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AVX Question

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#26 Michael Covington

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Posted 25 March 2018 - 08:45 AM

large right angle snap ring pliers that open wide enough could do the trick instead of needle noses , right angle needed nose pliers big enough could as well. 

Right, using needle nose pliers was a kluge.  Snap ring pliers (retaining ring pliers) or even a lens spanner (for lens retaining rings) would be other options.



#27 epsiloneridani

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Posted 27 March 2018 - 02:06 AM

Thanks Frito and Michael, the snap-ring pliers did the trick. I did find that, even after loosening the retaining ring, I couldn't tighten the socket head screws on the ADM dual saddle to the point of tension; I had to leave them disengaged perhaps half a turn, which allowed the DEC to rotate more freely, though still eliminating slack.


Edited by epsiloneridani, 27 March 2018 - 02:18 AM.


#28 Michael Covington

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Posted 27 March 2018 - 09:03 AM

Thanks Frito and Michael, the snap-ring pliers did the trick. I did find that, even after loosening the retaining ring, I couldn't tighten the socket head screws on the ADM dual saddle to the point of tension; I had to leave them disengaged perhaps half a turn, which allowed the DEC to rotate more freely, though still eliminating slack.

Something's still not right, then.  Maybe back off the retaining ring further.



#29 EFT

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Posted 27 March 2018 - 08:58 PM

There are only two ways that the ADM saddle can be a problem.  The first is if the saddle is contacting the DEC axis housing directly.  I have seen this happen on occasion typically around the rectangular hole at the top of the housing where the worm interfaces with the ring gear.  If that is happening you should see some marks on the recessed portion of the saddle at the base.  If that is happing, then it is, from a practicality point, easiest to slightly sand the recessed area so that it no longer contacts the housing.

 

The other way is if the ring gear is being squeezed too tightly between the axis "shaft" and the saddle.  While this is technically not supposed to be a problem, the reality is that it is.  Using a thinner plastic "bearing" in there solves that problem. 



#30 Nippon

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Posted 08 April 2018 - 05:38 PM

The sample to sample difference in these mounts seems amazing. Mine was smooth as butter right out of the box. I just installed an ADM dual saddle with no issues at all and it still moves with just finger pressure even loaded with my Edge 8 and 16 pounds of counterweight. Is it correct to assume that AVX problems have little to do with design and engineering and everything to do with poor consistency in the machining and assembly?



#31 EFT

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Posted 08 April 2018 - 07:04 PM

Rare is the AVX that moves so easily out of the box.  The problems with the AVX are related to both design and manufacturing.  The basic GEM design is fine although it could be more polished.  The lack of ball or thrust bearings on the DEC axis is a serious design issue.  The AVX could have been substantially improved over the old CG-5 and many similar mounts if it had been designed with bearings on the DEC axis, even just a single ball bearing and thrust bearing as is done with the RA axis.  The increase in the number of bearings to four on each axis in mounts like the CGEM is a very important design improvement in those mounts.  The use of simple cast axis "shafts" is a very inexpensive way to do things but is far inferior to steel axis shafts like those used in a similar Vixen mount (note that the Vixen mount is generally heavier and substantially more expensive for a reason).  The CGEM and larger sized mounts also use much stiffer and more durable steel axis shafts.

 

Manufacturing inconsistency is another matter.  It is clear that there is a lot of inconsistency in the cast aluminum parts used as well as the partial machining necessary to use them.  Cast aluminum without strict quality standards is not particularly good for high precision mechanicals when compared to parts made from properly pretreated and/or post treated metals.  Add to that the clear inconsistency in the final assembly of mounts where too much grease may be used and too little care taken to weed out bad assemblies, and you have a product that has a lot of variability from unit to unit.



#32 u2drvr

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Posted 09 April 2018 - 02:30 PM

I had the same problem with the ADM saddle...I added nylon washers under the saddle mount and that fixed the problem. I also removed the sticky grease, polished the ring gears, and used a small amount of superlube. Works great now and I routinely get 1.5" or better guided 5min subs.



#33 Michael Covington

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Posted 09 April 2018 - 06:39 PM

I had the same problem with the ADM saddle...I added nylon washers under the saddle mount and that fixed the problem. I also removed the sticky grease, polished the ring gears, and used a small amount of superlube. Works great now and I routinely get 1.5" or better guided 5min subs.

