What's better than the center of a circle? A spare car key without leaving home! I started Tom's Key Company (tomskey.com/?Tomah...) so you can get quick and affordable DIY spare car keys and fobs shipped to your front door.
You can find the center of a circle easily with a ruler! A little geometry lesson about chords and you'll be there.
Need a square? Find one on Amazon: www.amazon.com/s/?_encoding=UT...
1. Just 2 chords would be enough. 2. The chords need not be of same length. 3. Draw a perpendicular line from exact mid-point of these chords. 4. Point of intersection of perpendiculars would be centre. 5. Although not required, but a third chord and it's mid-point perpendicular would pass through the centre confirming the accuracy of the location of the centre.
Good method. Technically, you only need two chords, but it doesn't hurt to do the third one just to ensure you're accurate.
ONE chord is enough! Draw it near the rim of the circle, but make it easily divisible by 2. Mark the centre of this chord. Place a square on this reference mark on the chord and draw a perpendicular line right across the circle. The middle of this line is the centre of the circle.
From the looks of this description, all you would need is two cords, not three, the third only verifies the result of the first two!
Look at 2:02 the lines clearly don't even meet up at the exact same point. So 3 of even 4 chords is better than two. I watched the suggested videos with same technique after this one and their lines don't exactly match either at center.
There is an easier way. Take the point of that square and put it on the edge of that circle. Mark the points where the square ends pass over the edge of the circle. A line through that cuts that circle right in half. Now, you just need to move that point to another location and repeat the process. The single most important thing I ever learned in geometry class.
Yup, that’s how you do it! Faster and easier.
The perpendicular bisector of a cord will also bisect the circle it was drawn in. You only need two bisected cords to point to the center that may be different lengths as well so long as the are bisected, or cut into equal parts.
Fantastic! So glad I found this - helped me immensely on a project I’m working on.
If you already have a rectangle and set the right angle, then use the points where ends in the circle, and join them with line. The cross section of 2 line of that kind is center of circle. Much simple, just a few seconds.
Nice job. Something I need to do right now!! Thanks for showing us.
My high school got rid of shop class. "Go to college or work at McDonalds....." Thank you for posting this so people like myself can learn.
Sorry to hear that. Shop class lessons have helped me years later and they were fun as well. Stopping shop classes is a bad idea. Yea for youtube.
I had shop class in middle school. You didn't miss anything.
Probably because the government felt they had more important things to fund, instead of shop teachers, and dumped the money into funding endless wars, getting us nowhere.
Awesome! Thanks for sharing! It bet this would spare me a lot of time when trying to find a circle! ☺
Thank you from the bottom of my heart!
See now this helped me understand many other uses fro my square also. Thank you. Lance & Patrick.
The classic way to do this is to use a compass. Place the point of the compass at the edge of the circle and draw an arc that extends roughly beyong the centre of the circle. Keep the compass opened to this length and place its point againt, at what is roughly the opposite side and draw another arc. The two arcs will intersect at the diameter line. Repeat a third and fourth time to draw an intersecting diameter. The advantages of the compass method should be obvious.
Philippe Panzini, Sir, Heartiest congratulations. It is a very elegant method . Actually when you draw the first arc that cuts the circumference of the original circle at two points, then that chord joining these two points are at right angles to a diameter, so one only needs one arc really as the chord is easily halved. Again congratulations for such a solution which can only be described as, geometrically beautiful, gracefully concise and simple, admirably succinct.
Isnt that trisecting an angle?
Isnt that trisecting an angle?
I hate to split hairs, but you use a compass to find direction. You probably mean a pair of compasses ? :)
erik dee
3 chords of EQUAL lengths ANYWHERE with in the circle. Take HALF of the line going through the circle and draw a perpendicular segment at the middle area of the circle and where the three PERPENDICULAR segments intersect is the CENTER of the circle ! U R A GENIUS SIR ! TY !
You sir are the cat's meow. I'm making a shopvac filter retainer and need to drill a hole in the center of a paint can lid. Thank you for sharing.
I enjoyed your video. It was very helpful. Thank you!
Interesting and easy way to understand by Tomahawk sir.He explain very nicely and he explains bit by bit from Aaron Luke
Divider set to the radius of the circle. Point of divider to outside of circle and swing arc with pencil end marking the center. Repeat at several places of the outer circle. Much easier/accurate.
Two chords, parallel, equidistant from the circumference, the diagonals from where the chords intersect the circumference will cross in the middle.
