See how to find the center of a circle using only a square and a pencil.
This is the easiest and fastest way to do it.
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Draw Your Circle
Trace the object that you need to find the center of.
You can do this directly on your wood, but I would do it on paper first, just to check that your technique is accurate.
Tip: Be sure that only the lead of your pencil is touching the object.
You don’t want the edge of your pencil to get your angle off on your trace.
Draw 2 Chords
A chord is simply a straight line that intersects the circle in 2 places.
We’ll need to find the mid-point of these lines.
Tip: Make the chord a length that is easy to divide by 2.
Place your pencil tip just off-center near the top of the circle.
Bring the inside corner of your square to the tip.
Swing the square around until it intersects the circle.
Look for it to land on a number that is easy to divide by 2.
Draw that line.
Then carefully mark the center point of it. (Simply divide by 2.)
Now repeat on the other side of the circle.
We want to have a pretty wide difference of angle on these two lines, so start again off-center of the top, but on the other side, so your angle will be in the other direction from the first chord.
Draw Mid-Point Line
Next, we want to draw a perpendicular line through the midpoint of the chords, toward the center.
Line up the inside corner of your square with the midpoint of one of your chords.
Tip: When your square is aligned, the midpoint measurement should be touching the circle.
Draw the line from the midpoint toward the center of the circle.
Repeat for the other chord.
You Found the Center!
Where those two new lines intersect is the center of your circle.
Check Accuracy
You can verify the accuracy with a compass, if your circle is small enough.
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