This is what I did...  http://www.covington...ex.html#x171113

But tell me more about what you did.  What exactly did you polish?  And where did you get the nylon washers?

 

My dec axis turns about 1/3 as easily as a CGEM dec axis.  (Requires 3x the force.)  Is that about right?



#34 u2drvr

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Posted 09 April 2018 - 06:57 PM

This is what I did...  http://www.covington...ex.html#x171113

But tell me more about what you did.  What exactly did you polish?  And where did you get the nylon washers?

 

My dec axis turns about 1/3 as easily as a CGEM dec axis.  (Requires 3x the force.)  Is that about right?

Nylon washers from Lowes - $0.62

I did a lot...

- Removed all the sticky "grease" used by Celestron

- Polished ring gears inside and out

- Polished worm gears

- Replaced/adjusted worm bearings (ceramic bearings)

- Polished all other bearing surfaces

- Replaced the nylon/hdpe "bearings" with PTFE (from Ed Thomas)

- Replaced RA thrust bearing with an angle bearing

- Reassembled with a light coat of Superlube on all bearing surfaces

- Fine tuned worm and spur gear backlash

- Added bubble level to tripod

- Installed most of the ADM accessories

- Repaired motor control board after an overload caused a ferrite bead to pop off...repair worked, but replacement board also on order.

 

RA now moves pretty free, but Dec is much better than it was, but still stiffer that I would like. Both move very smoothly and I can get good stars on 5 min guided subs...probably longer, but I haven't tried yet. I'm considering doing a belt mod to replace the spur gears because that's where most of the backlash is, but I'm not sure it's worth the effort. Besides, I'll probably sell it soon anyway to fund a bigger/better mount (leaning towards the CEM60).


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#35 Whuppy

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Posted 09 April 2018 - 07:02 PM

Nylon washers from Lowes - $0.62

I did a lot...

- Removed all the sticky "grease" used by Celestron

- Polished ring gears inside and out

- Polished worm gears

- Replaced/adjusted worm bearings (ceramic bearings)

- Polished all other bearing surfaces

- Replaced the nylon/hdpe "bearings" with PTFE (from Ed Thomas)

- Replaced RA thrust bearing with an angle bearing

- Reassembled with a light coat of Superlube on all bearing surfaces

- Fine tuned worm and spur gear backlash

- Added bubble level to tripod

- Installed most of the ADM accessories

- Repaired motor control board after an overload caused a ferrite bead to pop off...repair worked, but replacement board also on order.

 

RA now moves pretty free, but Dec is much better than it was, but still stiffer that I would like. Both move very smoothly and I can get good stars on 5 min guided subs...probably longer, but I haven't tried yet. I'm considering doing a belt mod to replace the spur gears because that's where most of the backlash is, but I'm not sure it's worth the effort. Besides, I'll probably sell it soon anyway to fund a bigger/better mount (leaning towards the CEM60).

There have been a few people that have done the belt mod. Seems to be more trouble than it's worth. You have to reverse polarity to the motor and the spur gears actually account for very little backlash, which you can adjust to get most of it out. Backlash also occurs at the worm and ring gear (adjustable) as well as inside to gearbox on the motor (not adjustable)... a +1 on the Cem60, it made my life a whole lot easierlaugh.gif


Edited by Whuppy, 09 April 2018 - 07:04 PM.


#36 Michael Covington

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Posted 10 April 2018 - 08:05 AM

Tell me more about the polishing.  Are there pictures of this process anywhere?



#37 u2drvr

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Posted 10 April 2018 - 01:35 PM

Tell me more about the polishing.  Are there pictures of this process anywhere?

Nothing complicated...just a buffing wheel, polishing compound and jewelers rouge. Sorry, but I didn’t take pictures.


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#38 rmollise

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Posted 11 April 2018 - 06:06 PM

Here's the bottom line on these and similar mounts. If there is genuinely something wrong with your mount, doing things like this can help it. However, if the mount is functioning OK, if it's performance is OK. If its goto accuracy is good and the tracking PE is within 15 - 30"  or so peak to peak, leave it alone. You are not going to turn it into a premium mount. And unless you are mechanically inclined, you run the risk of creating more problems than you fix. In fact, I'd say that if the mount does have problems, and you can't get it repaired or exchanged by Celestron or your dealer, having someone who knows their stuff--like Ed Thomas--work on it is a must for most of us. ;)


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#39 EFT

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Posted 11 April 2018 - 07:15 PM

I agree with Rod.  If it ain't broke, don't fix it.  This is particularly true with mounts like the AVX that don't cost "much" to start with but can easily be made worse.  A CGEM is far easier to work on an improve than an AVX.  When it comes to the AVX, if you plan on keeping it for a long time or to use it as a portable imaging mount, you might consider trying to improve on it.  Otherwise it is probably not worth the cost.


