CGEM 800 EdgeHD DEC Balance Problems?

[collangm]

Hi,

I have a newly purchased Celestron CGEM 800 EdgeHD scope and mount but am having some trouble balancing the damn thing as described in the manual - excerpt:

Balancing the Mount in DEC

Although the telescope does not track in declination, the telescope should also be balanced in this axis to prevent any sudden motions when the DEC lock lever is loose. To balance the telescope in DEC:

1. Loosen the R.A. clutch lock lever and rotate the telescope so that it is on one side of the mount (i.e., as described in the previous section on “Balancing the Mount in R.A.”).

2. Tighten the R.A. lock lever to hold the telescope in place.

3. Loosen the DEC clutch lock lever and rotate the telescope until the tube is parallel to the ground.

4. Release the tube —

GRADUALLY — to see which way it rotates around the declination axis. DO NOT LET GO OF THE TELESCOPE TUBE COMPLETELY!

5. Slightly loosen the knobs that holds the telescope to the mounting platform and slide the telescope either forward or backward until it remains stationary when the DEC clutch is loose. Do NOT let go of the telescope tube while the knob on the mounting platform is loose. It may be necessary to rotate the telescope so that the counterweight bar is pointing down before loosening the mounting platform screw.

6. Tighten the knobs on the telescope mounting platform to hold the telescope in place.

Like R.A. balance, these are general balance instructions and will reduce undue stress on the mount. When taking astrophotographs, this balance process should be done for the specific area at which the telescope is pointing.

The problem is that with the OTA setup as indicated (with front cap removed + 9x50 finder scope, diagonal and 40mm eyepiece attached) the scope will not balance horizontally when the DEC clutch is loosened. I have tried to push the scope as far forward as possible on the mount but still no joy. Is this even possible?

I also noticed that when balancing in RA there appears to be a slight 'sticking' for want of a better word. It's only slight but noticeable as it stops the off-set balance from moving the scope when in the EAST side. Is this what is termed as 'Stiction' and is it something I should worry about and/or get back to the supplier to remedy?

Thanks in advance for any comments...(Come on Clear Skies!

)

Gary

[RobH]

Hello Gary.

When trying to balance in DEC, do you have the finder attached, plus any imaging kit or eyepiece in place?

My Edge 11 has to be a long way forward even with all the kit on the back, plus my moonlite focuser too.

You could always attach some weight to the rear handle too.

Rob

[collangm]

Hello Gary.

When trying to balance in DEC, do you have the finder attached, plus any imaging kit or eyepiece in place?

My Edge 11 has to be a long way forward even with all the kit on the back, plus my moonlite focuser too.

You could always attach some weight to the rear handle too.

Rob

In answer to your question RobH, the OTA has the 9x50 spotting scope, SCT adapter, 90-degree diagonal and 40mm EP that came with the scope. The front protective cover has also been removed, as detailed in the manual. Even when fully set forward (and removing the back-stop screw) the scope still wants to swingupwards - i.e. the EP end is pulling down against gravity and the corrector plate (light-gathering) end is pointing straight upwards.

Gary

[RobH]

Sounds like some weight is needed on the front end then. I got muddled up and thought you had problems the other way! I know that people attache fishing weights etc to SCT's....with my old LX200, I gaffa taped weights to the OTA in various places.

Not having a CGEM, I can't advise on your other issue I'm afraid.

Rob

[astro mick]

Gary.

Get a couple of 1 kilogramme wrist or ankle weights.Try one Kilogramme first ,secure using narrow velcro ties to-wards Top end of the tube.

Also ro-tate the OTA around in the cradles,and test at various points.

But i would imagine that if your tube is bottom heavy,weighting the Top carefully should help.

Mick.

[collangm]

Thanks guys, but surely a scope sold as a package shouldn't need additional weights added to it to enable it to balance correctly and as exampled in the supplied user manual?

Plus, if I add more weight to the front I may then need to purchase additional weight to balance the scope in the RA axis...?

My brain hurts!!

Gary

[ollypenrice]

Maybe the 40mm EP is the catch here. Pretty heavy. But you are right, it should balance as standard. I doubt that the weight needed to balance in Dec will have much effect in RA because the new weight will be closer to the mount than the counterweights.

Olly

[mag10]

There is definitely a problem with your installation.

I have the same kit (800 Edge HD CGEM) and have never had problems balancing.

Even with a 80mm guide scope on top, and a Stratus EP (a big heavy hummer), it's a simple matter of shifting the OTA forward or back, depending on the accessories I have on it.

Perhaps you could post a photo of your set-up.

It might help to locate the problem.

[collangm]

Here are some images taken of the scope balanced in RA (and then locked off for safety) with the DEC clamp released. No matter where the OTA sits on the mount it still swings down (i.e. back heavy). I even removed the spotting scope and diagonal/EP to see if this improved matters. I think I may even have a little 'stiction' in RA aswell?

[ollypenrice]

I'm stuck. Anybody?

