Author Topic: Experience/opinions on Zhumell Z8 altitude axis  (Read 134 times)

propdiagairil

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Experience/opinions on Zhumell Z8 altitude axis
« on: December 29, 2017, 01:49:15 PM »
I've seen numerous recommendations for theZhumell Z8. Does anyone have experience with it that can comment on its altitude axis. It looks like they went for a fairly complex design for an inexpensive Dob. Complexity comes at a cost - either in dollars or quality. My concern is about reliability and smooth operation. If they did a good job, that's fine. I'm always a little leery of designs that are more complex than necessary.



climopepvi

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #1 on: January 09, 2018, 07:11:43 AM »
It has the ability to slide forward and back to balance the scope. Otherwise it's a simple pivot.

vuicapathvie

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #2 on: January 11, 2018, 12:08:05 PM »
I looked at the manual, but it seemed a bit vague. Are the sliding bearings just tightened into the slide area with the two bolts, essentially locking them in place until the bolts are reloosened by the user?

Once mounted, are the outboard knobs on the bearings used as controls for friction based tensioning of the axis?

Tawakal Stahlberg

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #3 on: January 12, 2018, 09:04:45 AM »
The alt. bearing large black knobs are tightened or loosened by the user to obtain the desired amount of resistance. The abilityto adjust the location of the bearings along the tube with the two bolts on each side allows the user tofine tune the balance point of the OTA. You have to remove the tube from the base to adjust the location of the side bearings - this is why they provide thegraduated scale, to help you get them in the same spot oneach side. There is nothing about this aspect of the design that feels cheap or prone to break over time, IMO. I have an Apertura AD10 (same as the Z10).

elunmolunch

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #4 on: January 13, 2018, 02:04:37 PM »
Quote
It has the ability to slide forward and back to balance the scope. Otherwise it's a simple pivot.


Quote

The alt. bearing large black knobs are tightened or loosened by the user to obtain the desired amount of resistance. The abilityto adjust the location of the bearings along the tube with the two bolts on each side allows the user tofine tune the balance point of the OTA. You have to remove the tube from the base to adjust the location of the side bearings - this is why they provide thegraduated scale, to help you get them in the same spot oneach side. There is nothing about this aspect of the design that feels cheap or prone to break over time, IMO. I have an Apertura AD10 (same as the Z10).


Jim, Clay,

Thanks for the info.

One last question. Is there any tendency for the friction setting to work its way looser or tighter through repeated normal movements of the axis?

Thanks again,
Sid

globleferep

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #5 on: January 13, 2018, 04:49:33 PM »
Quote
I looked at the manual, but it seemed a bit vague. Are the sliding bearings just tightened into the slide area with the two bolts, essentially locking them in place until the bolts are reloosened by the user?

Once mounted, are the outboard knobs on the bearings used as controls for friction based tensioning of the axis?


Yep, theZhumellmanualsare vague about how to use the features of their scopes, andhave a number of errors. The pictures are helpful in assembly though.

You have itright if I am reading you correctly. The two bolts on each sideare tightened to a fixed position slide position of the owner's choosing. It can take some experimentation to find the best point. Onceestablished for the eyepieces/accessoriesused it should be fine. If one is using heavy 2" eyepieces it will beall the way at one end. The outboard knobs are friction adjustment. They work to some extent, but if you have an eyepiece that is seriously out of balance and haven't shifted the pivot and/or counterweighted the friction clampstend to allow the tube to slowly drift down (or up).

Louis Sullivan

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #6 on: January 22, 2018, 08:39:18 PM »
Quote
Quote

I looked at the manual, but it seemed a bit vague. Are the sliding bearings just tightened into the slide area with the two bolts, essentially locking them in place until the bolts are reloosened by the user?

Once mounted, are the outboard knobs on the bearings used as controls for friction based tensioning of the axis?


Yep, theZhumellmanualsare vague about how to use the features of their scopes, andhave a number of errors. The pictures are helpful in assembly though.

You have itright if I am reading you correctly. The two bolts on each sideare tightened to a fixed position slide position of the owner's choosing. It can take some experimentation to find the best point. Onceestablished for the eyepieces/accessoriesused it should be fine. If one is using heavy 2" eyepieces it will beall the way at one end. The outboard knobs are friction adjustment. They work to some extent, but if you have an eyepiece that is seriously out of balance and haven't shifted the pivot and/or counterweighted the friction clampstend to allow the tube to slowly drift down (or up).
Sounds like a pretty sensible system for balancing, short of something adjustable on the fly, which would add cost and complexity.

