How do I make a plunge cut with a circular saw?

Safety

What you'll need

• Circular saw with a retractable guard lever
• Clamped straightedge or guide
• Clamps
• Eye and ear protection
• Jigsaw or pad saw for the corners
• Cable and pipe detector, for anything fixed in place (optional)

Step by step

1. Decide whether you should be plunging at all.If you can start from an edge, do. If the cut is in a fixed floor or wall, a plunge saw on a rail, an oscillating multi-tool or a jigsaw started from a drilled hole are all safer. Reserve the hand-held plunge for a free workpiece on a bench or on foam.
2. Check what is behind the cut.In a floor: joists, cables, pipes, underfloor heating. In a wall: cables run vertically and horizontally from sockets and switches. Use a detector, lift a nearby board or take a small inspection hole first. This step is not optional in a fixed structure.
3. Set the blade depth just past the material.Barely through — about one tooth clear of the underside. This limits how much blade is exposed, reduces the overrun at the ends of the cut, and reduces the energy available if it does kick.
4. Clamp a straightedge to guide the shoe.A plunge cut wants to wander at the moment it enters. A clamped guide takes that away, and gives the shoe something to be pressed against while you pivot in.
5. Mark where the blade actually starts and stops.Because the blade is a circle, when the top surface is cut to a mark the underside is already cut further along in both directions. Work out the overrun by resting the saw on the mark and looking at where the blade meets the surface, and start the cut correspondingly short at each end.
6. Set the saw up on the front of the shoe.Retract the lower guard with its lever and hold it. Rest only the front edge of the shoe on the workpiece, with the blade tilted clear of the surface and lined up with the cut. Grip the saw firmly with both hands, one on the main handle and one on the front handle.
7. Start the motor and let it reach full speed before it touches wood.A blade entering under acceleration grabs. Full speed first, every time.
8. Pivot down slowly and evenly.Using the front edge of the shoe as a hinge, lower the blade into the work in a smooth controlled arc, keeping the shoe hard against the guide. Do not push forward while you are pivoting — the blade should sink, not travel.
9. Once the shoe is flat, release the guard and cut forwards.Let the lower guard drop back down against the workpiece as soon as the shoe is flat. Then feed forward normally to the far mark.
10. Finish the corners with a hand tool.Stop the saw and let the blade come to a complete stop before lifting it clear. Then complete the under-cut corners at both ends with a jigsaw, a pad saw or a hand saw so the cut ends square.

Tips

• Never plunge backwards, and never withdraw the saw while the blade is turning.
• A track saw is designed for this: it plunges vertically on a rail with the blade shrouded throughout, which removes almost all the risk. If you cut worktops or fitted floors regularly, hiring one for a day is worth it.
• For a sink or hob cut-out in a worktop, drill a corner hole and use a jigsaw with a down-cut blade rather than plunging — the finish matters and it is not a cut worth taking risks over.

Common mistakes

• Plunging with the blade already touching the timber — The blade grabs the surface as it accelerates and throws the saw sideways along the workpiece.
• Setting the blade far deeper than needed — It increases the overrun beyond your marks, exposes more blade, and stores far more energy if it kicks.
• Cutting the top surface exactly to the mark — The underside is already cut past it in both directions. On a visible piece that overrun shows for ever.
• Holding the guard back after the cut has started — The guard must be free to close the moment the shoe is flat. Holding it open through the whole cut leaves a spinning blade exposed when the saw leaves the work.

Questions people ask