finding the centre of a circle

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Hacksawbob
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finding the centre of a circle

Post by Hacksawbob »

I had the fun of drilling a few things in my fan this weekend. new mirrors and removing a sheered bolt etc. I got the automatic centre punch pretty close and it worked out OK in the end but I was thinking if I had some hollowed out bolts done on a lathe bored out to take the centre punch it would take the guess work out of it. M8 M10 possibly an M6 (maybe too thin) has it been done already? a good idea?
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Re: finding the centre of a circle

Post by Huyton_Blue »

I only replied so you would not feel ignored,I have no idea what you're talking about.

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Re: finding the centre of a circle

Post by R0B »

Why were you drilling your fan bob? And why has it got mirrors on it.Dont they stop it revolving
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Re: finding the centre of a circle

Post by skysurfin09 »

Christ Bob ! You've got to get out more.....
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1664
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Re: finding the centre of a circle

Post by 1664 »

I know how to find the exact centre of a circle but after the title you totally lost me

so are you still after finding the centre or do I have the wrong end of the stick?
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skysurfin09
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Re: finding the centre of a circle

Post by skysurfin09 »

Sticks?..Sticks?... I thought that we were talking studs here.
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Hacksawbob
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Re: finding the centre of a circle

Post by Hacksawbob »

Sticks and studs may break my bones, but fans can never hurt me.

What you don't have mirrors on your fans?

This might make more sense
Centre punch stud face spot bollock centre

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Re: finding the centre of a circle

Post by 1664 »

my method won't practically work on something that small in size
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Hacksawbob
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Re: finding the centre of a circle

Post by Hacksawbob »

How do you do it on something bigger?
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Re: finding the centre of a circle

Post by Mocki »

i have a nut with a tube which the centre punch fits in, which i made up for drilling studs out of a zorst years ago,
have no idea where it is now mind .....
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Re: finding the centre of a circle

Post by Oldiebut goodie »

Isn't a fan a Welsh van?
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Re: finding the centre of a circle

Post by Mocki »

wouldnt that be a llfan?
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Re: finding the centre of a circle

Post by jamesc76 »

In my tool box at work I have loads of different sized nuts with washers welded to the top to take my centre pop, works well and i know they will be bob on!
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Re: finding the centre of a circle

Post by 1664 »

Hacksawbob wrote:How do you do it on something bigger?
The widest part of a circle is it's diameter - which MUST pass through the centre

For something large: Get a tape measure, place/fix on one side of the circle and run it out across the circle to the other side.
Keeping an eye on the measurement at the edge, move the tape along the edge of the circle both ways and you will see that the distance decreases the more you move around and away from the exact centre line regardless of which direction you move away from it.
So, get the tape into it's maximum measurement position and the use a pencil to draw a line both sides of the tape measure itself roughly where the circle's centre position is so you have some thing that looks like this equals sign, = ,roughly in the centre of the circle.
Now take the tape and do the same from a position on the edge of the circle 90 degrees round from the first, find the maximum and draw lines both sides of the tape roughly in the centre (which should overlap the previous two lines roughly).
If you just do it twice at 90 degrees to each other you will see a small square where all 4 lines ( 2 x 2 sides of the "tape itself "lines) intersect. Draw straight lines from each corner of the square to it's opposite and where they cross is the circle's centre; so it looks like an 'x' in a box on a voting slip.
The more measurements you take the more accurate it will be, but do it in pairs at 90 degrees to each other and you will end up with more than one 'square' in the middle slightly rotated from each other. Don't panic; just join opposite 'square' corners again and they should all still cross in the same place.

For something small just draw one line along the tape edge but do a few of them and where they all intersect is the centre.

Simples!!
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Re: finding the centre of a circle

Post by kevtherev »

yup
that's how I do it
biggest diameter, two places. intersected
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