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Coarse focuser knob removal, ES AR152 achromat

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#1 Fossil220

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Posted 01 February 2020 - 01:23 AM

Greetings, 

 

I am prepping my AR152 achromat as a narrowband imaging rig. I am preparing to order a Sesto Sento 2 for her to wear, but wanted to check fitment before I did so. Here, I ran into a slight snag. Once having removed the fine focus knob, I do not see a means to remove the coarse knob.

When the fine knob is removed, a grub screw is exposed on the side of the coarse knob. Upon loosening that, I can detect no new freedom of movement in the coarse knob that would suggest that this is the proper course of action. Reasonable application of force yields no progress here.

I also see a pair of slots in the side of the coarse knob that seem tailored to fit a spanner type wrench. Applying such a wrench here would then seem to remove a threaded cap restraining the coarse knob. I don't know if I'm interpreting this arrangement correctly, and at any rate, do not have a spanner to fit.

I'd like to have some surety before proceeding. I am of some mechanical aptitude, but the answer is not obvious to me. 

 

I am in the capable hands of this group. Have you any thoughts on this?

 

Ray

 

 

Attached Thumbnails

  • AR152 coarse knob.jpg


#2 mikerepp

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Posted 01 February 2020 - 01:30 PM

I have never tried to take the coarse knob off so take this for what's it worth.  The set screw may need to be tightened.  It may be a jack screw and by tightening it will loosen the threaded portion and allow it to be unscrewed.



#3 Fossil220

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Posted 02 February 2020 - 12:12 AM

Mike, Thank you.

That is a good thought. I'll test your idea in the morning. (fingers crossed)



#4 airbleeder

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Posted 02 February 2020 - 09:44 AM

   It's been a while since I removed mine, but I used small needle nose pliers to carefully removed the slotted nut. I would not tighten the screw, if anything loosen it. You don't want to chance stripping it.

 

Edit: A disclaimer, whatever you use if you remove this nut, be careful to not damage it because I believe it's brass.

 


Edited by airbleeder, 02 February 2020 - 10:06 AM.


#5 spacemunkee

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Posted 02 February 2020 - 09:57 AM

Don't know if it helps, but I had rigged my ZWO EAF onto my AR152 a while back and I just removed the coarse focus knob on the other side.



#6 Fossil220

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Posted 03 February 2020 - 11:20 PM

I got sidetracked over the clear-ish weekend with a comm issue between laptop and mount, but cloudy skies now bring me back to this project.

 

   It's been a while since I removed mine, but I used small needle nose pliers to carefully removed the slotted nut. I would not tighten the screw, if anything loosen it. You don't want to chance stripping it.

 

Edit: A disclaimer, whatever you use if you remove this nut, be careful to not damage it because I believe it's brass.

I am glad to hear that this nut is removable without direct celestial intervention. 

 

I've been very restrained in the force I've applied thus far, being very aware that I don't have the proper tool for the job. I'm finding it referred to online as a pin wrench. I have inquired of a friend to see if he has the proper size in his collection. Failing that, I'll give the needle nosed pliers a go. I have a pair that should fit the bill around here.....somewhere.

Otherwise, there is always the fortuitous dig through the $5 tool bin at Autozone. grin.gif

 

Ray


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#7 Fossil220

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Posted 11 February 2020 - 10:35 PM

Knob removed.jpg Update:

My friend got back to me on Monday regarding my request. It turns out that he did not have a spanner of the correct size. Within hours of that news, though, I found a scrap motor shaft adapter at work that could be, well.....adapted. grin.gif    A little hand tool work this evening resulted in a "socket" that fits rather well.

 

The outcome of all this is that I was able to quickly remove the coarse knob retaining nut without any damage, and measure the outer diameter of the the focuser. 24.8 mm, in case you have use of that datum. 25mm is the diameter that the Sesto Sento 2 is designed to fit, so this is the good news I was hoping for. 

 

I'm grateful for the for the assistance and advice. 


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