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OAG-L focuser replacement part for non-mini cameras

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#1 Palmito

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Posted 25 August 2021 - 04:06 AM

As I own a non-mini guiding camera, I am currently designing a part to replace the focuser of the ZWO OAG-L.

 

The goal is the reduce the distance so that backfocus can be achieved.

 

Once design completed the part will be machined aluminium stainless steel (harder than aluminium --edit2).

 

The first iteration was a 12mm high part. I am printing a 6mm and 4mm version.

For maximum versatility I am thinking 4mm might be better as spacers can always be added.

 

What do you guys think, is 4mm good?

--edit: One thing that comes to my mind, is that with this full length thread design, I'll need a counter lock ring, mine is 1.5mm thick. So maybe 4mm is slightly too short --

 

12mm test run:

OAG-L_nfrp_12_1.jpg OAG-L_nfrp_12_2.jpg OAG-L_nfrp_12_3.jpg

 

6mm design:

OAG-L_nfrp_6.png

 

4mm design:

OAG-L_nfrp_4.png


Edited by Palmito, 25 August 2021 - 06:24 AM.

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#2 Palmito

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Posted 25 August 2021 - 06:09 AM

I believe 100% of the force is distributed on the first two threads only, anyone with mechanical knowledge who can confirm this ?

 

If so, the 4mm version would leave me with 3 threads which should be enough.

 

 

Here is the 4mm prototype with a counter lock ring:

OAG-L_nfrp_4_2.jpg

 

And the 6mm:

OAG-L_nfrp_6_2.jpg


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#3 Palmito

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Posted 25 August 2021 - 12:02 PM

I iterated a bit to adjust everything, pretty happy with the results.

 

I only need to decide if 4mm thick is enough. In about two weeks I should receive the machined stainless steel adapter.

 

Really looking forward to test this, as I own a 12x8mm sensor guide camera, it will be a life changer compared to my current 8mm OAG optical conduit.

 

OAG-L_nfrp_4_3.jpg OAG-L_nfrp_4_4.jpg


Edited by Palmito, 25 August 2021 - 12:18 PM.


#4 ChrisWhite

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Posted 25 August 2021 - 07:26 PM

Nice work.  For the purposes of supporting only a guidecam I would simply use the 3d printed adapter and be done with it.  No need to go stainless. 


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#5 nateman_doo

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Posted 25 August 2021 - 09:20 PM

Also, stainless will be much heavier on the optical train. 

Aluminum is a far better option. 


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#6 Palmito

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Posted 26 August 2021 - 03:09 AM

Thanks for your feedbacks.

 

Nice work.  For the purposes of supporting only a guidecam I would simply use the 3d printed adapter and be done with it.  No need to go stainless. 

Well 3D printed threads are not very solid, I am more concerned about flexure rather than guidecam falling off, the USB cable would hold it anyways.

Another concern is the higher coefficient of linear thermal expansion of plastic.

 

 

Also, stainless will be much heavier on the optical train. 

Aluminum is a far better option. 

I have to admit I didn't even think about weight lol.gif

 

I have now calculated expected weights and steel is 3 times heavier than aluminium but the part is so small I think it is negligible:

  • PLA: 3g
  • Aluminium: 10g
  • Stainless steel: 29g


#7 ChrisWhite

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Posted 26 August 2021 - 06:25 AM

<p>

Thanks for your feedbacks.

Well 3D printed threads are not very solid, I am more concerned about flexure rather than guidecam falling off, the USB cable would hold it anyways.
Another concern is the higher coefficient of linear thermal expansion of plastic.


I have to admit I didn't even think about weight lol.gif

I have now calculated expected weights and steel is 3 times heavier than aluminium but the part is so small I think it is negligible:

  • PLA: 3g
  • Aluminium: 10g
  • Stainless steel: 29g

Not a concern here. A printed part would be plenty stiff and strong. You can certainly spend the money on stainless, but you won't see any performance advantage.
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#8 Palmito

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Posted 26 August 2021 - 06:44 AM

Not a concern here. A printed part would be plenty stiff and strong. You can certainly spend the money on stainless, but you won't see any performance advantage.

 

Well I am lucky enough to have it done for free by a friend of mine smile.gif

 

But I'll try printing a PET-G version of it, very eager to try it before the part is machined



#9 ChrisWhite

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Posted 26 August 2021 - 02:31 PM

Well I am lucky enough to have it done for free by a friend of mine smile.gif

But I'll try printing a PET-G version of it, very eager to try it before the part is machined


Win win!
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#10 Palmito

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Posted 28 August 2021 - 04:12 AM

\o/ I just installed the 3D printed part and reached backfocus.

 

I had to add a tilt plate between the camera and the EFW, else I was missing 1mm.

 

The M48 3D printed "fullframe sensor guide" worked like a charm.

20210824_191548.jpg

 

I have drilled a hole in the M68 tilt plate in order to access grub screw while mounted, but didn't need to adjust prism position in the end.

 

ZWO says you need a 48mm image circle, but I disagree, it is tight but you can manage 44mm.

The prism is 12x12mm, but optical conduit 12x8mm, so you get a 2 times 2mm "margin" on the height which makes it just fit in 44mm.

 

20210828_105535.jpg

 

PS: yes my cameras are half pink lol.gif  ... do not let them see the sun even for a day


Edited by Palmito, 28 August 2021 - 04:34 AM.



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