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Celestron CGE Mount "Odd Sound" Diagnosis...

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#1 jrbarnett

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Posted 10 October 2013 - 01:04 PM

Yeah, I know. Trying to diagnose mount sounds in the context of an internet forum is one step more insane than those AAMCO commercials where the customer is trying to verbally describe odd automotive sounds to a mechanic, but I have a gift for conveying sound with the written word, so here goes...

I've been using a new C9.25 Edge HD OTA on my venerable, much loved, Celesrton CGE (not CGE Pro) mount. I have a Bennett RA/Dec port mod kit on the shelf, and have thus far (5 years) had no trouble with the mount using "Marty cables" in place of the stock Cat 5 RA and Dec cables. I won't install the Bennett kit unless and until I actually need it, and may elect to have Ed at Deepsky Products do a baby hypertune on the mount and install the kit at that time. But I digress.

Over the last few session, despite me being careful to properly balance the OTA, the Dec gear train has been making odd noises under particular circumstances. RA and Dec slews are nice and quiet with the OTA aimed west of the meridian. The Dec slews get noisy, however when the OTA is aimed east of the meridian and the Dec axis is slewing through the center 40-45 degrees of its range. Here how I would describe the sound:

Bzrzrzrzrzrzrzr (normal slew motor/gear noise)...Brch'..brch'...brch't..t..tch'...brch'...brch' (stuttery sound like a shovel blade entering sandy soil in cyclical cadence)...Bzrzrzrzrzrzrzr (back to normal slew sound once through the noisy portion of the range).

Any ideas?

It also looks from the foam in the Pelican case where I store the mount as if some of the lubricant has liquefied and leaked out of the motor housings, probably due to high heat dark sky trips. Is there any way to get a peek at the gears and worm without totally stripping down the mount? I'd like to visually inspect the lubrication situation. Could that be related to the sounds I'm hearing?

Regards,

Jim

#2 WesC

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Posted 10 October 2013 - 03:38 PM

Interesting... I have had my fairly new CGEM make a similar sound on occasion. I can only assume that its a balance issue. Maybe from changing out eyepieces?

My plan is to soon purchase a dovetail weight that I can use to tweak the balance throughout the night.

#3 jrbarnett

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Posted 10 October 2013 - 03:49 PM

"My plan is to soon purchase a dovetail weight that I can use to tweak the balance throughout the night."

Wes, that actually sounds like a pretty darned good idea. I was changing loads. Next time I'm out I'll see if I can make the sound go away by rebalancing with the particular eyepiece in use. I also have one of the Televue bronze 2" to 1.25" adapters designed to keep weight similar when swapping from heavy 2" eyepieces to lighter 1.25" units. I may play around with that, too.

Regards,

Jim

#4 David Pavlich

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Posted 10 October 2013 - 09:08 PM

Hey Jim...do you balance the Dec axis horizontally and vertically? That may help.

David

#5 Eddgie

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Posted 11 October 2013 - 07:45 AM

If you hear a sharp clicking noise on occasion, I believe (and as you said, hard to describe a noise) you are looking at worm gear bearing failure.

If it goes away and only happens infrequently, you may be able to go a long time without incident.

Mine has been doing this about a year, and it is only once in a while.

It is up for sale though, and I guess that I will have to replace the worms bearings to get it to sell.

Not a hard job at all. Well documented on the CGE 1400 Yahoo group (though the one document there does a complete rebuild and to replace the bearings is far less complicated than a quick scan of the rebuild document would suggest).

I would do both bearings on both axises though. Most of the wear is from slewing where the motors turn far more than normal tracking so even if it is the RA bearings the DEC won't be far behind.

You can get replacement bearings for about $30 for four. Less maybe.

I don't know if the "Ceramic" bearing kits that sell for $50 are worth the extra money. If you were a Texas Roller Girl Jammer (Hot Rod Honeys are my favorite team and Voodoo Doll is the hottest rollergirl of them all) and needed speed, then maybe ceramic. But for this application, any good ABEC 7 bearing will be fine.

Not postive this is your problem, but it is a common one and symptom is sharp click.


Here is Voodoo Doll. Abs like crazy. I asked her what her secret was one day while we were skating.

