Paper properties ? do you know ?

[WJW]

Good day all,
I would be very grateful if anybody can give me a value, or direct me to information regarding the shear strength of an A4 Type sheet of paper ..... a strange request i know !
But i need this value to help with calculations for a punch i need to design.
All information / advise will be gratefully received

 

[CADShark]

What I think you need to be asking yourself is what WEIGHT of paper are you using, not what size. Thicker the paper, higher shear strength. Standard "copier" paper is 20lb. And trust me they make some really heavy paper out there. I used to be a printing press operator. Are you only going thru one at a time or a whole bunch?

 

[ornerynorsk]

Paper and paperboard products range from 1 to 5 tons per square inch shear strength. Example: 20 lb bond averages ,004 inch thick. A punch 2 inches diameter has a cutting line that is 6.283 inches long, multiplied by thickness = .0251 sq in cutting area, multiplied by tonnage, = 50 - 250 pounds cutting force required, THEORETICALLY! In actual practice, many factors will come into play, such as the geometry of your punch edge (flat or hollow)sharpness, coatings on the paper, number of layers being cut at once, etc. Good luck!

 

[WJW]

the paper will be a standard (uk) A4 sheet of paper there are 384 x 4mm holes going in there (just one sheet), am going to stager the punching in 4 stages so at any one time 96 holes will be being punched out. i just need to get a idea for torque requierments, if you have a 'ball park' value of shear i can use for a standard sheet that would be grate. (the standard density in the uk is 80 grams per sheet)
Thanks for your time on this !
Cheers
Wes

 

[dvd]

As ornerynorsk stated you will reduce the forces required by not using a flat ended punch. By using a punch that has "shear" you will not be blanking the entire hole at one instant. The forces will be less but will need to be applied over more of the punch stroke (so that the total amount of work will be the same.) By grinding an inverted vee, or a radius, into the end of the punch you can balance the forces so that the paper won't shift and you won't put a bending stress on your punch. Look at your typical desk paper punch and you will notice that the punches are not flat on the bottom. That is why it is takes less force to punch holes with a paper punch than would be predicted using the punch circumference x paper thickness x shear strength. You should decide on your punch geometry and then conduct some force experiments to determine the forces required for a single punch.