Thumb screws and milk washer mod for the dob

[DAT]

Does anyone know how/where to get thumb screws (in the UK)) to replace the screws to adjust the secondary on a Stellalyra? I understand bob's knobs are an option but they seem expensive. I believe I need 35mm but not sure on the thread required. Is it a question of taking a screw to a hardware store and seeing if they have one that matches?

I see that a lot of people have chosen to add a washer to the secondary to allow rotation which is not possible because of the indentations the 3 collimating screws fit into. How important is this modification? If the scope is collimated or the secondary does not need to be rotated, is there any benefit to this?

I have read a few threads but could not find the answer to these questions, thanks in advance

 

Edited April 10 by DAT
another spelling mistake

[Clarkey]

I can't remember the exact size, but the ones I replaced on my 200p were M3 or M4 from memory. If you take one out and measure it....

As for purchase, standard thumb screws are cheap as chips online. Try to get a similar material to the existing ones to prevent galvanic corrosion.

As for the washer, personal preference really.

[Kon]

See here about the screws:

https://stargazerslounge.com/topic/420499-gas-giants-knobs/

 

Regarding the washer modification, you need to undo all the secondary screws to allow the washer to insert. It's worth doing it as the base of the secondary is rather soft and eventually the screws will dig into it. I wouldn't bother doing it until you start playing with the collimation. I have done it on both my Dobs .

 

[wookie1965]

 

[DAT]

Thanks for the replies, I think I need M4 x 35mm stainless steel screws. Have found some fairly cheap on eBay (about £6 for 5). Will leave the washer modification for later as I think collimation is looking good for now, might even be able to see something in the next week or so…

[dweller25]

21 minutes ago, DAT said:

Thanks for the replies, I think I need M4 x 35mm stainless steel screws. Have found some fairly cheap on eBay (about £6 for 5). Will leave the washer modification for later as I think collimation is looking good for now, might even be able to see something in the next week or so…

Collimato perfecto 🙂👍

[bosun21]

I bought mine from eBay of which there is a huge selection. I chose the black ones as this will prevent any stray light reflections. I have also fitted the washers to all the dobs I've owned past and present. The indentations on the Stella Lyra dobsonians I've owned have prevented the secondary mirror being rotated correctly. I have just carried out the same mod to my Skywatcher 10" Flextube dobsonian. I also spray paint the washers matt black before fitting.

[DAT]

4 hours ago, bosun21 said:

I bought mine from eBay of which there is a huge selection. I chose the black ones as this will prevent any stray light reflections. I have also fitted the washers to all the dobs I've owned past and present. The indentations on the Stella Lyra dobsonians I've owned have prevented the secondary mirror being rotated correctly. I have just carried out the same mod to my Skywatcher 10" Flextube dobsonian. I also spray paint the washers matt black before fitting.

Is it worth painting the screws or is that overkill? The ones I have ordered are steel and could reflect stray light…

 

[bosun21]

18 hours ago, DAT said:

Is it worth painting the screws or is that overkill? The ones I have ordered are steel and could reflect stray light…

 

I only had to paint the threads once when I also bought black ones with steel threads. I just placed a bit of masking tape over the ends of the threads when painting.

Edited April 12 by bosun21
Typo

[PeterStudz]

On 12/04/2024 at 07:41, bosun21 said:

I only had to paint the threads once when I also bought black ones with steel threads. I just placed a bit of masking tape over the ends of the threads when painting.

It depends on how far you want to go. I flocked and blackened everything when I did mine, including the back and sides of the secondary. 

For silver screw threads I slipped on a small section of black heat shrink tubing (for electrical insulation) which I had at home already. Just slipped over the tops of the threads where they stick out. Only worry about paint directly to metal is that it can flake off and you don’t want that ending up on your mirrors. 

Haven’t a clue if it makes a difference but it only took a few minutes and cost me nothing.