"Lots of crunches."

I know you think that this has little to do with worm gear bearings, but I don't think she uses cermaics..

Voodoo Doll.. Bet you looked...

#6 EFT

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Posted 11 October 2013 - 10:57 AM

Sounds like there might be a couple things coming to a head. The leaking of oil indicates that the original petroleum-based grease is breaking down and separating. This is very common in these mounts and high temperatures certainly accelerate the problem. So you might be loosing some lubrication in the mount which is resulting in gear binding in some spots. It is also possible that you have gotten some debris in the gears that is causing binding. The worm bearings are another common problem area. The originals are inevitably installed with too much preload. As a result the bearings are damaged and sometimes completely fall apart after a fair amount of use. I had one recently where one of the bearings was literally in pieces. This obviously impacts the performance of the mount and can result is a lot of bad noises. Overall, there is probably nothing serious wrong with the mount, it's just that after 5 years it needs a tune up to get it back up to top shape.

In regards to the mount making noising in some areas and not others, one thing I can say is that mounts are dynamic systems in regards to balance so that as the balance changes in different parts of the sky, this can have the effect of bring out sounds that don't seem to happen in other parts of the sky. In addition, if you bring your mount back to the home position all the time when you finish and start from the same position, you don't change the position of the worm wheel that you are working on. As a result, that a bad area will stay in the same place and will seem to reflect a bad area when pointing to a certain part of the sky, when in reality, it is a bad area when moving over a certain part of the worm wheel.

#7 jrbarnett

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Posted 11 October 2013 - 11:40 AM

Thanks Ed Moreno and Deepspace Ed.

I'm going to take the motor covers off and take a gander at what's happening when it passes through that chattery segment.

I also saw on Celestron's support site that they were now recommending use of Klubertemp synthetic grease or Mobil 1 synthetic grease for relubing. Do you suppose that they've recently moved from petroleum greases to full synthetics?

The oily residue in my case sure smells and looks like dino-butter.

Ed Thomas, after I have a peek I may just send you my mount and my unopened Bennett RA/Dec socket mod kit, and let a pro handle it (a tune up and kit installation). I dunno what it is, but I am really enamored with this mount despite it's various design weaknesses. It's my main travel mount as it combines nice capacity with reasonable portability and good GOTO software/firmware. I feel compelled to keep it running. It is the last of Celestron's US made mounts, after all. It kind of marks the end of an era.

- Jim

#8 WesC

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Posted 11 October 2013 - 11:40 AM

So Ed, would you suggest that at the end of a session instead of homing the mount, a user should release the locks and push it to home so that different parts of the worm are being used every time?

#9 David Pavlich

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Posted 11 October 2013 - 12:17 PM

Sending your mount to Ed is a good idea. I haven't used Ed, but I did have a CGE done by Doc Clay and the improvement was quite good. As an aside, Ed wasn't in business when I sent my mount to Doc Clay.

David

#10 EFT

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Posted 11 October 2013 - 12:36 PM

Celestron is using a different grease now from what they use to be and based on the lack of a petroleum smell, it is likely synthetic. However, this isn't true for everything they make. The OTAs still appear to have petroleum-based grease in them.

A lot of people still really like the CGE mount and most of CGEs are worth tuning up over time and continued use.

#11 EFT

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Posted 11 October 2013 - 12:44 PM

So Ed, would you suggest that at the end of a session instead of homing the mount, a user should release the locks and push it to home so that different parts of the worm are being used every time?


Not necessarily. If you are using PEC, then you want to be using the same parts of the gears. However, if you start experiencing problems like Jim and you are in a permanent installation or have not otherwise moved the mount, then releasing the clutches and changing the position so that you are on a different part of the worm wheel after getting tot he switch positions can tell you if you simply have a bad spot on the wheel that is causing a problem in a particular part of the sky. In general, the mount shouldn't really care what part of the sky it is pointed at, but shifts in balance or problems with the worm wheel may make it appear to have a problem like that. There are other possibilities of course, like a cord getting stuck at a certain position or something else getting caught when the mount is pointed in a certain direction, but those things are often more obvious. It's a matter of trying to narrow down what the problem might actually be.

