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Focuser issue on Stowaway 92 mm

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#1 gnowellsct

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Posted 19 September 2020 - 02:07 PM

This is not strictly speaking an astrophotography issue though it could be if I ever want to pile a camera on top of all this stuff.

 

BUT, the reason I come here for your combined wisdoms is that if there is a forum here where people worry about focusers, it would have to be this one.

 

The issue is rotation of the entire h-alpha assembly at the flange point where the focuser is joined to the tube.  The AP Stowaway does it, the CFF does not.

 

Here is the video.   To the casual view the CFF and the Stowaway look the same, remember that the AP Stowaway is in the first half of the video, the CFF in the second.  The CFF has the black flange knobs; the Stowaway has silver/aluminum.

 

I'll be calling FT next week I'm wondering if the fix is as simple as changing the flange screws on the AP.

 

Greg N


Edited by gnowellsct, 19 September 2020 - 02:08 PM.

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#2 gnowellsct

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Posted 19 September 2020 - 04:40 PM

Upon further inspection the screws on the flange between CFF and Stowaway are identical, one is anodized black, the other silver.   They have nylon

tips.

 

Both sets of screws are greased but the AP conspicuously more so.  I guess it needs to be degreased.  And then re-greased with a very light touch.

 

Greg N



#3 gnowellsct

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Posted 20 September 2020 - 01:03 AM

Crickets.  Hmm.  Well, maybe this ISN'T as common as I thought.  -GN



#4 andysea

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Posted 20 September 2020 - 01:46 AM

I will look at my Stowaway and report back. I haven't had any rotation issues but I only had the ASi 6200 on it. The filter wheel is offset but the moment arm is a lot smaller than your setup.


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#5 rockstarbill

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Posted 20 September 2020 - 02:05 AM

I put well over 12 pounds on that focuser and had pinpoint stars. I find this hard to believe.


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#6 gnowellsct

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Posted 20 September 2020 - 08:46 PM

I put well over 12 pounds on that focuser and had pinpoint stars. I find this hard to believe.

Well I hope you saw the video.   Pinpoint stars are not the issue.  The scope delivers excellent stars (but I don't do photography, I assume you mean rotation).  The issue in this case also is that this is a very leveraged load it may be that the force in inch-pouds is 1.6 x 12 = 19 inch pounds of force at the end (for the sole XW30), not counting the weight of the powermate, diagonal, and etalon.  So depending on how much moment arm your imaging stuff has it may actually exert less torque.  I imagine that camera designers try to keep everything compact for this reason.

 

S.I. has offered to send me some no-tip aluminum screws for a brute force solution.

 

Tonight I took the screws out soaked them in dish soap to remove all grease.  I cleaned the threads on the flange with some solvent.  Then I cleaned the race on the flange with solvent followed by dish soap and a good drying.

 

And....it has been holding at a very difficult angle these past 40 minutes.  It took some doing though, getting it to hold was not just a "set it and forget it" proposition.  It may be there was some residual moisture on all the parts that I thought I had dried.  

 

So the principle has been demonstrated that it can hold.  The issue here is that for that "buttery smooth feel" they put a little bit of lube on the screw threads and if that gets down on the tip of the screws and thus into the race, one is cruisin' for a bruisin'.  

 

Right now everything is lube-less some day when feeling ambitious I might back the screws out so the top half is exposed and dab a tiny bit of grease on the upper part with a q-tip.  

 

So I have made progress, and at least as of now have demonstrated that this focuser can hold (almost) as well as the CFF.  I say almost because with the CFF I didn't have to triple check the torque on all components.  The build of course is virtually the same as the CFF, it's by the same company, the same nylon tipped screws on the same flange.  

 

But if I take this scope on a solar vacation (as we have an eclipse in a couple of years) I will want to take the all metal screws just in case.   It might be that even ONE metal screw would add sufficient force to halt the problem.  I could mark the top of that one with some nail polish and that would be the one to loosen first if I had a hankering to rotate the entire rear focuser.

 

Thank you for your responses.

 

Greg N

 

Greg N


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