| Author |
Message |
    
Lars
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 04, 2005 - 01:26 pm: | 
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I would appreciate if someone could give me some advice regarding removal of screws with treadlock applied. I am trying to dismantle a third party lens, but none of the screws can be undone. I have tried all sorts of solvents and even heat, but nothing works. More torque will only ruin the screws.
Any ideas are welcome. |
charlie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 04, 2005 - 03:15 pm: |
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If you know the brand used, the manufacturer may have some suggestions. |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 04, 2005 - 07:24 pm: |
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Acetone or MEK will soften all anaerobic threadlocks.The problem is keeping enough of the solvent on the screwhead long enough to ensure full penetration.Heat will also destroy the bond, but only if the temperature is high enough.I do not know how you applied the heat. The only method I have found to work is to turn up a copper rod to fit over the screwhead.The copper rod is heated with a micro propane torch.
Are you sure that threadlock has been used? The fit and thread form of some screws is such that when they are driven by powered drivers, they can really lock up.This is especially true when they are driven into soft alloys.
If the lens has seen a bit of DIY, it is more than possible that the threadlock is on the head of the screw also.It is this that causes the jam,more so than lock on the threads.
If you have a drill press the following method will remove the most stubborn screws without damage.Mount driver bit in chuck and position lens under bit using a padded wooden V block.Apply downward pressure on the screw using the drill handle and rotate the chuck to loosen screw.This is method I use to loosen really stubborn FD mount screws with worn + slots.With a good driver bit it works every time |
Stuart Willis
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 10, 2005 - 06:12 am: |
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Lars - I believe you are referring to set screws - otherwise known as grub-screws. Depending upon the camera model and the metallurgy these are now becoming a bit of a problem on 40 year old (+) cameras. The screws are mostly of brass or steel and in many instances (ie: most) are into female aluminium. Due to galvanic action (dissimilar metals) corrosion they are sometimes as though welded up forever. - and acetone (the standard medium for softening thread-lock varnish) won't help.
Some of those set screws can have aged and become brittle. Even the most perfect-fitting screwdriver which you MUST have, may do no more than break away
A good standard practice whenever seeking to remove set-screws on old cameras is apply a drop of WD40 on them and leave for a day or so before attempting to unscrew them.
Mostly you win. But if not the last resort is to apply a pencil-point butane torch on the aluminium section (if safe and pracical to do so). And then go straight to work with a perfectly fitting screwdriver and applying very firm downward pressure when unscrewing.
If you break away one side of the screwhead then you are looking at what can be a very difficult extraction job a requiring a high precision drill-press or mini-milling machine.
Drilling a perfetly axial hole down the centre of a 1.5mm steeel screw is not a happy-making task.
Hope this helps
Stuart Willis |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 10, 2005 - 04:42 pm: |
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If Lars was referring to grubscrews that have become seized through galvanic action, then the following method will allow their removal with 100% success every time.
Degrease each screw hole and then place one small drop of 25% acetic acid on the grubscrew. To prevent run off you may have to do individual screws. Leave to soak for up to 60 mins, renewing acid drop as required. Once acid has dissolved corrosion, remove grubscrew with proper driver.
Here in UK there is a domestic cleaner called 'Cillit Bang' that works just as well as the acetic acid. It is also great for removing corrosion from battery contacts/housings as well. It is meant to be for cleaning shower cubicles and removing lime scale.
I have used both the acid and more recently the cleaner with 100% success on many lenses.
The use of acetic acid in this way was given to me by an ex RAF fitter, who used to maintain the petrol engines in the high speed rescue launches. The alloy cylinder heads used to corrode onto the long head studs. When cylinder compression failed to lift the heads, he would build a Plasticine dam around each stud and fill with acetic acid. Left overnight the heads were easily removed next day. This war time expedient has proved very useful to me over the last 35 years in all manner of mechanical restorations. |
