Associate editor Matt Kenney answered a question about finding the radius of an arc (FWW 6-10) He gave a formula for this purpose, but it is not clear whether the formula was for any arc, or only for the arc in question.
radius = H/2 + Wsquared/8H
Whence came the numbers 2 and 8? Are they derived from the arc in question?
Please forgive my inability to express algebra on my computer.
Tom Higby
Replies
Radius to an arc
If you want to find the radius without the math, take a set of dividers and draw arcs from the existing arc, After you intersect 4 or 5 arcs, you will have the point of origin of the arc. Measure from the original arc to the point of the intersections and you will have your radius(just like the old days).
dan
Needs a picture
Tom-
It's a shame that Kenney didn't supply a picture to show how his answer was developed. If you look at the geometry, you'll see that a right triangle is involved. From the familiar Pythagorean relationship of the three sides of the triangle:
(R - H)squared + (W/2)squared = R(squared)
Following through with the math and simplifying give's Kinney's equation.
Danart, your method will determine the line of the radius but not the length of the radius.
Any pair of arcs with a radius greater than the distance between them will intersect, but only the ones with a radius equal to that of the original arc will intersect at the centre of the arc.
This has come up several times over the years. If you go to the search and enter Layout, Radius, Chord it will bring up a thread from Oct 2009 titled A layout issue with lots of good info in it.
I have no idea how to put a link to the old stuff into a post with this new format or I would have.
Rich
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