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Canon FD 2.8-3.5 35-70mm repair problem
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PostPosted: Tue Jul 06, 2021 11:59 am    Post subject: Canon FD 2.8-3.5 35-70mm repair problem Reply with quote
I bought this lens recently and unfortunately it seems to have been damaged in shipment.
My money was returned and I am trying to fix it if I can. The focus ring would barely move
due to the threads being jammed up. I took it apart, but I am having a hard time putting it back
together. I can not get the parts to thread together. Perhaps the threads are damaged. As you can see they
are fairly thin. Any suggestions? The threads in the top photo look a little merged together, while the second
set look pretty good.


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PostPosted: Tue Jul 06, 2021 12:15 pm    Post subject: Re: Canon FD 2.8-3.5 35-70mm repair problem Reply with quote
uddhava wrote:
I can not get the parts to thread together. Perhaps the threads are damaged. As you can see they
are fairly thin. Any suggestions? The threads in the top photo look a little merged together, while the second
set look pretty good.

At first glance the threads look pretty OK. Unless you have quite a bit of experience re-mounting the threads the job may be a bit tricky. Before re-mounting I would clean the threads thoroughly, for instance with a soft toothbrush and a solvent like propanol or acetone (water and a good detergent may work as well if you've no solvents at hand): Sometimes some dust may inhibit the correct position of the two threads. It often helps if you

1) check the correct position of the two threads before trying to engage them (so that you know approximately the correct starting position) and

2) to turn the two treads in both directions while trying to re-engage them

Take some time, do not hurry ... after five or ten minutes you should have it.

S


PostPosted: Tue Jul 06, 2021 12:33 pm    Post subject: Reply with quote
Thanks for the tips!
One thing I noticed when I took it apart was lubricant on the threads.
Any idea how much to use?


PostPosted: Tue Jul 06, 2021 1:32 pm    Post subject: Reply with quote
uddhava wrote:
Thanks for the tips!
One thing I noticed when I took it apart was lubricant on the threads.
Any idea how much to use?


Depending on the grease you have (ie its viscosity), and depending on how precise the tread is machined, you'll need "a little", "very little" or "next to nothing" Wink

It may be helpful to put a little grease on a soft paper and then to rub it carefully into both treads.

S


PostPosted: Tue Jul 06, 2021 2:06 pm    Post subject: Reply with quote
I've received one of these lenses a while ago (it was cheap) and it had (and still has...) the same problem as yours due to a deformation of the focusing barrel which is not round any longer but ellipsoid. Until now, I couldn't solve the problem, and putting less or more grease doesn't make any difference. I guess the part with the meter and feet scale is just a little bit too thin and loses its shape too easily.


PostPosted: Tue Jul 06, 2021 3:06 pm    Post subject: Reply with quote
Alsatian2017 wrote:
I've received one of these lenses a while ago (it was cheap) and it had (and still has...) the same problem as yours due to a deformation of the focusing barrel which is not round any longer but ellipsoid. Until now, I couldn't solve the problem, and putting less or more grease doesn't make any difference. I guess the part with the meter and feet scale is just a little bit too thin and loses its shape too easily.


I put mine together now and it focuses, but very stiffly. While putting it together I noticed where it was especially stiff
and saw that the inside threads were flattened at that spot. Apparently someone dropped the lens on the side.
It is not very easy or pleasant to use so far.


PostPosted: Tue Jul 06, 2021 4:06 pm    Post subject: Reply with quote
uddhava wrote:
Alsatian2017 wrote:
I've received one of these lenses a while ago (it was cheap) and it had (and still has...) the same problem as yours due to a deformation of the focusing barrel which is not round any longer but ellipsoid. Until now, I couldn't solve the problem, and putting less or more grease doesn't make any difference. I guess the part with the meter and feet scale is just a little bit too thin and loses its shape too easily.


I put mine together now and it focuses, but very stiffly. While putting it together I noticed where it was especially stiff
and saw that the inside threads were flattened at that spot. Apparently someone dropped the lens on the side.
It is not very easy or pleasant to use so far.


Congratulations Like 1


PostPosted: Tue Jul 06, 2021 4:12 pm    Post subject: Reply with quote
stevemark wrote:
uddhava wrote:
Thanks for the tips!
One thing I noticed when I took it apart was lubricant on the threads.
Any idea how much to use?


Depending on the grease you have (ie its viscosity), and depending on how precise the tread is machined, you'll need "a little", "very little" or "next to nothing" Wink

It may be helpful to put a little grease on a soft paper and then to rub it carefully into both treads.

S


Thank you, Steve. I managed to get the lens back together, but unfortunately because of a flat spot
on one the side of the lens it does not focus smoothly. I don't know if there is away to fix that problem.


PostPosted: Tue Jul 06, 2021 7:24 pm    Post subject: Reply with quote
uddhava wrote:
I put mine together now and it focuses, but very stiffly. While putting it together I noticed where it was especially stiff
and saw that the inside threads were flattened at that spot. Apparently someone dropped the lens on the side.
It is not very easy or pleasant to use so far.


You could try re-cutting the thread.

I have successfully repaired a badly damaged filter thread using the thread cutting tool shown below (German term is „Gewindestrehler” – check out different types at Google or ebay). The tool has to match the thread type and pitch.

No machines needed, the re-cutting can be done by hand. It just takes some time. Carefully remove all metal shavings when done. It's certainly advisable to separate the part from the rest of the lens for cutting the thread.



PostPosted: Tue Jul 06, 2021 9:03 pm    Post subject: Reply with quote
fdlenses wrote:
uddhava wrote:
I put mine together now and it focuses, but very stiffly. While putting it together I noticed where it was especially stiff
and saw that the inside threads were flattened at that spot. Apparently someone dropped the lens on the side.
It is not very easy or pleasant to use so far.


You could try re-cutting the thread.

I have successfully repaired a badly damaged filter thread using the thread cutting tool shown below (German term is „Gewindestrehler” – check out different types at Google or ebay). The tool has to match the thread type and pitch.

No machines needed, the re-cutting can be done by hand. It just takes some time. Carefully remove all metal shavings when done. It's certainly advisable to separate the part from the rest of the lens for cutting the thread.


Interesting idea.
I may have some thread cutters sitting around somewhere.
Thank you
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