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Cem70 RA balance falls to one side? Let’s fix it, no extra parts required

Beginner DIY Equipment Mount
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#1 Blackhawk163

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Posted 26 October 2021 - 02:33 PM

So who here has struggled with their brand new cem70 and found that after initial balance both in Dec and then RA in the horizontal positions you go back to zero position, disengage the clutch and the RA starts to swing either east or west before settling into the balanced horizontal position?

Sure, you’ve seen the YouTube videos describing 3d balance and how you need to add washers, elaborate clamps etc. heck I’ve done it, only for my sct to look like something out of mad max.

 

The fix is so simple. Now I did this with my gear all attached, and outside during the lull from the  No'reaster but I think it's better done inside with no wind, and maybe no gear attached.

 

 I loosened the two small grub screws as well as the top Allen screw and the side Allen screw (not marked on my pic) Gently adjust the RA counter weight bar either left or right with the clutch engaged, disengage the clutch and watch where the ra axis starts to swing. Repeat until you notice no movement East or west. The adjustments are tiny, so take your time! Slowly tighten everything up, constantly checking the balance. 
 

Do this right and Voilà you now have a balanced mount on the RA axis that doesn’t require clamps on the counterweight bar or other contraptions. 

If this is a retread of an old topic here on CN then I apologize. Quick video here

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#2 Tony Bonanno

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Posted 26 October 2021 - 03:30 PM

Hi Blackhawk 163,

I tried your fix, but it didn't help in my case. When I released the RA axis lock, the mount and OTA would want to sway to one side, even though the RA and DEC were balanced.  It turned out that the position of the counterweight bar/assembly wasn't the problem, but rather the balance of the accessories' weight on the OTA.  I found by moving my ASIAIR PRO and some other accessories to a different position on the OTA, the problem went away.  My mount's (CEM70) counterweight bar came to perfect alignment without leaning to one side or the other.  May not be the case for some users, but worked for me.

Cheers,

Tony


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#3 Blackhawk163

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Posted 26 October 2021 - 03:41 PM

Hi Blackhawk 163,
I tried your fix, but it didn't help in my case. When I released the RA axis lock, the mount and OTA would want to sway to one side, even though the RA and DEC were balanced. It turned out that the position of the counterweight bar/assembly wasn't the problem, but rather the balance of the accessories' weight on the OTA. I found by moving my ASIAIR PRO and some other accessories to a different position on the OTA, the problem went away. My mount's (CEM70) counterweight bar came to perfect alignment without leaning to one side or the other. May not be the case for some users, but worked for me.
Cheers,
Tony


Hey Tony, thanks for the reply! I'm curious, did you make your adjustments with or without first balancing everything on the horizontal? Or was your mount naked when you tried it?

I'm loathed to take everything off just to see the result. Lol

I did mine fully loaded, and it has me thinking if that's what skewed my result. I will say that I can't get the Dec to stay fully balanced yet, and that I know it is an issue with placement of accessories (focuser and OAG) as it still swings in one direction just like the ra used to.

#4 Tony Bonanno

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Posted 26 October 2021 - 04:01 PM

Hey Tony, thanks for the reply! I'm curious, did you make your adjustments with or without first balancing everything on the horizontal? Or was your mount naked when you tried it?

I'm loathed to take everything off just to see the result. Lol

I did mine fully loaded, and it has me thinking if that's what skewed my result. I will say that I can't get the Dec to stay fully balanced yet, and that I know it is an issue with placement of accessories (focuser and OAG) as it still swings in one direction just like the ra used to.

Mine was fully loaded.  And everything was balanced horizontally perfectly, both RA and Dec.  I had my OTA, camera, ASIAIR Plus, guiding scope, EAF, etc. all on the mount.  However, when I put the mount back into the "start" position (pointing towards the North polar axis), with the counterweight bar pointing straight down towards the ground and the Dec axis lined up as in zero position, if I released the RA axis lock, the mount would sway to one side.  After re-arranging the "weight" on the OTA, the problem was resolved.  I don't know why it took me so long to think about the weight of what was actually on the OTA ??


Edited by Tony Bonanno, 26 October 2021 - 05:46 PM.


#5 Blackhawk163

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Posted 26 October 2021 - 05:53 PM

Mine was fully loaded. I had my OTA, camera, ASIAIR Plus, guiding scope, EAF, etc. all on the mount. Everything was perfectly balanced in DEC and in RA, but when I put the mount back into the "start" position (pointing towards the North polar axis), with the counterweight bar pointing straight down towards the ground and the Dec axis lined up as in zero position, if I released the RA axis lock, the mount would sway to one side. After re-arranging the "weight" on the OTA, the problem was resolved. I don't know why it took me so long to think about the weight of what was actually on the OTA ??


Ah OK makes sense. Yeah mine would sway naked or loaded. But in my case the mount counterbalance bar assembly definitely had a bias towards the west side pier. I'm glad that's resolved as guiding in the ra hardly ever hit below 1.0 the Dec pretty much saved everthing as that would be a consistent +/- .4-.5

I'm eager to see what guiding will be like now on a more balanced mount. Of course rain for the foreseeable future.
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#6 Tom M

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Posted 26 October 2021 - 06:04 PM

Before doing this I found it is necessary to make sure things are 3D balanced on the DEC axis. If they aren't then you can definitely get a "false reading" as that imbalance will impact the CW offset balance. I also found that I have basically no spare room for adjustment and had to max out to the limit to get things balanced. However, once it was done it worked fine with both an FLT-91 and also a C11.


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#7 Blackhawk163

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Posted 28 October 2021 - 06:29 PM

Before doing this I found it is necessary to make sure things are 3D balanced on the DEC axis. If they aren't then you can definitely get a "false reading" as that imbalance will impact the CW offset balance. I also found that I have basically no spare room for adjustment and had to max out to the limit to get things balanced. However, once it was done it worked fine with both an FLT-91 and also a C11.

Oh absolutely. I touched on it on the video. Dec absolutely has to be balanced before anything anyway. I've seen some YouTube videos where people balance the ra first then Dec but then never rebalance the mount again afterwards.

So I got some clear skies last night and yup guiding was much better, even if the seeing wasn't. It felt so darn good to see an personal investment pay a little. I can't wait for winter and steady skies to come around.

Edited by Blackhawk163, 28 October 2021 - 06:30 PM.

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