I want to make a cardboard lamp, but i want it to look like half a sphere.

Given a cardboard thickness of x, and a circle width of y, how many elements do I need and what radius do the elements need to be? Anyone got a formula for that?

thanks alot!

example of lamp and segments

  • 1
    $\begingroup$ by half a circle, do you mean half a sphere? could you be more clear? my interpretation is that you want to stack up many cardboard circles to make a half of a sphere. Is this right? $\endgroup$ – stanley dodds Apr 30 '16 at 14:34
  • $\begingroup$ so does my answer use the correct interpretation? It looks like it does from the image you have given - thanks for that, also. $\endgroup$ – stanley dodds Apr 30 '16 at 14:52
  • $\begingroup$ yes, i meant half a sphere! (not native english) $\endgroup$ – pvc May 4 '16 at 18:11

I have interpreted your question as meaning that you want a stack of cardboard circles, making a half sphere when glued together.

If this is the case, then you will need $y\over2x$ individual cardboard rings.

Starting from the bottom, if you are on the $n^{th}$ ring up (the first ring at the bottom is $n=0$) then the formula for the ring's radius is $\sqrt{\left({y\over2}\right)^2-(nx)^2}$

Correct me if my interpretation is wrong.

  • $\begingroup$ thank you, this is wat I was looking for. $\endgroup$ – pvc May 4 '16 at 18:12
  • $\begingroup$ thank you, this is wat I was looking for. I now know that I was looking for a circle's chord. For the individual ring amount, is that correct? Isn't it: ((y/2)/x) ? $\endgroup$ – pvc May 4 '16 at 18:21

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