The enemy of the good ...

[Joel Shepherd]

... is the better, in the words of Rod Mollise (and maybe others).

I want to share the story of how I've effectively destroyed my Advanced VX mount, in part to help my fellow astronomy buffs recognize an idiot when they see one, and in part to help other folks who are feeling a bit like idiots (for whatever reason) feel less so. Kind of a public service.

(Also, I accept full responsibility for this: do not read this as a ding against Celestron or anyone else, please.)

I got an AVX mount last spring: seemed like a good balance between cost, weight, and usefulness particularly given the bright urban skies it works (worked) under. With a bit of practice I was able to somewhat reliably get reasonable 2-minute unguided lights from it (http://www.astrobin.com/users/JoelShepherd/), But I wanted better.

So this summer I sent the mount off to get hypertuned. Happily (?) most of the US Pacific Northwest was on fire this summer so I didn't miss it much. It's hard to see anything through thick smoke. When it came back, I was pleasantly surprised by the balance being more sensitive and the gearing being quieter. But it had developed some backlash and play. I decided to tackle that myself.

On the first pass, I figured out how to open things up enough to tweak a bit of play out of the DEC shaft and a bit of backlash out of the RA motor gears. But then the DEC axis seemed too tight (motors struggled to get it moving) and RA was still exhibiting backlash that the hand-controller adjustments weren't managing well. So I opened it up again.

There seemed to be some play in the RA shaft, so I gained access to the ring-nut's set screws (hole under the main electronics panel) and went to adjusting it. As I did so I noticed a crunchy noise under it and decided "What the heck: I'll take it off, clean and regrease it and the washers/bearings underneath and put it back." So I took the ring nut off and -- not thinking -- tipped the RA housing downwards. The RA shaft slipped out.

Okay, I thought, I'll slide it back in. After several back and forths, along with a bit of cleaning and regreasing, I slid the RA shaft back in the housing. It hung up on the large sealed bearing below the worm gear. I gave the shaft a light tap with a hammer, cushioned by a block of wood, and it dropped through but not all the way.

In an unthinking moment, I gave it another light tap. It didn't move. One more. No movement. I pulled it back out but by that time the damage was done. I hadn't removed the worm gear and had jammed the teeth on the steel RA shaft against the softer brass worm, deeply gouging them.

After removing the worm, trying to polish out the gouges and re-installing it, it's pretty clear that that worm is finished and depending on whether I can replace it or not, so is the mount. It turns, but basically disengages the RA shaft at the point where the damage occurred, making it useless for AP and mostly useless for everything else.

The good news, I suppose, is I now know far more about how to disassemble an AVX mount than I've seen documented elsewhere, but obviously to no good effect. I'm embarrassed by my lapse in attention. I used to make a living building and tuning bicycles costing many thousands of dollars, and had (had) a pretty good feel for mechanical things. Now, apparently, that's been lost, much to my AVX's detriment. There is a backup mount but still ... feeling chagrined. A 50% success rate with 2 minute unguided exposures is much, much better than no tracking ability at all. The enemy of the good is the better (and a bit of wandered attention).

[FenlandPaul]

An entertaining read - thank you for posting and making me feel in good company about all the damage I caused to my beloved Austin Mini a decade or so ago. It all looked so simple in the Haynes manual, and that socket set made me feel like a REAL man!!

[RobertI]

Sorry to hear about your mishap and thanks for taking the time to share. I think I shall consider Rod's words and your experience before I attempt to make 'improvements' to my set up in future!

Rob

[SteveNickolls]

Sheeh, I feel for your loss. Takes a better man to admit to something like this.

Cheers,

Steve

[happy-kat]

Gosh a painful read but sharing is good as hopefully it will help others to take that pause.

Good luck in finding a worm gear replacement.

[Dave Lloyd]

That's terrible luck but I'm sure it's possible to have a new component machined if you can't get a spare. With most machinery there are places that specialise in cannibalising old stuff for spares.

[Scorpius]

Did a quick search for a replacement AVX worm but no luck. Have you tried to contact Celestron? If they don't offer a replacement would it be possible to have a machine shop fabricate one using the damaged one as a template? I also have an AVX & have been toying with the idea of having it hypertuned. Who performed the service for you - Deep Space Products? If Celestron doesn't offer a replacement, wonder if DSP would sell you one or provide contact info for the OEM? Too bad this has happened but if you could find a new worm, perhaps the mount could still be salvaged?

If not & you decide to sell it for parts - let me know...

[Joel Shepherd]

Once I get past feeling like a dolt, I'll probably look into a replacement part, though I'm concerned that the teeth on the RA shaft are damaged in a non-obvious way as well. Speculation, but ... it really didn't take much to do the worm in. There is a definite but (by human scale) shallow groove cut across the top of the threads and you could feel burrs between threads at that point as well. Makes you appreciate the precision of engineering even in a modest "consumer"-grade mount.

To happy-kat's comment, if this slows someone down enough to avoid wrecking their own gear it'll have served a good purpose.

Thanks all -- Joel.

