andym Posted April 29, 2009 Share Posted April 29, 2009 Okay, I have a circular bit of plastic, say like a plastic coin. How can I accurately find it's centre? I've tried thinking of several ways but can't think of a satisfactory one? TIA Andy Link to comment Share on other sites More sharing options...
perry Posted April 29, 2009 Share Posted April 29, 2009 try this http://www.instructables.com/id/How-to-fin...er-of-a-circle/ Link to comment Share on other sites More sharing options...
Graham T Posted April 29, 2009 Share Posted April 29, 2009 Easy. Draw a line anywhere convenient across the circle. Then, draw another line at right angles to & passing through the centre of this line. This line is then the diameter. Bisect this line & you have the centre TAAADAAAAAA! Link to comment Share on other sites More sharing options...
andym Posted April 29, 2009 Author Share Posted April 29, 2009 Thanks very much guys. I knew there would be a relatively simple way, I just couldn't fathom it out. Regards, Andy Link to comment Share on other sites More sharing options...
Darius at Home Posted April 29, 2009 Share Posted April 29, 2009 or... Draw two tangents to the circle - straight lines that just touch the circle but do not cut through it. Draw lines at right angles to the tangent lines where they tough the circle and these will intersect at the centre of the circle. Darius Link to comment Share on other sites More sharing options...
Gundylunch Posted April 29, 2009 Share Posted April 29, 2009 (edited) Hi Andy !! Draw round your circle with a pencil, then using a set square if you have one draw a vertical line down each side, just touching the edges, then 2 horizontals to form a square, then 2 diagonal lines across the square from corner to corner and hey presto !! where the lines intersect is your centre, SIMPLES !! ( Spoken in Meerkat !! ) Edited April 29, 2009 by Gundylunch Link to comment Share on other sites More sharing options...
kitnut617 Posted April 30, 2009 Share Posted April 30, 2009 Here's how you do it just using a compass and ruler, Link to comment Share on other sites More sharing options...
Mike Posted April 30, 2009 Share Posted April 30, 2009 How do you do this on a 1mm piece of rod then? Don't tell me... Mk.1 eyeball Link to comment Share on other sites More sharing options...
kitnut617 Posted April 30, 2009 Share Posted April 30, 2009 You could say the same for all the others Mike, practically impossible with any of the methods, Mk.1 eyeball will have to do there I'm afraid. But I should have said you do this on a piece of paper then transfer it to the plastic circle or it can be done straight off the styrene card. Mind you if you have drawn a circle with a compass on some styrene you already have the center point don't you. Link to comment Share on other sites More sharing options...
wyverns4 Posted April 30, 2009 Share Posted April 30, 2009 How do you do this on a 1mm piece of rod then? Don't tell me... Mk.1 eyeball Not forgetting a big dose of guesstimation! Christian the Married Link to comment Share on other sites More sharing options...
little-cars Posted April 30, 2009 Share Posted April 30, 2009 There is also a simple tool that is based on an engineering square called a centre square. I have them for £8 for a 2.5 inch one. Link to comment Share on other sites More sharing options...
Mike Posted April 30, 2009 Share Posted April 30, 2009 There is also a simple tool that is based on an engineering square called a centre square. I have them for £8 for a 2.5 inch one. Paul - Down to what sort of size is that accurate to? I've seen them before, but always shied away because I figured it wouldn't work well with a couple of mm piece of styrene rod Link to comment Share on other sites More sharing options...
little-cars Posted April 30, 2009 Share Posted April 30, 2009 I'll have a play later and let you know! Link to comment Share on other sites More sharing options...
Mike Posted April 30, 2009 Share Posted April 30, 2009 I'll have a play later and let you know! Gracias Link to comment Share on other sites More sharing options...
xffw45343tg Posted April 30, 2009 Share Posted April 30, 2009 ... a compass... So which direction is North then? Kirk-the-pedant Link to comment Share on other sites More sharing options...
spike7451 Posted April 30, 2009 Share Posted April 30, 2009 Here's how you do it just using a compass and ruler, Yup,that's how I was taught. Merv Link to comment Share on other sites More sharing options...
