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Old 14-05-2010, 02:29 PM
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Stu Ward
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Bob's Knobs

After my last few days playing around getting the hang of Collimation, i see the potential benefit of Bob's Knobs

But looking at their website, i can find the Secondary knobs for my Skywatcher Dob, but i can't see where the Primary ones are

I've fired off an email to them, but they have not replied

Anyone know if the Meade 8" Lightbridge set will work ?
Its not clear that the Primary's are compatible

Thanks

Stu
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  #2  
Old 14-05-2010, 04:27 PM
ericc (Eric)
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Hi Stu--
I cant tell you if the Bobs Knobs will fit your Sky Watcher Dob,but rest assured that by fitting Bobs Knobs to the secondary and primary will make your life alot easier--its money well spent!
I have just fitted a set to my Bintel(GSO)secondary and they are bloody fantastic.The primary has large knurled knobs as standard(abit like Bobs Knobs).
I also found that fitting heavy duty primary springs work well for me.
Im sure someone else will chime in with the right info.
Good luck!!
Cheers-Eric
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  #3  
Old 14-05-2010, 04:49 PM
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barx1963 (Malcolm)
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I had a similar query and received an answer from Bob himself, took a couple of days.
You will love Bobs knobs, bought an entire set, primary, secondary and springs, worth every cent!
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Old 14-05-2010, 05:07 PM
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Kevnool (Kev)
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Search the posts for bobs knobs as there is info here.
Cheers Kev.
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Old 14-05-2010, 05:27 PM
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Looks as though i am not going to be able to add knobs to the primary
Bob has got back to me and confirmed that the knobs won't work on my Skywatcher as the Locking nuts are too close to the adjustment screws

Spose i could still use Secondary knobs
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  #6  
Old 14-05-2010, 06:20 PM
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Kevnool (Kev)
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On my scope the locking screws are not in there because there useless.
The locking nuts will give you grief and destroy the collimation.
If you have really tight compression springs (thats a mod) the mirror dont move.

Replace your springs / throw the locking nuts or screws away/ bobs Knobs.
Thats my opinion.

Cheers Kev.
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Old 22-05-2010, 08:29 PM
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Quote:
Originally Posted by ericc View Post
Hi Stu--
I cant tell you if the Bobs Knobs will fit your Sky Watcher Dob,but rest assured that by fitting Bobs Knobs to the secondary and primary will make your life alot easier--its money well spent!

Cheers-Eric
Very much agree. For the money we spend on other items in this hobby, this is a fairly low cost option that makes things quicker and easier. Even if you only manage to get one set that will fit.
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Old 23-05-2010, 04:10 AM
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bmitchell82 (Brendan)
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Loose the lock screws they are snot, like Kev says as soon as you lock them in, you loose your collimation. bobs knobs will be something youll love! good luck
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Old 23-05-2010, 08:20 PM
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big_dav_2001 (Davin)
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Funnily enough i was just about to post about my addition of bobs knobs to my 12" Dob today... I also got the whole works; primary, secondary, springs, and telrad knobs...

I was surprised how flimsy the standard GSO springs are in comparison to Bob's...It always held its collimation pretty well before upgrading, but with these new springs, its not going to take one hell of a hit to bump it out of collimation again....

I also agree with Kev and Brendan, the thicker/stronger springs make the locking screws unnecessesary...

They definately make collimating sooo much quicker and easier...

Davin
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Old 24-05-2010, 11:02 AM
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yusufcam (Colin)
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Quote:
Originally Posted by bmitchell82 View Post
Loose the lock screws they are snot, like Kev says as soon as you lock them in, you loose your collimation. bobs knobs will be something youll love! good luck
yes, had the same problem with the lock screws.

the trick was, i found, to just loosen them the smallest amount to accomplish the collimation. then when they were retightened they didn't move the mirror.

bit of a pain, but it appears since using this approach to be locked in and hasn't lost collimation since.

regards
Colin

Last edited by yusufcam; 24-05-2010 at 11:57 AM.
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Old 24-05-2010, 03:04 PM
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The lock screws are not really a problem. Just handle them the same way you would handle the adjustment screws. That is, tighten them slowly while keeping an eye on your favorite collimation tool.
For example, if you use a barlowed laser collimator with a rear window such as the TuBlug or the BLUG then keep your eye on the center spot shadow while tightening the lock screws to preserve collimation.
Jason
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Old 25-05-2010, 04:21 PM
Ingle (Alex)
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Apologies if this is a hijack but where is the best place to purchase Bob's Knobs? Is there an Aussie retailer or do you just go direct to Bob?

