6 replies to this topic

[Durobot]

Hello, good folks of Cloudy Nights!

 

Recently I have cheaply bought a (used) Celestron 25x70, and to my dismay, it came to me broken. Returning it is not an option, I don't want to just throw it away, and so I want to try fixing it. I'm seeking advice on disassembly and repair. Here are the photos, they're too large for the forum, and there's an animation of the focuser's threads so I uploaded them to Imgur.

 

It seems to have these two problems:

 

1) The focusing knob/wheel rotates, but the eyepieces don't move. I can move them manually, in fact i can pull out the eyepieces and the bridge easily. The central.. shaft? has a small (\~1 mm diameter) hole with fine threading on the inside. I suppose this is where the pin that engaged the focuser's threading used to be.

I was able to use my endoscope to confirm that there's indeed an oblong longitudinal window on the inside of the tunnel where the central shaft moves, and as I turned the focusing wheel i was able to see the threading moving past that window.

So I'm looking for any information of the size and shape of the pin that's supposed to engage these threads, and how to install the central shaft once this pin is in place.

 

2) The bridge is broken at the hinge. When inserted into the binocular, the eyepieces keep together, so this is not a huge problem.

 

Someone tried to repair the binocular and there are traces of glue in the hinge of the bridge between the eyepieces.

I have tried unscrewing the focuser, made a makeshift tool for it, but my key started bending, and the focuser wouldn't budge.

 

Currently I am considering two options:

1) Leave the hinge as it is, and try finding a thin threaded pin to replace the missing one, or the more radical option -

2) Replace the shaft with a threaded rod, drill out the hinge and use the threaded rod with nuts to hold the hinge together; drill a perpendicular hole in the rod and insert a piece of softer (copper?) wire instead of the pin to prevent damage to the guiding threads in the focuser.

 

Also, In case you're wondering, I don't think there is anyone who professionally repairs binoculars in a small country where I live, so I have to be my own repairman.

Edited by Durobot, 08 September 2024 - 12:50 AM.

[sevenofnine]

Welcome to C/N! 

 

There are a few C/N members who seem to specialize in repairing damaged/old binoculars. Hopefully, they will see your post and give you better advice. In my experience, your binos look beyond repair as a binocular but might be salvageable as a monocular. When I was a youngster an adult gave me a broken pair and I simply hack sawed off the broken side and used the other mono style. Fortunately, the good side had the individual focus ocular so it worked great. You might consider that as a solution if all else fails. Best of luck to you! 

[pat in los angeles basin]

does the pin that broke and the helical of the focus drum look like this? (celestron 15x70 skymaster pro in my case). Pin broke- jamming into the slot of the helical causing the drum to lock in place. I managed to loosen all the respective parts to get AT the drum to see how much damage was done to the helical where the pin jammed (the endo scope would be good use for that!)

 I found a metric thread stainless phillips machine of close to appropriate length, added a short piece of brass tubing to make it appear like the portion of the pin that rides in the helical and soldered it over the screw, filed the head down to the same diameter as the tubed portion. Managed to get the  thing back together- and the focus while slightly "lumpy" (due to the damage done to the PLASTIC helical) functions acceptably.

[pat in los angeles basin]

entirely TOO much plastic in the celestron skymaster  line  of binoculars BTW.  Regards, Pat

 As to the broken hinge.....I haven't the slightest idea how to repair that.   Good luck! , Pat

[Durobot]

Hey, Pat!

 

I have never seen the broken pin with my eyes - at first I wasn't even sure there was supposed to be a pin. I have never opened binoculars before, so had no idea.

My 25x70 came in the condition you see in the photos above.

 

Yesterday I found a small screw that fits the hole / threading, and discovered there was a piece of the original pin still inside.

I have managed to drill, then push out that piece (broke one drill bit, oh well), and now I can drive my screw all the way through the shaft.

 

That's not very useful though, as, turns out there's no clearance between the shaft and inner wall of the tunnel it slides along (see the photo). Somehow I was hoping there would be some. Now I have no way to insert the shaft with my makeshift pin in it into the tunnel, at least not without taking off the focusing drum.

 

How did you remove it? I have tried unscrewing the whole thing, but it wouldn't budge. I just bent the tool I made for this. Admittedly, it was not made of steel, probably some alloy, but I was still hoping to get some movement at the very least.

 

I am considering devising a new, thinner shaft with a hook on its end to engage the helical threading. Would need sort of some (plastic?) spacers / washers to  keep it centered in the tunnel, I guess.

Attached Thumbnails

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[pat in los angeles basin]

Despite the break on my pin- I was fortunate enough to find a hard flat screwdriver that I managed to scribe enough of a "flat" to allow the driver to remove the broken pin section(on mine the  pin was brass) traded out for a stainless machine screw with a bit of brass tubing to increase  the diameter to approximate the original pin dimensions. As far as I know there 's no way to repair the helical as the nylon reinforced plastic - once gouged  won't  be able to to smooth it out.

[Durobot]

It looks like I have managed to fix it.

It may not be ideal, but at least the binocular is now usable.

 

Before I post the photos, I must say I started this repair with next to no knowledge about the focuser. More specifically, I didn’t know how to disassemble it. My initial attempt to do it failed, and damaging it  in the process was the last thing I wanted. So I acted on the assumption I can’t take the focuser wheel off and can’t remove the central tube. In the end, I have removed them both – accidentally, but not before getting to the end of the process.

 

Anyway, my idea was to make a new shaft out of a bolt. This shaft has a “tongue” or “beak” protruding at the right angle at the end. I cut it out of the bolt’s head. This beak’s purpose is to engage the threads on the inner surface of the focusing wheel / barrel.

I’d do it differently now that I know you can disassemble the focuser just by pushing the central tube out (after unscrewing the bronze tripod adapter screw under the plastic cap with Celestron logo).

 

The new shaft is thinner than the original shaft (used a M6x70 bolt cut to about 60 mm length) allowing me to maneuver it inside the tube so that the beak protrudes through the cutout in the tube, meshing with the helical thread on the focusing barrel’s inner surface. BTW I was mildly shocked to learn it’s just a single piece of plastic, I though the threads are metal.

 

Since the shaft is thinner, something has to hold it in the center of the tube. I have 3D printed a plastic (PLA) tube to act as a sabot, and also pushing the yoke between the eyepieces in the direction of the user. On the other end I have used a washer and a nylon lock nut. Have considered adding Locktite, but it doesn’t seems to be necessary.

 

As for the eyepiece hinge – I have cut the original shaft trying to keep the plastic skirt / shroud around the hinge area. Then, when trying to drill a 6 mm hole through it, I found out that this shaft and right eyepiece’s yoke are separate elements, as the shaft fell out. I have discarded the plastic skirt and cut the remaining part of the original shaft almost flush.
I then drilled another 6 mm hole through the left eyepiece’s hinge. Sorry, eyepieces, that’s the best I could do

 

The order of assembly is: position the shaft in the central tube so that the beak / tongue engages the focusing barrel threads, put the plastic tube over it and slide it into the central tube till it rests on the beak (it should still protrude), put the right eyepiece (the remaining part of the central shaft with the newly drilled hole) onto the shaft, slide it forward until it rests on the plastic tube, put the left eyepiece onto the shaft (using the new hole), push it forward, put on the washer and the lock nut, tighten the lock nut, but not too tight – the hinge has to be able to turn.

 

Here’s the final result:

Album: Celestron 25x70 repair

5 images

0 comments

 

One thing I would definitely change is the width of the beak. 1.38 mm is way too thin, I'd go twice this value.

 

Now it looks like I have to collimate this Celestron, as it sometimes gives me double vision...