Edgar Posted April 30, 2009 Share Posted April 30, 2009 So which direction is North then?Kirk-the-pedant Opposite to South, and you can find that, on a sunny day, with a faithful old, non-digital watch. Edgar Link to comment Share on other sites More sharing options...
xffw45343tg Posted April 30, 2009 Share Posted April 30, 2009 Not a very useful tool for drawing construction lines on the perimeter of a circle though eh Edgar? Pair of compasses would be far more useful... Link to comment Share on other sites More sharing options...
kitnut617 Posted April 30, 2009 Share Posted April 30, 2009 Not a very useful tool for drawing construction lines on the perimeter of a circle though eh Edgar?Pair of compasses would be far more useful... I would check your dictionary Kirk, Oxford, Websters, Britannica, any one will do and you'll find it's 'compass', a pair of compasses would mean you have two of them Link to comment Share on other sites More sharing options...
xffw45343tg Posted May 1, 2009 Share Posted May 1, 2009 Others would beg to differ- and perhaps I'm just showing my age. The words "more properly" used to be important. It's like "pair of trousers". One garment, two legs. Shall I get off my hobby horse now? Link to comment Share on other sites More sharing options...
kitnut617 Posted May 1, 2009 Share Posted May 1, 2009 (edited) Ah!! yes Wiki --- but lets see, date the dictonary I'm using, hmmmm --- 1930, seems these 'modern' words go further back than "others" like to make out Edited May 1, 2009 by kitnut617 Link to comment Share on other sites More sharing options...
xffw45343tg Posted May 1, 2009 Share Posted May 1, 2009 Not sure I understand your point kitnut. I'll admit to being lazy in using Wikipedia to make my point but try here if you'd like me to be a little more academic in asserting that "compasses" is the 'better' term for the thing you draw arcs with and "compass" for the navigating instrument. The writer suggests the OED is also somewhat confused about the etymology (I have no argument that it is pre-1930 & I don't think Wikipedia claimed differently) so I'm willing to concede that if Mike can now find the centre of his circles to his own satisfaction, he should use whatever instrument he likes. I'll stick with "compasses" and, like my old English teacher Mr.Pope, continue to twitch when others use the other word. :-) Link to comment Share on other sites More sharing options...
kitnut617 Posted May 1, 2009 Share Posted May 1, 2009 Wiki is a place where you and me (or anyone else) can edit what's written in the text, which can mean some mis-information or information passed on that some people regard as being true. Although there is some truth to what is most times added, it shouldn't be regard as gospel. I have to admit that I've always know the instument as being a compass, a compass compasses two points. I'm in the drafting (draughting) trade, trained in Poole Polytech in Dorset and the instructor called it a compass. My Dad is/was an architect from just after WW.II, he calls it a compass, his Dad (my Grandad) was also an architect, he called it a compass and my Grandad on my Mom's side was an architect and a Professor of Architecture at London University before and after WW.II, he called it a compass, I never heard any of them ask for a pair of compasses. As an aside, my Grandad on my Dad's side designed and did the architecture for the first ever airport buildings and hangers at Heston aerodrome. Robert Link to comment Share on other sites More sharing options...
xffw45343tg Posted May 1, 2009 Share Posted May 1, 2009 Discretion being the better part of valour, I'm going to bow to that impressive pedigree Robert. "Compass" has it and I'll get my coat. So how do I trisect an angle with just a "compass" then? PS/ I should have said Andy not Mike earlier, though they both seem to have got the answer they wanted. Link to comment Share on other sites More sharing options...
Mike Posted May 1, 2009 Share Posted May 1, 2009 Boblogi ewyllysia dadlau am unrhyw darostwng. Link to comment Share on other sites More sharing options...
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