CGEM DX - binding, now slop in DEC axis
Posted 26 June 2013 - 10:32 AM
So, did I simply not notice the slop when I bought it? Or did I possibly introduce this messing with the backlash screws? I only made slight adjustments, maybe 1/2 turn to loosen one and tighten the other.
At this point I'm wondering if maybe it's not meshed fully and I need to open it and make an adjustment or two? The slewing last night was fantastic and smooth, until you hop over the merdian, then the OTA shifts, and it's back to running smoothly.
Since I'm likely to crack this bad boy open anyway, should I just proceed with a Hypertune as well? It's a used mount.
Suggestions? Something I'm overlooking? I've owned a regular CGEM before, and a CG-5, and I didn't have DEC axis play in either.
Posted 26 June 2013 - 10:40 AM
Half a turn is a big adjustment. You'll want to use finer increments.
Posted 26 June 2013 - 10:49 AM
If you tighten down the DEC worm too much, you will get binding, noisier slews, and the risk of burning out the motor.
Posted 26 June 2013 - 12:03 PM
John, I suspect you're right that I may have overcompensated in the adjustments.
It seems like an abnormal amount of slop. There was a tiny tiny amount in my other GEMs, but nothing quite like this.
Just so that I am clear, it is "push-pull" with the two adjustment screws, correct?
Posted 26 June 2013 - 09:59 PM
if you can't turn it comfortably with your finger tip, the motor won't be able to either.
Posted 27 June 2013 - 07:55 PM
However, in most cases with these mounts, eliminating all backlash is not possible. The gears are simply not of high enough precision to allow for a tighter mesh. The best you can generally do is minimize the backlash and that is easiest to do by making the adjustment with the axis slewing. That way you can hear the gears start to bind and back off from that point slightly.
Posted 29 June 2013 - 09:01 PM
I was thinking of tearing it down anyway, but if I'm going to break down the mount and make adjustments and clean it up, I might as well Hypertune it also and get everything done in one shot. I just spent a ton on new gear though, gotta see if I can squeeze a few more bucks past the "CFO".
Posted 30 June 2013 - 12:53 AM
At least for CGEM (not sure about DX), I found that Dec balance was very critical for proper guiding performance. I had to balance on all 3 axes and what made this difficult was that the standard saddle was heavier on one side than the other - and I'm not talking about just the weight of the knobs. Achieving good Dec balance turned out to be much easier with an ADM saddle than the stock saddle. Perhaps as a previous owner of a CGEM you already know all this, but just thought I'd throw this in as one of the things to check.
Posted 30 June 2013 - 09:31 AM
Ironically, Anthony from ADM is where I got the OTA on this particular setup. I planned to follow up with him shortly on a few hardware bits, but have to let the dust settle some after my recent spending spree building up two separate rigs.
Posted 30 June 2013 - 04:00 PM
However, I did find something else interesting... I removed the saddle plate temporarily to get it out of the way while I was trying to diagnose. The retainer ring on the top of the DEC shaft had quite a bit of marring above one of the ring holes.. This mount was bought used, and had a trip to Celestron before me. It was to address the cogging issue. I don't know if they swapped in a new mount all together, or went in and did some work, but whoever handled the assembly/disassembly was seemingly careless. It's just boggling how near perfect this mount is in RA to have this much slop in DEC.
Posted 01 July 2013 - 04:19 PM