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#40 Michael Covington

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Posted 12 April 2018 - 08:56 AM

Yes, all I have done to mine is (as you know)  (1) adjust the retaining ring at the bottom of the dec axis, which had gotten too tight; (2) add a washer so that tightening the counterweight bar would not affect it.

I think misadjustment of this retaining ring is common and leads to a lot of problems that people describe involving the saddle and the nylon ring under it -- the actual trouble is at the other end of the axis.


Edited by MCovington, 12 April 2018 - 09:11 AM.


#41 Michael Covington

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Posted 12 April 2018 - 08:57 AM

I agree with Rod.  If it ain't broke, don't fix it.  This is particularly true with mounts like the AVX that don't cost "much" to start with but can easily be made worse.  A CGEM is far easier to work on an improve than an AVX.  When it comes to the AVX, if you plan on keeping it for a long time or to use it as a portable imaging mount, you might consider trying to improve on it.  Otherwise it is probably not worth the cost.

I also have a CGEM which works well.  I am wondering how much it would benefit from hypertuning vs. saving up for a CGX or a Losmandy.

The main appeal of the AVX is better PEC.  I use the AVX for shorter unguided exposurs and the CGEM when autoguiding.


Edited by MCovington, 12 April 2018 - 08:57 AM.


#42 EFT

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Posted 12 April 2018 - 03:44 PM

Look at it this way.  If the CGEM is doing what you need it to do, then leave it alone.  If it can't be guided well due to mount error, then consider having it worked on.  With these two things in mind, you also have to remember that there is no way to make the CGEM perform like a premium mount.  Tuning it won't allow you to suddenly go unguided for any significant amount of time.  It won't let you start working with a C11 guided for deep sky imaging any better than before tuning since it is a bad mount/scope match in the first place.  It won't let you go for unreasonably long guided subs.  The mount simply has limitations in precision that cannot be solved without replacing significant parts and even then, since the mount is a total system, not just its individual parts, improvement will be limited.

 

If you can't guide with a reasonably sized refactor on there then it probably needs work.  If you can't off-axis guide with a C8 within reason on there, then it probably needs work.  If you can't do unguided planetary imaging or video astronomy, then it probably needs work.  The mount can almost always be improved to smooth out error and reduce some of the periodic error, or even just to improve the ability to balance the mount (which is not unimportant) but it is a relative improvement.  A very poorly performing mount will show a lot more improvement than a mount that is already performing very well.  You will not see the same amount of improvement in the performance of a good mount vs. a bad mount.  That is simply the limitation of the mount's design and manufacture overall. 

 

You have to keep your expectations reasonable.  When you do, these mounts can perform very well and can be improved to perform better for imaging that is within the reasonable performance of these mounts.


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#43 Michael Covington

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Posted 12 April 2018 - 06:16 PM

I think it is within spec.  I can autoguide a C8 at f/7 with a guidescope.   It has never been serviced or lubricated and I am the 3rd owner.



#44 EFT

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Posted 14 April 2018 - 12:29 AM

I personally think that the C8, even at f/10, is a well matched SCT for the CGEM.  It's long focal length is challenging, but by weighing so much less than the C9.25 or C11, the mount is not stressed at all and performs better all around.  You can add a good guiding system and a heavy imaging system and still be well below the mount's reasonable imaging capacity.


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#45 Michael Covington

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Posted 14 April 2018 - 09:49 AM

An under-loaded mount is a good mount.  And one thing I tell everybody is that telescopes gain weight as you add accessories.  The listed weight of the telescope is not what it is going to weigh when it's all set up!
 



#46 Michael Covington

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Posted 14 April 2018 - 09:50 AM

Do you consider the CGX a substantial step up from the CGEM?



#47 EFT

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Posted 14 April 2018 - 10:20 AM

No.  Same motors, same worms, same ring gears.  While they may have tweaked the electronics, adding more power to the motors in a "balanced" mount is not really that meaningful except when starting a slew.  Makes no difference when tracking. 


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