For Round Holes
To determine tonnage for hot rolled mild steel (typically used in bar size angel iron, channels, tees and zees) with a 50,000 psi strength, consult Chart 1.
Example: to punch a 4″ diameter hole through 20 gauge mild steel, the chart shows 11.3 tons are required.
For ASTM A-36 steel (typically used for structural size wide flange, H and I beams, tees and zees) with a 60,000 psi shear strength, read from Chart 2.
Example: to punch a 1/4″ round hole in No. 10 gauge A-36 steel, the chart shows 3.2 tons is needed.
For Irregular Shape Holes
To determine tonnage for punching irregular shaped holes (square, rectangular, obround, triangular, etc.) multiply the length of metal to be cut by the multiplier given for a 1″ length in Chart 4.
For example: The shear length (or total distance around a 1″ x 2″ rectangular hole) is 6″. To punch such a hole in 20 gauge mild steel multiply 6″ x 1.01 (from Chart 4) = 6.06 tons. For stainless steel, this would be 6 x 1.50 = 9.0 tons.