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Minor Issue with Zhumell Z8 Mount

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#1 Coolkid70

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Posted 20 April 2011 - 11:25 PM

Hello everyone, this is my first post at Cloudy Nights. I'd like to say that I think that this is a great community and there are so many people who give expert advice. It is quite an honour to be among you.

I purchased a Zhumell Z8 a month ago and have recently been putting into use. (From what I understand, there is a "curse" where the skies become cloudy when you receive your scope. I too have been affected!) Overall, I am very pleased with my scope, but I am having a minor annoying issue with the mount. Moving the scope around is smooth in general, except when I try to raise it along altitude axis (i.e. toward zenith). When I let go of the scope, it falls back down a degree or two, then settles. This is a rather annoying problem, especially at high magnification. I attempted to adjust the tightness of the two black bolts / screws on the side of the mount, but it doesn't improve the situation without destabilizing the scope.

I would very much appreciate any suggestions you might have with this issue!

#2 Kfrank

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Posted 21 April 2011 - 12:21 PM

Sounds like a balance problem - ie, the OTA is nose-heavy.

I have had this problem with my C6SE and SV80 scopes which are on manual, alt-az mounts. Here, however, I was able to compensate for the problem by moving the scope laterally in its dovetail saddle. You will have to add weight to the rear of the OTA.

Tightening the alt axis tension will help to a certain extent but if the balance problem is great enough, you can't compensate with tension without compromising the smooth motion of the scope on the alt axis.

Perhaps some small magnetically attached weights and experiment with positioning.

Good luck.

#3 SteveG

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Posted 21 April 2011 - 12:40 PM

I would place your most used eyepiece in the focuser, and re-balance the scope using the balance scale on the altitude bearings. It took a while, but here's how I did mine:

Sit on a chair inside your house with the scope in front of you. With the eyepiece & finder (most used) in place, loosen the bearings and position the scope at an altitude of 45*. If the scope moves down you need to raise the bearings, and visa-verse.

It would be very helpful to get a "screwdiver" style allen wrench to make these adjustments. One thing I noticed, if I balanced the scope flat (at 90*), it would be off balance at higher altitudes. The 45* balancing point worked best for me. Adjust in 1/8" to 1/4" increments for perfection. I recently bought this scope and was pleased with how well it balanced.

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#4 Rob E

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Posted 21 April 2011 - 12:52 PM

Sounds like a balance problem - ie, the OTA is nose-heavy...

Perhaps some small magnetically attached weights and experiment with positioning.

Good luck.



A great part of the Zhumell (GSO) Dobs is that the ALT bearings are adjustable so weights are very rarely needed. Once you get it tuned to your liking, you are good to go 90% of the time.

#5 Kfrank

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Posted 21 April 2011 - 01:37 PM

Sounds like a balance problem - ie, the OTA is nose-heavy...

Perhaps some small magnetically attached weights and experiment with positioning.

Good luck.



A great part of the Zhumell (GSO) Dobs is that the ALT bearings are adjustable so weights are very rarely needed. Once you get it tuned to your liking, you are good to go 90% of the time.


Thanks, I wasn't aware of that.

#6 Coolkid70

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Posted 22 April 2011 - 10:44 AM

Thanks everyone. I'll give that a try and let you know how it goes.

#7 clchildress

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Posted 22 April 2011 - 10:47 AM

FWIW, adjusting the ALT bearing placement on my Z8 made a world of difference. I haven't needed any counterweights, even with some of my 2" hand-grenade EPs with a 2" barlow in the focuser. Just a wonderfully thoughtful bearing system in general, in those Zhumell scopes.

#8 Coolkid70

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Posted 07 May 2011 - 03:27 AM

I checked into the mount issue carefully today. I found that there is a very slight bit of space where the telescope rests on the mount. Everything is stable when the scope is lowered (in the altitude direction). On the other hand, raising the scope causes it to rock very slightly in the mount, causing the problem I described earlier.

I thought about trying to fix this by using a bit of paper to fill the space, but I'd like a more permanent solution. Any ideas?

Thanks!

#9 Coolkid70

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Posted 08 May 2011 - 10:16 PM

Just to update the situation, for posterity: I tried to remedy the problem by buying some felt with adhesive backing. It more or less fixed the problem, but I think that I overdid it. It turned out that only one side of the mount needed to be adjusted. When I added the felt to the side that did not need correction, inserting the scope caused the wood / plastic to buckle slightly (and it was a serious pain to remove the OTA). I've removed the felt and everything seems to be fine now.






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