You don't find the center of a circle, it finds you
Thank you! I am making my own nigh stand and this really helped 👍
You're the man thanks for sharing that. I read those sane instructions and had no idea what a "cord" was. That's a super helpful tip. You just saved me some cash $$.👍🏽👍🏽
+BloodSweatnBassOutside Glad it helped you! No pressure, but consider sending a tip my way since it saved you $$$. Half of all tips go straight to helping people in 3rd world countries Build Better Lives. Learn more here: tomahawkdiy.com/about. You can provide a donation via the "Support This Channel" on my channel page (kzhead.info). Whether you donate or not, have a great great day!
IF you take your rafter square and place it with 2 points of contact on your circle, you can then take a speed square and line it up with the inside corner of the rafter square, projecting 45 degrees to the middle of the circle. Repeat twice with markings to find middle. i dont know if you undestand what im trying to say, but its a much easier and faster way of finding the middle of a circle.
/watch?v=XA4hIxJQkVU that video explains what i was trying to explain
You just solved a problem I had. Thank you very much!
+Henry Bulger Glad to hear it helped!! Now you have the chance to help people in some of earths most dire circumstances solve a problem such as no clean water, no shelter, no medical care, hunger, etc.. TomahawkDIY is a business with a mission. No pressure, but donations are always appreciated. www.paypal.me/TomahawkDIY or Venmo @TomahawkDIY if you want to send one. 50% of donations are sent to help people Build Better Lives in some of earths most dire circumstances (TomahawkDIY.com/about).
I just stick a ruler on the circle and find its maximum, draw a line, then do the same when roughly perpendicular to the first line. where two diameters cross has to be the center.
Yes!!! Exactly how I do it. All these other ways are just a waste of time and no more accurate. If the circle is not exactly a circle, then it doesn't work but nor do any of these other techniques.
👏👏👏👏 parabéns o método mais simples e prático perfeito
hey man, believe this is the best and easiest way to find the center of a circle on youtube! i will be able to use this to solve many prob's in shop!
great trick to know thanks dude !!!
Thanks Tomahawk, great video for even me to understand :)
Nice work dude!
Dude, place the top of the right angle tool anywhere on the circle, like you did. The two points where the angle arms intersect the circle form a diameter - connect them. Repeat it at a different starting point. The point where two diameters intersect is your centre of the circle.
Very help full mate thankyou
there is a much simpler way, put the point of the square on the circumference. angle does not matter, make a mark where the outside of the square crosses the circumference on both legs. join those 2 marks, move the square anywhere and position similar to the first time. make 2 more marks and join theme. where these lines cross is the center.
+Karl Newman great suggestion!
Karl Newman, Sir, very nice indeed. When the right angle of a triangle touches the circumference of a circle, then if (note if) the two sides forming the right angle cross the circumference of the circle at two points, the chord joining the two points will be a diameter of the circle.
I'm waiting for the video !
theres even an easier way
D/2 and measure?
And now the MUCH easier way: take a piece of paper and place it under the wood. Then use a sharp knife to cut out a paper circle with the exact size of the wood. Now take that paper circle, fold it in half twice and where the folds cross is the center. And if you cut off a tiny bit of tip of the folded paper and then fold it out again you'll have a perfect template for marking the center on the wood.
+JC130676 Great suggestion. I tried it out and your idea is one of my favorite 3 ways! kzhead.info/sun/iLmFYpiBm4eono0/bejne.html
JC130676 the best way for sure!
Clevah!
What if your circle is 8 feet more or less in diameter? Where you going to get some paper like that?
@@MeyersCTR use size A -84
Genius!!! So that math stuff really does work!
Thank you very much 😊
I learned more in this video than in 4 years of high school.
