74 replies to this topic

[Dynan]

mrkhagol - Sounds like you need the typical 'Celestron Fix'...send it back for repair/replacement. I wouldn't accept a brand new mount that acts as such.

[StarBurger]

A suggestion because we have seen this in the past----Is the spiral cord connector in place between the main body DEC plug and the moving DEC axis plug ?

[mrkhagol]

Yeah Dynan..it looks like that's what I have to end up doing..this just sucks..because it'll be sending something back again to Celestron..the first one being OTA which took a BIG hit when it on dropped on concrete floor..because it was heavy to handle and the safety screw of dovetail got stuck in mount notch.... ..so celestron is already trying to fix that..I've contacted them again and see what response I get...

 

Starburger - spiral cord connector plugs into RA mount area ..it doesn't go upto dec mount area or anything like...

[StarBurger]

Just to be sure we are talking of the right connector:

[mrkhagol]

Starburger - I feel like a complete idiot.
Dec cable was not even connected.completely misread instructions. Just plugged the cable in and Dec axes moving as it's supposed to.
Thanks for posting the picture.

[Dynan]

D'OH! 

[StarBurger]

Wonderful mrkhaghol!

You have made my day !

I love to help.....

[mrkhagol]

Starburger I should be the one saying that..on making my day...thanks again.
Now if the weather can clear up then I can start doing alignment later...
Dynan - I agree with Homer Simpson dialogue😉.

Edited by mrkhagol, 14 October 2019 - 01:27 PM.

[ipscgal11]

Thanks so much for the solutions, explanations and discussions! Bravo Mike C, Nikko, & Wade#237 for your input!!  I like the washer/spacer idea esp. aluminum or steel but will use hose washers if that is all I can find.  Right now my AVX is tracking away on the Leo Triplet with the locking nut on backwards! 

[const]

Single washer for 3/4" hose helps my AVX. I was so amazed how simple is the solution that I even registered here to say thanks to the people who diagnosed the problem! Guess now I have to start posting pictures...

[tom_fowler]

Mine also seized but for a completely different reason.  Right in the middle of a slew, the declination axis seized, and the harder I tried to free it, the tighter was the seize.  So I took the declination axis assembly apart.  The rotating shaft was so tightly welded to the case that I literally had to use a small sledge hammer to free it.  After I got the shaft out, I inspected it and did some research.  What I found is that mine seized due to galling, which can actually weld pieces of metal together.  It is especially a problem with sliding surfaces (such as bearings), and aluminum is especially prone to it.  The bearing in question is the central bearing in the assembly, about halfway down the shaft.  On mine, both surfaces had pits and raised areas.  I cleaned off the grease (or what was left of it), and used fine sandpaper to smooth out the bearing surfaces.  Eventually I got it smooth enough for the parts to fit together and the shaft to rotate.  Then I re-greased with lithium grease and put the declination assembly back together.  So far it seems OK, though I found out about a new kind of grease, Calcium Sufonate bearing grease, that is supposed to be better than lithium grease.  If I have to take the mount apart again, I'll use that.  I did notice that, prior to the total seizing of the mount, that it had become stiffer in declination.  That is the warning sign.  Obviously, Celestron cut a corner by using a sleeve bearing instead of a ball bearing in this mount.  Unfortunately retrofitting a ball bearing looks to be impossible.

[AstroNikko]

Thanks for sharing! Sorry to hear about your experience. I'm curious, how heavy is your typical payload, and how much counterweight do you use?

 

I noticed galling as well during my rebuild, and took a similar approach to smoothing out the plain bearings using 400, 800, 2k, 3k sandpaper, but was still left with some pitting in the bearing surface.

 

 

I replaced the lubricant with Super Lube Synthetic Grease with PTFE (NLGI 2), but upon later inspection noticed that the grease was darkening with aluminum particulate. Which tells me it may not be sufficient for this type of application.

