Bobs Knobs or 30mm M4 Nylon Bolt

[Bart]

I have a 10" GSO Dob. Thinking about Bob's Knobs for the Secondary adjustment screws. However, should I just go for these ?

10 Nylon Plastic Screw Sets, M4 Nut, Washer & Bolt 30mm | eBay

Thanks for any comments?

Bart

[jimmyjamjoejoe]

Right size, but dunno how easy they'l be to do by thumb.

Out of interest, anyone know the size needed for a 200p primary? (both locking and adjustment)

[Damo636]

I have these on both my dobs Barry. You need 3 of 8168-227

WDS 8168 Thumb Screw, Plastic Hand Knobs - WDS

The thread on the nylon ones would strip very easily with the pressure required to hold the secondary in collimation.

[Psychobilly]

M4 Nylon screws will be "bendy"...the tips will also distort under pressure...Because of this I wouldn't of thought they would hold collimation that well

You can get brass screws fitted with plastic knobs on ebay - I bought a range of differrent sizes last year...

Peter...

[SeedyF]

I too have the WDS ones, fitted yesterday. They are only 25mm not the 30mm recomended by Bobs Knobs but with a washer they work fine. Cost 6.76 including delivery for 3.

I did notice that WDS does another M4 in steel that is 35mm long. Might be worth considering.

[Damo636]

There's more than enough clearance with the 25mm ones, even with a washer added.

[Peter Drew]

Another - for nylon screws for the same reasons posted by Psycobilly.

[johninderby]

Another way is just to buy the knobs and a length of stainless threaded rod. Then you can have custom thumbscrews of exactly the right length. The knobs on their own are quite cheap from WDS. The short lengths of stainless rod on eBay are cheap and Loctite is also fairly cheap on eBay.

If you fancy something more expensive Rob at Epsilon can make thumbscrews to order in brass, aluminium or stainless steel and with or without nylon tips. List of standard sizes here but they can be ordered in any size/material with knurled heads or Delrin ones.

http://www.epsilon-telescopes.co.uk/products/thumbscrews.htm

John

[Catweazel]

There's more than enough clearance with the 25mm ones, even with a washer added.

Hi, did you replace the Alan Key screws with these? Are they the same as the ones that you mentioned in your first post? I am after some for my secondary mirror adjustment only. Thanks. CW

[Damo636]

Yep, these replaced the allen screws on the secondary on both my Newts.

[Bart]

thanks Gents, for some reason WDS must think the republic must be on the other side of the world with the prices they charge.

Cheaper to buys Bob's.

Bart

[Catweazel]

Yep, these replaced the allen screws on the secondary on both my Newts.

That's great, thanks Damo

@Bart, yeah, the postage, even within UK, is outrageous at WDS