Both of my Ioptron mounts, a CEM70 and a CEM40, perform well. However they both suffer from a build flaw wherein the counterweight bar is not accurately aligned with the DEC axis mount. This results in a tendency for the RA axis to swing either clockwise or anticlockwise when all is otherwise correctly balanced. It is possible- apparently - to fix this misalignment by moving the CW bar slightly within its housing by adjusting the top bolt and two side screws. However - the bolt being very tight - I found this difficult and neither did there seem to be sufficient play to make the adjustment.
A simple fix that does not incur the hazard of opening up the housing is to attach some 'side' weights to the CW bar –to the left or right as needed to counteract the swing. A simple way to do this is to remove the locking screw from one of the counterweights and replace it with a 30 cm M10 or M8 screw thread rod as appropriate. Weights comprising nuts and washers are tightened into place near the end of the rod and then the end attached onto the original locking screw and handle via a longbolt. This - now lengthened and weighted bolt is then used to tighten the weight back onto the CW bar and simply rotated until the correct point of vertical balance is achieved.
Tim
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It's actually not that difficult to rebalance the center shaft, though definitely a bit annoying. Opening the screws as you describe takes just a few seconds and then you need to try a few times to push it into the right position, which involves mainly luck 😬
I thought about doing the method you described, but found that it's more hastle long term. Just my 2 cents on this.
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I have the same problem with my CEM70. On mine there is not enough play to adjust 100% within the "housing".
I have drilled and threaded an extra hole in one of my counterweights and use an 8mm rod and a tiny weight right next to the counterweight. I start adjusting with the weight on top of the counterweight, and slowly rotate the counterweight until balance.
This works fine, but I wish iOptron could have machined this toy to a higher standard.
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I just add a weight (washers) with a string that makes the mount slightly rotate anti clockwise all the time. This guarantees that gears are always engaged. I've been doing this for years with my cem25p and my cem70.
It looks like jerry-rigged but it works like a charm and keeps my guiding error low (<0.24 for cem70).
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Indeed. It's strange how they are such good mounts in many ways but fall down on this simple feature of their build.
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I have the CEM70ec and practically each time I take my Newtonian off the saddle for maintenance, I have to rebalance it differently although I have marks of where the Newtonian was placed beforehand. I looked at the option to loosening the 3 screws for the counterweight bar and adjust it that way but as the imbalance is each time different, I decided for a 3rd axis counterweight. I bought a clamp and added a treaded rod (M8?) with washers at the end held by nuts. Simple and fast to adjust something a manufacturer disregarded to address in first place.
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I just add a weight (washers) with a string that makes the mount slightly rotate anti clockwise all the time. This guarantees that gears are always engaged. I've been doing this for years with my cem25p and my cem70.
It looks like jerry-rigged but it works like a charm and keeps my guiding error low (<0.24 for cem70). That is an interesting and simple way but presumably, with respect to the gear engagement, you can always achieve the same just by balancing slightly east heavy?
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s achieve the same just by balancing slightly east Can you post a picture of this sometime? I've always had a 1/4 magnet that I land on the side of the counterweights in order to balance properly.
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Sure. Like I said, it looks jerry-rigged but it works and it is simple:   |
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I've never considered whether the CW Bar is aligned (or not) on my base model CEM70 ~ I just 3D balance on both axes (with a slight bias on the CW side of the RA for resistence).
If there is any anomaly in alignment, 3D balancing eliminates any perceivable effect in guiding.
On the bottom of my CW Bar is a SmallRig Super Camera Clamp into which is screwed a 1/4 x 4" rod and upon which I can slide on a small custom counterweight or two. That is then rotated on the CW Bar to eliminate any drift in the Right Ascension axis.
Another 1/4 x 4" rod is screwed into one of the sides of the DEC Plate (with appropriate weights) to eliminate minor drift in the Declination axis.
I've been doing this for a little over a year, and (as long as I am on solid ground) it has contributed to an appreciable improvement in guiding.
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I also have a misaligned CEM40. I engaged in this long post on Cloudy Nights when I first noticed. My steps have been: - Try to move the shaft per iOptron instructions, but there wasn't enough play to get it straight
- 3d print a device with fender washers and the same smallrig clamp mentioned above, which did perfectly balance it
- The mount went to iOptron for a warranty repair on the DEC, and I also brought this up. They acknowledged it, but then did nothing to fix it, saying it was fine
 - Now, I just use it as is, with the RA always slightly out of balance due to the CW shaft, EAF, Rotator... something. It honestly seems to guide perfectly well (0.3-0.6") with a slight imbalance, no matter what the reason (CW bar or lopsided rig) in my case
CW bar off-axis weight:  |
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I was motivated to realign the CW on my CEM40, too.
Since then, I've discovered that it doesn't matter where the CW is along as it can balance the mount. It's a perfectly reasonable thing to consider moving the rod. This is the same thing as adding a lateral weight as described above. Balanced is balanced, you might say. But it looks funny and insults our desire for symmetry.
These methods can keep a free mount centered. but they won't work to fix a scope that is itself unbalanced side-to-side, since it constantly moves sid-to-side. So this stage of centering is best conducted with no scope or weights attached. Then add the scope and test DEC balance again, this time moving accessories around, adding lateral weight to the scope or shifting its dove plate to the left or right on the mount.
In reality, the mount is strong enough to overcome slight imbalances. So we may let this kind of thing get under our skin and overthink it.
Or, one can invest in a strain wave mount, which seems to care less about balancing.
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Lots of interesting comments and a variety of fixes ! Here is a photo of my 5 kg CEM70 mount with an M10 bar screwed in in place of the tightening bolt. This fix was super easy because it was the central bar of an old azimuthal mount that I happened to have lying around, It was heavy enough to work straight off without needing any additional weights or washers. It even had a handle on for tightening already  |
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