 

For metal-on-metal sliding surfaces, a molybdenum disulphide (or moly) grease like AeroShell 64 might be better. I recently purchased a cartridge of AeroShell 64, and plan to use it for lubricating these aluminum plain bearings as well as the worm gear and 30T brass spur gears. Each of which have significant sliding action.

 

Ball and roller bearings still appear to be in good shape when using Super Lube Synthetic Grease with PTFE (NLGI 2). There doesn't appear to be any darkening of the lubricant like there was with the plain bearings. I'm uncertain about its performance though as I haven't yet done any comparison tests with other types of grease.

[AstroNikko]

One other way the DEC axis can seize up is when clutch pushes the saddle off axis and it binds with the casing. Something to keep an eye out for.

 

If you find you keep having to adjust the position of the clutch knob, it's likely pushing the saddle off axis. Eventually the saddle, or worm wheel, or both, will start rubbing against the casing. To fix, you simply loosen and recenter the saddle on the axis, and tighten it down again. There four screws that hold the saddle in place, but there's no centering mechanism to keep the saddle from sliding off axis.

 

The best way I've found to center the saddle on the axis is not to center the holes of the saddle on the screws. Before tightening, take up the slack around the screws by rotate the saddle counter-clockwise so that the screws are against the sides of their holes. This will help to keep the saddle center as the screws are tightened. Also make sure that the clutch is NOT engaged while tightening. Then gently start to tighten the bolts in sequence North, South, East, West. At first, only tighten until each screw is fully seated, making sure the saddle is rotated on the axis to keep the screws in position within their holes and the saddle center on the axis. Then repeat the sequence, making 1/16 turns for each screw with each sequence until they're all tight. Be sure to check the clearance periodically by rotating the the axis by hand. It should rotate smoothly without binding at any point of the rotation.

 

I had this issue happen to me again last night while tuning the DEC axis. With the clutch released, I noticed at one point in the rotation where it had became difficult to rotate. Listening closely, I could hear something rubbing. When the clutch was engaged, the motor would experience higher load at that point in the rotation as well. Re-centering the saddle fixed the issue.

 

I've had this happen once before. Upon inspecting the worm gear, I found that either the outer casing or the saddle had etched a line around the worm wheel about half way up the outer surface. Luckily it didn't cause any serious damage, but it had caused the axis to seize up.

 

The RA isn't susceptible to the same issue though, because the clutch is part of the RA axis casting. Whereas for the DEC, the clutch is part of the saddle, which is attached to the DEC axis casting.

[Steve_M_M]

Thank you everyone on this thread.  I have no idea how this type of "repair" isn't necessary for every single AVX mount utilizing the lock nut screwed on the right way.  My new to me AVX I bought today is up and running.  Lowes has the bushing in stock...  https://www.lowes.co...hing/1000364199

[AstroNorth_Alex]

Hi everyone,

 

I thought I'd post to this thread as I just had my Dec axis on my AVX seize up and I don't know what I should do exactly.

 

My AVX is 4 years old and was working fine until last week. I had my C8 set up inside as I was removing my corrector plate to clean it inside and out. I had the AVX mount set up and just manually set the scope so it was pointing at zenith (so the corrector plate wouldn't fall out when I loosened the ring screws etc.), I had no power going to the mount at all. I had 1 of my counter weights set up as well and balanced it quickly but decent enough.

 

Everything was fine until I was finished and re-installed the corrector plate and went to disengage the clutches and move the mount back to the park/original position. RA was fine but then DEC suddenly started feeling stiff and the more I tried to loosen in either direction it just kept tightening up. I could hear what sounded like rubbing before it seized on me and then could no longer move it period.

 

I've read a few posts including ones on an issue with the counter weight bar and having the top casing (locking collar) potentially bind with the mount causing a seizure, plus this post regarding galling etc.

