Rivet and other holes in boiler plates must be drilled and not punched. Holes must be carefully located on the plates from the layout diagrams. Plates which are not to be heated for flanging or other purpose, as in the case of shell plates, may have the holes drilled as soon as they are laid out. It is well to bear in mind that, in plate edges which lap, rivet holes are drilled in one plate according to the lay-out diagram, and these holes serve as guides for drilling the lapping edge of the other plate. When two plates are thus drilled in contact, they must always be taken apart afterward and the metal chips and burr (rough edge of the hole) removed, otherwise the joint would not be tight after riveting together.

The principal drilling machines of the boiler shop are multiple and portable drills. The multiple drill (also called the gang drill) is a vertical-drilling machine with several drill spindles mounted at adjustable intervals along a straight carrying bar. Portable drills are either pneumatic or electric driven, and are much used for drilling holes in plates after the parts of the boiler are assembled and temporarily held together by a few bolts. Portable drills save shifting the position of heavy boiler parts for drilling. The ratchet drill, for drilling by hand, is useful in confined spaces, but its work is slow.

Holes for boiler tubes, usually about 3 inches in diameter, are drilled in the tube sheets by a tube-hole cutter, which cuts a disc of metal from the hole instead of cutting this metal out in fine chips.