Collimation screws - Replacement

[keme]

Afternoon Folks

 

So i received my Skywatcher 200p dob, and after a few days got my collimation laser.  Problem so far is that one of the screws on the secondary mirror has been threaded so i am unable to get the hex to grip.  Are there replacements to be bought?  If so are there better ones to choose from rather than hex?

[DRT]

Hi,

I use these bolts on my Newtonians as they are much easier to adjust than having to use an Allen key...

http://www.wdsltd.co.uk/product/3338/adjusting-screw-steel-metric-wds-605/

You need the M4 45mm long version - part number 605-200445

Derek

[Floater]

Or there's always Bob's Knobs. One of the most satisfying mods available ...

(Not the cheapest, I'll admit. But as a Scotsman I know that money's not everything ...??)

[DRT]

7 minutes ago, Floater said:

Or there's always Bob's Knobs. One of the most satisfying mods available ...

(Not the cheapest, I'll admit. But as a Scotsman I know that money's not everything ...??)

As one Scotsman to another, the one's I linked to are identical to Bob's Knobs but about 1/3rd of the price ?

[keme]

From the original scotsman.  Cheers for the replies, ordered from the first link   Getting some nice skies up here unfortunatly until the screws arrive I am missing out

[Dave In Vermont]

One little piece of advice about collimating a Newtonian - whatever type of mount matters not:

If you are using any tools, Allen-wrench or such, do the deed with the telescope either level - or with it's nose (the front of the tube) pointing somewhat down. This is so when you drop the wrench or a bolt - it won't free-fall down the inside of the tube and strike the primary-mirror. Even dropping a little bolt down inside is no fun to retrieve.

+1 for Bob's Knobs! They are also available for SCT's.

Dave

[DRT]

Another tip: when replacing the collimation bolts make sure you replace them one at a time so that the secondary mirror does not become loose. Remove one hex bolt and then replace with one of the new ones and screw in until you start to feel resistance from the secondary, then move on to the second one and repeat the process until all three new bolts are in place. You should then find that the secondary hasn't moved very far and collimation should be quite easy to achieve with just a few small adjustments  

[keme]

Cheers for the tip Dave, last thing I want is something dropping where it shouldnt cheers

[Charic]

18 hours ago, keme said:

........one of the screws on the secondary mirror has been threaded so i am unable to get the hex to grip.  Are there replacements to be bought?  

I would check using one of the other bolts to ensure the hole itself has not been threaded too, otherwise the new replacement may fail.

You could re-tap the hole or replace the 'spider' at worse. 

[Charic]

14 hours ago, Floater said:

One of the most satisfying mods available ...

Its a modification I have considered many times over, however its the reach or lack of reach on my 200P scope thats my real concern. The BK's make's for a simple no-nonsense tool less operation, however if I can't reach them, its an un-neccessary upgrade IMO!

With my eye at the focuser observing the collimation process, I just cannot physically reach the original adjusters with a tool, I just don't have the reach, therefore my process involves me moving between focuser and adjusters, it's not a smooth operation, and I originally thought this was one reason why BK's existed in the first place, to make the process easier, but no, I have to ask Mrs Charic to assist me!  I have also considered spring loading the  collimation adjusters, buts its of my opinion that the mirror cell has more scope (pun intended) to bounce around under spring tension, during transportation rather than the stability of being compressed against the original 'O' ring.

I do understand the benefits of tool-less adjustment, it will benefit some users, and of course,  there are cheaper bolts out there, that said, I would still like to see what's actually in the Bob's Knob's kit, for when you look at what your replacing (check their images) the BK's appear to have design spacers  on the collimation adjusters (something you must  consider if your new bolts are longer).

For now though, things will stay the same on my scope!

 

Edited August 12, 2017 by Charic

[keme]

Cheers for the replies, received the screws on the first link. work perfect, managed to collimate just fine, but 45mm might be a tad too long. all 3 stick out a bit, 40 might have been better, but the heads are just the right size that they stay within the shadow of the secondary mirror.

Cheers Folks

[DRT]

Glad to hear it worked out. I bought a batch of the 45mm ones because I wanted to use them on a range of sizes of scope (8", 12" and 16") and agree you could get away with the sorter ones for an 8".

Happy collimation

 

[Ricochet]

On 12/08/2017 at 11:03, Charic said:

Its a modification I have considered many times over, however its the reach or lack of reach on my 200P scope thats my real concern. The BK's make's for a simple no-nonsense tool less operation, however if I can't reach them, its an un-neccessary upgrade IMO!

With my eye at the focuser observing the collimation process, I just cannot physically reach the original adjusters with a tool, I just don't have the reach, therefore my process involves me moving between focuser and adjusters, it's not a smooth operation, and I originally thought this was one reason why BK's existed in the first place, to make the process easier, but no, I have to ask Mrs Charic to assist me!  I have also considered spring loading the  collimation adjusters, buts its of my opinion that the mirror cell has more scope (pun intended) to bounce around under spring tension, during transportation rather than the stability of being compressed against the original 'O' ring.

