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AstroTech/APM 3.7" coarse focus knob removal for autofocuser?

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#1 YAOG

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Posted 19 May 2020 - 04:05 PM

Hi,

 

I'm having a hard time getting the coarse focuser knob off of an A-T/APM/LUNT/TS etc. 3.7" focuser to install an autofocuser stepper motor. Has anybody managed to do this with the 3.7" focusers yet? As in the photo, the bottom knob is the coarse focus, I removed the outer grub screw used as a cover then removed the two grub screws on the black knob inside the focuser body that seem to hold the knob on but the knob itself refuses to come off. I don't see anything else holding the big black knob on, am I missing something? 

 

Thanks in advance!  

 

APM-37-Deluxe_pinion.jpg

 

 

 

 



#2 YAOG

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Posted 20 May 2020 - 04:49 AM

Ha! I broke out the loupe and a headlight to have a closer look into that dark hole that normally has a pretty silver grub screw as a cosmetic cover. After having already loosened then removing two grub screws from drilled and tapped holes 90 degrees apart in the large coarse focus knob and the knob refusing to come off something was not right. 

 

So a very close look was in order and what I found was a second grub screw in the hole over the focuser pinion shaft flat. Out it came and off the knob went and on went the coupler for the new ZWO EAF just in from ZWO in China. 

 

I have never seen a second grub like this but it might have been there to ensure the grub screw never backs out. Anyway, mystery solved.



#3 ris242

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Posted 20 May 2020 - 05:19 AM

Ha! I broke out the loupe and a headlight to have a closer look into that dark hole that normally has a pretty silver grub screw as a cosmetic cover. After having already loosened then removing two grub screws from drilled and tapped holes 90 degrees apart in the large coarse focus knob and the knob refusing to come off something was not right. 

 

So a very close look was in order and what I found was a second grub screw in the hole over the focuser pinion shaft flat. Out it came and off the knob went and on went the coupler for the new ZWO EAF just in from ZWO in China. 

 

I have never seen a second grub like this but it might have been there to ensure the grub screw never backs out. Anyway, mystery solved.

ive seen grub screws locking on top of other grub screws in 90 degree turning actuators or things that knock or vibrate could come loose. i wouldnt have thought it would be needed here unless they believed rotating one way and then the other, it could work loose, or they ran out of longer screws.



#4 YAOG

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Posted 22 May 2020 - 12:59 PM

Ah, here is the final result after finding the third grub screw in a two-hole knob, the gurbs were stacked for some reason but all good now!

 

Parallax-AT130 ASIAIR PRO full system-4.jpg  

 

 


Edited by YAOG, 22 May 2020 - 01:00 PM.

  • eros312 and havasman like this

#5 junomike

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Posted 23 May 2020 - 08:03 AM

I've only encountered dual grub screws in Recractor cells (Wedge Alignment)

Good to see it's all working as planned.




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