Formula for Determining Finished Good Roll Diameter

[d-wright]

We have a formula we use to determine finished good roll diameter but it does not seem to be very accurate.

Does someone have a formula that they could share that would meet our needs? We are trying to determine roll diameter for packaging prior to running the parts.

 

[Stijloor]

What is your current formula?

Stijloor.

 

[d-wright]

I have attached the spreadsheet we are currently using

 

[Frank T.]

d-wright,

This page may be of some help or you could just change the formula in E5, of your spreadsheet, to:

=IF(E4>0,"GIVEN",SQRT(((48*F4*D4)/3.14159)+C4^2)).

Hope this helps.

 

[Tim Folkerts]

I agree the formula doesn't seem very good. if nothing else, when you have a length of 0, the outer diameter is only 0.37" while the "inner" diameter is 3"!

I would go back to geometry. The volume of the material is V = L*W*t
When it is wrapped on a cylinder, the volume of the "cylinder with the center missing" would be V = pi*(R_outer^2 - R_inner^2)*W

Setting these equal and doing a little algebra gives

R_outer = [ (12*L)*t/pi + R_inner^2 ]^0.5 or
D_outer = [ 48*L*t/pi +D_inner^2]^0.5

The 12 is to convert from ft to inches; t= thickness; L=length;

or in your spread sheet SQRT(48*F4*D4/PI()+C4^2)


This seems to work pretty well. There might be a bit of a "fudge factor" needed if the material has any gaps as it is rolled.

I get 13.36" for a 150' roll, compared to your 13.03. And I get 3" for a 0ft roll, which is what it should be!


Tim Folkerts


P.S. Looks like Frank beat me to the punch. Nice to see we get the same formula

 

[d-wright]

thanks for you help.

 

[Stijloor]

P.S. Looks like Frank beat me to the punch. Nice to see we get the same formula

Math Wizzards....

Stijloor.

 

[d-wright]

Math Wizzards....

Stijloor.

gotta luv em