#12 Eddgie

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Posted 11 October 2013 - 02:19 PM

They are excellent mounts and worth the investment to repair.

The newer mounts have many improvements, but when you get to the role of doing the job of pointing and tracking, the CGE is still a very competent mount.

And it looks slim and compact compared to many of the newer mounts.

Most of my own failures have been resolved by spraying Deoxit into the cable sockets. Whenever the mount does a runaways in DEC (every couple of years) I Deoxit the sockets and away I go for another couple of years.

Otherwise, mount has been an excellent piece of equipment.

#13 WesC

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Posted 11 October 2013 - 04:02 PM

So Ed, would you suggest that at the end of a session instead of homing the mount, a user should release the locks and push it to home so that different parts of the worm are being used every time?


Not necessarily. If you are using PEC, then you want to be using the same parts of the gears. However, if you start experiencing problems like Jim and you are in a permanent installation or have not otherwise moved the mount, then releasing the clutches and changing the position so that you are on a different part of the worm wheel after getting tot he switch positions can tell you if you simply have a bad spot on the wheel that is causing a problem in a particular part of the sky. In general, the mount shouldn't really care what part of the sky it is pointed at, but shifts in balance or problems with the worm wheel may make it appear to have a problem like that. There are other possibilities of course, like a cord getting stuck at a certain position or something else getting caught when the mount is pointed in a certain direction, but those things are often more obvious. It's a matter of trying to narrow down what the problem might actually be.



Thanks Ed! :waytogo:

#14 jrbarnett

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Posted 11 October 2013 - 07:43 PM

Thanks for the tip Ed Moreno.

However, Cat 5 cables were a foolish choice for this role. They are not designed for the temperature ranges or environmental conditions, nor for anything other than a stationary role. Gary's solution really is a superior way of connecting the RA and Dec cables from motors to electronics pier.

Band-aids like "Marty Cables" and Deoxit cleanings are just that. They help ensure good contact only. At some point the joints connecting the sockets to the underlying control PCB will break due to flexure of the socket housing caused by tension applied to the stiff plugs during slews and you'll (or the next owner'll) be looking at a Bennett style repair. It's a bit of a ticking time bomb.

Regards,

Jim

#15 neilson

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Posted 14 October 2013 - 12:30 AM

Hi,
I have a CGE mount and recently I have been noticing terrible noises when slewing to certain parts of the sky. It sounds like the gears tearing up or even bearings. My mount was stored when new and has just started being used early this year. I have a hard time believing my noises are bearings but If one was overtightened during assembly then it could be going bad. And I have heard of that happening.

I decided to work on this today in the daylight in my shop.
I have marks on my counterweight bar so I know where to place the weights when using my SCT setup. I tried slewing the mount and the noises started. So I decided to check the balance. Sure enough it was off balance. I remembered I had changed laser brackets and made a few other changes that were enough to mess up my balance. I rebalanced my mount and put new marks on my counterweight bar. Then I slewed my mount in all kinds of directions and the noise never came back. While slewing I placed my hand on the counterweight there was just a slight noise but it wasn't what I heard before. So I slewed in the other direction and there was that noise. I tried this in other locations and got the same results. It was just a case of being a little off balance. I got lucky this time. But it could have just as easily been a bearing. If it's a bearing Ed's good at fixing these.

Neilson

#16 EFT

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Posted 14 October 2013 - 09:36 AM

Hi,
I have a CGE mount and recently I have been noticing terrible noises when slewing to certain parts of the sky. It sounds like the gears tearing up or even bearings. My mount was stored when new and has just started being used early this year. I have a hard time believing my noises are bearings but If one was overtightened during assembly then it could be going bad. And I have heard of that happening.

I decided to work on this today in the daylight in my shop.
I have marks on my counterweight bar so I know where to place the weights when using my SCT setup. I tried slewing the mount and the noises started. So I decided to check the balance. Sure enough it was off balance. I remembered I had changed laser brackets and made a few other changes that were enough to mess up my balance. I rebalanced my mount and put new marks on my counterweight bar. Then I slewed my mount in all kinds of directions and the noise never came back. While slewing I placed my hand on the counterweight there was just a slight noise but it wasn't what I heard before. So I slewed in the other direction and there was that noise. I tried this in other locations and got the same results. It was just a case of being a little off balance. I got lucky this time. But it could have just as easily been a bearing. If it's a bearing Ed's good at fixing these.

