across the flats

[mr. piper]

i don't know whether i am in the wrong section with this one, but anyway, a friend of mine has a s/steel stockholding. he sells a lot of bar, when someone asks for a hexagonal bar, it is dimensioned across the longest diagonal, i.e. from point thru c/l to point. what he needs is a quick way of converting that dimension to an "across the flats" measurement. as in a bar of 25mm point to point is 25 * X =Z, where X = < 1.0, Z = a/f and also a way of changing from a/f to the greatest dim. as Z * Y= 25.where Y is >1

so what is X & Y

[Dsg]

Imagine a right angled triangle with extremities at the centre of the hexagon, a point of the hexagon and exactly half-way along a flat side. The 90 angle is at the centre of the flat and the angle between the line from the centre to the point and the line from the centre to the flat is 30. If F=flat dimension and P=point dimension - then using the formula that cos30=0.5*(square root of 3) then you can prove that:

P=F/sqrt 3  &  F=P*sqrt3 (I think !!)

[Loosehead]

Imagine you are essentially taking a line through the 2 opposing equilateral triangles rather than a full diagonal. So in round figures lets say the diagonal measure is 20ml, that means the diagonal is 2 x 10ml now bisect one of the flats to the centre of the hexagon and you have a right angle triangle, the short side of which is 5ml and the long side is 10ml. Then simple pythagorus gives us sqrt((10x10) - (5x5)) ie 8.66 so the af measure is 8.66x2=17.32. for a general formula based on the trig use COS(30)xN where N is the diagonal length. COS(30) = .866 so to get the af measure just multiply whatever the diagonal is by 0.866 for going the other way just divide the af measure by 0.866, viola

[Loosehead]

PS when I say long side, I mean Hypotenuse.

[Dsg]

Great minds Loosehead ! Shame I forgot to include the 0.5 in my final formula ! Well done.

[landie]

Why has he got a stockholding if he doesn't know what he's selling? You measure hex bar across the flats.

[mr. piper]

DSG & LOOSEHEAD, thanx for your input i will pass it on to my mate, i know exactly how you do the trig, i was just to lazy to do it myself as i can't hold a pen to clever these days, but thanx anyway!

and LANDIE, (i bet you have a land rover!) correct as stated, but it was me who would not have known how to dimension a hex bar, not my mate , he has been in business for 20 years, but cheers anyhow.

[landie]

You're welcome, didn't mean to sound facetious.