 

I was hoping someone could help me with what I should do and if the mount can be salvaged. I reached out to Celestron support and they noted it's past warranty so they recommend shipping to them and they'll quote a repair if possible etc. That will cost me $100-200 for shipping alone plus whatever it would be for them to fix.

 

I haven't taken apart the mount at all as I'm not that well versed in the details to do that, so was hoping someone could guide me.

 

What I've done:

 

1) When I remove the counter weight bar, the set screws on the bottom of the DEC axis are out of alignment with the access holes by at least a quarter rotation so I can't get to them to loosen in an attempt to adjust the tension as some suggested in the posts regarding the counter weight bar collar causing a seize.

 

2) Clutch disengaged on the DEC axis cannot move the DEC axis no matter how hard I try.

 

2) When I remove the saddle (unscrew and remove the 4 screws) and try to move the inner ring the saddle screws in to, no luck.

 

3) When I hook up the mount to power and go to move the DEC axis using the hand controller, the outer ring gear works fine and is rotating.

 

I'm attaching pics of my mount as reference if it helps in any way.

 

 

To me it seems like the rotator shaft on the inside is seized up as I can't move the saddle for the life of me, but I'm a newbie when it comes to disassembling or playing with the mount.

 

Any help is very much appreciated as I'm dead in the water right now without a mount as the AVX is all I've got. I'm looking to upgrade and get the ZWO AM5 but that won't be for a while unfortunately.

 

Thanks,

Alex

Edited by AstroNorth_Alex, 21 August 2023 - 10:08 PM.

[AstroNikko]

First of all, make sure the clutch lever isn't making contact with the drive housing. With use, it has a tendency to get closer to the housing when tightened down. You can adjust it's position by loosening the center screw, removing the handle, and repositioning it on the end of the clutch pin.

I've gotten the DEC stuck before when the saddle slid off center from its mounting on the spindle of the axis. When it becomes off-center, the saddle can rub against the body of the DEC axis and potentially bind up.

This may not be your issue though if you're still able to rotate the axis using motor control. In that case my best guess would be the clutch pad on the end of the clutch pin may have gotten wedged somehow between the saddle and the ring gear / worm wheel. But with the saddle removed, I doubt that's the issue.

I'm not sure what is causing the axis to seize in your case. You may need to disassemble to inspect further.

If you're still able to rotate the axis using motor control, try rotating the axis until the set screws on the tension ring line up with the access ports on the base. You want to make sure you back the grub screws out generously so that they don't catch on the threads when unscrewing the tension ring. Using a lens spanner or pin spanner, rock the tension ring back and forth (loose/tight) until it unthreads easily. Threads are likely torn up a bit from the set screws, especially if there was any slippage.

[AstroNikko]

To add to this, I think the reason you have to keep adjusting the handle on the DEC clutch is because as it's tightened, it can gradually push the saddle off center. Which will eventually lead to the saddle rubbing against or binding with the ring-gear/worm-wheel and/or the DEC axis housing.

The best method that I've found to help keep the saddle centered is to give it a twist before tightening down the bolts. This will center up the saddle pressing the bolt holes of the saddle up against the same side of each bolt, relatively speaking clockwise.

This helps to keep the saddle centered while tightening the bolts. Make sure to alternate between bolts when tightening. So rather than tightening clockwise 12, 3, 6, 9 o'clock; tighten using the sequence pattern 12, 6, 3, and then 9 o'clock. Go easy at first to make sure they're all being evenly tightened and the saddle hasn't slipped before cranking down on the bolts.

[Skywatchr]

Hi everyone,

 

I thought I'd post to this thread as I just had my Dec axis on my AVX seize up and I don't know what I should do exactly.

 

My AVX is 4 years old and was working fine until last week. I had my C8 set up inside as I was removing my corrector plate to clean it inside and out. I had the AVX mount set up and just manually set the scope so it was pointing at zenith (so the corrector plate wouldn't fall out when I loosened the ring screws etc.), I had no power going to the mount at all. I had 1 of my counter weights set up as well and balanced it quickly but decent enough.

