best way to measure spider

[Daniel-K]

whats the best way to measure your spider to make sure its central>?

[sbooder]

I use a modded pair of Vernier.  I took the depth gauge off so it would fit in the tube, but this will only work for tubes with a diameter to take the rest of the vernier.

[Steve Ward]

Simplest way is with a wooden BBQ skewer cut to suit the diameter and a sharp pencil.

Mark from one side the the other and then split the difference ... 

[bambuko]

One thing to bear in mind (if you doing it to typical "made in China" OTA, with four vanes, one of which is right next to focuser hole and the scope tube made from "aluminium foil"), is that you can easily distort the tube where it is weakest (next to focuser opening).

So even if four vanes are equal length, it doesn't gurantee that secondary centre is where it should be!

So before you start meauring spider vane length, make sure that scope tube is indeed round and un-distorted!

[LeeB]

I use a large set of dividers

[sbooder]

I use a large set of dividers

Similar idea to the vernier but better I think, I just did not think dividers...D'OH! 

I used to use a homemade cap for the front with a peep hole dead centre, I would take out the primary and look through the peephole and when I could see through the centre bolt hole in the spider without interruption I was there, it worked a treat.

[faulksy]

i use a steel rule, but a good way is measure the o/d of the tube use some deviders,and draw the circle you then have the centre ready, cut around the arc and place over the open end of your scope, were the deviders put a hole in your card/paper thats were the centre bolt for your secondary should be

[Tinker1947]

If you cut a piece of paper so it fits inside the tube, then fold it several time to find the centre, cut a small hole in the centre and the screw that holed the secondary should be in the centre of this hole as thats the centre of the tube...

[Daniel-K]

What's a divider?

[Stu]

This sort of thing, doesn't always have the threaded piece, can just be free moving.

Stu