A word of warning to Skymax 102 Owners and a Solution - Loose Nut in OTA

[etsatlo]

My Skymax 102 has been serving me well, however with the addition of a binoviewer and 6x30 right angle finder it has become more and more back-heavy. I've shuffled the scope as far forwards in the AZ Pronto mount as I can but it's still not quite balanced fully.

Looking to change the dovetail bar for a longer one I soon realised I had no idea what size the mounting screws currently used were. Easy, I'll just unscrew one and find out. Now normally I'd have searched Google for half an hour before doing anything to the scope to learn from others' mistakes but this Saturday morning I just fancied tinkering.

Well that served me right.

I undid one of the 2 dovetail mounting screws and promptly heard a 'ping' as the previously unknown nut dropped onto the other side of the tube.

Cue minor heart attack.

Fortunately it had missed the mirror and the corrector lens so all was good but now I had a loose nut floating about in the tube.

I fortunately had some very strong magnets knocking about so I used a few of those stacked together to hold the nut in place so it couldn't slide around.

Trying to get a loose nut onto a bolt was a pretty unenviable task.

My now post-event Googling revealed that I'd need to remove either the corrector plate or the primary at the back. I got as far as starting to unscrew one of the screws on the corrector plate before chickening out and tightening it back up. I hadn't really planned on ever collimating the Mak (just as well as there are now collimation screws) and I didn't intend be the cause of it going out of collimation.

After some ideas of maybe getting a wire in through the back where the diagnonal slots in; maybe trying to get a spot of super glue on the inside of the tube to hold the nut in place I resorted to trying again to gently get the bolt back in to the nut.

 

The solution was as follows.

I removed by retaining magnet I'd used and gently tipped the OTA until the nut was roughly over the hole. I then put a wooden skewer into the hole in the OTA to get the nut properly aligned. As it was the rear screw dovetail I'd undone I managed to put the OTA back onto the mount and slide it so the screw hole in the OTA was hanging off the back of the mount. This gave enough space for me to use a screwdriver to gently insert the screw try to get the two to marry up. Took a couple of attempts but eventually it bit.

One very fortunate design 'feature' of the OTA is that the seam where the two ends of the flat metal sheet meet once they're rounded to form the tube are adjacent to the hole. This meant that nut had something to push up against meaning I could apply some torque without the nut and bolt spinning together.

Some more gentle rotations got it to a point where it was seated enough to be able to nip it up properly.

Apologies for the rambling but I wanted to offer a different solution to the world that didn't require taking the OTA to bits!

P.S. As a note to anyone at Skywatcher/Synta who may ever read this, please God glue or weld those nuts in place. A dovetail is a very common thing to upgrade and using a standard Phillips head screwdriver makes it look very much like a user-serviceable part. I understand costs have to be saved but a spot of glue to hold it in place can't break the bank or add too much to labour costs.

[johninderby]

Just removing the corrector plate is easy and unlikely to affect collimation. Skymax180 but same internal nuts on the dovetail bar. On the 102 the corrector plate cell just unscrews.

Edited August 24, 2021 by johninderby

[vlaiv]

Been there, done that

Well, not actually that with SkyMax, but whole thing is very familiar to me.

I had 130m Newtonian scope and I decided to flock it and clean the primary mirror. Primary mirror cell is held in place by three screws - and those are screwed in some nuts.

Once you unscrew the screws - well nuts become loose

Fact that it is open tube - does help a bit, but not as much as you would think at it is almost meter long and not very wide. How on earth am I going to get the spanner in there to hold the nut while I put the screw back in?

In the end - it was DIY solution of very long wooden handle and taped spanner at one end

 

[JamesF]

19 minutes ago, johninderby said:

Just removing the corrector plate is easy and unlikely to affect collimation. Skymax180 but same internal nuts on the dovetail bar. On the 102 the corrector plate cell just unscrews.

Similar situation with the Skywatcher 127 Mak (screw-on cell).  I guess all of them are a very similar design.  I agree that taking the corrector off shouldn't be a major deal if you need to and if you should need to collimate afterwards, whilst I'd say it's not as easy as for a newt, it's hardly a nightmare.  Just takes a bit of patience.  In fact it's just occurred to me that setting the OTA up horizontally on the mount with a camera on a stand a metre or so in front, feeding a view of the front of the OTA back to a screen where you can see it whilst twiddling the collimation screws might be quite helpful as a way of getting things pretty close.  I'll have to try that next time.

In my case however, it's usually the nut behind the OTA that causes most of the trouble.

James

[johninderby]

Like the way Bresser fits the dovetail to their small maks. Just simply unbolts.👍🏻

Edited August 24, 2021 by johninderby