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Mark Henthorne

Allen head bolt won't budge

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I am about to defork my old 8" LX50. Before doing so, I decided to attach a Losmandy dovetail plate. The first three Allen bolts I managed to remove from the scope, all very tight, but once the initial "snap" was overcome, no problem. Radius bracket duly attached.

However, moving on to the second set of three bolts at the eyepiece end of the OTA, I could only remove two of the three bolts.

This last one just wouldn't budge. I've not only managed to put a barley sugar twist in the Allen key in my attempts, but also rendered the Allen key recess in the bolt head virtually useless, despite using the correct size key.

Now if this was something rather less delicate than an OTA, I would not be too worried about attempting a saw cut across the head of the bolt with a view to trying a conventional screwdriver. I suspect though, that whatever approach I take, the end result will be to lose the head shearing off, leaving the body of the screw in situ. In the greater scheme of things, that probably would not matter overly as the radius block would still be held in place with two bolts.

Any pointers from anyone who has found themselves in this situation and managed to resolve it, would be most welcome.

Mark

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If the allen key won't budge it, then a screw driver slot or mole grips are not going to work either.

The only thing I can sugget is to take the whole assembly to a bench vice, nip the bolt head in the vice, and turn carefully.

The vice will hold the bolt / the tube will give you enough leverage to have an impact.

Prepare yourself for the bolt to shear off if the worst happens and the threads still don't want to budge.

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The best penetrant I have used is Kano Kroil,its pink & it works-extremely well.

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Might not have Kano Kroil on the Isle of Man, is it also known as penetrating oil? That could be found in a good DIY, hardware or car spares shop.

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Another penetrating that you may find is called Plus Gas,  just be extremely careful about using these fluidsnear your optics. As I understand it, silicon based fluids can wreck optics ??

If you use the saw cut method it may snap the bot colse to the scope and leave you with nothing to 'grab' hold of.

I would grind / drill the head off the bolt this releases the tension on the bolt which can help. You should have enough of the bolt still protruding to allow you to use some grips.

Dave.

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If you can get on the head, the vice idea is a good one. Otherwise grinding or drilling the head off maybe the only option. If it wasn't such a delicate bit of kit there are other far more effective techniques to remove it.............

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Hi, I know it sounds wrong, but try to tighten the bolt ,then try and undo, this sometimes works if used with a penetrating fluid left to soak for a few hours.  John.

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I had a similar situation with an allen bolt holding the corrector plate retaining ring. The head was damaged and an allen key would not work, I tried an appropriately sized Torx type bit in a screwdriver holder and this worked for me. Once removed I slotted the bolt before refitting.  

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I have has this happen on a couple of the bolts on my LX10, once when fitting a bracket and once when deforking exactly as you are doing.  I used a hacksaw the first time and my Dremel with a disk the second time to cut a slot in the head both times and it did then come out without too much of a fight.  That said it was just the head that rounded out on both occasions; if you've managed to twist the Allen key then it must be tightly bound.

How about heating the bolt and then cooling it?  I wouldn't suggest a blowtorch on your scope, but maybe use a soldering iron on the bolt head for a while.  Heating and cooling might be enough to release the threads so the slot method would work.  Penetrating oil might help, (not WD40 which is a water dispersant, not a penetrating oil) but if you are going to leave it for a while to work orientate the scope so any oil that makes it inside the case doesn't then run towards the mirror or corrector before you can remove it.

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If the hexagon on the bolt is damaged then some of the suggestions probably won't work. I would try a mole grip, it won't twist like an allen key and you will have more leverage. If the head snaps off you will be able to remove the plate, this should expose some threaded portion for which there are other options for removal. :smiley:

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It sounds like the bolt in question was the first  one to be done up and has been subjected to lots of clamping force.

It may be prudent to cut / file the bolt head off and lift the dovetail plate off, this will relieve any residual clamping force. in addition you will have some of the bolt left protruding to get a good grip on, if it shears in the bolt hole it is likely it will shear flush and then you will be up the creak without a paddle.

A picture of your predicament would be useful so we can see the problem and aid better advice.

Good luck it sounds like you have a patient task on your hands.

Edited by Pig

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Thanks very much to all of you for the many replies above, especially IanL. Looks like I may finally have an excuse to go buy a Dremel! I remain reluctant to use any penetrating oil anywhere where I cannot be sure where it might go, so I have ruled that out. WD40 as was noted, is a water repellent only, and I only ever use that sparingly, wiped over the paintwork of the OTA, and never close to the optics. Unfortunately, the rounded nature of the bolt head does not lend itself to using mole grips. They'd likely work if I managed to file flats on opposing sides of the head. I suspect in the end, the head will shear, which at least will allow me to mount the second radius block for the Losmandy plate. I also noted a suggestion to "tighten", but unfortunately, I am a little late for that. I have a boxed set of bits for power driving, which as well as the Torx also included Allen heads, but no luck when I still had a recess that was undamaged. The heating idea with a soldering iron certainly has merit, but I am just a little wary of what might happen with the delicate nature of the OTA. So, to conclude, it looks like a Dremel to cut a screwdriver slot this weekend. The end result will either be a bolt removed, or a head shearing. Either way, I should be able to mount the second radius block and the Losmandy plate.