I have a Bintel 10" Dob (about 2005 model) that I would be interested in getting knobs and springs for. I believe is a Guan Sheng scope, will they know what I am talking about if I go somewhere other than Bintel?

Cheers

Alex

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Old 25-05-2010, 04:32 PM
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Quote:
Originally Posted by Ingle View Post
Apologies if this is a hijack but where is the best place to purchase Bob's Knobs? Is there an Aussie retailer or do you just go direct to Bob?
That's easy! Bob ships for free worldwide, why go elsewhere?

Cheers
Steffen.
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Old 26-05-2010, 05:46 PM
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bmitchell82 (Brendan)
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Or even better jason get rid of the old skywatcher primary cell and put something in that works i just recived my new orion optics 10" mirror cell! happy days!
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Old 08-06-2010, 02:33 PM
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So i've been out and bought myself a new set of knobs and springs (well getting them shipped direct from Bob)

Does anyone know if Instructions come with the springs, or where i can find out how to replace them safely ?

I have this recurring thought that i'm going to undo something and springs are going to fly out, the mirror crash to the ground and leave me sobbing in a heap on the floor !!!!!!

Stu
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Old 08-06-2010, 04:19 PM
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Quote:
Originally Posted by Stu Ward View Post
I have this recurring thought that i'm going to undo something and springs are going to fly out, the mirror crash to the ground and leave me sobbing in a heap on the floor !!!!!!
Yes, that's what is most likely to happen. On the way to the floor the mirror will also travel down the tube and shatter the secondary…

Seriously, if you think before you do and take your time it's going to be a breeze. Here's how I do it:
  • mark the position of the mirror cell's mounting frame in the tube
  • unscrew the frame from the bottom of the tube (get help if you're not confident you can support its weight with one hand once it pops out)
  • put the frame and cell mirror down on a clean table
  • mark the relative position of frame and cell
  • remove the locking screws, put them away
  • remove the collimation screws, take the mountig frame off the mirror cell (take care not to rip off the fan cable if there is one)
  • remove the old springs that should now be sitting on top of the mirror cell, put the new ones in their places
  • replace the mounting frame and insert the collimation screws, compressing the springs down to about 1/2 to 1/3 of their length.
  • (optional) turn the cell over and verify the position of the centre mark
  • put the cell back into the tube and replace the screws.

Cheers
Steffen.
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Old 08-06-2010, 04:58 PM
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JethroB76 (Jeff)
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Or you could unscrew and replace one collimation screw/spring at a time.
This should be relatively easy unless you have a closed mirror cell
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Old 17-06-2010, 07:32 PM
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Quote:
Originally Posted by Stu Ward View Post
So i've been out and bought myself a new set of knobs and springs (well getting them shipped direct from Bob)

Does anyone know if Instructions come with the springs, or where i can find out how to replace them safely ?

I have this recurring thought that i'm going to undo something and springs are going to fly out, the mirror crash to the ground and leave me sobbing in a heap on the floor !!!!!!

Stu
My set of Knobs arrived this morning, so i couldn't wait to install them when i got home. However i found a real problem

Now i'm not sure if Sywatcher have changed their design, or i have suffered from some misinformation from here

I purchased a full set :
Primary knobs
Uprated Springs
Secondary Knobs

I detached the mirror housing from my dob and then removed the mirror ( V V V carefully )
Then took the Primary adjusting screws from the base so that i could replace the weak springs, but wait a minute, there are no springs !!!!

My dob's primary springs are infact little rubber washers, but no drama i will just replace them with the springs

Next problem

The Primary adjusters' thread supplied by Bob are about 2mm wider than the screws they are supposed to replace !!!
So the Primary adjusters will not go in the base.
And as the factory screws are much shorter the springs are useless !!!

The Secondary Knobs seem fine

So i have paid around $90 for a set of Secondary adjusters.
I have informed Bob via email that there may have been a Skywatcher design change that he is unaware of.

I feel sad

Stu
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Old 18-06-2010, 06:01 PM
morls (Stephen)
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Sorry to hear of your problems Stu. I'm looking at doing the same sort of mod on my 8" skywatcher collapsible dob. Maybe we're just stuck with the original primary screws?

Stephen
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Old 18-06-2010, 07:43 PM
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I couldn't find any primary knobs for SkyWatcher dobs on Bob's site. Which ones did you get?

Cheers
Steffen.
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