19 replies to this topic

[Juggernaut]

Hi,

 

The screws are stripped on my "collar" that holds the eyepiece in my 2 speed crayford focuser. I cannot find a place to buy a new one - mostly because I cannot figure out what it is called.

Does anyone know what it is called and as a bonus to me, know where I can buy it?  

(I did email skywatcher but no answer yet).

Thanks for the help!

 

Clear skies!

Paul

Attached Thumbnails

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[SeattleScott]

Generally an eyepiece holder or visual back. Add 2” or 1.25” to search parameters, depending on the size you need.

[dswtan]

With the set screw (the silver bit) and knowing it's the end of a focuser, try searching on an "eyepiece holder" of the appropriate size (opening size and thread size).

[BlueMoon]

Or drill it out slightly larger and retap it for larger screws.

[SeattleScott]

https://agenaastro.c...isual-back.html

Here is an example. The issue will be matching the thread connection size. This one is T2 but yours looks wider.

Here is one with M54 thread:
https://agenaastro.c...rs-2956253.html

Edited by SeattleScott, 15 February 2025 - 01:47 PM.

[sevenofnine]

That part looks like it goes to a Dobsonian reflector's 2 speed Crayford focuser and not a SCT. Another member was having trouble finding it too. If Sky-Watcher can't help you, I suggest contacting this company for assistance. Good luck! 

 

https://www.scopestuff.com/.

[Bob4BVM]

Or drill it out slightly larger and retap it for larger screws.

This is better-than-new-one solution !

 

Get a #22 drill bit and a 10-32 tap to re-do the holes.

Replace screws with 10-32x1/2" NYLON THUMBSCREWS.

 

All that will cost less than a new tube, and will never strip out again, And nylon screws wil not mar you EP's

 

-B

[Juggernaut]

This is better-than-new-one solution !

 

Get a #22 drill bit and a 10-32 tap to re-do the holes.

Replace screws with 10-32x1/2" NYLON THUMBSCREWS.

 

All that will cost less than a new tube, and will never strip out again, And nylon screws wil not mar you EP's

 

-B

Hi,

A few questions.

1) would it make the screws a M4?
2) With the hole so close to the edge (see picture), do you think I might crack the metal?

Thanks!

[3C286]

The screws are stripped on my "collar" that holds the eyepiece in my 2 speed crayford focuser. I cannot find a place to buy a new one - mostly because I cannot figure out what it is called.

Does anyone know what it is called and as a bonus to me, know where I can buy it? 

Just to check: Can you clarify which threads are stripped? Is it the male thread on the visual back where it screws into the focuser, the female thread on the visual back where the thumb screws screw in or the threads on the thumb screws?

 

 

If it's an issue with the thumb screws, Bob's advice will fix it. If you don't live in the US, you probably want to use metric because non-metric thumb screws are very hard to source.

 

 

If it's the visual back's wide male threads that have stripped, here's one approach: It looks like the visual back from my Sky-Watcher ST80 that I replaced:

 

 

I take it that it's from your Sky-Watcher 250P collapsable Dob? If so, I assume it's a 2" visual back rather than the ST80 which is a 1.25" visual back so the threads might be different. Can you measure the thread size with callipers?

 

For my ST80 visual back, it was 43mm (major diameter) with 1mm pitch. I got a Baader M43x1mm to T-2 adapter (€33):

 

https://www.baader-p...1a-to-t-2a.html

 

Once you get to T2, it gives you all kinds of options like a Baader ClickLock or the 1.25" Baader Ultra Short which gives you extra inward focus. Alternatively, there may be a 2" Baader ClickLock thread that interfaces directly to your focuser. Not cheap though...

 

https://www.baader-p...to-4-1inch.html

 

 

Good luck

Tak

[Juggernaut]

Just to check: Can you clarify which threads are stripped? Is it the male thread on the visual back where it screws into the focuser, the female thread on the visual back where the thumb screws screw in or the threads on the thumb screws?

