I need a calculation to determine the outside diameter of a roll of film.?

Question

I know the thickness, the footage and the core diameter.

Answer 1

First work out the circumference of the core.

pi * diameter = circumference

Then divide the footage of film by the circumference, this will give you how many times the film wraps around the core.

Work out how many wraps you have and multiply it by 2 (as you get a layer either side on one plane or another be it x or y).

Now add the wraps thickness to the original core diameter, this gives the outer diameter.

Can you supply the other numbers and I can do it for you.

Answer 2

The first answer is a little wrong

The reason is that the diameter increases with more turns.

Rather, do this as a volume problem.

Let W be a variable for the unknown width; it will cancel out.

The volume of the core is pi * (core radius)^2 * W

The volume of the film itself is W * length * thickness.

Add these together to get overall volume, then use the formula for volume of a cylinder again to get overall radius.

You're done!