1. Place the right angle point of the square on the circumference and mark the two points where the two formed cords cross the circumference further away from the right angle point. These two points would be a diameter of the circle hence divide by two to get the centre. 2. Hammer two nails on a flat surface and rotate the wooden disc on the flat surface such that its circumference always touch the two nails. Use a stationary pencil above the rotating wooden disc to mark the resulting circle and move the pencil to minimise the size of the drawn circle, which when minimised, that would be the centre. 3. insert a nail in the circumference, tie a string to the nail and hang the disc. The vertical line would be a diameter and so either repeat twice, or else divide one diameter by two. If the string is tied at its centre and the upper half is what suspends the disc while the other half is weighted to fall at a lower height , the diameter is easily recognised, so mark it and half it. 4. Insert a long nail through the disc face and use two knife edges to balance the disc in between the edges , wait till the disc stops oscillating and the vertical line through the nail would be a diameter, then mark it and half it. 5. Using a strip of paper, measure the circumference, divide by six and mark six equidistant points on the circumference. Any chord joining two adjacent points will be the radius and if one joins the three most distant pair of points, then the intersection would be the centre . 6. Using a light nail, hammer it on the circumference, tie a string to it, tie the other end of the string to the ceiling to make a pendulum, oscillate the pendulum in the plane of the disc and find the periodic time. Repeat this experiment two or three times. Knowing the length of the string and the periodic time of the pendulum, the only unknown is the radius of the disc and through the using t(x)=sq((L(x)+R)/g) one can find the radius (R), use it as a chord , make an equilateral triangle using the cord and one can find the centre. This is due to the fact that the centre of mass of the circle is at its centre. 7. Make a simple centre square. 8. Drill a lot of little holes around the centre. Pass a nail through one of the holes and attach it to the end of a long flexible rod. Rotate the wooden disc and watch for vibration . That hole which does not produce any vibration would be the centre, provided the wood is homogeneous in density. 9. Float the wooden disc in water. Load it with a pin point load through a cantilever. That location of that point load which does not cause any inclination to the floating disc is the centre. 10. Balance the wooden disc flat on the thumb, the pointer and middle fingers after you chalk the lower face , spin it as you throw it up, catch it with one finger as it drops, let it rotate for a while and notice the point of rotation being cleaned off the chalk. Well that would be the centre. 11.Balance the disc flat on a knife edge , which would indicate a diameter, rotate flat and repeat where the two diameter will intersect at the centre, or divide a diameter by two to get the centre . 12.And finally one normally marks the centre before one makes the circle and so one should be careful in not sanding it off while sanding and smooth finishing the two faces on the circular disc, and then having to find a method how to refind the centre! Hope you enjoyed this and students would have something to think about.
Sure
One Question, Sir. On the first chord, you chose an arbitrary length of eight inches, right? Then the other two chords have to be the same length of eight inches and then the midpoint and the rest of the procedure, right? Thank You !
Nice, thank you
Thanks! Your video was great and to the point. Good math-ing.
I have a large circular canvas I want to do a painting on. This is going to be a big help.
Thanks for watching
Good technique
This is a long process. Since you have Right angle, use that to draw two diameters intersecting at center. Actually we can draw a circle with a Right angle by nailing two points as diameter, have a try.
I can't tell you how helpful this was, thank you!
with a compass you create the perpendicular bisector of the chord. Same compass perpendicular bisection of that is center cause it is the diameter. nomesayun?
Measure the circumference with a flat tape then divide that by 4 then draw 2 lines from one side to the other & there is your centre.
Thanks man!
take a square sheet of plywood....draw two lines from the vertices of the square.....set a nail at this intersection so as to pass through plywood into another sheet( at the desired radius ) which has been clamped to the table of your band saw....start the band saw and rotate the plywood square....cutting out the circle....remove from the band saw table and extract the nail....drill the hole to size as required.....done
I would draw a line on 2 diameters that crosses each other and make sure the centre point measurement from the edge is exactly the same.
I dont understand how you know where to draw your cords? 8 inch okay but how far up and how did you get a perfect triangle in the middle
Nice trick...but you don't really need three cords, two are enough and they don't even need to be the same lenght. All it takes is to raise a perpendicular from their middle toward the inside e of the circle...their crossing point is the middle.
You are right. 2 lines are enough, in theory. But what if you did a mistake drawing one of them ? No way to know you did an error. Invisible !! You will find a point, drill a hole and then, discover later that the hole is not in the center. Very bad, isn't it ? :-( So, always find a way to verify your job. For instance, draw a third line and if one of them is wrong, you will immediately notice that they do not intersect in one point but draw a triangle. And then, you do not drill a hole but find the error and fix it before drilling. That's the way one have to work seriously :)
Wow! Who'd have thought?
Only need one cord line. A line perpendicular to the cord at its midpoint intersects the center of the piece. Continue that line to the edge past the cord line. The midpoint of that line is the center of the circle.
remige2006 Drawing three chords confirms that the mid point has been found. With two chords it is possible to miss the centre because of a poor measurement. Measure three times drill once!
Yeah, I reckon.
What about using dividers
So what do you do when all 3 lines don’t intersect at the same point?
Just draw ant triangle, marking the mid-points of any two side. Use a set square to draw perpendiculars and where they cross is the centre.
Falou meu amigo. Fron brazil. Tanki
make 3 points on a circle. drawn a straight line from a to b and b to c. draw a 90* line from those 2 lines to the center. The intersection of those 2 90s will be your actual center.
light bulb moment. Thank you. Very easy and very cool.
