So the tooth scrapes a chip rather than digging into the material. A positive-rake tooth, which is correct for wood, grabs in steel - and grabbing breaks teeth and can throw the workpiece. The negative angle keeps the cut controlled and is the defining difference between the two blade types.

Only if the saw runs at an appropriate speed, which most wood saws do not. Metal blades are designed for far lower surface speeds, and running one at wood-saw speed overheats and destroys it quickly. Dry-cut metal saws exist as a separate machine class for exactly this reason.

At least three at all times, which is what governs blade choice for tube and section. Too few and a tooth catches on an edge and chips; too many in thick material and the gullets pack with chips and the blade overheats. Match tooth count to wall thickness rather than to the metal type.

Aluminium chips weld to the tooth, and a loaded tooth stops cutting entirely. Aluminium-specific blades use a wide gullet and a tooth form that clears the chip, and a lubricant or wax is normally applied. Using a steel blade on aluminium loads it within a few cuts.

In production cutting of steel, where its longer life between changes outweighs the higher purchase price and cuts the downtime spent swapping blades on a running line. For occasional site cutting, carbide is the sensible choice, since cermet's advantage only shows across enough cuts to repay the difference and it is more brittle if the cut is interrupted or the work is poorly clamped.