Rob Stevens

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #7 on: January 25, 2018, 01:30:48 PM »
It is way better than adding/removing magnetic weights to/from the OTA.

artufanchess

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #8 on: January 25, 2018, 11:36:29 PM »
The alt bearing on the Zhumell and clones are definitely best in class. They work very well and hold up over time.
The azimuth bearing is a little trickier and usually requires some modifications over time.

Lamichael Evans

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #9 on: January 31, 2018, 11:46:27 AM »
Quote
The alt bearing on the Zhumell and clones are definitely best in class. They work very well and hold up over time.
The azimuth bearing is a little trickier and usually requires some modifications over time.

Interesting, I would have thought that the az bearing would be simpler and more reliable. What is it that goes wrong? How are the problems resolved? Is the Z8 any better or worse in this regard than other Dobs?

mingchepspatu

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #10 on: February 02, 2018, 09:59:35 PM »
I'm speaking from Z12 experience, from the original CorrecTension-style (Orion'n name for springs attached at the center of the alt bearings), the solid aluminum altitude tension knobs, to the current black plastic tension knobs. The adjustable system is highly-thought out, well-executed, and elegantly simple. The adjustments possible with this system are very fine. You must do adjustments with the supplied hex key- off the rocker boards.

The knobs don't loosen or tighten themselves out of adjustment.

mosretouless

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #11 on: February 04, 2018, 10:37:01 AM »
I agree hat this is a great, well thought out Alt system. I found the best overall balance by setting it up with my heaviest eyepieces for perfect balance at 45 deg. The clutch brake system works fine to tighten up the altitude at lower or higher positions. I also prefer the lazy Susan AZ bearings.

calfkommomu

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #12 on: February 09, 2018, 12:28:24 AM »
Quote
Quote

The alt bearing on the Zhumell and clones are definitely best in class. They work very well and hold up over time.
The azimuth bearing is a little trickier and usually requires some modifications over time.

Interesting, I would have thought that the az bearing would be simpler and more reliable. What is it that goes wrong? How are the problems resolved? Is the Z8 any better or worse in this regard than other Dobs?
The Zhumell azimuth axis is on par with other designs. Some prefer it, some don't. The lazy susan roller bearing has a tendency to offer less
sticktion than Teflon on laminate which some prefer. Iincreased the sticktionof the roller bearings by just adding two felt furniture pads just outside
the bearing. I had to peel off some felt layers to get the feel just right for my preference. Another issue with the bearing over time is that the tiny
roller bearing under the tension adjustment thumbscrew tends to fall apart and stop working over time. Replacing with a heavier duty roller bearing fixes
that issue. Both mods are easy and cheap to do.

Donald Jansen

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #13 on: February 09, 2018, 03:53:59 AM »
All right, thanks for all of the good info everyone. The Z8 sounds like a winner. I have gone back and forth in my mind many times on various scopes types and sizes, but the Z8 seems to be the front runner now.

ryepittimy

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Re: Experience/opinions on Zhumell Z8 altitude axis
« Reply #14 on: February 09, 2018, 10:57:35 AM »
Quote
Quote
Quote
The alt bearing on the Zhumell and clones are definitely best in class. They work very well and hold up over time.The azimuth bearing is a little trickier and usually requires some modifications over time.
Interesting, I would have thought that the az bearing would be simpler and more reliable. What is it that goes wrong? How are the problems resolved? Is the Z8 any better or worse in this regard than other Dobs?
The Zhumell azimuth axis is on par with other designs. Some prefer it, some don't. The lazy susan roller bearing has a tendency to offer lesssticktion than Teflon on laminate which some prefer. Iincreased the sticktionof the roller bearings by just adding two felt furniture pads just outsidethe bearing. I had to peel off some felt layers to get the feel just right for my preference. Another issue with the bearing over time is that the tinyroller bearing under the tension adjustment thumbscrew tends to fall apart and stop working over time. Replacing with a heavier duty roller bearing fixesthat issue. Both mods are easy and cheap to do.
A link to a much better bearing can be found in the Reflector Forum's "Mega-Mods for Zhumells" thread. I highly recommend the thread for a read. It is well worth your time, IMO.