Bob's Knobs For Sky-Watcher 200P...

[Guest]

I got my Sky-Watcher Skyliner 200P Dobsonian just before lock down started, earlier this year. 

I'm thinking of upgrading the secondary mirror holder to Bob's Knobs. Does anyone know what size would fit mine? 

[Jiggy 67]

Try looking here, I fitted these to my 200PDS, just read carefully for the correct ones

https://www.firstlightoptics.com/bobs-knobs-collimation/bobs-knobs-celestron-sky-watcher-newtonian-collimation-knobs.html

Edited October 27, 2020 by Jiggy 67

[Guest]

1 hour ago, Jiggy 67 said:

Try looking here, I fitted these to my 200PDS, just read carefully for the correct ones

https://www.firstlightoptics.com/bobs-knobs-collimation/bobs-knobs-celestron-sky-watcher-newtonian-collimation-knobs.html

It's 30mm between the top of the secondary holder and the back of the flat, so I'm wondering if I'll need the 35mm ones? 

See the red line on the photo. 

Edited October 27, 2020 by Guest

[Jiggy 67]

Mine are the 30mm and they fit perfectly 

[Barry-W-Fenner]

Hi Merlin.

I also purchased the 30mm for my 200p

I purchased some 5 x 25mm thumb screws for the primary mirror from ebay for £2.94 they were from China and took a couple of weeks to arrive but work perfectly.

It might be worth checking the gauge of the secondary thumb screws. If they are also M5 you can get them at 30mm long on ebay for around £3 also.

When I get chance I can check to see if one of my 25mm primary screws fit the secondary. That way we know it is also M5

Alternatively if anyone else knows the size that would be great. Yiu could buy 6 screws for around £6 and do both primary and secondary.

Cheers

 

Edited October 28, 2020 by Barry-W-Fenner

[Guest]

I've got some M5 bolts that don't quite fit in the threads, so I'm obviously not going to literally force the issue.  I've measured the inside diameter roughly with a vernier gauge and it appears to be around 4.5mm?🤔  Agreed about eBay, it's a damned sight cheaper!

[Barry-W-Fenner]

9 minutes ago, merlin100 said:

I've got some M5 bolts that don't quite fit in the threads, so I'm obviously not going to literally force the issue.  I've measured the inside diameter roughly with a vernier gauge and it appears to be around 4.5mm?🤔  Agreed about eBay, it's a damned sight cheaper!

Good to. Know. I will try one of my M5 primary bolts in the secondary, but like you say not force it. If it doesn't fit I assume that the bobs knobs for the secondary mirror are 4mm

[Barry-W-Fenner]

The secondary bolts are definitely Smaller.

I would say they are 4mm x 30mm. If its any indication I used a 2mm Allen key to screw/unscrew.

Worth a look on fleebay, even if they are wrong it's £3 lost and I will owe you a pint to make up for it.  Just make sure the screw head is not to large to protrude over the secondary holder to much.

I just searched "M4 x 30 thumb screws" and loads came up. The flater headed ones are best rather than the chunky heads.

 

Edited October 28, 2020 by Barry-W-Fenner

[Guest]

In the end, I've just ordered a set of Bob's Knobs from Auntie FLO for the secondary mirror.