Spider Vane Tightness

[Spec-Chum]

How tight should they actually be when tightening with the thumb screws?

My vanes are quite taut but I've noticed that the thumb screws on the outside of the OTA can rock slightly, thus changing their angle and moving the secondary enough to knock collimation out. Manually moving them back puts it right again, but still...

[bingevader]

Apparently, it is possible to kink them if you over-tighten them (not sure how, as you're stretching, not compressing them), but I've not experienced that myself and I'm quite ham-fisted!

Also, any angle off the vertical can result in extra diffraction spikes, but that's easily adjusted.

Sooooo, as long as you're happy with the collimation, then finger tight enough to hold the secondary in place should do it!

Cheers

[Islander]

Finger tight. Overtightening could twist the vanes.

[Steve Ward]

Finger tight is plenty , once everything is centred . . .

Steve.

[Spec-Chum]

Thanks guys.They're certainly finger tight already but I'm still getting drift. I'll try tightening them more but I fear I may make the OTA oval so the dust cap won't go on.It's hard to explain what I mean by the bolts rock so I will again astound you with my MS Paint skills:

Of course that's grossly over exaggerated but I hope you get the idea...

[NGC 1502]

As already said, finger tight is enough, so you get a 'twang' when you flick them.

But it sounds like you still have problems. Looking at the diagrams you posted, it looks like the bolts that go through the tube are coming out of line when under tension. Maybe some DIY may sort this.

Hard to tell without seeing this up close, but perhaps the holes in the tube are oversize for the bolts, and as you tension them, they twist out of line ? You could try using 'repair washers' like these http://www.a2stainless.co.uk/Penny-repair-Washers_B22S5.aspx my local DIY shops all sell these in lots of sizes. Look for some that have an inner holes just large enough to take the bolts. The washers can be curved in a vice to match the tube diameter.

This could work to fix the problem. If you are stuck to source the washers, drop me a PM with the bolt diameter and tube diameter and I'll have a look in my shed, sea what I can find and hopefully pop some in the post, free of course.

Maybe I've read the issue wrongly, and another idea is needed........

Hope you sort it, Ed.

[Spec-Chum]

Thanks Ed.

It's not that big an issue really, they quite rarely move on their own, but the fact that they can move at all is just starting to play on my mind; I just thought they needed tightening but if I tighten them any further the end cap becomes very tight.

Edit: They don't go out of line as I'm tensioning them; they just move around too freely even when tightened as tight as I can get them and not distort the OTA.

[NGC 1502]

Thanks Ed.

It's not that big an issue really, they quite rarely move on their own, but the fact that they can move at all is just starting to play on my mind I just thought they needed tightening but if I tighten them any further the end cap becomes very tight.

I use shower caps on the open end of my Newts, they always fit well and keep the dust out. It took me a while to find ones that were not pink or with flowers on..................

Cheers, Ed.

[Spec-Chum]

Quick update on this, and a daft question.

I had a brief look again last night and very minimally tightened all 4 bolts which didn't really do a lot but I've been thinking of a better way to describe my issue.

The daft question is, and this has been the issue all along really, when I push one of the bolts out of kilter on purpose should it "spring" back to straight, or stop at an angle?

I start all straight, like the top of diagram below and I, on purpose, gently push 1 bolt down so it resembles the bottom pic but it stops like this and doesn't spring back to straight like in the top pic.

They really do seem too easy to move and then they stop in their new, wrongly angled, position which introduce rotation error on my secondary. If it's bad enough one (or sometimes even two!) of the primary clips goes out of view and the primary centre spot is then way off. I "manually" adjust the bolts back to being straight again (top pic) and it's all bang on again.

Do they just need to be tighter, or this by design and I'm just meddling too much and should leave the bolts alone and stop pushing them about? haha

[NGC 1502]

Had a think (very dangerous for me )

This could perhaps work - the bolts that pass through the tube to hold the spider vanes, I'm assuming they are threaded to take the tension nuts on the outside of the tube.

Is the part of those bolts that come inside the tube threaded ? If so, how about putting a backnut on those threads inside the tube, you could tension the nut on the outside, then tighten the backnut inside, clamping the bolt square to the tube, and this should stop the bolts from twisting out of line.

Does this make sense ? or maybe I'm not seeing the problem correctly.

Regards, Ed.