I do understand the benefits of tool-less adjustment, it will benefit some users, and of course,  there are cheaper bolts out there, that said, I would still like to see what's actually in the Bob's Knob's kit, for when you look at what your replacing (check their images) the BK's appear to have design spacers  on the collimation adjusters (something you must  consider if your new bolts are longer).

For now though, things will stay the same on my scope!

 

I suggest using the barlowed laser method for easily collimating the primary without the need to grow longer arms.  

[keme]

Collimation was kind of a pain to start with.  No matter what I did I couldnt get the laser to line up with the doughnut, there was a point where all screws were tight and wouldnt budge anymore.  Anyway slackened the main screw for the Secondary ever so slightly and this made things 100 times easier, possibly over tightened at factory? 

[Charic]

2 hours ago, Ricochet said:

I suggest using the barlowed laser method for easily collimating the primary without the need to grow longer arms.  

Totally agree, its the method I often recommended.

[DRT]

2 hours ago, Ricochet said:

I suggest using the barlowed laser method for easily collimating the primary without the need to grow longer arms.  

What is the advantage of the barlow?

A laser beam is straight - putting a lens in front of it cannot make it more straight, but it can make it not straight. It also introduces yet another device that might not be perfectly aligned with the light path.

I use a Hotech laser very successfully. I can't imaging why I would want to stick it in a barlow  

[Charic]

16 minutes ago, DRT said:

What is the advantage of the barlow?

Accuracy and efficiency?............just looking for the article.......but just discovered some sad news about Nils?

Edited August 17, 2017 by Charic

[Charic]

23 minutes ago, DRT said:

What is the advantage of the barlow?

Check this article http://www.micosmos.com/enlaces/collimation_with_a_Barlowed_Laser.pdf
 

The amount of slop in any system, and the laser tool itself, often  they come  with sealed adjusters, are more often in need of  further collimation before the tool could be classed as accurate? therefore from experience, and reader reports, I don't have no faith in laser tool accuracy, but I find this method very quick and efficient, despite how inaccurate the tool may become! 

Unless I use a smaller donut? its unlikely I can get my scope any more collimated than it is, using this Barlow method.
Of the methods I have used, sight alone, 35mm film cap, Cheshire tool and laser, the laser is the last tool on my list.

I also don't think spending more on a laser gets you a better result, unless you can accurately get that laser to fit 100% the same everytime,without any sloppiness. I still check and monitor the collimation of the laser tool itself, but only use the Barlow method for when I need to do a quick test, better still a Star test.

 

Edited August 17, 2017 by Charic

[Ricochet]

1 hour ago, DRT said:

What is the advantage of the barlow?

A laser beam is straight - putting a lens in front of it cannot make it more straight, but it can make it not straight. It also introduces yet another device that might not be perfectly aligned with the light path.

I use a Hotech laser very successfully. I can't imaging why I would want to stick it in a barlow  

As will be better explained by the article Charic linked, the point of the barlow is not to make the laser more straight, but to diverge the beam, effectively turning the laser into a narrow torch that illuminates the centre spot of the mirror. This means that it doesn't matter if your laser is slightly miscollimated, the focuser doesn't centre it perfectly or if you didn't quite get your secondary position absolutely perfect, because the beam still illuminates the centre spot. Instead of the usual laser method of primary collimation by getting the laser beam to return down the hole it is projected from, which with cheaper lasers might be harder to judge than it should be, you centre the shadow of the centre doughnut on the angled face of the laser (in my case I have a dot in the very centre of my primary as well as the doughnut so the shadow of the dot disappears down the laser hole as an additional check). 

For your case I would expect that your Hotech laser is of such quality that you can use it in the "normal" method with no issue, but the barlowed laser method allows the use of any any cheap laser and any cheap barlow to achieve the same accuracy. Note that it has to be a barlow, a powermate or telextender won't work because of the difference in how they work. 

[Charic]

1 hour ago, Charic said:

discovered some sad news about Nils?

.......apparently Nils  passed away in the last few days

RIP Nils.

[Dan13]

On 11/08/2017 at 16:23, DRT said:

Hi,

I use these bolts on my Newtonians as they are much easier to adjust than having to use an Allen key...

http://www.wdsltd.co.uk/product/3338/adjusting-screw-steel-metric-wds-605/

You need the M4 45mm long version - part number 605-200445

Derek

Hi Derek, appologies for reviving a very old price but you have linked exactly what I'm looking for. Would you be aware if these would fit a 130pds at all please? 

Many thanks

Dan 

[wookie1965]

https://www.google.com/url?sa=t&source=web&rct=j&url=https://m.youtube.com/watch%3Fv%3DMUE8fxqH3Qc&ved=2ahUKEwiqyp2rms3pAhXNMMAKHdPkCDEQwqsBMAB6BAgJEAM&usg=AOvVaw1Zwe1N9CyRJMfy1vKdkfig

I did this on my 200p made collimating a doddle plus make sure your laser is accurate if someone hasn't already mentioned it.