Primary disaster!

[Ricker]

Guess what? I have just been trying to remove my clips from my SW 250 and the first two screws I have tried have sheared. Felt tight but seemed to turn. Guess it was just the screw twisting. So I now have a mirror cell with 5 clips .

Think I will leave it at 5 for now but would ultimately would like to sort it out. Did you sort yours Jez? If so how?

My first thoughts are to contact my brother in law to see if he can sort it (works in an engineering shop). But this will require me removing all other clips. I am very cautious now as the other clip screws seem to be equally tight. Is this normal?

Rich

[mitchelln]

I believe the screws are held in with a Loctite type substance. I guess SkyWatcher are worried that if the screws become loose the mirror may shift and get damaged. So they effectively glue them in.

[kirkster501]

My SW Dob 12" version has three clips..... Wonder why a smaller mirror version has six ?

[Zakalwe]

Tigthen them slightly before trying to unscrew them. This will break the seal on the threads. And then back them in and out as you unscrew them. If there is Loctite on the threads it will build up and jam the thread as you unscrew it (and hear the bolt).

[umadog]

As the others have said: don't worry about it. Tiny, tiny mark. Paint over it, though, so it can't scatter light where you don't want it. I have a mirror with much worse damage than that and it performs very well.

There is a lesson for others, though: when working around a mirror and removing screws, always put a soft cloth over the mirror.

[Sky Clad]

As an aircraft maintenance engineer, sheared bolts are quite a common thing when you consider how many screws and bolts hold them together!

Generally the smaller the shank of the bolt, the harder it is to get out, so if you have to drill it out and damage the existing threads in the process, it isn't the end of the world. You can just drill out the offending 'stub' and re-tap a new, (but oversized) thread, and simply fit an oversized bolt to suit the thread you have just cut.

Alignment of the new hole you are drilling should not be a problem provided you take care and drill out the old stub as slowly and centrally as possible. If during the initial stage of drilling, the hole you are cutting is appearing to be getting 'dragged' over to one side, then angle the drill (by leaning it) back to where you need it to go by about 30 degrees until it looks like the cut is going down the middle of the offending stub.

Hope that all makes sense!

I never cease to be amazed at the amount of people whom overtighten bolts unnecessarily, however if a thread locking glue has been used it can be a real pain, and I think there isn't a huge amount that you can do about it unfortunately.

Hope you have it all sorted now and without too much further drama

[Moonshane]

I'd certainly recommend stainless steel replacements if you ever take them out.

[Zakalwe]

I'd certainly recommend stainless steel replacements if you ever take them out.

Most SS bolts (grade A2) are softer than ordinary mild steel and are even easier to shear/round the heads off. If you go for this route, then specify grade A4 (marine grade). Much tougher.

[glowjet]

Rich, if you can live with it for a while, I would do so until such time that you want to remove the mirror to carry out maintenance / flocking etc. Trying to drill out broken studs is not an easy matter, if you have had no previous experience, especially if the surrounding material is soft, your drill can wander and you end up with a hole far larger than you intended. If, as you say, you have a Brother in law as an engineer, who will have machine shop tool facilities I should take the matter up with him, as at the appropriate time you can remove, or break, all the screws and then he should be able to drill out and re-tap for some new stainless steel ones

[1parsec]

If a high grade retaining compound loctite is used it can make getting fasteners out again a bit of a headache.

Anything stronger than 222 grade causes a lot of grief on fasteners.

I have often had to use some heat the area which softens the loctite and usually allows bolts to come out much more easily.

The part needs to be heated to 180 degrees + to do the job. A hot air gun / electric paint stiripper can be used.

Obviously some paint may be effected but this is and easier job to touch up than struggling with drilling out sheared bolts etc.

Dave.

[jetstream]

If those bolts are loctited the the heat may help...depends on the grade of loctite.To remove broken bolts,stripped etc -if nothing else works I use my TIG welder to weld a nut onto bolt stub & unscew,the heat helps loosen the bolt and soften the loctite.BUT-you have to watch warpage issues on what your welding,with this small off job though it would only take about 5 sceonds of welding after prep.Its handy to know someone with a welder.Drilling and tapping works too,but if the bolt is in aluminum (soft) then it can be hard to maintain exact alignment of new hole.All depends on the accuracy needed on the job.

[jetstream]

I forgot something too-my buddy has a impact torque driver for small bolts & screws.Once tightened the driver can be adjusted to give the proper torque(& bolt stretch) when it is hit with a brass mallet.But here is the really good part-if something is stuck or frozen-STOP-before the screw head is damaged, put the right scewdiver bit in driver,set driver the "other" way-loosening mode & giver a light smack.He has bailed me out with this thing lots & between the two of us most bolts come out.You bolts are sure bent(some) I would do some checking of the threads with new good bolts. Other replies are great-as in drilling new holes in another spot & tapping or using less clips etc.A bunch of good solutions here.

[jezhughes]

Guess what? I have just been trying to remove my clips from my SW 250 and the first two screws I have tried have sheared. Felt tight but seemed to turn. Guess it was just the screw twisting. So I now have a mirror cell with 5 clips .

Think I will leave it at 5 for now but would ultimately would like to sort it out. Did you sort yours Jez? If so how?

My first thoughts are to contact my brother in law to see if he can sort it (works in an engineering shop). But this will require me removing all other clips. I am very cautious now as the other clip screws seem to be equally tight. Is this normal?

Rich

Hi mate

I left the broken one in, tightened with the 1 remaining screw on that clip so effectively have 5 1/2 clips. 1 clip really doesnt matter in my opinion. I haven't used my newt properly since as i have a focuser replacement to make, but the mirror still sits rock solid in the seat and i'm happy with just the 5 clips. Have done a few visual tests and haven't noticed any difference. apart from my awful collimation ..

[jezhughes]

Hi mate

I left the broken one in, tightened with the 1 remaining screw on that clip so effectively have 5 1/2 clips. 1 clip really doesnt matter in my opinion. I haven't used my newt properly since as i have a focuser replacement to make, but the mirror still sits rock solid in the seat and i'm happy with just the 5 clips. Have done a few visual tests and haven't noticed any difference. apart from my awful collimation ..

also to add, i flocked the back of my primary too which has seated the mirror even firmer in the base. i could probably take all the clips out and it wouldn't go anywhere!

[Tinker1947]

If you haven't managed to release the screws yet,,,,use something like bluetack to make a fliud tight well around the screw/s then pour in some Coca Colo (that the stuff people drink) leave over night and there come out the next day.....