Thank you all again, and if anyone has any pointers regarding the deforking, that advice would also be very welcome. I have a new AZ-EQ6 GT waiting for this OTA.

Mark

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I've had success using... Wait for it... Large cutters, not to cut but positioned vertically, squeeze as hard as you can then try twisting :D

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ok another solution is to reinsert the 2 bolts and tighten them as normal  back to their original positions ,this may loosen the stuck bolt the fraction it needs , also the stuck bolt may need to be tightend first basically to " break " its seal and it will then hopefully  loosen off better . have used this method on big  pipe line wedge flanges , that realy get stuck ,

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It's really good to have so much input, and I hope return the favour in future posts. I will report back at the end of this weekend as to what happened and the methodology employed. Just for good measure, I have enlisted the support of an aircraft engineer and fellow astronomer, so hopefully the pair of us won't "muck up" in any major way on Sunday.

Mark

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If you can make a well to hold some fluid over night, maybe bluetack will do it,,,leave it soaking over night in Coca Cola (that's the fizzy drink) it will free it.....:)

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leave it soaking over night in Coca Cola (that's the fizzy drink) it will free it..... :)

Now that's one I've not heard before...

James

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How about trying a screw extractor? Never tried them so cannot say if they would be suitable in this case. Just Google and you get all the necessary info.

Never heard of the Coca Cola trick before. I do know that Coke used to contain Phosphoric Acid, don't know if it still does. That would attack any corrosion that might be the cause of stuck threads but I would have thought that the concentration of acid would be very low so any attack would be minimal. Perhaps someone here could do a quick ph test on Coke?

Nigel

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If the shaft of the bolt can be drilled a screw extractor could work. Used them a few times when I was in the RN

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Screw extractors are the work of the devil. If they snap (and most of the cheap ones will) then instead of a stuck bolt that can be drilled out, you are left with a chunk of high-speed steel than will blunt every drill bit known to man. Spark erosion then becomes necessary....

Take all your Allen keys that made out of a bit of bent steel and bin them. They are guaranteed to round off the head.

Invest in a good (Teng are very good and cheap)  Allen socket set like this

http://www.amazon.co.uk/Teng-M3812-Socket-Metric--Square/dp/B0001P0XMY/ref=sr_1_2?s=automotive&ie=UTF8&qid=1379585651&sr=1-2&keywords=teng+allen

These will not round the Allen head off. Bear in mind that tools wear out, so using the set of Allen keys that you've had for years are probably worn. The same applies to screwdrivers.

These will shift if as long as you haven't mullered the head already.

Forget cutting a slot and using a screwdriver. I can never fathom why people suggest this. It never works on a stuck bolt.

Forget WD40. It's a water dispersant, not a penetrating oil. Forget Coca-cola, unicorn tears etc etc ...if you want a penetrating oil then get a good graphited penetrating oil. Its highly likely though that that's not what is needed though, as penetrating oils are normally needed when the bolt has rusted. The likelihood is that the bolt might have a drop of Loctite on it. If so, try tightening it slightly first to break the bond.

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Interesting that a few people should mention that WD40 is a water-dispersant.  I've always considered it thus and been mildly irritated when people try to use it as a lubricant, but on reading the manufacturer's blurb about it these days it seems WD40 can do just about anything except make tea.

James

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 on reading the manufacturer's blurb about it these days it seems WD40 can do just about anything except make tea.

James

They might have a "slightly" vested interest in making these claims though.

Its really only a light machine oil with some perfume added. Smells nice though!

This is a proper penetrating oil

http://www.beal.org.uk/lubrication-cleaning/aerosols/graphited-penetrating-oil-aerosol/spray-400ml-/prod_3107.html

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I agree with Nigel - a left-hand threaded screw extractor may be your safest bet .... like these:

http://www.screwfix.com/p/screw-extractor-5-piece-set/18643

I had a similar problem once - domed head hex socket, rounded out and nothing to grip on the outside either.  I finally solved it by carefully drilling down through the head and into the body of the screw - hollowing it out.  I started with a small diameter drill and gradually increased the drill size till most of the core was removed and just a thin hollow shell was left. Removing material from the centre of the screw weakened it and I was able to remove it fairly easily by just jamming a flat blade screwdriver into the hole I had created and twisting it.   But after that, I invested in a small set of extractors and that's what I'd try first next time!

Adrian

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