Punching and Drilling

Bolt holes in structural steel are usually produced by punching (within thickness limitations).
The American Institute of Steel Construction (AISC) limits the thickness for punching to the nominal diameter of the bolt plus 1⁄8 in. In thicker material, the holes may be made by subpunching and reaming or by drilling. Multiple punches are generally used for large groups of holes, such as for beam splices. Drilling is more time-consuming and therefore more costly than punching. Both drill presses and multiple-spindle drills are used, and the flanges and webs may be drilled simultaneously.

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