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The sickening crunch of breaking kit.


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HI ALL

Last night I had something of a disaster, there I was, stood out in t' cold getting ready to see if I could get my recently purchased Neximage 5 to take some pretty pictures of Jupiter. I was just adjusting my telescope (A bog standard Sky Watcher 200P Newt on an EQ6 Pro mount) to get the image centred and focussed when there was a loud crack, followed by a second as the two bolts securing the telescope rings onto the dovetail bar both snapped. Needless to say, telescope camera etc hit the deck with the aforementioned sickening crunch. I suspect that it must have landed camera first, this is not going to be taking pretty pictures of anything, it is dead, deceased and definitely not just asleep !!  The finder- scope similarly is a write off I suspect, the objective lens having detached itself tho somehow not broken. Somehow the telescope itself seems to have survived ok. It was half full of gravel and the collimation was knocked out of the park, but the mirror looks ok and the focuser still appears to work.

I am always careful about balancing the telescope, having the correct weights etc so I am at a l;oss to know what if anything I did wrong. I suspect not a lot, after all the telescope was not in motion when it went. So  has this happened to others ? is it one of those things where everyone tells you how your model is well known for self destructing or whatever, and you wonder why nobody told you before you bought it.

If this was just straight mechanical failure, one of the bolts had some hidden weakness or something then I am bothered. My other scope is a Sky watcher 300 on the same EQ6Pro mount. The assembly of tube rings, dovetail bar etc looks equally vulnerable, whilst the dt bar is the wider, Losmandy type, the rings are still only attached by a very similar two bolts. The bolts are a bit bigger though not massively so (M10 rather than M12) though the scope weighs very much more, being at the limit of what an EQ6 can carry. However the assembly is presumably designed and built to carry the weight it says it can carry and presumably the bolts SHOULD be strong enough. I know hidden defects can be there, and if one bolt goes, the other has no chance.

So at last my question. Is there any alternative and perhaps stronger way of attaching the scope to the mount.  Any thoughts mot gratefully received, and my apologies for being so long winded.

NEIL

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One bolt might go but two ??

That is a different matter and has to be something other then a chance "breakage".

All I can think of is both were tight and contracted in the lower temperatures and so snapped. I suppose if both were at a simialr tension then one going could put additional stress on the other and so that followed suite.

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Ouch! :(

I got my Skywatcher 10" Newt about 18 months ago.

One of my first observations was that I really don't like the whole dovetail arrangement for bigger scopes. It's not a method of mounting that I'd have invented. 

But whatever method is used would still likely employ just a pair of bolts to secure the rings.

I don't use mine so often and don't add any expensive kit but I'd really be nervous about doing so on the bog standard kit.

Sorry, I've got no useful advice.

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That's really bad luck. Never heard of an issue with these bolts before, though the t bolts for adjusting the mount to match your latitude have had some bad press. We're all going to be worrying a bit now I suspect and maybe looking into replacements. When you think of the really expensive kit relying on the two bolts it makes sense to look into it. Thanks for posting and hope you get the majority of your kit sorted soon. Might be covered on your home insurance if you have accidental damage.

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I would expect just one bolt to be adequate to hold the scope to the dovetail (a bit of a play with http://www.tech.plymouth.ac.uk/sme/desnotes/boltb.htm shows the breaking strain of most bolts to be measured in tonnes) so for both to go it would presumably either be a common fault in manufacturing both bolts or a fault in assembly. While their breaking strain is tonnes it's remarkably easy to put massive strains on a bolt by overtightening them.

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Thus far, Ronin has the most plausible explanation - the cold pushed the envelope past the breaking point. Get photographs, please. And I'd be furious that this could happen - and make certain the place of purchase knew this too! A shrug and a "Too bad" would be met with a reminder that in this age of internet and wide-range ability to spread the word, it's not wise to leave customer concerns un-adressed and/or ignored.

You'll recover,

Dave

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One bolt might go but two ??

That is a different matter and has to be something other then a chance "breakage".

All I can think of is both were tight and contracted in the lower temperatures and so snapped. I suppose if both were at a simialr tension then one going could put additional stress on the other and so that followed suite.

Good shout. This seems the most plausible explanation to me.

Feel for you, OP - the stuff of nightmares.

Regards

John

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One bolt might go but two ??

That is a different matter and has to be something other then a chance "breakage".

All I can think of is both were tight and contracted in the lower temperatures and so snapped. I suppose if both were at a simialr tension then one going could put additional stress on the other and so that followed suite.

My first thought was this. Still have to be very unlucky to have both snap though. I'd like to bet there's more chances of winning the lottery.

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My sympathies, and as others have said, for both bolts to go is unfortunate in the extreme.  I would have thought that one bolt would hold in place until you could, at least, get the scope off the mount.

Thanks for sharing the experience, I won't be tightening bolts quite so hard myself now.  Hope you get yourself sorted out with replacement equipment soon. 

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Presumably it should be possible to attach a third and possibly fourth ring at either end of the dovetail, meaning attachment by 3 or 4 bolts rather than 2??

