Posted: 1/15/2006 11:22:41 AM EDT
Assuming you don't have any machinist's tools, what is the easiest way to find the exact center of a circle if you need to drill a hole in the center of an object?



Measure diameter. Divide this by 2 ... This is the distance from any edge of the circle to the center (the radius).



Have a compass? Set it for the radius of the circle. Stick the pointy end on any part of the circumference, draw a small arc near the center of the circle. Move the pointy end to a different part of the circumference, draw another small arc near the center. Where the two arcs you drew intersect is your center.



Isn't there some rule that you draw a triangle inside the circle (with the corners touching the circle), and then draw perpendicular lines from the center of each side of the triangle  and where they cross is the center of the circle? Or did I just dream that  it's probably been over 30 years. 

This isn't a democracy, it's a cheerocracy !

Can't you just draw a line in one direction across the middle and then another at 90 degrees from it and where they intersect is the center? Like a scope's crosshairs?
G 

Caution: Nudity, profanity and references to drug use

use a compass set at about center. put the needle on the circle and make an arc neer center .repeat this several times around the circle and the center will become apperant



I just tried it on paper and it worked for me 

Friends Dont Let Friends Put AR Parts On AKs
Everything is better with a bit of Kalashnikov www.ArizonaShooting.com 
Oops, that's it. G 

Caution: Nudity, profanity and references to drug use

Yeah, but how do you find the half way point to draw the line on? This is the question. 


Alternately a perpendicular from a chord will cross center. (an equilateral triangle inside a circle is 3 chords)
If using barstock, set on barstock on flat surface and lay pencil on same flat surface and draw a line along the end of the barstock. Do this at least two more times rolling the barstock so it's sitting on a different point. Then take a small square and draw perpendicular lines from the 3 chords you drew. The center of the barstock should be at the intersection or inside the resulting triangle of error. 


In CyberChase, the kids cut a piece of cloth the same size as the circle and folded it in half twice to find the center.



Fold it in half....and then fold it in half again. X marks the spot.
ETA: KISS 


Compass, two arcs and a line through the points where the arcs cross.Then divide the straight line in two.



Don't listen to him! It's pure sorcery! 

There But For The Grace Of God, And The Contract With Satan, Go I.

It's where the crosshairs intersect...



Bisect it with a compas. Perfect center every time.



Draw two chords on the circle. They can be any length and the ends don't need to touch, or they can overlap.
Construct a line perpendicular to each chord. Their intersection is the center of the circle. Here is a link to show you how to construct perpendiculars  www.math.csusb.edu/courses/m129/perp.html regentsprep.org/Regents/math/construc/perp.htm How else are you going to reconstruct a broken gear when you only have a piece? You can't draw a triangle inside a circle, and besides, that is a redundant solution. 


To find the middle of a line with a compass and ruler, set the compass to any distance shorter than the line.
Place the point on one end of the line, and draw and arc that crosses the line. Without changing the compass adjustment, place the point on the other end of the line and draw another arc that crosses the first arc. The two arcs intersect at two places. Place a ruler across those two intersections, and draw a line. Where that line crosses the first line will cut the first line in half, and will be perpendicular. 


Simply amazing. All of you and your genious.



Drill the hole first. What size circle do you want?



Let me take one shot at it from 300 yds..........
There's your answer. Sorry, jus' felt like a little ing was in order tonight. 

Sleep does not come easy to my village. 'Tis the season of cattle lowing.  Originally Posted By Londo, 12/19/2005
Dissatisfied with your liberal education? Visit www.flashbunny.org 
"Right about....there"
If its paper in the shape of a cirlce, fold it over in halfs.... Bingo.... Why make things so hard? 

I am the signature virus, please put me in your signature so I can spread
Too bad you look like a serialkiller.<img src=/images/smilies/smiley_evilGrin.gif border=0 align=middle> Otherwise, hell, Id do you. Lumpy196 
I'll assume you came up with this idea on your own even though I posted the same thing half way up the page. However since I am assuming you came up with this idea on your own...you and I are the only ones on this board with any common sense. 



Oh yeah. just saw that. Definantly keep it simple.... 

I am the signature virus, please put me in your signature so I can spread
Too bad you look like a serialkiller.<img src=/images/smilies/smiley_evilGrin.gif border=0 align=middle> Otherwise, hell, Id do you. Lumpy196 

Mission accomplished, thanks !



Welcome to the 5th grade.



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