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Source for new Canon bushings to replace the worn?
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PostPosted: Mon May 24, 2021 7:05 pm    Post subject: Source for new Canon bushings to replace the worn? Reply with quote

From http://forum.mflenses.com/viewtopic.php?t=82727
fdlenses wrote:
...
Of course, this lens had worn focusing bushings:



Is there any source (yet) for replacement bearings? Do all Canon lenses with these bushings use the same size?


PostPosted: Tue May 25, 2021 2:00 am    Post subject: Reply with quote

This would be really interesting to know ,as I've got some nFD with issues


PostPosted: Tue May 25, 2021 10:02 pm    Post subject: Reply with quote

Answering a question about the technique used for restoring bushings shown in another thread:

I have restored these bushings by “recoating” them with heat shrink tube. Adding one or two layers (depending on the bushing type) happens to match the original diameter pretty closely. The slots the bushings fit into are 4 mm wide.

I have no experience with long term durability, though.

  • I do not know how well the new rubber coating keeps sticking to the metal core after some use, especially for the smaller size bushings. Self-adhesive heat shrink tube could be worth trying.
  • I do not know if the rubber is resistant to lubricants in the long term. I can, however, tell that the no-name brand tubes I have used do resist exposure to excessive amounts of naphta and PTFE grease for at least a few days. I remember someone recommending the “clear plastic” heat shrink tube type for its better resistance to lubricant. Still have to try that.
  • I do not know how fast the rubber is going to wear.

But I would rather restore the bushings every other year than having a loose floating element in a high-end lens. My lenses do not see a lot of use anyway.



I have also tried machining new bushings. Or rather I had a friend machine them for me:



IIRC the material is Polyoxymethylene (I will have to ask my friend again) which should be durable and resistant. Machining them required very sharp tools. Unfortunately, I do neither have the skills nor the tools for machining bushings as I need them.

I always wanted to try 3D-printing but haven't yet. Creating 3D models of the bushings would be rather simple. But again I don't know how resistant/durable the 3D printing filament would be.

BTW, a questions to the English native speakers: What is the proper term for these parts? Is it “bushing”, “bearing”, “guide roller”? Are all terms equally good?

BTW2, heat shrink tube is also good for replacing this “bumper” of a Canon T90 mirror box:



PostPosted: Wed May 26, 2021 3:27 am    Post subject: Reply with quote

They are called Cam followers.

https://patents.google.com/patent/US6549341B2/en


PostPosted: Tue Jun 08, 2021 11:35 am    Post subject: Reply with quote

Most interesting thread for users of canon lenses. Any step by step procedure per lens explaining how to proceed (possibly with pics or video) would be invaluable and would deserve a sticky if you ask me.


PostPosted: Sat Jul 10, 2021 6:29 pm    Post subject: Re: Source for new Canon bushings to replace the worn? Reply with quote

visualopsins wrote:

Is there any source (yet) for replacement bearings? Do all Canon lenses with these bushings use the same size?


What are the approximate dimensions? Inner diameter, outer diameter, length?

S


PostPosted: Sat Jul 10, 2021 6:45 pm    Post subject: Re: Source for new Canon bushings to replace the worn? Reply with quote

stevemark wrote:
visualopsins wrote:

Is there any source (yet) for replacement bearings? Do all Canon lenses with these bushings use the same size?


What are the approximate dimensions? Inner diameter, outer diameter, length?

S


Good question! (I don't have any f these lenses; just thought the topic would be of interest to those who do have them)

It occurs to me surgical tubing of correct dimensions stretched over the metal core may work better, last longer, than shrink tubing.


PostPosted: Sat Jul 10, 2021 7:49 pm    Post subject: Re: Source for new Canon bushings to replace the worn? Reply with quote

stevemark wrote:
What are the approximate dimensions? Inner diameter, outer diameter, length?


Outer diameter is 4 mm (for every type of cam follower I have encountered so far). Inner diameter is 2mm (there might be a second slightly smaller size, I am not sure). Length is 3.7 mm for the cam followers. Length is 1.5 mm for the type of cam that connects the focusing ring to the actual focusing helicoid. Some types have a recess the screw head goes into.

visualopsins wrote:
It occurs to me surgical tubing of correct dimensions stretched over the metal core may work better, last longer, than shrink tubing.


For some types the metal core has not a simple tube-like but a more irregular shape. For those I use up to 4 different sized pieces of shrink tube in 2 layers, the smallest one only about 0.5 mm wide. I am wondering if surgical tubing might be too soft to stay in place at these small dimensions. I have never tried it but it seems to be rather soft, isn't it?


PostPosted: Sat Jul 10, 2021 8:07 pm    Post subject: Re: Source for new Canon bushings to replace the worn? Reply with quote

fdlenses wrote:
stevemark wrote:
What are the approximate dimensions? Inner diameter, outer diameter, length?


Outer diameter is 4 mm (for every type of cam follower I have encountered so far). Inner diameter is 2mm (there might be a second slightly smaller size, I am not sure). Length is 3.7 mm for the cam followers. Length is 1.5 mm for the type of cam that connects the focusing ring to the actual focusing helicoid. Some types have a recess the screw head goes into.

visualopsins wrote:
It occurs to me surgical tubing of correct dimensions stretched over the metal core may work better, last longer, than shrink tubing.


For some types the metal core has not a simple tube-like but a more irregular shape. For those I use up to 4 different sized pieces of shrink tube in 2 layers, the smallest one only about 0.5 mm wide. I am wondering if surgical tubing might be too soft to stay in place at these small dimensions. I have never tried it but it seems to be rather soft, isn't it?


There's always glue. Smile


PostPosted: Mon Aug 16, 2021 8:06 pm    Post subject: Re: Source for new Canon bushings to replace the worn? Reply with quote

fdlenses wrote:
stevemark wrote:
What are the approximate dimensions? Inner diameter, outer diameter, length?


Outer diameter is 4 mm (for every type of cam follower I have encountered so far). Inner diameter is 2mm (there might be a second slightly smaller size, I am not sure). Length is 3.7 mm for the cam followers. Length is 1.5 mm for the type of cam that connects the focusing ring to the actual focusing helicoid. Some types have a recess the screw head goes into.


I would use PTFE (Polytetrafluorethylen = "Teflon"):

1) extremely resistant to most chemicals
2) wide temperature range (-270°C to +260°C)
3) lowest coefficient of friction of all polymers

Should work pretty well, and certainly will not disintegrate, not even after decades!

I just have ordered some 2 x 4 mm PTFE tubing; let's see how it works Wink

S

PS back in the mid-1990s Minolta Switzerland was offering replacement kits for the plastic (PTFE?) bushings inside the Minolta AF 1.4/85mm. These high precision replacement bushings were made of brass which was working pretty well. Might be a solution for the Canon FD / nFD problems as well Wink