Damaged screw-thread

[carregwen]

Can anyone suggest a solution to a jammed screw-thread?

I have a Sigma DG UV screw-on filter and a Cokin Z-Pro adaptor ring. One screws into the other. Both are 77mm thread. I am normally extremely careful and don't do them up tight. But they are stuck fast - I think there must be some grit in the thread. I tried a rubber tourniquet, and I tried placing it flat on a rubber surface then pressing down and tuning the top one. Didn't budge. I thought of heating them in warm water, but wouldn't they both threads expand?

It costs £70 for replacement. Of course, I could just change over the UV with filter ring attached when I want it on a different lens.

[Radu Dinu Cordeanu]

Hi,
I see you had nothing to do! Well!Usually cooling suddenly with liquid nitrogen.You may try pooring a small quantity of fluid oil or heating it.
Success!!!!!

[Donald]

Can anyone suggest a solution to a jammed screw-thread?

Regretfully, no.

The thought of this happening has struck me previously, along with a realisation that I do not have the knowledge or skill to do anything about it, other than get angry and say lots of naughty words. Please do tell if and when you get a solution.

[Dave Humphries]

Hi Rob,

Temperature may provide a solution, as you say, you need a differential so, either cool the inside one, or heat the outside one (compared to ambient temp of the other side), which will require carefully holding half the assembly in a cold or hot liquid, or pressed against a surface that is cold or warm.

If plastic, the use of a penetrating oil (like WD-40) might have nasty consequences, but if metal, should be ok, the knack being to get it into the thread, not all over, so grip is further reduced.

Was the "rubber tourniquet" you used one of those "stuck jar lid remover" things, or just rubber bands? The former (I always have one in my gadget bag) might be easier to use.

Or sacrifice the cheaper half by cutting it?

Good luck, (I have a feeling you will succeed eventually - desparation will lead to 'nothing to lose' application brute force)

[Steve S]

Have you tried a rubber strap wrench. They have lots of grip and won't scratch anything.

[Colin Southern]

I've had the occasional similar thing - my biggest observation is that any pressure on the outside of the ring just makes it worse, but if you can secure one of the rings without attempting to distort the ring then it usually comes off without too much of a fight.

So in order of desperation ...

1. face up on a rubber mat,

2. try to stick the ring to a flat surface using some kind of tape (eg duct tape) (wrapped right around the surface "in reverse" (ie sticky side up)

3. cut two small notchs through the thread 180 degrees apart, and use something like a steel edge as a giant screwdriver

Ideally you want something that allows opposing torque on the threads, but without any kind of compression (expansion would be ideal).

[carregwen]

Have you tried a rubber strap wrench. They have lots of grip and won't scratch anything.

Yes, I tried one of those and I put quite a bit of pressure on it.

[carregwen]

try to stick the ring to a flat surface using some kind of tape (eg duct tape) (wrapped right around the surface "in reverse" (ie sticky side up)

Ideally you want something that allows opposing torque on the threads, but without any kind of compression (expansion would be ideal).

I thought of drilling two holes through the adaptor ring, it won't affect the use of it as an adaptor ring, then screw it to some timber. That will make it solid, but how to turn the UV filter is the problem.

[rick55]

The idea of one warm, one cool, sounds to me most likely to relieve it. I take it the adaptor is the inside threads, and the filter is outside? You could set the adaptor in cold water, and pour warm water into the filter. If it's plastic, you'll have to refresh the warm water repeatedly, which will be a pain, but plastic conducts heat so slowly that you need to give it time.

I don't know how much advantage you'll get from screwing the adaptor to a piece of wood, since you're probably already getting more torque on that than on the filter. But it might make it easier to deal with. The holes don't have to be across a diameter: if you drill two holes on the same side, the wood won't be in the way of getting at the filter.

Good luck;
Rick

[carregwen]

OK, I got it off. If the same thing happens to you, and you get desperate, you might want to try this at home.

1. Drill a small hole either side of the flat flange area of the adaptor ring, as shown below at points (A).
2. Screw the adaptor ring to a piece of timber.
3. Clamp the timber to a work surface.
4. Drill a small hole in the side of the UV filter as shown at point (B). Be careful you don't run through and break the filter glass.
5. Using a small old phillips screw-driver, or some pointed tool, and place tip in the hole. Holding the tool at an angle whack the end of it with a hammer. Make sure you are going the right way to unthread it - not tighten it further!
6. If it happens again, just put it back on your rig and give it another whack.

That's the thing about CiC - we tell people how to respect their gear.

I can't believe it was that tight - I hit it pretty hard. The threads seem OK.

I'll count that as a plus point for today.

YOU READ THIS PATENTED METHOD HERE FIRST!

[Donald]

That is amazing. Reading that brought the broadest smile I've had for a while.Sure isn't something I've never seen in any of the Canon user manuals!

But - good on you. You're a braver man than I. But now that we have the (illustrated) instruction manual - Bring it on ... as they say!

