Bi-Metal Hole Saws

56 bi-metal hole saws — 32 Milwaukee HOLE DOZER™ and 24 Diablo — from 3/4" through 6", plus three Diablo sets: an 11-piece, a 14-piece general purpose and a 17-piece assembled for plumbers.

Bi-metal is the general purpose choice, and the material decides the saw, not the size. A bi-metal saw is high speed steel teeth welded to a spring steel body: it cuts wood, plastic, drywall and sheet metal, which covers almost everything a rough-in actually goes through, and it is the cheapest thing to burn up when you hit a nail. When the work is thicker steel, stainless, cast iron or abrasive board, teeth like these dull fast and the answer is a carbide tooth hole saw. When the work is tile, stone, porcelain or glass there are no teeth at all — a diamond grit saw abrades its way through instead, and putting a bi-metal saw on tile ruins the saw and usually the tile.

The arbor is not included, and it is the thing people forget. A hole saw is a cup with a threaded back; the arbor screws into it and carries the pilot drill that keeps the cup from walking. There are two thread sizes, and the break is at about 1-1/4": saws below it take the small thread, saws at and above it take the large thread. Buy the arbor once, match it to the sizes you actually drill, and confirm the shank — 3/8" for most drills, 7/16" hex where the tool or the saw size calls for it. Arbors and pilot bits are stocked separately, and the three Diablo sets here ship with theirs.

Slow and steady, not fast and hard. Hole saws want low RPM and constant feed pressure. Running one at drill-bit speed glazes the teeth and cooks the weld line that holds them on, and the saw is finished long before the hole is. Back out periodically to clear chips, and on metal use cutting fluid.

The slots in the side of the cup are for getting the plug out. Once a saw cuts through, the slug stays inside and has to be pried free before the next hole — the side slots exist so a screwdriver can reach it. Cut depth is fixed by the height of the cup, so material thicker than that means cutting from both sides or moving to a deep-cut saw.

A set is worth it if you drill more than two sizes. The Diablo 17-piece plumber set carries the sizes that come up on a rough-in rather than an even spread, and the Milwaukee HOLE DOZER kits do the same in 15 and 16-piece configurations. Below that, singles are cheaper — and singles are what you buy anyway to replace the two sizes in the kit that wear out first.

Bi-metal saws sit with the rest of the hole saws, alongside step drill bits, flat boring bits and masonry bits in tools.