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Astroscan Repair

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#1 DAVIDG

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Posted 08 November 2019 - 10:32 AM

 A couple of weeks ago I was digging around on Ebay and spotted an Astroscan that the seller stated was purchased directly from the Edmund store soon after they started marketing them.  From the pictures it did look like it might be one of  the original versions since there was no badge on the optical window that covers the area were the diagonal stalk is mounted.  I made the seller an offer and it was accepted.

    A few day later the scope arrived well packaged but in transits just the bouncing around caused the glue seams on the body to fail and the body split. I contacted the seller and he was willing to help but wanted to make a claim with the shipper. To me it wasn't worth the hassle since I was planning to disassemble the  scope anyway for cleaning so repairing the body wasn't going to be a big issue.

   Here is  a picture of the split seam.

 

 

             - Dave 

 

split body.jpg

 

split body 2.jpg


Edited by DAVIDG, 09 November 2019 - 10:06 AM.

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#2 DAVIDG

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Posted 08 November 2019 - 10:48 AM

 The next step was to remove the optics. Both the optical window and mirror are held in place by large metal snap rings. I covered the optical  window with a piece of cardboard to protect it in case something slipped and used a pair of needle noise pliers to grab  one end the snap ring and work it loose from the body. I then used a piece of duct tape stuck to the window to left it out.

   To remove the mirror you first need to remove the metal counter weights that are on each side of the mirror. There is a screw that holds each in place so you unscrew those and left each weight out of the tube. 

  Next you have to reach down inside the tube and grab the end of the metal snap ring and work it out of the groove that it is seated in. You need to be careful not the damage the mirror in this process.

   With the snap ring out you can left the mirror out the tube. Under the mirror is an urethane foam pad. It is the  major cause of why these scope loosing optical alignment. The foam turns to dust after a few year and won't hold the mirror in place. The foam pushes up on the back of the mirror and holds it against the snap ring which maintains the alignment of the mirror. More about this in the next posts. 

   So with the optics out  I used JB-Weld to glue the body back together and used duct tape to hold it in place until the glue setup.

 

              - Dave 

 

taped seam.jpg


Edited by DAVIDG, 08 November 2019 - 04:25 PM.

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#3 DAVIDG

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Posted 08 November 2019 - 10:51 AM

 The next day the glue was dry and the body back to being solidly held together. While the glue was drying I replaced the three felt pads on the base the ball of the body rides against and the three on the feet. That made a huge difference in the motion of the scope. Now nice smooth motion and it stayed in place when I let go.

 

                - Dave 

 

repaired seam.jpg


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#4 DAVIDG

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Posted 08 November 2019 - 11:07 AM

 Now to put the optics back in place. Both the mirror and optics window were washed and the inside the scope cleaned out so nothing would get back on the optical surfaces.

    The critical part to getting the optics to align is the foam pad under the mirror. It applies even pressure on the back of the mirror pushing it up against the retainer ring. The original one was made of urethane foam which reacts with air and falls apart after a number of years. This cause the mirror to be able to move and become misaligned. My foam pad came out in pieces so I needed to make a replacement. I used a disk I cut from close cell polyethylene foam used in packing. It will not deteriorate like the urethane material.

  The disk was cut the same size as the mirror ie 4.25". I used 4.25" mirror blank to test the fit. The area were the mirror sits is concave since the base is a ball and the thickness of the foam pad needs to be  such that it  pushes  up on the back of the mirror enough to hold it in place but also allow the snap ring to be installed. I found out by using the mirror blank to test the fit that  the foam pad was too large in diameter vs it's thickness. After a few tries of reducing the diameter of the foam pad, I found that with the diameter at 3-1/2" it  fit the concave area so that the edge of the pad would push up on the back of the mirror so the snap ring could be installed and kept the right amount of pressure on the mirror.

 

           - Dave 

 

mirror blank and foam pad.jpg


Edited by DAVIDG, 08 November 2019 - 04:27 PM.

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#5 DAVIDG

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Posted 08 November 2019 - 11:21 AM

 Now it was time to install the mirror. I taped a piece of paper over the surface to protect it and had to leave two edges exposed since these were the snap ring would make contact with the edge of the mirror. If the paper was a full disk, it would get  caught under the snap ring.

   I wore cotton gloves and placed the mirror down inside the tube and over the foam pad. I made sure that the foam pad was centered before placing the mirror in place so it would apply even upward pressure on the mirror. With the mirror in place, I put one side of the snap ring in the groove and was able to squeeze the other side so it would snap into place with no damage to surface of the mirror. I then removed the paper cover.

   Next was the optical window. I used a piece of duct tap stuck to the center to lower it place. With the window and diagonal in place I could check the optical alignment. It was dead on the money ! I then careful snapped the retainer ring in place.