 

 

If it's an issue with the thumb screws, Bob's advice will fix it. If you don't live in the US, you probably want to use metric because non-metric thumb screws are very hard to source.

 

 

If it's the visual back's wide male threads that have stripped, here's one approach: It looks like the visual back from my Sky-Watcher ST80 that I replaced:

 

 

 

I take it that it's from your Sky-Watcher 250P collapsable Dob? If so, I assume it's a 2" visual back rather than the ST80 which is a 1.25" visual back so the threads might be different. Can you measure the thread size with callipers?

 

For my ST80 visual back, it was 43mm (major diameter) with 1mm pitch. I got a Baader M43x1mm to T-2 adapter (€33):

 

https://www.baader-p...1a-to-t-2a.html

 

Once you get to T2, it gives you all kinds of options like a Baader ClickLock or the 1.25" Baader Ultra Short which gives you extra inward focus. Alternatively, there may be a 2" Baader ClickLock thread that interfaces directly to your focuser. Not cheap though...

 

https://www.baader-p...to-4-1inch.html

 

 

Good luck

Tak

Hi,

 

It is just the thumb screws that are stripped (only 1 of them).

I guess it is called a visual back. Unfortunately still cannot find it - only smaller ones so far.

The thread size is 54mm. Pitch seems to be 0.5

Does that help any?

Thanks!

Edited by Juggernaut, 15 February 2025 - 05:00 PM.

[SeattleScott]

https://agenaastro.c...an-2956254.html

This should work, a fairly elegant if expensive solution.

Or, possibly this
https://agenaastro.c...4e-2956251.html

Edited by SeattleScott, 15 February 2025 - 05:37 PM.

[Inkie]

Hi,

...
2) With the hole so close to the edge (see picture), do you think I might crack the metal?

Thanks!

Possibly, yes, but nothing stops you from simply drilling a brand new hole, and tapping it correctly with the thumb **** hope to use, anywhere else along the large metal tube, including more 'inboard' of the current hole's position close to the rim.  For cleanliness sake, fill the old hole with metal putty, or slips a stubby screw back in there, short enough that it's lower end doesn't emerge from the orifice and interfere with loading of eyepieces.

[Juggernaut]

Possibly, yes, but nothing stops you from simply drilling a brand new hole, and tapping it correctly with the thumb **** hope to use, anywhere else along the large metal tube, including more 'inboard' of the current hole's position close to the rim.  For cleanliness sake, fill the old hole with metal putty, or slips a stubby screw back in there, short enough that it's lower end doesn't emerge from the orifice and interfere with loading of eyepieces.

Ha. Good point.

I bought a tap set and will give it a try. At the very least it will be good to have a back-up even if I can find a new one.

 

Thanks!

[rgk901]

just use one screw is stripped? Get a nicer/longer nylon one and done?

it's even preferred to use one screw to keep a repeatable registration of collimators/eyepieces.

[BlueMoon]

 

With the hole so close to the edge (see picture), do you think I might crack the metal?

As pointed out you could drill  new hole a bit further away from the edge or as I've done numerous times use a drill just large enough to clean out the old threads and then measure for the next size larger screw to retap the hole. That way your not removing any additional material or risking a crack. Cheers.

[PalomarJack]

Agree with all the "Repair It" replies above. It will take less time than to try and find a replacement and you will feel better about it, too. But use Nylon screws, that way they ware out instead of the adapter. And, keep a few extras on hand.

Edited by PalomarJack, 17 February 2025 - 07:39 PM.

[BrianSh]

I’ll add to the chorus of “repair it” recommendations. I just did this for the first time with a visual back on a Skywatcher refractor. Ordered some #8-32 1/2” nylon thumbscrews from Amazon, picked up a screwdriver-like triple tap from the local hardware store (like this: https://a.co/d/dPTHSsH), and just gently hand tapped the holes to #8-32 without even needing to drill. Took about 5 minutes, and the thumbscrews are a nice improvement over the originals. A little long, but easy to trim to length with a utility knife and smooth the end with an emery board.

