Help needed with newer Dob base!

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Larry 1969
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Help needed with newer Dob base!

#1

Post by Larry 1969 »

Hello!
Some of you may recall I was chasing azimuth play and notchy tracking on my 1 year old Skywatcher 10" collapsible goto dob.
I got it apart and found the 13 inch roller bearing had pressed sharp indentations into the 2 large metal plates that it is sandwiched in between.
I contacted Skywatcher and they replied it would take at least 60 days to get what I need......
I went to the hardware store and purchased a 12" lazy Susan bearing, read some "How too's" and have come to the conclusion my mount is a bit different.

Pic 5 is the top side of the base. The bearing is between those 2 metal discs ( you obviously can only see 1).
Pic 4 I'll call the hub. It bolts through the base and holds the bearing in place.
Pic 3 is the hub assembled into the base.
Pic 2 is the ring gear and the large washer above it. This is held to the hub with a stack of washers, 2 dished washers and a nut that adjusts the clutch.
Pic 1 is 3 feet that are screwed to the upper portion of the mount. These 3 feet sit directly on the outside diameter of the bearing.

The diameter if my new bearing is only 10.5" compared to the original 13". I would have to relocate these feet or find a bearing with the proper diameter.
Thickness also comes into play. If I discard the old bearing the hub will sit that much lower in the base. This would increase the distance between the ring gear and worm gear.
That coupled with the thicker bearing is causing me fits!

Any suggestions?
Thanks!

Larry
Attachments
KIMG0108.jpg
KIMG0111.jpg
KIMG0112.jpg
KIMG0109.jpg
KIMG0110.jpg
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.

For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with a refurbished Windows 10 laptop.
Explore Scientific HR coma corrector
Full spectrum modded Canon T3i (APS-C size sensor)
Larry 1969
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#2

Post by Larry 1969 »

I think I have it figured out.
The difference in installed height between the original bearing and the lazy Susan bearing is .125".
I'll have my son machine a 1.25" spacer to install under the hub and all should be well.
I'll report back after testing.

Larry
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.

For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with a refurbished Windows 10 laptop.
Explore Scientific HR coma corrector
Full spectrum modded Canon T3i (APS-C size sensor)
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Lady Fraktor
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#3

Post by Lady Fraktor »

Have fun! :)
🇸🇰
Proper Telescopes: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNGDX 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen ED115s f/7.7
Mounts: Celestron AS-GT, Celestron CG-5 w/ Argo Navis & tracking motor, SLT w/ pier & tripod mods, Manfrotto 028b w/ SV M2C, Mantrotto 055Pro w/ 128RC, TAL MT1C, Vixen SXP w/ HAL-130 & half pier
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man1
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#4

Post by man1 »

Hi Larry,
I think the little extra work will be well worth it. I would also be checking for any play in the worm drive, while you have it all apart.

Looking good..!!!

Cheers, man1
Orion XT10i custom, Orion GiantView BT-70, Bushnell Natureview 20-60x65
SkySafari6 Pro, SkyFi 3, ASI290MC, T7C
Larry 1969
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#5

Post by Larry 1969 »

Thanks Man1!

I can't seem to locate the source of my 3 degrees of azimuth lash.....
The old posts I was reading showed the source of the lash to be the large washer above the ring gear. It had a D shaped hole in it that engaged a flat on the shaft.
Mine is round so that can't be it....... The worm drive is spring loaded to the ring gear. I don't suspect any lash there but it's hard to check since it needs to be assembled.

Also, what about lubrication of the Lazy Susan bearing? I could apply some light oil in there but I don't want it to be attracting dirt and causing regular maintenance.
I don't think this set up is made to take apart regularly.

Larry
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.

For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with a refurbished Windows 10 laptop.
Explore Scientific HR coma corrector
Full spectrum modded Canon T3i (APS-C size sensor)
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man1
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#6

Post by man1 »

Larry 1969 wrote:
Wed Sep 18, 2019 10:46 pm
Thanks Man1!

I can't seem to locate the source of my 3 degrees of azimuth lash.....
The old posts I was reading showed the source of the lash to be the large washer above the ring gear. It had a D shaped hole in it that engaged a flat on the shaft.
Mine is round so that can't be it....... The worm drive is spring loaded to the ring gear. I don't suspect any lash there but it's hard to check since it needs to be assembled.

Also, what about lubrication of the Lazy Susan bearing? I could apply some light oil in there but I don't want it to be attracting dirt and causing regular maintenance.
I don't think this set up is made to take apart regularly.

Larry
I would not lubricate it, it will only attract dirt and it will be very difficult to clean unless completely submerged in a cleaning fluid to dissolve grease or oils.
I don't know what your worm drive setup looks like on your scope, but I would try to find if there is any play in it. Turning the worm shaft by hand and having a mark on the ring gear. Hard to explain without seeing the setup you got, but I think you know what I am talking about.

