Length or material on a roll

This question comes up periodically...check this thread:

http://cr4.globalspec.com/thread/13976#comment140483

If you have a scale you could weigh it to compute the length left on the rolls.

You might also want to take a look at this thread:

http://cr4.globalspec.com/thread/10628.

I have made a spread sheet that allows you to input numbers into it and it will give you your lengths based on the calculations the were derived from the discussion you mentioned.

I find it gets very close to the actual length of the rolls we use here. I can e-mail it to you if you like.

I don't know about him but I'd love receive it on my email: duconems@yahoo.com. thanks

that would be great

rwindbigler@yahoo.com

I have sent it to you both I hope it works for you.

OD + ID x #wraps x .131

We manufacture belt conveyors and also use rubber/vinyl material and this is the formula we use for calculating materials at inventory.

This formula works on any thickness of material.

We have material that is 1/32" thick to 1/2" thick.

the formula you provide is a good formula if you know the # of wraps. However the count for wraps can be up in the thousands for the types of material we run. Spiral calculating formulas work well to find the number of wraps.

The spread sheet I created does both calculations and takes into account the thickness of the core as well as the material and will also calculate the number of wraps on the roll and provide you with the lineal footage.

I hope it is helpful to those that needed it and if any others would like to have it let me know. I would not have been able to get it figured out without the help from others in this forum.

Thanks

I WOULD LOVE A COPY OF YOU FORMULA FOR INVENTORY PURPOSES

Yes...the length of an archimede's spiral.

L= length

r₀= radius of outside roll diameter

r_i= radius of core diameter

t= thickness of material

pi= 3.1416

This should get you Very close. The complete formula folllows. (1n) is a natural log. Most of the time the difference in answers between the short and long versions are of little consequence. If the material is Very thick, use the long version for better accuracy. Hope this helps you.

What is very thick ?

Thank you.

Hi Sal

Sorry for delay. I should have been more precise.

The short calculation doesn't take into account that each layer has a bottom radius and a top radius. So the thicker the material the less accurate the short version becomes.

I've used both on fairly thin materials like papers and films that are wrapped tightly and at known lengths of 5000+ feet and the answers were correct within a 1 1/2 feet of the total length.

Of course, neither takes into account any air space that may exist, but they are good tools for accurate estimation.

Jeff

All the mathematical methods are fine if you have any real dimension for the thickness of the material on the roll. However, GRP mat and cloth does not really lay well on the roll and thus the thickness is arbitrary.

We manufacture in GRP - see www.explorermarine.co.uk - and we buy glass by weight in kg. Hence we would do the easy stock take and count the rolls and weigh each one, and deduct the weight of the empty card tube.

Good counting

HM

You got several very good answers here, didn't you?!? I'd go for the "by weight" method myself, but only if you have to relocate the rolls anyway. Otherwise, the "measurements and math" methods are less effort. I'm also thinking that unless you are seeking very quantitative results, a simple diameter ratio might be ballpark-y enough. Full roll diameter/100% : partial roll diameter/x and solve for x.

Say the full roll is 36" for simplicity's sake. 36"/100% : 18"/x; then 36x = 1800, and then x = 1800/36 = 50%, or half of a roll. Most any fractional percentage can be determined by this method, and the carboard tube doesn't have to be subtracted.

Because we have a good scales here and we do a lot of other work by weight, I believe we are going to use the weight method. Our rolls are not always wound as tight as we would like because they go through several process's, (but the end result is consistent in weight) so the measuring does not always seem to be a good guide. Yes I have gotten several good replies and formulas. I will save much of this information because we do use other types of rolled stock where it may come in helpful for the future. I appreciate all of the replies I have gotten you have all been great.

RW

I used to work in the paper industry. We had the same problem. Go here and check out the math. If you know the caliper thickness of the sheet, outside diameter of the roll and the outside diameter of the core, this will work for you.

http://findarticles.com/p/articles/mi_m3116/is_/ai_n15691841

Thanks that was a very helpful website.

If we imagine that the roll is unwound and laid flat on the floor,the total area at the side of the roll will be equal to length multiplied by thickness. This gives the entire area on the side.This is equal to the area of the one of the sides after rolling in the roll form.Area on the side of the roll is equl to area of the outer dia minus the area of the inner dia.Now we can equate the first part with the second.

To know the length we have to divide this area by the thickness of the sheet.The result is accurate if the rooll is wound tightly.Otherwise we shoud take the factor of bulk density also in to account.

A lot of Data na d a lot of help thanks to all>>