Circle Diameter

Check this out:

http://www.1728.com/circpart.htm

Excellent...thanks Mikey

Thank you very much Mr. Mickey. Its very usefull for me

I'm intrigued. Mikey's answer will give you an answer, but it is interesting to speculate why you need to calculate the diameter, rather measure it. I propose we solicit guesses.

I'm going to say that you are not doing this purely as a math exercise, and that you you have a flat in a shaft that you can measure, but you don't have access to the diameter of the shaft... but you need to know the diameter... maybe to find materials to replace the shaft with one of your own construction.

Thanks guys,

I made a small tool to insert solid rivets (military applications) in a manual press and the head needed to fit snuggly in the tool to avoid deformation.

You should start by adding more lines.

that is from the center of the circle to the 2 end points of the long line.

then a line from the centre perpendicular to the long line.

Then mark the facts that is known. ie equal angles and distances.

by now you should be able to use the standard formulas to calculated the radius and diameter.

There is no formula, just high school geometry.

Draw a right triangle from the center of the circle that bisects the line segment. Now, one side of the triangle is D/2, one is 0.25/2, the other is D/2-0.07.

Apply Pythegorean theorem. Solve the equation that yields, it is not quadratic, D^2's cancel.

There is a formula called Properties of Intersecting Chords or something like that. It says the products of the 2 parts of 2 intersecting chords are equal.

So if you draw a diameter thru the chord at right angles, can write

0.07*(D - 0.07) = (0.25/2)², giving D = 0.293"

Often comes in useful. More often I'm looking for height h from centre of chord to circumference, giving a quadratic, which however reduces to linear if h<<D.

Apply Pythagoras' Theorem. Draw lines to the centre of the circle. Consider the shapes of the triangles and the known dimensions and go from there.

diameter is .29321"

General formula is:

D=Csquared/4H + H

where D= Diameter

C= Chord length = 0.25"

H = Radial distance from flat to circle = 0.07"

Put your values in this formula and you get D= 0.2932 approx.

Cheers,

Barrie