replacement secondary grub screws

[ddtwelve12]

ive been looking at replacing my grub screws on my secondary before they get mard

so looked at bobs knobs and coughed and spluttered at the price found a uk site that can provide said knobs for way cheaper but also found they do a grub screw with either brass or nylon tip insert would that be better ?

also what size is the main mirror bolts on the skywatcher flextube 8inch please

[Moonshane]

Better and cheaper is http://stargazerslounge.com/topic/193369-collimation-tip-bottle-washers/

[ddtwelve12]

theres not enough movement in the spider to put washers in of any kind on my scope

[Moonshane]

Not even half a millimetre?

[russ.will]

If you haven't got 1/2mm to spare, I'd suggest there's probably other issues that need looking at first, such as focuser alignment.

FWIW, I don't rate the milk bottle washer - better to put a thin metal washer in there. When you put plastic in the middle, you end up with a material that is compressible, can move and will just result in requiring collimation more often.

Keep it all metal, get it right once and you'll end up doing it far less often.

Russell

[Moonshane]

I disagree with Russ but each to their own. My a secondary collimation needs doing about every two years by a smidge of a turn if at all. Find your own way that works and sick to it.

I do agree with Russ about available adjustment though.