I'd certainly contact the supplier and David Hinds, the importer.

Olly

[astro mick]

Can you slide the OT further forward in the mounts dovetail.

Failing that!!!!

Mick.

[collangm]

Can you slide the OT further forward in the mounts dovetail.

Failing that!!!!

Mick.

Not without removing the safety 'end-stop' screw at the rear of the dovetail. I have tried this and moved it as far back as I thought safe to do but this still made no difference. Can I assume then, from my attached images, that there is something wrong here and that the OTA should remain horizontal when the clutch is released (when balanced correctly) - ?

Gary

[collangm]

There is definitely a problem with your installation.

I have the same kit (800 Edge HD CGEM) and have never had problems balancing.

Even with a 80mm guide scope on top, and a Stratus EP (a big heavy hummer), it's a simple matter of shifting the OTA forward or back, depending on the accessories I have on it.

Perhaps you could post a photo of your set-up.

It might help to locate the problem.

Hi mag10, do you have any pictures of your setup in DEC balance with the clutch disengaged? Just thought it might be useful to show a comparison when I go back to the supplier (Dave Hinds) about this...?

Thanks,

Gary

[mag10]

I think I can see the problem.

Take out that rear "safety" knob. (It's useless, as you'll never be looking down, and thus the OTA can never slide off that way).

I'm sure if you just slide the OTA forward a bit, you should be OK.

As you see, I have quite a bit of extra kit on my OTA and it balances fine (you can see on the 2nd picture that the clutch is completely disengaged).

I hope this will help.

Jerome

[steppenwolf]

I agree with Jerome, remove the back 'safety' detent it is superfluous in normal use and this will allow you to move the telescope much further forward to achieve balance. The front one is the that has a true value as you telescope will either be looking up or maybe (just maybe) horizontally but never down.

[collangm]

Thanks guys, I've now removed the rear safety stop screw and managed to achieve balance...of sorts :s

I'm convinced my mount is suffering from 'stiction' in both the RA and DEC. Now that balance has been achieved in DEC there appears to be a small amount of friction in the DEC axis if I try to move the OTA out of balance. Is this normal as it appears the same in both DEC and RA or is this 'Stiction'?

I'm afraid I'm still a little new to this term and so couldn't categorically confirm whether what I am seeing (feeling) is that what is stated...?

Any further advice before I contact the retailer would be most helpful.

Thanks,

Gary

[steppenwolf]

With the RA and DEC clutches disengaged, both should rotate easily with no sticking at all. Are you sure that the clutches are fully released?

[collangm]

Yep, both fully released, but as stated this is only slight friction and only when the weight or scope is at a certain point in rotation - for RA it seems to be when the OTA is in the Eastern position. For DEC it is when the OTA is horizontal with the floor. This maybe just because all the weight is bearing down on the bottom of the axis at both of those points? It simply impedes full (hands-off) rotation under it's own weight/momentum if moved slightly by hand...

Gary

[mag10]

Sorry, I can't help you with the friction problem, as I've never experienced it.

Maybe the RA and DEC elements weren't properly lubricated during assembly...

At the price these mounts cost, there should be no such problems to contend with, and I would certainly contact the retailer about it.

And hoping your retailer is less cavalier than the Celestron customer-service people. When I first bought my telescope, I sent an e-mail to the customer-service dept. about problems I had with the alignment, and also trouble understanding the hand-controler. The answer I got was so off-hand it bordered incivility. I had to remind them that even if the the price paid for their product wasn't so dear, good business practices should ensure a minimum of respect to their customers. After that they were a little more forthcoming and polite, but I was really surprised at their initial response, and also at their lack of astronomical knowledge:

The alignment problem I had was that I had fully aligned the scope, but when I asked the GOTO to find the Moon, it was about 50" off.

Forget the fact that the tone of their answer was almost uncivil, any "real" astronomer (which I am far from being, and was even less then) would have immediately

suggested that I had perhaps programmed the mount for Eastern Standard Time, instead of Daylight Saving Time (which would account for a 50" discrepancy in the position of the Moon).

I eventually found the error myself, but the Celestron people did not even mention the possibility! Incredible No?

As to the hand-controler problem, I wondered about the fact that when I asked the system for "lunar rate" (or sideral rate) I would not get a confirmation of this on the screen. The answer came back. "There is no confirmation". Just like that. No explanation or query about the context of why I would want to enter a rate after a GOTO search.

I'm mentionning this because it's important, and I don't want you to make the same mistake I did:

After your mount is aligned and you ask the GOTO to find the Moon (or a planet), DO NOT return to the menu and ask for "lunar rate" or "sideral rate". Just let the mount do its thing. Apparently if you go into the menu after that and ask for a rate, it throws the whole system out of whack, and your alignment is out the window.

This I got from my retailer after I complained about losing alignment, as the Celestron people did not deem it important enough to tell me.

Don't get me wrong. I like my C800 a lot, but let's just say I had to figure a lot of things out for myself.

Good luck.