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Outside clamp of focuser tube

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#1 machvolum

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Posted 03 April 2021 - 02:00 AM

So this sounds stupid, but I'm sure someone has had to deal with this at some point and I am looking for some advice. I have an old Edmund Scientific Rank refractor and the original thumb screw that holds the eyepiece in has stripped out finally. Is there such a thing that clamps around the outer diameter of the focuser tube that replaces the need to use the tiny screw hole? Specifically one that has a brass compression ring or even better that has a self centering mechanism? I bought a couple different items and they aren't quite what I am looking for. They are extension tubes from svbony with compression rings. I had the thought of welding one of these extension tubes to the focuser tube... but that isn't something I want to do to this scope.

 

The outside diameter is 1.365 in or 34.65 mm

 

Cheers!


Edited by machvolum, 03 April 2021 - 02:12 AM.


#2 clearwaterdave

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Posted 03 April 2021 - 02:58 AM

This is the second such question in two days that I have ran into.,Tha answer is that piece is called a visual back.,and they are available at Agena Astro.,or maybe ScopeStuff.,There are lots to choose from so be ready for that with make and model.,good luck.,



#3 machvolum

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Posted 03 April 2021 - 03:03 AM

This is the second such question in two days that I have ran into.,Tha answer is that piece is called a visual back.,and they are available at Agena Astro.,or maybe ScopeStuff.,There are lots to choose from so be ready for that with make and model.,good luck.,

Thank you for your reply. I will look these up. Does it clamp to the outside of the drawtube? Also, do you recommend any specific brand?

 

Cheers!



#4 machvolum

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Posted 03 April 2021 - 03:26 AM

A visual back is closer to what I have been searching for, unfortunately there are no threads on the drawtube. :(

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#5 clearwaterdave

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Posted 03 April 2021 - 06:54 AM

Those look like threads on the bottom.,are there some on the other side? How was it attached to the focusers drawtube? Were you viewing  straight through..,without a diagonal.,.?



#6 apfever

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Posted 03 April 2021 - 08:43 AM

The threads are the rack to focus the drawtube.

I suggest getting a tap and making new threads in the old hole.

That would probably be the easiest, fastest, cheapest, and least intrusive approach to the scope. 

Coordinate the tap with a fine thread nylon bolt and get both at the same time. 

 

You might need to drill the hole out to match the tap. Have basic tools like a drill and drill bits? Your drawtube looks to be aluminum which will tap easier. It is quite possible that you can find a tap to work with the existing hole since aluminum will be more forgiving of an undersized hole to start. Talk to the hardware guy at the store you go to.  Use drill bits to size the existing hole, or mike the stripped screw.  


Edited by apfever, 03 April 2021 - 08:43 AM.

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#7 machvolum

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Posted 03 April 2021 - 02:14 PM

Those look like threads on the bottom.,are there some on the other side? How was it attached to the focusers drawtube? Were you viewing  straight through..,without a diagonal.,.?

The inside of the drawtube is scored as to prevent light reflections I think, but there was just the one thumb screw that held an eyepiece in. Nothing threads into it now :( It wasn't real secure from the beginning..

 

The threads are the rack to focus the drawtube.

I suggest getting a tap and making new threads in the old hole.

That would probably be the easiest, fastest, cheapest, and least intrusive approach to the scope. 

Coordinate the tap with a fine thread nylon bolt and get both at the same time. 

 

You might need to drill the hole out to match the tap. Have basic tools like a drill and drill bits? Your drawtube looks to be aluminum which will tap easier. It is quite possible that you can find a tap to work with the existing hole since aluminum will be more forgiving of an undersized hole to start. Talk to the hardware guy at the store you go to.  Use drill bits to size the existing hole, or mike the stripped screw.  

Yes I was thinking something along those lines. I really don't want to tap one hole and have it fail at another time by removing the screw constantly to change eyepieces. I was thinking something along these lines by making 3 holes offset by 120 degrees and permanently attaching an adapter. http://www.primordia...76drawtube.html Seems pretty straightforward. Has anyone else attempted something like this?

 

Cheers!!



#8 machvolum

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Posted 03 April 2021 - 02:29 PM

Of course the other option which defeats the purpose of having a classical telescope is to change the focuser entirely.. The focuser housing threads onto the tube. I'm not sure what the thread pitch is, but the tube is 76mm in diameter. I'll have to find a thread pitch gauge, but this is pushing this into a bit more adapter territory and I would prefer to keep the original focuser as it is really smooth and the nylon nut that applies pressure to the tube still works really well.



#9 davidmcgo

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Posted 03 April 2021 - 02:54 PM

Just get a larger size fine thread tap and nylon thumbscrews.  File the thumbscrew tip down until the threads are full diameter and it will hold light diagonals and vintage eyepieces just fine and the nylon will strip before the aluminum.

 

My Edmund Voyager has the same style focuser and I don’t stress it with anything heavy and am gentle with the thumbscrew.

 

Dave



#10 machvolum

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Posted 03 April 2021 - 03:11 PM

Just get a larger size fine thread tap and nylon thumbscrews.  File the thumbscrew tip down until the threads are full diameter and it will hold light diagonals and vintage eyepieces just fine and the nylon will strip before the aluminum.

 

My Edmund Voyager has the same style focuser and I don’t stress it with anything heavy and am gentle with the thumbscrew.

 

Dave

Lol well... I forgot to mention, I am looking to hang a dslr camera on this laugh.gif I taped the svbony adapter onto the drawtube the other night to capture some images, it worked quite well, but I uncovered another issue that I hadn't considered that only became apparent with a long exposure.. the internal baffles were warped and protruding into the beam.. as such I Ray traced the tube and am 3d printing some new baffles laugh.gif 

The last picture is one of the old baffles.

 

Cheers!

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#11 machvolum

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Posted 03 April 2021 - 03:27 PM

This is the adapter taped in place. 

 

Cheers!

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#12 machvolum

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Posted 03 April 2021 - 03:53 PM

I think I may have found a solution. It is technically a visual back!

 

It is a compression style when it is inserted and you turn the screw it applies radial pressure on the rubber rings that not only centers the adapter, but it applies force to hold it in place. It also has a T-adapter on the other end.. it's kinda pricy but requires no modification to the drawtube!!

 

https://www.highpoin...apter-sca-ta125

 

Thank you for all your wonderful suggestions! I will be sure to post my results when I get this thing!! This form is absolutely amazing and I think I would be lost without all of your collective knowledge!!

 

Cheers!


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