Plug Cutters

A plug cutter is a hollow cylindrical cutter that bores around a core rather than through it, leaving a short plug standing in the waste. Snap the plug free, glue it into a counterbored screw hole, pare it flush, and the fastener disappears under a patch of the same board it came from.

That last part is the entire argument for them. A shop-bought dowel is birch or beech regardless of what you are building; a plug you cut yourself is walnut if the project is walnut, and if you cut it from an offcut of the actual board you can line the grain up so the repair reads as figure rather than as a dot.

Using them

• Drill press, not a hand drill. A plug cutter has no point to centre it and cuts on its full rim from the first moment. Freehand, it wanders and chatters. This is the one accessory here that genuinely requires the press.
• Cut plugs in a wide offcut, not a narrow one. You need material around the cutter, and you want to be able to choose grain direction.
• Cut them face-grain. Plugs cut from the end of a board are end grain: they drink finish, go dark, and announce themselves. Cut into the face and the plug matches.
• Free them with a bandsaw or a chisel, slicing under the row rather than levering each one out.
• Orient the grain before the glue goes in. Rotate the plug until its grain lines up with the surrounding board. Ten seconds of fiddling is the difference between invisible and obvious.
• Leave them proud and pare down. Chisel or flush-cut saw, then sand. Sanding a plug flat from proud is easy; filling a plug you set too deep is not.

Sizing

Plug cutters are sized to the plug they produce, and that has to match the counterbore it fills -- a 3/8in cutter and a 3/8in Forstner bit. Tapered cutters exist and are worth knowing about: they produce a slightly conical plug that wedges tight, which is more forgiving of a hole that isn't perfectly round.

The alternative

For utility work, a dowel in a drilled hole does the same job faster and the end grain shows. That is completely fine on a shop cabinet. On a piece where the surface matters, cut the plug.