[carregwen]

That is amazing. Reading that brought the broadest smile I've had for a while.Sure isn't something I've never seen in any of the Canon user manuals!

But - good on you. You're a braver man than I. But now that we have the (illustrated) instruction manual - Bring it on ... as they say!

Kind word, Donald, but I doubt that either Colin or Sean will like me advocating whacking a £60 UV filter with a hammer and screw-driver!

[Steve S]

Glad you got it apart OK. Perhaps a little lube on the threads will keep this from happening again.

[rick55]

So once your subtlety paid off, were you able to figure out what caused the problem? E.g., was it gritty as you continued unscrewing it?

Cheers,
Rick

[Colin Southern]

I thought of drilling two holes through the adaptor ring, it won't affect the use of it as an adaptor ring, then screw it to some timber. That will make it solid, but how to turn the UV filter is the problem.

Hi Rob,

I know that this is redundent now, but I was actually meaning to secure the UV filter with my suggestion ... I'd figured it would take the compression off the threads, and that you'd be able to generate enough torque on the adaptor by hand anyway..

[carregwen]

Glad you got it apart OK. Perhaps a little lube on the threads will keep this from happening again.

Thanks, Steve. I'll add that one to the wife's monthly lube rota!

So once your subtlety paid off, were you able to figure out what caused the problem? E.g., was it gritty as you continued unscrewing it?

It felt a little gritty. I gave it a brush, and I may smear it gently with oil. I go down the beach a lot, and the sand is very fine. Maybe it was that.

I know that this is redundent now, but I was actually meaning to secure the UV filter with my suggestion ... I'd figured it would take the compression off the threads, and that you'd be able to generate enough torque on the adaptor by hand anyway..

I tried that, Colin. I've been told in the past that by applying pressure in too specific a point(s) you actually make it more difficult as you increase the pressure. The thread on the UV that was stuck is 'female' so squeezing it too much could make it more difficult, as far as I could see. Ideally, you would want to heat it and expand it, without affecting the 'male' thread on the adaptor. When I tried it, I secured the UV in a soft all-round clamp then used one of those rubber grip mats wrapped around the adaptor ring and tried turning it by hand. I hurt my hand and it wouldn't budge. The hammer did it! By hammering the UV there is hardly any pressure on the thread of the UV, and because the adaptor is screwed to a base its thread is not effected either. It works, but you need to be bold.

[Bill44]

The secret to non stick is a very small amount of finely powdered graphite smeared on the threads.

[Steaphany]

This happened to me a while back.

I found a dealer selling aluminum filter covers which are used to cap the ends of a stack of filters. I bought them to save space by replacing my collection of filters occupying a variety of manufacturers cases into the volume and shape similar to that of a lens. Well, that part worked as planned.

About a week or so later, it's a warm afternoon and I decide I need a filter that's located about the middle of the stack. I unscrew one side and that goes as planned, now comes the surprise, I try to release the needed filter from the remaining stack and it's stuck. Fearful that these two may not be the only stuck pair, I completely disassemble the filter stack and return the filters to individual cases. Ok, it's just a single pair of filters that I have to deal with, but these are not cheap UV protection filters but more costly specialty filters. Well, no matter how much torque I apply, the pair is fused solid. With frustration mounting, the thought of shooting the photo I had originally in mind long gone, I decide to put the filters down and try later when I'd be less likely to break the filters as my mood evolves to anger.

The following morning, it's nicely cool from the prior evening, I pick up the filter pair, and with the slightest finger tip torque, they turn. No effort at all and nothing like the prior day's horror.

I'm suspecting that even though both filters had aluminum frames, being from different manufacturers, they could easily have been manufactured with different aluminum alloys possessing different thermal expansion rates. I have not done specific testing to prove this out, but it would explain my experience. Another factor would have been if the morning's ambient temperature was too cold moving the filter pair from a warm too tight through the safe zone into a cold too tight state.

My recommendation is for photographers to note the temperature when they assemble lens and filter elements. Later, if the temperature is warmer or colder and you find something stuck, try to return the pair to the temperature when they were assembled. This will work, even if you have no temperature gradient between the two, because the alloy differences will provide the needed effect.

Rob,

Do you recall the ambient temperature when you put the Sigma DG UV screw-on filter and the Cokin Z-Pro adapter ring together versus the temperature later when you were trying to get them apart ?

[Wirefox]

Marigold gloves! I will leave the rest to your imagination

oh and Rudu's nitrogen suggestion will work provided it is only applied to one of the components...unless of course they are disimilar metals/alloys

Steve

[Colin Southern]

oh and Rudu's nitrogen suggestion will work provided it is only applied to one of the components...unless of course they are disimilar metals/alloys

... assuming that he doesn't get a nasty burn to fingers or eyes as it boils violently as it comes in contact with the much warmer metal (or the glass doesn't shatter from being cooled so violently)

Honestly - when it comes to liquid nitrogen, my advice is to keep a healthy distance away from it