Roll stock calculator

  • Thread starter Bouchard, James
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Thread Starter

Bouchard, James

Does anybody have a formula or spread sheet to calculate the number of feet of material on a core if you know the OD of the core, the thickness of the material and the outside diameter of material on the core? I have to measure the amount of material left on the core and don't want to have the un roll each one. The cores are about 6 inches OD with about a half inch of material on the core making the diameter over the material about 7 inches. The materials vary in thickness from a few mils to 1/64

James Bouchard
The cross sectional of material is equal to the the difference between the total cross sectional area minus that of the spool... A-a. It is also equal to the thickness of the material multiplied by the lenght. Therefore:

L = PI(R2-r2)/t


Steve Bailey

The cross-sectional area of the rolled-up material (PI/4)*(OD^2 - ID^2) is equal to the material length times its thickness.

Steve Myres, PE

How about [pi/4]*[OD**2-COREDIA**2]/thickness? IOW, calculate the area of the ring of material (as seen from the side) and divide by the web thickness to see how many linear inches it would take to make that much area.
The area of cross-section of the roll can be expressed in two ways. When stretched out in a straight line it is a rectangle of area L*T where L is the length in inches, and T the thickness viewed edge on.
When rolled on the drum, this same cross-section will be pi*R^2 - pi*r^2 where R = outer radius =(D/2), and r = inner radius (=C/2).
So we have L*T = pi{D^2/4 - C^2/4}
L = pi/(4T){D^2 - C^2} inches
Length = pi/(48T){D^2 - C^2} feet
= (0.06545/T){D^2 - C^2) feet (T,D and C in inches)
Try this in real life. It will be sensitive to the value of T you use, so measure that carefully.