 

Everything was fine until I was finished and re-installed the corrector plate and went to disengage the clutches and move the mount back to the park/original position. RA was fine but then DEC suddenly started feeling stiff and the more I tried to loosen in either direction it just kept tightening up. I could hear what sounded like rubbing before it seized on me and then could no longer move it period.

 

I've read a few posts including ones on an issue with the counter weight bar and having the top casing (locking collar) potentially bind with the mount causing a seizure, plus this post regarding galling etc.

 

I was hoping someone could help me with what I should do and if the mount can be salvaged. I reached out to Celestron support and they noted it's past warranty so they recommend shipping to them and they'll quote a repair if possible etc. That will cost me $100-200 for shipping alone plus whatever it would be for them to fix.

 

I haven't taken apart the mount at all as I'm not that well versed in the details to do that, so was hoping someone could guide me.

 

What I've done:

 

1) When I remove the counter weight bar, the set screws on the bottom of the DEC axis are out of alignment with the access holes by at least a quarter rotation so I can't get to them to loosen in an attempt to adjust the tension as some suggested in the posts regarding the counter weight bar collar causing a seize.

 

2) Clutch disengaged on the DEC axis cannot move the DEC axis no matter how hard I try.

 

2) When I remove the saddle (unscrew and remove the 4 screws) and try to move the inner ring the saddle screws in to, no luck.

 

3) When I hook up the mount to power and go to move the DEC axis using the hand controller, the outer ring gear works fine and is rotating.

 

I'm attaching pics of my mount as reference if it helps in any way.

 

 

 

 

 

 

To me it seems like the rotator shaft on the inside is seized up as I can't move the saddle for the life of me, but I'm a newbie when it comes to disassembling or playing with the mount.

 

Any help is very much appreciated as I'm dead in the water right now without a mount as the AVX is all I've got. I'm looking to upgrade and get the ZWO AM5 but that won't be for a while unfortunately.

 

Thanks,

Alex

Take the DEC motor off.  That way there is no stress on the worm gear.  It is possible the clutch was too tight and made the DEC drum egg shaped.  But without the motor is the safest way to be trying to force it around to get to the set screws on the locking collar.

[AstroNorth_Alex]

Thanks AstroNikko and SkyWatchr.

 

The clutch is fine. I adjusted it a couple of years ago as I did have it bind to the housing one night and learned to adjust it.

 

I decided to venture into taking apart the DEC axis, removing the motor and all. I was able to get the tension ring at the bottom of the axis off finally with some effort for sure as it was tight. I nudged it enough to line up the tension set screws with the access holes.

 

I was able to remove the DEC shaft with some light tapping as simply letting it drop out or even pulling it out didn't work.

 

I'm at the point now where I'm going to wipe clean and regressed the DEC shaft as simply re-assembling it has shown the DEC shaft won't settle into the housing by simply turning until it drops into place. I don't want to tap it into place as that sounds excessive.

 

I'm hoping by wiping it clean and re-greasing it will help as I'm finding the existing grease black in some areas and sticky, that can't be good, but I'm no expert.

 

I'll keep you posted if I get it re-assembled and working again 

 

Thanks for the help 

 

CS,

Alex

Edited by AstroNorth_Alex, 24 August 2023 - 02:57 PM.

[AstroNorth_Alex]

My AVX is done I'm afraid. While cleaning and greasing I noticed there was some marring inside the housing, most likely where it seized.

In either case, the DEC shaft would not settle in the housing no matter how much I tried, it was a no go. I watched videos of others that tore down and rebuilt the mount and they didn't have any of the trouble I was having settling the DEC axis shaft in the housing.

If it is salvageable, it's well beyond my skills.

I'm officially dead in the water until I can buy another mount. That will be quite some time unfortunately.

