Trades Math - Find The Center Of A Circle Using Squares

One of the easiest methods to find the center of a circle accurately is to use a compass and perpendicular bisectors. However, on a job site a compass is not always readily handy, but you’ll always find squares. So using those squares I’m going to show you how to accurately find the center of a circle using three different methods.

[rex]

Machinist: That's WAY off!
Carpenter: On the money! Nice!

[etherealeagle]

Perpendicular bisector of a chord passes through the center of a circle. Nice practical application of geometry. Thanks for posting.

[weejim]

Brilliant, this to me is why YouTube was invented. Helping people solve problems & teaching people useful skills. Not for just having a rant or meltdown. Very informative, thank you. 👍👍🙏

[tiltedstudio]

These are great! Just a quick note on method #1: the only thing that really matters about the square placement for the first two marks is that the apex of that square angle sits on the edge of the circle. You're marking two chord lines which meet on the circle edge and are perpendicular to each other. If you do this, the hypotenuse of the triangle created will by definition pass through the centre of the circle. The point is that you don't need to fret about making these lines the same length - it will work for any placement if the apex is on the circle.

[bikerbobcat]

Artist and HVAC guy here, thank you so much for this. So simple, so useful.

[RoyDees-tk]

I have worked in a machine shop over 40 years and never knew about this simple method. Thanks so much for sharing!

[walsakaluk]

A bit hard for very small stock, but in the adsence of a centre square these methods are excellent first geometric principals for locating centres on circular material.
NICE VIDEO AND EXCELLENT REMINDER TO PAY ATTENTION AT SCHOOL.
👌👍🖖

[stickyfox]

The angle formed by two secants is half the included arc angle. If you draw two secants at 90 degrees they will include 180 degrees or half the circle; making the triangle's base a diameter whether or not you drew an isosceles triangle. I forgot about this trig formula after high school but it comes up again and again in machining and drafting.

[adamgravelin]

i tried to google this the other day and google assumed i was doing all of this on paper. this is a great video for practical situations where you need to find the center. i ended up fumbling my way into the second method just trying different things, but i needed to draw a perfectly plumb line through the center of my circle and i ended up holding a framing square, a combo square and a level attatched to the combo square. it was a lot of moving parts to line up, but it did the trick.

[bobadams]

Very good video. Clear and to the point, and very practical.

[IkanGelamaKuning]

My teacher taught me this in 1990. Thanks to him for this useful knowledge.

[ChestnutForge]

Many thanks for this. It is a great training video I will use for others to learn from.
As a blacksmith if you are a machinist or a welder, I will open a conversation on that basis. but within a few minutes I will be asking for solutions to this and other problems. That is because the smith needs to BUILD his tools and jigs. In my shop I have an engine lathe, a mill, 2 drill presses, a hundred year old ironworker, 2 anvils, press brake and will expect to make hammers, tongs, forges, bolster plates and rivet/rivet tools as needed.
This video goes to the core competency necessary to create real world items from someone elses imagination.😀👍

[pyme]

If they taught it like this in high school math, more of us would've paid attention! 😃

[ImtheGhostMagnet]

A much simpler method, use the framing square and triangle to measure the diameter, devide by 2, you have the radius, scribe a line at the radius distance, rotate the circle and scribe a second radius line and where it bisects is the center.

[eadgbefreak]

I've always used method 3, which I learned in geometry class. Method 1 is cool too. Method 2 I know works well because they sell a jig, that basically "holds the squares" for you.

[TheOfficialDjProduct]

I don't know if I'll ever need this. But interestingly enough you could do the last method with just a tape measure.
Using it as a straight edge you could do 3 sides, then using the tape as a straight edge you could connect the 3 lines and find the center.
And you could find the center on much larger circles (for however large your tape is), with whatever tolerance you allow.

[drumcdoo]

Excellent video and straight to the point ~ no B/S and stretching out video for 5 minutes describing the type of scribe, where you got the measuring tools from and how to unbox them etc, before describing tip!

[AsianTankPilot]

The last method is what I learned in board drafting. We used a compass find the middle of each chord.

[Kleiner_Lutz]

I'm gonna immediately forget about this again until I need it some day and have to rewatch this video

[apeterson]

You and ICWeld are my favorite on youtube! Lots of skills in those pockets