   I had the scope out under the stars using a 26mm eyepiece. The views are very pleasing, stars are sharp and the moon very nice.  I also discovered that in the area by the focuser and inside the scope there is "112"  written. I don't know if this a serial number or not but if so that would mean that this one might be from one of the first group of Astroscans made. 

 

                - Dave 

 

mirror and foam pad.jpg

aligned optics.jpg


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#6 Alex65

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Posted 08 November 2019 - 11:46 AM

Great job on repairing that telescope and nice description on how you did it.

 

I would guess that your telescope is certainly from the 1976 production run as they were numbered in sequence. Mine is from a couple of years later and already in the 10000s.

 

I will need to refurbish my Astroscan one day and have taken note of your approach.



#7 apfever

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Posted 08 November 2019 - 04:02 PM

The tubes are ABS plastic and can be glued with ABS pipe cement. This is the plumbing glue that MELTS the plastic into a bond. Too much glue can end up puddling your plastic. 

The cases have a fairly large mating area so it is possible any glue might seem solid initially.  I use JB plenty, don't recall any particular time with ABS.  Any experience out there test wise for JB on ABS? Give me a 10-4 on that. 



#8 rolo

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Posted 08 November 2019 - 04:19 PM

Never seen one split apart like that before. Most if not all that I've owned have been out of collimation. Sometimes it's the mirror other times the secondary. Once collimated they're decent scopes.



#9 wfj

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Posted 08 November 2019 - 05:30 PM

I had one with the broken down foam. Came here, and learned a simple fix. Cut up small "strings" of polypropylene foam (polypropylene lasts far longer than urethane - and much urethane foam degrades because it isn't neutralized properly)  and shoved them through the tripod screw hole at the base of the Astroscan.

 

It's a tedious repair, because you have to "distribute" the foam and keep on pushing in more uniformly, until the mirror it uniformly supported against its retaining ring.

 

Once I did that, it was perfectly collimated. Next issue was the diagonal, which was distorted because it was glued on improperly, so doing it properly made for good images beyond 100x.

 

I've been working on a collapsible, pocket fold-up newt that incorporates a very nice Carton mirror. It's a tedious project where I over/under design various components, break things, rework the design, rebuild, use, ... The point for me is to retain much of the Astroscan in a pocket, like Horace Dall's cassegrain, just lighter, simpler, better mounted.


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#10 clamchip

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Posted 08 November 2019 - 07:31 PM

The tubes are ABS plastic and can be glued with ABS pipe cement. This is the plumbing glue that MELTS the plastic into a bond. Too much glue can end up puddling your plastic. 

The cases have a fairly large mating area so it is possible any glue might seem solid initially.  I use JB plenty, don't recall any particular time with ABS.  Any experience out there test wise for JB on ABS? Give me a 10-4 on that. 

I use ABS and PVC cements in my job for the little bit of plumbing I do, mostly air

conditioning condensate drains.

They give you about 2 seconds to work with and then lock up solid and there's no

second try if you get it wrong.

But a excellent choice for these types of plastic.

 

Robert


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#11 DAVIDG

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Posted 08 November 2019 - 10:49 PM

 The reasons I used the JB weld was it is strong, has a long pot life so I could get things aligned and if  I got any excess on the outside of the seam I could wipe it off and not damage the shiny surface. A solvent based adhesive like what is used on ABS and PVC dissolves the plastic and then reforms the materials across the joint. It is a chemical weld but it quickly dissolves the plastic when it comes in contact will it so you have to work fast and if you get it anywhere you don't want it will dissolve that area as well and make a rough surface that is easily visible.  

 

                           - Dave 


Edited by DAVIDG, 09 November 2019 - 10:05 AM.

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#12 Chuck Hards

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Posted 08 November 2019 - 11:22 PM

I'm just glad to see duct tape used somewhere in the process.  


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#13 apfever

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Posted 09 November 2019 - 01:00 AM

Any serial number inside the focuser bump out?



#14 AstroKerr

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Posted 09 November 2019 - 04:00 AM

Fine works!

 

Occurs to me since it's abs, one might jig the scope, drill appropriate holes @ 8~10 locations, add ABS rod, one on one side drilled and tapped, one on the other just drilled (ledge for screw head) to the inside @ those locations, and secure with screws. Might try it if I have one split, although I think it'd be better to badger up a tool specifically for mirror removal / maintenance - Edmund must've had a tool, no?

 

A Mirror Removal Tool. Time to re-read the Astroscan threads, make some measurements.

 

Thank you, everyone who posts their Astroscan work waytogo.gif - you are pioneering, steel-eyed, well regarded!


Edited by AstroKerr, 09 November 2019 - 04:05 AM.