[Dave In Vermont]

As a bicycle-mechanic, I get to see the "work" of some other "mechanics" as well as the Tarzan-approach used by the proud, new owners of a set of tools.

An oft-quoted line of mine went 'viral' in major bicycle-forums: 'Anyone can be a ham-handed Gorilla. But it takes finesse to be a [removed word]-Cat.'

People are often surprised at the delicacy of some of the things that go into making a bicycle designed to tear-up the back-40 or go screaming down mountainsides. I'm no fan of people destroying delicate eco-systems on these machines - these non-motorized machines at that - so from my perch as a "wrench" I use my Bully Pulpit to chat with people and educate them about not harming nature. Now with telescopes and their peripheral mounts, etc. - my training as a mechanic has paid off in an intuitive understanding of how much torque to use on this and that.

Joel just found out the hard & expensive way what not to do. So I recommend to all you would-be 'Joel's' out there to consider a course in mechanics. There may not be one (yet) for astronomy-gear, but the mechanics of other systems are applicable across-the-board. Feeling inventive? Consider studying mechanical-engineering. Your mount and kitchen-toaster will thank you!

Happy wrenching!

Dave

[MartinB]

There you go Joel, send it up to Vermont for Dave to fix it with his intuitive understanding.

[Dave Lloyd]

There you go Joel, send it up to Vermont for Dave to fix it with his intuitive understanding.

It's true though. Turn enough drivers, wrenches etc you do get a feel for it. The main problem is with high hardness stuff which goes without warning. The golden rule is if it feels like a resistance don't force it.

[MartinB]

I'm embarrassed by my lapse in attention. I used to make a living building and tuning bicycles costing many thousands of dollars, and had (had) a pretty good feel for mechanical things. Now, apparently, that's been lost, much to my AVX's detriment.

I think there are things that Joel just doesn't need to hear!

[mcolbert]

good timing on this one - I'm at the stage of having completely dismantled my binos, seeing several issues (fungus and a slight chip!) and also (with great talent) twisted part of the body which doesn't!  Oh well, I can have fun with the prisms and the lenses!

Now you know why I only touch my 130 with the greatest of care!

michael 

[Joel Shepherd]

Ha, well, to extend Dave's and others' remarks, not only does it help to have some wrenching, etc., under your belt, I'd imagine it helps to have done it seriously somewhat more recently than 20 or so years ago.   At one time, I had no problem facing, chasing and building out a high-end Merckx with C-Record ... while the new, nervous owner sat and watched. But that was many moons ago and I realize now that I've fallen out of practice and am not as methodical, attentive and patient as I once was, at least when it comes to tweaking mechanical things. Live and learn, and learn again.

[Dave In Vermont]

I quite honestly didn't note that you are also a "wrench," Joel! But as one of us, I'm sure you understand what I was getting at. Like me, as well, you undoubtedly have some wonderful 'tales from the trenches' of some of the best goofs of all times - our own!

Should you ever get the urge to exchange a few of your glorious victories (or disasters) - feel free to get in touch. Vermont is going super-heavy into bicycles lately. Mixture of health-concerns and eco-consciousness. It's not only our mountains that claim fame by being 'green.' The people are, too.

Dave

[MartinB]

 Vermont is going super-heavy into bicycles lately. Mixture of health-concerns and eco-consciousness. It's not only our mountains that claim fame by being 'green.' The people are, too.

Dave

Funny you should say that!  My wife and I are heading off to New York on Saturday to visit our daughter and also have a 6 day cycling tour in Vermont arranged.

[101nut]

I feel your pain Joel!

I think one moral from this is that ,in general, if something is removed easily, it will go back into place with a similar force. More than that and you should wonder why ...

AndyG

[Dave In Vermont]

I feel your pain Joel!

I think one moral from this is that ,in general, if something is removed easily, it will go back into place with a similar force. More than that and you should wonder why ...

AndyG

I wonder if this also applies to child-birth.....?

I'll grab my hat...

Dave

[mcolbert]

like it Dave,  but sad to say that some (few) spend their lives trying so to do.

michael

[Joel Shepherd]

Dave - When (if?) our daughter is a little more amenable to traveling, Vermont, New Hampshire and Maine are all on our short list of places to visit, so we might see you there. In the meantime, yeah, I remember the refrain: "I was just riding along and ...".

[Dave In Vermont]

Do let me know if & when you have plans for daring to venture into the People's Republic of Varmint. I'd be happy to provide you with information on whatever types of places to go and things not to miss. But whatever you plan, you are assured of very nice people and fantastic views. We don't even allow any billboards on the sides of the highways - all two of 'em. Heck - we don't even use stoplights! The biggest arguments with cars you'd see are at 4-Way stop-signs: "Oh no! I insist! YOU go first!" "No way! YOU go first!" Etc. It's always people holding door's open for you. "Yes-SIR!" or "Certainly, Madam!"- are the most common refrain.

The only problem we have arr the people who come to look around - they NEVER want to leave!

Do check online for when Stellafane will be that year. Maybe you'll get lucky and be able to attend.

We reserve the right to arm bears,

Dave