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Variable diameter circle

  1. Mar 5, 2014 #1
    I am interested to see if there is a way of creating a metal ring which has a variable diameter, the only way I imagine that this can be done is using segments which come together to form a circle, once pulled away the diameter changes however, the problem I face is that when the segments are pulled out, they leave a gap as shown here:
    To fill this gap, additional segments would need to be manufactured and would defeat the purpose of having a variable diameter.

    Is something like this even possible, if not a perfect circle, is there a way of doing this to get a varying geometry which is very similar to a circle? I am interested to see any ideas at all that anyone may have about this even if they are nothing to do with segment please share.
  2. jcsd
  3. Mar 5, 2014 #2


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    Gold Member

    google "camera iris"
  4. Mar 6, 2014 #3
    That was exactly what I was looking for, Thank you.

    Just out of interest, can this be reversed? I mean rather than having a circle form on the inside is it possible to form the circle on the outside so that as the segments move it expands outwards?
  5. Mar 6, 2014 #4


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    Never heard of one like that but seems to me it could be made. The "circle" would probably be more like a polygon, but the more segments used the less that would be the case.
  6. Mar 8, 2014 #5


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    Science Advisor

    There are many unusual approximate solutions to such a problem.
    Maybe if you could identify the application it would be worth posting other solutions.
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