Neilson


Balance can definitely make a difference. When the mount is out of balance, the noises it usually makes become amplified and the motors get more noisy. Something else to be careful of with the CGE is to not over-tighten the clutches and to tighten the two clutches as evenly as possible. Over-tightening causes the axis to become stiff so that the motors struggle to turn it and everything gets noisy. Uneven tightening will cause a tilt in the worm wheel that is sufficient to cause binding with the worm and increased noise. A bad bearing will result in poor performance and might or might not cause the mount to be more noisy.

#17 jhayes_tucson

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Posted 14 October 2013 - 10:33 AM

I also saw on Celestron's support site that they were now recommending use of Klubertemp synthetic grease or Mobil 1 synthetic grease for relubing. Do you suppose that they've recently moved from petroleum greases to full synthetics?


Ed Byers recommends Lithium grease for his drives. So, yesterday (before I noticed this thread) I opened up my 2006 CGE mount and lubed all the gears with Lithium. Mobil One is thicker and might be a better idea, but it's hard to say. The synthetics operate over a wider temperature range and break down more slowly than the old petroleum based stuff. My gears looked pretty dry so anything is better than nothing. Clearly, if the mount is out of balance, the motors will have to drive a larger load and you may start to get significant wear over time. Balancing both axis will go a long way to making your mount last longer, point more accurately, and run quieter. If you use the mount regularly, re-lubing the gears on an annual basis is a good idea.

Even though they are widely available I agree that the cat-5 cables were not the best choice. They at least need right angle connectors so that they aren't getting torn up during slewing. I've used velcro and wire-ties to strain relieve the cables on my mount.

All and all, I have to agree with you guys that the CGE is a surprisingly good mount in spite its few "nits." When I first saw my C14 on the CGE, I thought that the mount looked a bit small for the size of the telescope. I've only had it for a few weeks, but so far, I've been quite impressed by it's stability, accuracy, and ease of use.
John

#18 EFT

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Posted 14 October 2013 - 12:18 PM

I also saw on Celestron's support site that they were now recommending use of Klubertemp synthetic grease or Mobil 1 synthetic grease for relubing. Do you suppose that they've recently moved from petroleum greases to full synthetics?


Ed Byers recommends Lithium grease for his drives. So, yesterday (before I noticed this thread) I opened up my 2006 CGE mount and lubed all the gears with Lithium. Mobil One is thicker and might be a better idea, but it's hard to say. The synthetics operate over a wider temperature range and break down more slowly than the old petroleum based stuff. My gears looked pretty dry so anything is better than nothing. Clearly, if the mount is out of balance, the motors will have to drive a larger load and you may start to get significant wear over time. Balancing both axis will go a long way to making your mount last longer, point more accurately, and run quieter. If you use the mount regularly, re-lubing the gears on an annual basis is a good idea.

Even though they are widely available I agree that the cat-5 cables were not the best choice. They at least need right angle connectors so that they aren't getting torn up during slewing. I've used velcro and wire-ties to strain relieve the cables on my mount.

All and all, I have to agree with you guys that the CGE is a surprisingly good mount in spite its few "nits." When I first saw my C14 on the CGE, I thought that the mount looked a bit small for the size of the telescope. I've only had it for a few weeks, but so far, I've been quite impressed by it's stability, accuracy, and ease of use.
John


The problem with lithium grease is not that it doesn't work, it is that it breaks down and makes a mess. When lithium grease breaks down it leaves behind a clay-like substance that just makes a mess. If you don't mind tearing down and cleaning your mount out every year or so, then lithium may be OK. If you want to be able to have the lubricant last for a while and not need to be cleaned out so often, then use a good, fairly thick, synthetic grease. PTFE-based SuperLube is what I recommend.

