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I've got screws loose... (macro takumar 50mm)
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PostPosted: Fri Jan 04, 2013 2:51 pm    Post subject: I've got screws loose... (macro takumar 50mm) Reply with quote

My beloved macro takumar 50mm preset has a wobbly aperture ring. This already happened before and the solution was to open up the front part and tighten 3 screws but after a year of no problems at all the wobbling started again and after opening I realized 2 out of 3 screws no longer fasten. I didn't look yet if it is the thread in the holes or the thread on the screws that's broken..
I have a picture from last time I was able to fasten the screws and when I open it up again I will make some decent pictures of the screws themselves (have to use some other macro lens though Crying or Very sad )

macro takumar opened by margreetz, on Flickr

What to do? Are these takumar screws standard size? Do I need to put in a screw just a little bit bigger? Any experience with either screw thread issues in general or specific this lens-issue?


PostPosted: Fri Jan 04, 2013 4:49 pm    Post subject: Reply with quote

Sounds like you tightened the screws too much.

The proper way would be to use a tap to make a slightly larger thread and use a wire thread insert, Helicoil or similar, but I'm not sure
they are available that small, 2mm is the smallest I think. Before going that far you could try glueing the screws with Araldite or similar
epoxy glue, it's still possible to loosen the screws, or you could try some thread locking fluid such as Loctite. I've even in the past
wrapped a tiny piece of aluminium foil round the screw and it's held OK.


PostPosted: Fri Jan 04, 2013 5:46 pm    Post subject: Reply with quote

peterqd wrote:
Sounds like you tightened the screws too much.

The proper way would be to use a tap to make a slightly larger thread and use a wire thread insert, Helicoil or similar, but I'm not sure
they are available that small, 2mm is the smallest I think. Before going that far you could try glueing the screws with Araldite or similar
epoxy glue, it's still possible to loosen the screws, or you could try some thread locking fluid such as Loctite. I've even in the past
wrapped a tiny piece of aluminium foil round the screw and it's held OK.


Thanks for your reply. I have only tightened the screws one or two times and was careful to not tighten to much because they are such delicate small screws. Sadly though this happened anyway, I am not the first owner so who knows really what happened to this lens from around 1965? When I got the lens it seemed to look pristine, both the screws and the lens in general.

My better half (and more technical inspired half) suggested loctite as well but I kinda like the aluminum foil idea! It is for sure the best start to try out because I'd rather do minimal permanent changing to the lens itself to get it working again.


PostPosted: Fri Jan 04, 2013 6:40 pm    Post subject: Reply with quote

Put Loctite 222 in the holes, a very tiny drop on the tip of a needle will be enough, blow out the dust first, apply some silicone oil to the screws and wipe the surplus off - all you want is the thinnest smear. Then put the screws back in the holes. The Loctite should set and bond to the body of the lens and less so to the screws because of the silicone.
I've used this method with good results.
If it was my lens and I wanted to keep it and it was unlikely to require taking apart again, I would just use the Loctite 222 and not bother oiling the screws.

Loctite 222 - is lower strength to allow removal.
http://uk.rs-online.com/web/p/pipe-thread-sealants/0514509/


PostPosted: Sat Jan 19, 2013 12:24 pm    Post subject: Reply with quote

Thanks!
I did some work on it and put in the screws with some loctite. I first tried with some alu foil, it did hold but only until I tried to turn the aperture ring. When I first got this lens I already read multiple internet blogs / forums showing the same problem and I now completely get why these screws are a problem.
The cone shaped part constantly rubs the heads of the screws every time the stop down aperture is used and the holes where the screws fit it actually consist of two layers that both can move slightly when using either one of the aperture rings. So in fact the screws get bumped, moved and wiggled constantly when using the lens.


macro takumar front part open by margreetz, on Flickr