Nobody replaces a blade at the right time. They replace it after the burned cut, after the piece that had to be recut, after the afternoon spent pushing harder than the saw should need. The edge went dull long before any of that.
The signals, in the order they show up
More pressure. The earliest sign, and the easiest to miss, because the change happens gradually and hands adapt. If you are leaning into a cut you used to feed with two fingers, the edge is going.
Sound. A sharp blade in wood makes a consistent shearing sound. A dull one changes pitch mid-cut and labors under the same feed.
Dust instead of chips. A cutting edge shears material into chips. A dull edge scrapes and abrades, producing fine powder. Fine dust from a circular saw or an auger bit is a clear verdict.
Burn marks. Friction heat instead of cutting. On hardwood this shows as scorched edges along the cut line. Burning also ruins the cut surface for finishing.
Wander. A drill bit that walks off the mark or a hole that comes out oversized means the cutting lips are no longer symmetrical.
Clean before you condemn
A large share of blades that feel dull are simply loaded with pitch. Resin from pine, adhesive from plywood and composite, and sawdust baked on by heat all build a layer on the tooth face. That layer increases friction, which increases heat, which bakes on more resin. It compounds fast.
The fix is unglamorous. Take the blade off. Lay it flat in a shallow pan. Wet the teeth with a blade cleaner or a household degreaser and let it sit for a few minutes. Scrub with a stiff nylon brush, not a wire brush, which can damage carbide. Rinse, dry completely, and put a light coat of a dry lubricant or a rust preventative on the plate.
A cleaned blade often cuts like a different tool. It costs a few minutes and no money.
Sharpening versus replacing
Carbide-tipped circular saw blades can be professionally sharpened, usually several times, and for a good blade the cost is a fraction of replacement. It is worth it for finish blades, dado sets, and anything with a high tooth count.
Cheap thin-kerf general-purpose blades are not worth sharpening. Neither is a blade with missing or chipped carbide, a visibly warped plate, or cracks radiating from the gullets. A cracked blade goes in the metal recycling, immediately.
Twist drill bits can be sharpened, either freehand on a grinder with practice or in a jig. The tricky part is keeping the lips equal length and equal angle, because an asymmetric bit cuts oversized holes and wanders. Spade bits are easy to touch up with a file. Auger bits reward a small file on the spurs and lips. Masonry bits and hole saws are generally replacement items.
Storage that stops damage
Most blade damage happens off the saw.
- Never stack blades directly on each other. Cardboard sleeves, dividers, or the original packaging.
- Hang blades on pegs rather than tossing them in a drawer.
- Keep bits in an index or a case where each has a position, not loose in a bag where the tips clack together.
- Keep everything dry. Surface rust on the plate is cosmetic; rust on a cutting edge is not.
The economics
A quality blade that cuts cleanly saves material, saves recuts, saves finish sanding, and puts less load on the motor and bearings. A dull one costs all of that quietly, spread across a whole job, which is exactly why it never feels urgent enough to fix.
Change the blade when it starts asking for pressure. That is the cheapest moment there will ever be.