Help collimating 200p

[toml42]

Decided it was about time to have a crack at collimating my skywatcher explorer 200p, but i've run into a problem.

I'm trying to adjust the secondary mirror tilt, but i'm having difficulty loosening the three allen screws on the end of the secondary mount, they're very tight and i'm worried the spider vanes will bend before the loosen. Was i meant to loosen something else first?

[NGC 1502]

Hi, I have the same scope. The 3 screws should loosen without undoing any thing

else. But maybe try loosening the larger central screw a bit, could do the trick.

Keep hold of the hub & spider as you loosen/tighten.

HTH, Ed.

[eyespy]

Yes there is a phlips bolt right dead in the centre , you have to loosen this first,it might be a bit stiff,also be carefull not to undo it just loosen it ...

[toml42]

Same problem with the philips bolt any ideas?

[Astro_Baby]

You could try removing the spider assembly altogether so you can get a grip on the secondary holder for the phillips screwdriver.

[NGC 1502]

I apologise if this is too easy, but you are trying to loosen anticlockwise ? Ed.

[TopHouse]

I replaced my central one with a proper hardened socket head because of exactly the same thing. Best option is definitely to work on loosening that center one, and make sure the philips driver you use is a proper fit or you could end up chewing up the slots in the bolt. If you just happen to live near me, which I doubt, I'd have it out for you in no time and even give you one of my spare socket headed ones. Just get a really good grip on the 'boss' in the middle of the vanes, once you manage to loosen that central one a little the grub screws will be fine.

[brantuk]

They do tend to be very stiff - you need a firm grip on the secondary and vane without touching the mirror surface. But don't slip and put the phillips screwdriver through your hand.

Make sure your tools are in good shape and that the screwdriver slots on the central screw securely with full contact - don't want to strip the head. I find it helps to hold the screwdriver like a dagger - gives me more purchase in that awkward position.

If that fails then maybe a tiny drop of penetrating oil in the screw head overnight will help. Clean thoroughly afterwards.

Protect the primary before you start by sellotaping a circular piece of card or cloth a few inches below the secondary to inside of the tube. Don't want to drop anything on it.

Hope that helps

[Bizibilder]

To undo the three screws put the short end of the allen key into the screw - this gives more leverage on the long end to undo them (if you're not already doing it that way of course!!). If you hold the secondary mount in your fingers with one of the spider "legs" across the palm (ie put your hand over the spider leg first so your palm is facing you - then grip with your finger tips) you should get enough grip to undo the screws

[toml42]

Got there in the end, got a firm grip on the mounting and had another go at the allen screws with a bit more force, once i got one of them to loosen everything else was fine. now i'm hopefully in perfect collimation (It was actually quite badly out!) just need to wait for the clouds to clear for a star test...

Cheers guys!

[Bizibilder]

It may be worth a look at various threads on the problems of these infernal secondary screws!! The main problem is that they "mark" the back of the secondary holder when you tighten them. So when you come to recollimate the screws tend to "drop back" into the marks made - thus preventing accurate collimation!! The cure is normally to put a washer over the secondary mount that the three screws can be tightened against - a chrome plated or stainless washer being preferred. This stops the problem.

Hope this helps.

[TheThing]

For anyone else in the same 'boat', a tip my old dad taught me from his naval engineering days - if a screw wont undo, try tightening it up a little first. This has got me out of trouble on many an occasion (that a a drop of ordinary vinegar on rusted bolts/screws).

[Bizibilder]

That idea makes complete sense!! (An old engineers dodge that actually works!) - Think as to which parts of the "tight" thread are in contact and "doing them up" actually "undoes" them!! 'Tis true.

[toml42]

hmm, that's quite handy, i'll keep that in mind