This is what you want. Works like a dream.

http://www.peak2valleyinstruments.co.uk/page_3175728.html

Looks like a nice piece of kit and worth investigating, but seems to be addressing the weakness of the dovetial-to-puck clamping system rather than the weakness of dovetail-to-rings attachment?

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very strange that 2 snapped, must be a fault with the bolts. if you over tightened them the threads would of failed first, temperature wise not a problem, than less you was using your scope at -20. or do others on here expect there wheels to fall off there cars if its cold out side. as you say m10 thats a big bolt to shear

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Thank you all very much for your helpful comments and sympathies.  I spoke to the Insurance Fairy today, and as it is a first claim they will pick up the tab to replace any bent or broken bits with no excess, so I can at least replace the camera , this is very dead the bout that I assume is the sensor chip is in several bits.  I will certainly take some photos and post them ( If I can work out how ). Its now nearly 2 am so I will leave it until tomorrow.

I have been trying to remember exactly what happened. The scope had just stopped after slewing onto Jupiter. As I reached out to focus, there was a surprisingly loud crack and one end of the scope lurched down, I tried to catch it, but before I could do so there was a second crack and we were on the deck. Fortunately It fell onto our gravel driveway, I was not in my usual place on solid concrete. I think gravel is a bit better to fall onto.  I can only assume that I must have over,tightened the bolts, a few days ago they had worked loose so I did tighten them up, but hey, I am no superman believe me, and snapping bits of steel has never been my party trick.

From everyones reaction, this sounds like a very odd thing to have happened after all A Sky-Watcher 200mm is no great weight, had it been the big 300mm one I would have been less surprised, that weighs a ton. I will certainly be taking the precaution of adding a second set of rings. So clearly this was very out of the ordinary and needs more looking into.  I will take photos and return.

Thanks again 

NEIL

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very strange that 2 snapped, must be a fault with the bolts. if you over tightened them the threads would of failed first, temperature wise not a problem, than less you was using your scope at -20. or do others on here expect there wheels to fall off there cars if its cold out side. as you say m10 thats a big bolt to shear

Having been in the mechanical field most my working life I must say this is simply not correct. Bolts frequently snap at over torque and seldom strip the threads, unless very soft material is used in their making. One result of over torque is crystallization of the metal. It makes perfect sense that if both were over done, one more than the other, perhaps, and then the cold overloaded the weakened bolt, the stress of the twisting as the first one failed, would probably finish off the other.

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That is tragic Neil, but with a positive outcome. I am sure Kalisinman is on the right track, I was also in the engineering industry for some years and would agree that the failure of one bolt, would stress the other to the point of collapse especially trying to hold the twisting motion of a 200P. But in my view the cause lies with the BOLT. Long we have laughed at the Chinese bendy bolts that need to be replaced, is this just a freak accident, or should we all now be wary of  Chinese bolts in general. Personally, I do not trust the quality of Chinese bolts, they are poor quality and where they are fitted to parts which come under any stress, I replace them with quality stainless steel. This just might be a one off accident, or will it happen again ?  who knows, With this knowledge, those with expensive camera/scope set ups can at least ensure that bolt failure won`t happen to them in the future :)

.

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That is tragic Neil, but with a positive outcome. I am sure Kalisinman is on the right track, I was also in the engineering industry for some years and would agree that the failure of one bolt, would stress the other to the point of collapse especially trying to hold the twisting motion of a 200P. But in my view the cause lies with the BOLT. Long we have laughed at the Chinese bendy bolts that need to be replaced, is this just a freak accident, or should we all now be wary of  Chinese bolts in general. Personally, I do not trust the quality of Chinese bolts, they are poor quality and where they are fitted to parts which come under any stress, I replace them with quality stainless steel. This just might be a one off accident, or will it happen again ?  who knows, With this knowledge, those with expensive camera/scope set ups can at least ensure that bolt failure won`t happen to them in the future :)

.

I would suggest that a bendy bolt wouldn't crystallize, I've seen this kind of reaction from over heat treated bolts that become brittle. It's all in the past now. Sad, but could have been worse. Stainless bolts are a fine idea. Marine supply places and now most home supply shops have.

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I would expect just one bolt to be adequate to hold the scope to the dovetail (a bit of a play with http://www.tech.plymouth.ac.uk/sme/desnotes/boltb.htm shows the breaking strain of most bolts to be measured in tonnes) so for both to go it would presumably either be a common fault in manufacturing both bolts or a fault in assembly. While their breaking strain is tonnes it's remarkably easy to put massive strains on a bolt by overtightening them.

Tensile strength is usually quoted in M or GN/m^2. So for a bolt of cross sectional area of just a few millimeters... Overtightening would do it, but it would have to be quite a lot, and then you'd still be unlucky if they broke. So, I agree that the bolts were probably Rubbish. Doesn't help the OP , sorry.

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Sorry to here about this but glad the insurers are going to help, and without an argument too. I'd be really sick if it happened to me.

I assumed, that as things got colder then everything contracts. Would it not be feasible that the bolts are not the main cause? They would contract but what they were screwed into/through contracted quicker/more thereby compressing/stretching the bolts (different material contracting at different rates etc) and this caused the bolts to fail?

I'm no engineer and it obviously isn't going to help the poor OP but an understanding of why it happened may help the rest of us.

Regards

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