CS,
Alex

[AstroNikko]

Hi Alex,

 

I'm really sorry to hear about the mount troubles. If I'm understanding correctly, it sounds like the race of the plain bearing located near the middle of the DEC axis may have excessive galling, and as a result is causing the axis to seize and not be easily reseated. If this is the case, it would be a point of failure in the mount. Some pictures could help confirm this.

 

It might be worth reaching out to Celestron Support for feedback and suggestions. If it's still under the warranty period, they may cover repairs due to the nature of the point of failure despite the mount being disassembled.

 

When I disassembled the DEC axis of my AVX, I noticed galling along the race of the plain bearing. I opted to sand down the surface to a polished finish, but I don't recommend doing that for 2 reasons:

1. Sanding removes material and widens the tolerance gap, introducing further error in the axis.
2. Sanding by hand like I did is impossible to do perfectly, which also introduces error.

Before and after pictures of the DEC plain bearing in my AVX. I sanded the race using 400, 800, 2000, and 3000 grit wet/dry paper. The pitting still present along the race after sanding is the result of galling.

 

 

 

That said, I am able to use the mount still. Although I primarily use it for visual and planetary imaging, and occasionally wide field DSO with a pixel scale greater than 3 arcsec/px. The mount typically guides between 2 and 3 arcsec RMS. If Celestron isn't willing to help you out, you could try doing the same as I did if you're confident in your ability.

 

More details of my build are outlined in this twitter thread. I wish you the best with this.

 

Clear skies,

 

Nikko

[agara]

I have the same issue.  A couple nights ago my AVX froze as I was manually setting it to the index marks for alignment.  In fact, I couldn't separate the Declination shaft from its housing.  I finally used WD 40 and a mallet to pound it out.

The lower end of both Housing and Declination race were severly damaged.  I have no idea why it seized in the first place.  I'm now looking for an AVX Declination housing With Declination Axis.  I don't know where to find such a thing, if it exists.

Before this happened, Declination trackign error was 0.65".  I had no warning this might happen.  

 

I love the fact that the AVX is lighweight and did track well enough for Astrophotography.  But, I was always fiddling with it.  I had issues with Declination suddenly running away.

I sent to Celestron to fix.  They said there was no problem and sent it back.  Sure enough, when I used it again, the Declination Axis ran away again.  I ended up fixing it myself.  It was

an issue with the Declination drive cable shorting.  Too much grease.  Breaking the motor cover, etc.

 

   

[jwarner191]

Question: is there any advantage to using 1 or 2 weights if either way, you can get good balance?

[AstroNikko]

As a general rule, you want to try keeping the counterweights closer to the center of axis to reduce the moment arm. Which can help improve guiding results by reducing stress on the motors.

That said, the more weight you add, the greater the stress on the plain bearings in this mount, and the more likely you are to see galling in the races as a result.

With my 8" scopes, I use two Celestron AVX 12lb counter weights, along with two 3lb iOptron counter weights. I keep the weights tightly clustered on the shaft, and keep them as high on the shaft as I can. The iOptron weights give me a little more control when balancing, but also help with clearing the motor housing, and the handle of the altitude set screw.

Edited by AstroNikko, 02 September 2023 - 02:30 PM.

[AstroNorth_Alex]

@Agara - I was in the same spot as you when my DEC axis seized. I had to pound it out with a mallet. Mine seized because of the counterweight shaft collar at the top. It binded with the housing causing the shaft and housing to gall and seize. I read some articles about this and now have the collar on the counterweight bar reversed to avoid the issue. With AstroNikkos help I was able to sand down the galling in my housing and on the shaft and have my AVX up and running again with guiding between 0.7 and 1.2 depending on seeing etc. Back to where I was before. Thanks to AstroNikko for the help.

@jwarner191 - agree with Nikko on this. I originally had 1 counterweight at the very bottom of the bar but opted for 2 counterweights. Both are no more than half way down the bar but it is added weight.