluminium and like the one in your picture is one sided. Where as mine is made of cast iron and is double sided (see picture below). Here is a Criterion catalog featuring the Dynascope Deluxe: https://wiki.telesco..._Literature.pdf

 

My DEC assembly is also missing its setting circles pointer and it does not look like one was ever installed. I am a bit miffed about that. I will have to figure something out to replace it and possibly the RA pointer as well so they are matching.

 

I am starting to think that the maybe Criterion ran out of some of the normal parts when this scope was ordered and they just threw on some stuff that they had.

 

I hope some other Dynascope Deluxe owners would chime in with how their mounts are assembled.

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Edited by mfoose, 19 December 2018 - 12:10 PM.


#48 tim53

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Posted 19 December 2018 - 12:09 PM

You do not have to bake it.  I've used it extensively on my RVC-6N restomod scope.  See photo below:

 

dpp71kM.jpg

 

Every single black part you see is painted with wrinkle paint and not baked.  I've found it helps to do a couple of light coats and a heavier final coat.  It may even be a good idea to spray a base flat black coat first as when the paint pulls up to wrinkle, I could sometimes see the primer in the troughs.

I've been able to find self-etching primer in black.  Eastman I think.


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#49 KentTolley

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Posted 19 December 2018 - 12:24 PM

Another parts question: where could I find replacements for these plastic/rubber washers that were on the 1.5" shafts? They are 1.5" ID, 2.2" OD and about .075" thick.

It's a thrust bearing.  See MacMaster Carr.  I don't see why you couldn't use a needle-roller thrust bearing.    Macmaster has them with 1.5" hole.  They also have flat thrust bearings like the one you show.


Edited by KentTolley, 19 December 2018 - 12:29 PM.

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#50 mfoose

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Posted 19 December 2018 - 02:53 PM

Thanks Kent! I did find a near perfect match in needle-roller thrust bearings: https://www.mcmaster.com/5909k41 Unfortunately, most flat bearings have a wider OD then I need. 




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