How to find the center of a circle

How to find the center of a circle
This is simply a method to find the center of a circle, using very simple techniques. You'll need a ruler, a pencil and some way of measuring right angles.

You might want to use this technique to know where to drill the hole in the middle or draw concentric circles on the surface.

I can't take any credit for this as I probably learnt it at school, many eons ago. I just thought I'd add it because I saw lots of methods for drawing circles, using bits of string, wooden battens etc. but nothing for reverse engineering the problem.

If it's not correct then I can only blame my very poor memory.
 
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Step 1Draw a chord across the circle

Draw a chord across the circle
Draw a line across the circle near the edge so it cuts the circumference in two places. This is called a chord.

If you can also make the chord a nice easy length i.e. 10, 20, 24, etc this might make life easier in the next step.
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13 comments
May 22, 2008. 2:20 PMadmin says:
This is a great Instructable, but you need to add a main image of the final project to the intro step. Please do that and leave me a message when you have so that we can publish your work. Thanks!
Mar 17, 2011. 12:55 AMxAxrules says:
Using this for locating pots in a project box!
Aug 8, 2010. 6:38 PMiminthebathroom says:
your instructable is being applied as we speak, thanks ! ! !
Jun 9, 2009. 2:08 PMKLUTZYengineer says:
In the first step, the line that you proposed was a chord, is technically a "secant", not a "chord".
Oct 20, 2008. 10:23 AMclicclic says:
Thank you so much for this helpful technique. I wish I was smart enough to figure this out on my own; I've been stressing about perfectly centered holes on a number of recent projects and didn't know how to find the center. Thanks again - a huge help! clicclic
Jan 20, 2010. 9:09 AMbuteman says:
Well you put it here and it is something many will want to do.
I am starting a project in which I will need the centers of some circles.
I was going to do what you have done as part of my own instructable but now I will just give a link to this.
Thanks
Jun 4, 2009. 5:30 PMawsome says:
fairly simple...=)
Mar 20, 2009. 10:37 PMShut Up Now says:
its so simple once you know it! thanks for sharing!
Mar 20, 2009. 5:00 AMamakerguy says:
that is a cool way of finding the center.
May 23, 2008. 5:40 PMwalterr says:
A clear Instructable. If you use a tangent instead of a chord you automatically have the point from where to draw the perpendicular.

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Author:bunglesmate