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A Circle With Unknown Centre

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for anyone whos interested, heres my construction. done in MS paint, its pretty accurate.


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My english might be wrong but.


A line from edge to edge. A circle with centre in one of the intersections (border-line) and another circle in the other intersection. A line between the intersections of the circles. That line shows the middle of the circle. Then just repeat but approx 90 degrees rotated to get the other middle line to create a cross.


Not sure you understand and I think someone mentioned something like this. But as I said my english isn't too good.

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The construction that bloodhound made seems like a fairly simple way of doing it; just 2 perpendicular bisectors.

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Here's the method "Machinery's Handbook" gives:


To find the center of a circle, select 3 points on the periphery of the circle, A, B, & C. With each of these points as a center and the same radius, describe arcs intersecting with each other (Note - draw enough of each arc so there are two intersections through which you can draw a straight line). Through the points of intersection, draw lines DE and FG. Point H where these lines intersect is the center of the circle

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Guest satovey


I just joined the forum after reading this post.

I'm glad I did because in the process I remembered

how a bucket maker accomplished this with just

the compass.


In making wooden buckets, you envariably end up

with a circle grooved into the base of the bucket

where the bottom goes. To find the proper diameter

of the circle, the bucket maker would take the

compass and count 6 points around the inside

of the groove. He would adjust the compass

untill he had could go around the grove with

the compass six times exactly.


Once he could do this, he would use the compass

to score a pice of wood and cut his circle for the

base of the bucket.


You can use this method to find the exact center

of the circle.


First, Space your compass untill it is about

center of your circle.

Second, mark a point on the outer diameter of the circle.

Third, Begin to count around the circumference

of the circle and adjust your compass untill you can

count exactly six points beginning at your original

point and ending at the exact same point.


Now, place your compass on the point you made and

draw and arc through the circle.

Next, place the compas on the intersecting line of the

arc you drew and the outer diameter of the circle.

Move clockwise just to give you some order.

Draw a second arc trhough the circle.

If you want to be certain, go to the next point

at the edge of your circle where the second

arc crosses and draw a third arc.

All arcs will meet at the exace center of your circle.


All you need with this method is the compass,

so you can leave the ruler in your drawer. I

think it is also an easier method as well.

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Well, is it the same as drawing two chords? Then drawing the perpendicular bisector of each chord? The pt of intersection would be the centre of circle?

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