+sancochito75 check out my recent video showing 3 different ways based on the comments in this video...
Simpler , easier and totally accurate way is to use a compass, a lot quicker too!!
Thank you!
Drill the hole FIRST, then use a circle cutting jig on the bandsaw to cut out the circle.
This is a good theoretical exercise but in practice there are other easier and certainly quicker ways to do this.
Dude thanks!
Awesome
what a useful way to do it. It's only obvious when you know, but thank you !!
You're welcome!
Make a square and two perpendicular diagonals give you the center.
thank U very Much.....!
I see they didn't exactly line up.but can further locate the center by balancing it on a nail but since the density of the wood isn't uniform it may not work the same
That was just due to the fact the the circle had rounded edges and his placement of the square probably wasn't perfectly consistent.
if you draw both arms of a 90 angle and then connect the ends, you will receive a string of a circle. Do it elsewhere and you will have 2 of them... they will cross in center of a circle. :)
Thanks for showing me iv been going cookoo
Assuming you want lines on your circle ?
Genius!
I just make three marks anywhere on the circle, and find the center between each mark, and the intersection of them is the center.
+ Sooner Science Nerd Great suggestion. I tried it out and your idea is one of my favorite 3 ways! kzhead.info/sun/iLmFYpiBm4eono0/bejne.html
If you don't have a square, balancing a disk in a nail point (etc.) will also give you the center, when it balance is level...
Thank you!!
You're very much welcome!
just need 2 (3 just in case it's not a perfect circle) lines drawn edge to edge at the widest point. intersection is the middle.
Yes, but only if the circle is a perfect circle, your lines are exactly the same length, your right angles are exactly 90 degrees, etc. In the real world I would do three and they are off a bit a fourth, before drilling the hole.
Wow! Genius!!
So how do you find the off center ?
excellent. thanks you.
Welcome!
On the first "chord" the right angle does not go all the way to one of the sides.
Why not make 4 cords to ensure the same spot all around or why not do 8
Thanks
And all this time I thought geometry was hard!
All he had to do is draw a perfect square inside the circle, draw the 2 diagonals inside the square and the center is located.
+tracyofbg you are exactly right! See my updated video with 3 ways to find center of circle. kzhead.info/sun/iLmFYpiBm4eono0/bejne.html
Tomahawk DIY thanks for the update - some good suggestions there that look very easy to follow. Good work.
beats the algebra method. to much for me man. thanks
so basically the center is inside of the small triangle you made in the middle?
Thanks’ ~M~
Just use the inside of the carpenters square against the outside edge of the circle , touching at two points and then put a speed square to the point where the carpenter's square converge ......
I guess if +/- a 1/16" is good enough.
This is the most complicated way of center finding I have ever seen.
so drill the hole in the middle of the little triangle? close enough. ;)
Why not just fit your circular work into the 90 angle of your square then slide your 45 mitre square to the 90 apex and draw a line? Repeat x2 to find the center.
Something I learnt how to do over 60yrs ago.........Just use a pair of compasses, it takes half the time.
that's easy, it's always in the middle of it.
I would trace that circle on a piece of paper ...cut it out...fold it twice to form a quarter put it on that piece of wood and mark the center... just as simple as that 😁😁😁😁
You only need two cords and they don't have to be the same length.
😇🏆Great
Appreciate your support! 😊
just measure the diameter in two places 90 degrees to each other divide these by 2 and there you go....
now how do you find the center with out a measure
Using his tool (and without measures...): place the vertex of the right angle at the circumference and mark the two points where the sides cross it. Join these two points and you have a diameter. Do the same elsewhere, and trace another diameter. The center is where these two diameters cross eachother.
i said with out a measure or tool.. failure.. a right angle is a measuring tool.. try again .. heres your cookie
I will be the first to admit that I'm horrible in math/geometry but wouldn't it have been easier if you drew four cords/chords instead of three? Let's say they are also 8"; you mark the center of each cord/chord at 4". Then, you would draw a line connecting both pairs of parallel lines at the center. Where the two perpendicular lines meet would be your center. Oh, and I also suck at explaining things. :-|
When you draw a cord of any size and bisect the line, you have cut the circle exactly in half so if you are super accurate, doing 2 cords is enough to find the center. Doing a 3rd just helps improve accuracy. The problem with what you are suggesting is how do you ensure your lines are parallel? Not something you can easily do with just a square. If your circle was small enough that your square covered most of the circle you could use both sides of the square with out moving it but now you are measuring your lines and dividing by 2 and that is only going to work with a limited size range of circles.