Skywatcher flextube secondary adjsutment problem

[cathalferris]

I've got a small problem with my 12" Skywatcher dob secondary spider adjustment. In short, I'm not able to free up the philips screw that adjusts the height of the secondary in the tube. 

My very dumb question is: Is this philips screw in the centre of the secondary holder supposed to be free enough to turn? I would think that it should be to get that axial adjsutment.

Does that screw have threadlocker on it from the factory?

I can't get enough purchase on the 45 degree stalk that the secondary is glued to, to be able to turn the philips screw. I'm not weak by any stretch, and I have the proper size of Philips screwdriver. If the screw is supposed to be free, I'll remove the secondary mirror and get some proper leverage on the holder to get that screw turned.

I'm trying to move the secondary higher in the tube to perfect the collimation with the Cheshire/sight tube combo tool I have as well as putting a nylon washer at the base of the little hex-head screws in the spider to make it easier to get that collimation done..

[Paul73]

You will need to slacken off the three little sunken Allen key screws which deal with the tilt. The mirror is then free to move up.

Don't forget to leave the cover on the main tube just in case of dropped screwdrivers.

Hope that this helps.

Paul

[Steve Ward]

Or better still have the tube horizontal so that anything that slips from your grasp goes nowhere near the primary ... you'll need to remove the bottom cover to collimate ... 

[cathalferris]

I've always taken care with my protection of the mirror. I've read enough scare stories to make me think twice about working near a mirror. Bad enough that it's exposed when in use!

I have already backed off the allen screws to completely within the spider support, leaving the mirror support stalk free to wobble around on the spring. I just cannot get the centre screw to break its stiction and turn relative to the mirror support stalk. I'm trying to avoid using a grip wrench or bench vice on the mirror support, but I may have no other real choice to get this collimation done properly. Time to take the spider off and I'll bet some larger tools on it to break the threadlock.

[Paul73]

Good luck. Can't see that you have any other option.

Paul

[cathalferris]

I'm learning to dislike companies that use steel fixings in aluminium without using a corrosion preventing agent between the two..

I got a new air shock for my mountain bike, but the bolt holding one end of the existing shock has become so tightly bound that it will take an engineering company's expertise to get it out..

On the scope, the Philips head on the screw sheared off before the shaft of the screw turned for me. Probably need to get a replacement 45 degree holder now to return the scope to usability. I've got a few tricks to try to extract the screw shaft from the secondary holder, involving a gas flame. I've also asked the local Skywatcher dealer to try to obtain the correct spare from OVL if possible.

Advice to those that have Skywatcher dobs: unscrew the main secondary support screw and apply a grease to it before reassembly to ensure future collimation ability. Learn from my experience!

Sent from my GT-I9295 using Tapatalk

[Paul73]

Thanks for the advice. I had a similar issue with the screws that hold the clamps on the primary mirror. Must have snapped 3 of them getting the mirror released for cleaning.

Paul

[knobby]

Please don't hit me

[cathalferris]

Mirror was a fair bit too far down the tube according to the Cheshire device. If the centre screw wasn't as inset as it is, I could have lifted it and inserted a small circlip or two under the screw head to bring the mirror up, but because the screw is that deeply inset I did not have that option. At least once I get this screw out our secondary part replaced, I'll be able to collimate it properly.

I could have left it as it was with a non-centred illumination, but that level of misposition of the secondary would have bugged me long term.

Sent from my GT-I9295 using Tapatalk

[greglloyd]

Any ideas on how to get one of these stripped center screws out and what replacement screw is required?

I have one that has got stuck and the head has stripped also. My secondary is pretty much in the correct position below the focuser but may need just a slight adjustment. I'll also have no way to clean the secondary in the future if I cannot get it removed from the OTA. So would like to get this stripped head screw out and replaced.

[greglloyd]

I got the screw out ok :-)

But any idea what type of screw it actually is?

M4 x 40mm

M4 x 50mm

M5 x 40mm

M5 x 50mm

??

[coulthamst]

Have you had this scope long? If the centre screw was jammed in the diagonal holder, with the holder/secondary assembly loose in its support, you would have a reasonable claim on the manufacturer if the instrument was bought less than a year ago. If this is not the case, has the screw been damaged by someone's ill use?

[greglloyd]

It's a second hand scope which I've owned for about a year. It's not the threads that have stripped - it's the cross head. The actual screw threads and the secondary holder are just fine.

It was my fault, I tried to unscrew it when the 3 tilt adjustment screws were too tight. This made the centre screw very very tight and I tried to force it out.

I found out that by undoing the tilt adjustment screws slightly the screw now easily comes out (thanks to a forum thread I read elsewhere). So I am no longer stuck for collimation.

The screw now works totally fine, but I'd like to replace it for aesthetics and to ensure I don't eventually end up stuck if the head finally fails on it.