Cheaper than a new visual back, and now I have the tap and screws if I want to fix or “upgrade” anything else.

Edited by BrianSh, 17 February 2025 - 11:55 PM.

[Juggernaut]

Just to check: Can you clarify which threads are stripped? Is it the male thread on the visual back where it screws into the focuser, the female thread on the visual back where the thumb screws screw in or the threads on the thumb screws?

 

 

If it's an issue with the thumb screws, Bob's advice will fix it. If you don't live in the US, you probably want to use metric because non-metric thumb screws are very hard to source.

 

 

If it's the visual back's wide male threads that have stripped, here's one approach: It looks like the visual back from my Sky-Watcher ST80 that I replaced:

 

 

 

I take it that it's from your Sky-Watcher 250P collapsable Dob? If so, I assume it's a 2" visual back rather than the ST80 which is a 1.25" visual back so the threads might be different. Can you measure the thread size with callipers?

 

For my ST80 visual back, it was 43mm (major diameter) with 1mm pitch. I got a Baader M43x1mm to T-2 adapter (€33):

 

https://www.baader-p...1a-to-t-2a.html

 

Once you get to T2, it gives you all kinds of options like a Baader ClickLock or the 1.25" Baader Ultra Short which gives you extra inward focus. Alternatively, there may be a 2" Baader ClickLock thread that interfaces directly to your focuser. Not cheap though...

 

https://www.baader-p...to-4-1inch.html

 

 

Good luck

Tak

Hi.

That looks similar to what I need but mine is 2 inch. The pitch of the threads is 0.5 from what I can tell (I actually am not able to tell the difference between 0.5 and 0.75 pitch).

The scopestuff people unfortunately don't have the 30 mm part.

Can your piece still be purchased? Maybe whomever sells it might have a 2 inch (54MM) part?

Thanks!
Paul

Edited by Juggernaut, 18 February 2025 - 08:52 PM.

[3C286]

Sorry for the late reply

 

It is just the thumb screws that are stripped (only 1 of them).

I guess it is called a visual back. Unfortunately still cannot find it - only smaller ones so far.

 

That makes it simpler.

 

I bought a tap set and will give it a try. At the very least it will be good to have a back-up even if I can find a new one.

 

Great! Tap sets are essential. I'm sure you'll get lots of use out of them  . If you already don't have them, it's also good to have the appropriate drill bit sizes for the taps.

 

That looks similar to what I need but mine is 2 inch. The pitch of the threads is 0.5 from what I can tell (I actually am not able to tell the difference between 0.5 and 0.75 pitch).

The scopestuff people unfortunately don't have the 30 mm part.

Can your piece still be purchased? Maybe whomever sells it might have a 2 inch (54MM) part?

If you don't have a gauge, you can measure the thread pitch by measuring the distance between N threads and dividing by (N-1).

 

I've never seen replacements for these cheap visual backs from Synta for sale. I've heard of similar issues as yours so they seem to be common...

 

I think you're taking the right approach repairing it rather than replacing it or upgrading it with something like a Baader ClickLock. Am I right in thinking it's a single-speed focuser? If so, it's probably better to save the expense now and maybe think about replacing the focuser with a dual speed focuser, which will probably be higher quality and have brass compression rings.

 

Good luck with your repair.

 

Tak

[Juggernaut]

Hi all. Just an update.

 

Thanks for all the great advice and suggestions.

 

I tapped the screws holes to make them M4 (previously M3) and they are working great. M4 actually holding everything better than the M3 did.

I also ordered an adapter that should (hopefully) screw directly into the focuser tube into which I can screw the view-back and get the appropriate distance in the event that my 30mm view back completely fails.

Thanks!

Paul