How do I change a circular saw blade, and which way round does it go?

Safety

What you'll need

• The spanner or hex key supplied with the saw
• Replacement blade of the correct diameter and bore
• Gloves or a cloth (optional)

Step by step

1. Isolate the saw completely.Unplug it at the socket, or remove the battery. Do this before anything else, every time, without exception. This is the step that stops a blade change becoming a hospital visit.
2. Set the saw down safely and retract the guard.Rest the saw on its side on the bench with the blade clear. Retract the lower guard with the lever and hold it back, or on many saws lay the saw so the guard hangs open.
3. Lock the arbor.Press and hold the spindle-lock button, usually on the top or side of the motor housing. Turn the blade slowly by hand until the lock engages and the blade will not rotate. Some saws instead have a hole for a pin, or take two spanners.
4. Undo the arbor bolt — check the thread direction.Many circular saws use a left-hand thread on the arbor bolt so that cutting forces tend to tighten rather than loosen it. That means it undoes clockwise. If normal anticlockwise pressure is doing nothing, try the other way before assuming it is seized. The saw's manual and often a moulded arrow on the housing will say.
5. Note the order of the washers as they come off.There is an inner flange behind the blade and an outer flange in front. They are not symmetrical. Lay them down in the order they came off, with the same face up, and take a photo if you are unsure.
6. Clean the flanges and the arbor.A ring of compacted resin or a chip of timber trapped behind the blade holds it out of true, and the cut will wobble however good the blade is. Wipe both flange faces before refitting.
7. Fit the new blade with the arrow matching the guard.The teeth must point in the direction of rotation — on a hand-held circular saw, at the front of the blade the teeth travel upwards through the work. The blade and the guard both carry a direction arrow; make them agree. A blade fitted backwards rubs, burns, throws the saw about and will not cut.
8. Refit the outer flange and tighten.Flange the right way round, bolt in, arbor locked, and tighten firmly with the spanner supplied. Firm, not brutal — a bolt overtightened with a long lever can distort the flange and will be a fight to remove next time.
9. Check the blade before reconnecting power.Release the arbor lock and spin the blade by hand: it should turn freely, run true rather than visibly wobbling, and the guard should snap closed on its own. Check the riving knife still clears the blade and sits within a few millimetres of the teeth.
10. Reconnect and make a test cut in scrap.Listen and look. An unusual vibration or a burnt test cut means the blade is not seated or is on backwards.

Tips

• Keep the arbor spanner clipped to the saw or taped inside its case. A blade change deferred because the spanner is missing is how people carry on with a blunt blade.
• The lower guard must return under its own spring. If it hangs open or is sticky with resin, clean the pivot with a solvent and a brush — never wedge or tie it back.
• Store spare blades in their card sleeves or hung on a peg. Stacking bare blades chips the carbide tips against each other.

Common mistakes

• Relying on the switch being off instead of isolating — A trigger caught on a sleeve or a bench edge with a battery in place gives a running blade in your hand.
• Assuming a normal right-hand thread and forcing it — Rounding off the arbor bolt on a saw with a left-hand thread turns a two-minute job into a workshop repair.
• Refitting the outer flange the wrong way round — The flange only grips the blade properly one way. Reversed, it can let the blade slip on the arbor under load.
• Fitting the blade backwards — It does not cut — it rubs and burns, throws the saw around, and can shatter the carbide tips off.

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