#15 DAVIDG

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Posted 09 November 2019 - 09:45 AM

Any serial number inside the focuser bump out?

 Yes 112 is written inside the focuser .   The plastic on the body was dull so I polished it  with car rubbing compound. That brought it back to a nice glossy shine. 

    I'm working on  a wireless/ encoder less pointing system and I plan to use this Astroscan as a  test platform.

 

                                   - Dave


Edited by DAVIDG, 09 November 2019 - 10:10 AM.


#16 DAVIDG

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Posted 09 November 2019 - 10:04 AM

Fine works!

 

Occurs to me since it's abs, one might jig the scope, drill appropriate holes @ 8~10 locations, add ABS rod, one on one side drilled and tapped, one on the other just drilled (ledge for screw head) to the inside @ those locations, and secure with screws. Might try it if I have one split, although I think it'd be better to badger up a tool specifically for mirror removal / maintenance - Edmund must've had a tool, no?

 

A Mirror Removal Tool. Time to re-read the Astroscan threads, make some measurements.

 

Thank you, everyone who posts their Astroscan work waytogo.gif - you are pioneering, steel-eyed, well regarded!

 The two halves of the tube already have "ears" on one piece and mounting slots on the other.   I had the two halves glued back together in 10 minutes so I don't think one would need to reinforce the pieces. 

    The retainer rings fit in grooves cast into the plastic. The ring don't have any holes in the them like a typical snap ring. You have to work down through the opening at the top of the tube so you have limited space. It isn't difficult to reach down inside the tube and grap one end of the ring to work it loose from the groove.  If you working on  many of these it might be it worth to design some type of tool but for just one it is just as easy to use your hand to take the rings out. 

 

 

                 - Dave 



#17 apfever

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Posted 09 November 2019 - 10:05 AM

112!  112?  That's an oldie, noteworthy.  I have 751.  

 

BE Careful about the mirror!!!!!!!  Edmund very quickly fell behind in production and went to a different coating system using a layered coating process to figure the mirror.  The glass on those type mirrors is SPHERICAL  and you will lose the figure if you strip it.  I don't know of any way to determine what mirrors were figured by coating or figured in the glass. I don't know of the time frames or serial numbers when the layered coatings were used but it was early in production.  Heads UP. 



#18 DAVIDG

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Posted 09 November 2019 - 10:56 AM

112!  112?  That's an oldie, noteworthy.  I have 751.  

 

BE Careful about the mirror!!!!!!!  Edmund very quickly fell behind in production and went to a different coating system using a layered coating process to figure the mirror.  The glass on those type mirrors is SPHERICAL  and you will lose the figure if you strip it.  I don't know of any way to determine what mirrors were figured by coating or figured in the glass. I don't know of the time frames or serial numbers when the layered coatings were used but it was early in production.  Heads UP. 

 I believe I might have been  the one that informed everyone of the process they used for a while. I have one of their mirrors that first had a layer of chrome alloy applied to make it a parabola and over that was applied the aluminium. The reason why chrome was used is because the aluminium can be stripped, leaving the chrome and the parabola intact then recoated. Later on they may have switched to an all aluminium coating. If I did strip it and found afterward it was  a sphere it would be no problem for me to parabolize it. 

   The method was developed by Strong and discussed in his book "Procedures in Experimental Physics"   Here is  a picture of the serial number.

 

               - Dave 

 

astroscanserialnumber.jpg


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#19 AstroKerr

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Posted 09 November 2019 - 11:37 AM

Was thinking just screws, no glue =) didn't know about tabs, but should've expected them for alignment of halves.

 

Anyways, I had seven, now eight of these and a my left hand's in training - damaged the thumb and forefinger of the right - that might not be an issue, but a tool could be useful - handy, even.  Need to get in there...  

 

Thanks, Dave smile.gif



#20 Jon Isaacs

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Posted 10 November 2019 - 12:30 AM

I'm just glad to see duct tape used somewhere in the process.  

 

Why glue it?, just buy some red duct tape..

 

Jon


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#21 rigelsys

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Posted 11 November 2019 - 12:16 AM

As to glue for ABS I recommend ('cause I've used them for years and years and years putting ABS gadgets together)

 

SCIGRIP 4SC water thin  https://www.mcmaster.com/7517a4

 

SCIGRIP 16 medium drying bodied (if you need filler)   https://www.mcmaster.com/7515a11

 

These are ACRYLIC glues but since the A in ABS stands for acrylic, it works fine (especially since S stands for STYRENE and these glues contain methylene chloride, otherwise know as model cement :-)



#22 DAVIDG

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Posted 15 November 2019 - 10:46 AM

 If you need an original lens cap, Edmund still has them. You need to call their customer service line to purchase one. The cost is $9.95 plus a handling few. I just ordered one for mine.

 

                   - Dave 




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