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Question about Mounting a Pegasus Focuscube to William GTF81

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#1 BobNY

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Posted 13 December 2019 - 10:31 PM

I picked up a Pegasus Focuscube v2 today to install on my William Optics GTF81. When I removed the coarse focus knob I discovered there is a bearing that the shaft of the knob goes through. When assembled the knob and the bearing support the focus shaft in the housing. The coupler that comes with the Pegasus focuser does not fit through the bearing. The coupler would need to be attached on the outside of the bearing. At which point the bearing is ineffective and the shaft looses that support. If I go ahead and install it do you think things will be okay? Will the rigid mount of the focuser on the end of the shaft give the shaft ample support? I have attached a couple of pictures showing the bearing and coupler. 

Any advice is greatly appreciated smile.gif

 

IMG_2044.jpeg

IMG_2047.jpeg



#2 wrnchhead

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Posted 13 December 2019 - 10:37 PM

Hmm this is one of those things. I have that same scope, but use a Moonlite. I just took mine apart, and in my opinion, there is too much play in that end without the centering provided by the knob. 


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#3 BobNY

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Posted 13 December 2019 - 10:42 PM

wrnchead, Thanks for doing that! My gut is telling me the same thing. I was just hoping I was wrong frown.gif .

I may have to look at other options.


Edited by BobNY, 13 December 2019 - 10:43 PM.


#4 wrnchhead

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Posted 13 December 2019 - 11:00 PM

Since my post, I have been searching online for a 4mm ID 19mm OD bearing you could use in there, but the biggest I can find is 16mm OD. Something like this is surmountable, but it depends on a guy's handiness, ya know? If you have a lathe, it's easy. If you live in a apartment and have limited options for machining etc, it can be a real pain. 

 

I am thinking even some kind of conical spacer, that would center the shaft might be the easiest solution, but I can't really feel that solves the fact that all the play of that setup would depend on the pressure you put on the adapter shaft before tightening the set screw. Plus, temperature changes etc it would inevitably slip. A bearing and a sleeve to go between the bearing and the housing would seem simplest. But that bearing size may be available, I just had no luck on Grainger, McMaster Carr or Amazon and general googling. 



#5 BobNY

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Posted 13 December 2019 - 11:06 PM

Thanks for your effort!  I have been looking as well with no luck. I will keep looking.



#6 BobNY

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Posted 14 December 2019 - 12:10 AM

I think I may have found a solution. 

The existing bearing is 10mm x 19mm. I ordered a a 4mm x 10mm bearing I am hoping to insert into the 10mm x 19mm. If they fit like they should, I will end up with 4mm x 19mm. So far that's the best I could come up with. The bearing arrives on Sunday. We will see how it goes.



#7 wrnchhead

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Posted 14 December 2019 - 12:59 AM

Ah yes!!



#8 BobNY

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Posted 15 December 2019 - 03:10 PM

The 4mm x 10mm bearing arrived today and fit perfectly. Hopefully things go smoothly from here.

 

IMG_2060.jpeg

 

 


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#9 wrnchhead

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Posted 15 December 2019 - 06:06 PM

Awesome! I love when something works out with a simple solution 



#10 elineberry75

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Posted 15 December 2019 - 09:46 PM

Ran across this thread today.  I have a GT71 arriving tomorrow and I plan to mount a Pegasus Focuscube on it like you are doing.  I'm guessing I will need the same solution as the bearing you mentioned.  Would you let me know where you purchased it?  Also, what about the universal bracket mounting?  Were you able to use the mounting screws on the scope?  I had a problem previously on an Explorer Scientific refractor where the thumb screw was larger than the slots on the bracket so I just curious if I should expect the same problem with the WO GT71.



#11 OldManSky

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Posted 15 December 2019 - 09:51 PM

Ran across this thread today.  I have a GT71 arriving tomorrow and I plan to mount a Pegasus Focuscube on it like you are doing.  I'm guessing I will need the same solution as the bearing you mentioned.  Would you let me know where you purchased it?  Also, what about the universal bracket mounting?  Were you able to use the mounting screws on the scope?  I had a problem previously on an Explorer Scientific refractor where the thumb screw was larger than the slots on the bracket so I just curious if I should expect the same problem with the WO GT71.

If it's a newer GT71, you won't need the extra bearing.  The focuser is different, and the focus cube will bolt right on.

I just did this with my 5-month old GT71, and an EAF -- it doesn't use the knob as a bearing like the OP had.

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  • gt71onmount.jpg

Edited by OldManSky, 15 December 2019 - 09:51 PM.

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#12 OldManSky

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Posted 15 December 2019 - 10:00 PM

Another view for the newer GT71...

 

 

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  • eafongt71.jpg

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#13 elineberry75

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Posted 15 December 2019 - 10:12 PM

Awesome.  Thank you!  It is a new one so I should be good to go!


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#14 BobNY

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Posted 15 December 2019 - 11:29 PM

elineberry75, Sorry for the late reply. Probably better that OldManSky saw got to you first with the correct information for your G71 :).

 

It turns out the universal bracket needs some modification for the slots to lone up with the focus lock screw hole on my focuser. I have to open up the last slot a bit to clear the threads :(.  With the focuser and bracket pushed all the way in the last slot falls a tad short :( .


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