Just because gears "look" dry does not necessarily mean that they are not lubricated. A very thin coating of lubricant is all that is needed and all that will remain between the gears in the first place. Adding different lubricants to what is there is more likely to remove the lubricant that already coats the gear teeth and not completely coat the teeth surfaces with the new lubricant unless it is spread "evenly" round the gear. Lubricating only the worm is a bad idea. I do not recommend relubricating the gears without taking them completely out of the mount, cleaning them off, and then lubricating them before they are put back in the mount. This helps to ensure the best lubricant coverage of the entire diameter of the worm and worm wheel.

#19 jrbarnett

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Posted 14 October 2013 - 01:05 PM

John, did you simply loosen the four 2mm allen screws on each motor to gain access? Taking a peek at my gears is on my to-do list for weekend after next.

- Jim

#20 jhayes_tucson

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Posted 14 October 2013 - 01:27 PM

Thanks. Superlube sounds like a better idea than what Ed recommends. I'm a believer in regular maintenance so I don't mind cleaning, inspecting, and re-lubing the gears every so often.
John

#21 jhayes_tucson

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Posted 14 October 2013 - 01:38 PM

John, did you simply loosen the four 2mm allen screws on each motor to gain access? Taking a peek at my gears is on my to-do list for weekend after next.

- Jim


Jim,
Yes, just remove the four button head, hex screws on the covers. It's a bit tight but you can pretty much get at everything you need to add a little bit of grease. To clean it, you would need to take apart more of it and I didn't go there. Have some Q-tips available to clean things but be careful not to catch any cotton fibers in the gears. It's pretty easy to dab a bit of grease in the gears and then run the motor to spread the grease between the teeth. I like to use wire-ties for applying the grease. Neatness counts so just use as much grease as you need without leaving big gobs everywhere. It's not very hard. I should mention that you can't really get at the shaft bearings this way. If your noise is coming from the bearings, you are probably going to have to get them replaced. Good luck with it.
John

#22 jrbarnett

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Posted 26 October 2013 - 03:07 PM

Okay, so I opened it up this morning and...

The worm and big bronze gear have a neat and tidy coating of white lithium grease on them. This led me to poke around to try and figure out where the golden dino-oil on the white foam in the case for the mount head was coming from. On closer inspection it looks like there's a little bit of golden grease pooled in the corners of the housing that appear to have come from the teeth of the little silver-colored gear set (two identical gears) on the end of the motor and end of the worm assembly.

The tooth-to-tooth contact is now bone-dry. My question is this - should there be grease on the teeth of these small gears? Also, if so, why would Celestron use two different kinds of grease in the motor train?

Thanks!

- Jim

#23 EFT

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Posted 26 October 2013 - 04:27 PM

Okay, so I opened it up this morning and...

The worm and big bronze gear have a neat and tidy coating of white lithium grease on them. This led me to poke around to try and figure out where the golden dino-oil on the white foam in the case for the mount head was coming from. On closer inspection it looks like there's a little bit of golden grease pooled in the corners of the housing that appear to have come from the teeth of the little silver-colored gear set (two identical gears) on the end of the motor and end of the worm assembly.

The tooth-to-tooth contact is now bone-dry. My question is this - should there be grease on the teeth of these small gears? Also, if so, why would Celestron use two different kinds of grease in the motor train?

Thanks!

- Jim


The I am not sure what the white grease is, but it is not lithium. The petroleum based gunk is from everywhere else in the mount, the needle roller bearings, the taper bearings, the spur gears (small silver stainless steel gears) and everywhere else. There is usually a substantial over abundance of this stuff and it tends to separate and run out of the mount from all over the place and make a mess. That's the gold oil you see. Warm temperature definitely contributes to this.

Why Celestron used two different types of grease in this case (they don't do it anywhere else) is hard to say, but the white stuff definitely stays put better then the dino-oil. The worm and wheel surfaces may look pretty dry due to the relatively tight fit, but ideally they should have small amount of lubricant left on the teeth faces. The spur gears also need very little lubrication.

#24 jrbarnett

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Posted 26 October 2013 - 05:14 PM

Thanks Ed.

I'm going to use a headlamp and jeweler's loupe to see if there's any lubricant at all on the facings of the spur gear teeth. From afar it really looks dry. And yep, this particular mount has seen high heat, high elevation and extremely arid environments, as well as the usual (for here) more moist sea level maritime climate.

Regards,

Jim






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