Cheers, man1
Orion XT10i custom, Orion GiantView BT-70, Bushnell Natureview 20-60x65
SkySafari6 Pro, SkyFi 3, ASI290MC, T7C
Larry 1969
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#7

Post by Larry 1969 »

man1 wrote:
Thu Sep 19, 2019 12:17 pm

I don't know what your worm drive setup looks like on your scope, but I would try to find if there is any play in it. Turning the worm shaft by hand and having a mark on the ring gear. Hard to explain without seeing the setup you got, but I think you know what I am talking about.

Cheers, man1
Thanks again!

I understand what you're getting at. My problem is that the ring gear attaches to the hub which mounts to the lower portion of the base.
The worm gear and drive unit attach to the upper portion of the base so it has to be assembled for the gears to mesh. I can't see the ring gear when assembled.....
I'll figure something out.

Larry
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.

For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with a refurbished Windows 10 laptop.
Explore Scientific HR coma corrector
Full spectrum modded Canon T3i (APS-C size sensor)
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man1
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#8

Post by man1 »

Larry 1969 wrote:
Thu Sep 19, 2019 9:50 pm
man1 wrote:
Thu Sep 19, 2019 12:17 pm

I don't know what your worm drive setup looks like on your scope, but I would try to find if there is any play in it. Turning the worm shaft by hand and having a mark on the ring gear. Hard to explain without seeing the setup you got, but I think you know what I am talking about.

Cheers, man1
Thanks again!

I understand what you're getting at. My problem is that the ring gear attaches to the hub which mounts to the lower portion of the base.
The worm gear and drive unit attach to the upper portion of the base so it has to be assembled for the gears to mesh. I can't see the ring gear when assembled.....
I'll figure something out.

Larry
Hi Larry,
So, put it all together without the scope on it.... do all your adjustments to tighten the center properly. Then use your go-to control and go one unit forward in one direction.... while you apply a bit of pressure with your thumb on the upper unit that normally moves the scope. Once you have done that, go one unit the other direction. Feel with your thumb for any slack. Make sure that your reference for the overall movement (the magnet disc) is securely mounted and is stable in its position.

I have one question for you - I think you were saying your tracking is off by always 3 degrees. Are you sure it is always 3 degrees never more and never less in either direction?
If you have an iphone or a phone that has a build in compass, you can also lay your phone on top and use the internal compass to see if there is an offset without having the scope on it. The accuracy of the compass is not important, just used as a reference.

Cheers, man1
Orion XT10i custom, Orion GiantView BT-70, Bushnell Natureview 20-60x65
SkySafari6 Pro, SkyFi 3, ASI290MC, T7C
Larry 1969
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#9

Post by Larry 1969 »

My tracking wasn't really off, just notchy at times. I could hear the base make a click noise every 4 seconds or so and my pictures were terrible.
The lash I'm trying to eliminate is noticeable when I manually rotate the base back and forth. There is approximately 1/2" of free play before I feel any resistance in both directions.
My base is 20.5" in diameter so 1/2 " is equal to about 3 degrees.

I need to get my hub shim made, bearing attached and feet relocated first. I can try to access the lash afterward.

Thanks again!

Larry
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.

For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with a refurbished Windows 10 laptop.
Explore Scientific HR coma corrector
Full spectrum modded Canon T3i (APS-C size sensor)
Larry 1969
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Location: Pittsburgh PA USA

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#10

Post by Larry 1969 »

I have the hub shim made and set in place. The bearing is centered. I have the upper portion of the base marked to relocate the feet.
I need to purchase a bit of hardware like screws and such but I should be putting everything together tomorrow.
I'll take some more pictures and, if everything works out, I may post it in the DIY section since this is completely different than the older design.
Attachments
KIMG0114.jpg
KIMG0113.jpg
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.

For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with a refurbished Windows 10 laptop.
Explore Scientific HR coma corrector
Full spectrum modded Canon T3i (APS-C size sensor)
Larry 1969
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Articles: 0
Posts: 402
Joined: Fri May 17, 2019 12:33 am
Location: Pittsburgh PA USA

TSS Photo of the Day

#11

Post by Larry 1969 »

All done and, somehow the backlash is eliminated. At slew speed 5 I can reverse azimuth direction instantly!
Rotation seems very smooth. Can't wait for a clear sky!

Larry
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.

For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with a refurbished Windows 10 laptop.
Explore Scientific HR coma corrector
Full spectrum modded Canon T3i (APS-C size sensor)
Larry 1969
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Joined: Fri May 17, 2019 12:33 am
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#12

Post by Larry 1969 »

Well, I finally got to test it out Thursday night and all I can say is WOW!
I went from discarding 80% of my 15 - 20 second subs to discarding about 20%!
I couldn't get point craft to work in APT so I picked a couple brighter targets.
The Iris Nebula and M33. 100 20 sec subs. 50 darks and 200 bias.
Attachments
M33.png
Iris.png
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.

For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with a refurbished Windows 10 laptop.
Explore Scientific HR coma corrector
Full spectrum modded Canon T3i (APS-C size sensor)
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