Boring

Also called: drilling

Boring is the trade term for cutting a round hole of a set size into wood, whether the hole passes right through the piece or only partway in. It was traditionally done by hand with a brace, a crank-shaped handle that turns a cutting attachment called a bit, and is now often done with a powered drill or a dedicated boring machine.

Bits and braces

Any attachment fitted to a brace for boring holes is called a bit, and the right bit should always be chosen for the job. A ratchet brace can work close to a wall or in a corner, since it needs only part of a turn's stroke at a time rather than a full sweep. Bit types are suited to different work: the French bit, which resembles a metalworking drill in shape, is used for boring hardwoods; solid-nose auger bits have an unbreakable point, suited to tough work and to boring at an angle; and a bit with a spiral screw-feed guide point lets it bore across the grain using very little hand pressure. A set of three particular bits is mainly used to bore pilot holes for nails and screws. Gimlets bore small holes using hand pressure alone, without a brace, though a bit-form gimlet chucked into a brace bores heavier and faster than a handled one; because gimlets taper, they should be avoided on thin wood or near edges, where their shape tends to split it. Standard metal-boring twist-drills are also common in woodworking shops, mainly for small-diameter holes, though a twist-drill never cuts a hole in wood as cleanly as a properly sharpened wood-boring bit. Brad-point bits cost more than average, which is reason enough for some woodworkers to reserve them for jobs where hole quality particularly matters. An electrician's bit's extra length lets it bore deep holes, such as those needed for bed bolts, and an angle drill can bore into joist sides or corners where there is no room for a bit's normal in-line clearance. Self-drilling screws sidestep the operation entirely: their drill-shaped tip cuts through both wood and steel without any pre-drilled hole.

Marking out, depth, and clearing waste

A mortise's position is marked out for drilling by scoring a centre line along it. Depth is controlled in more than one way: wrapping masking tape around a bit marks how deep a hole needs to go, and a mortise's depth can equally be checked with a gauge, or by marking the bit itself with a file mark or a strip of tape. Dimpling the surface with a punch before drilling helps stop twist-drill bits from wandering off the mark. With fine bits specifically, a little grease and periodic withdrawal of the bit clears waste from the hole as work proceeds; if a fine bit jams, the brace is taken off and the bit pulled free with pincers.

Boring right through

Drilling through a board on a drill press calls for scrap wood placed beneath it, so the machine's table is not damaged as the bit breaks through. Boring thick stock from both faces to meet in the middle always leaves a slightly visible junction where the two holes meet; scoring a circle with the bit's spur before flipping the wood is an alternative that lets boring continue accurately from the far face instead. Going right through is not always needed in the first place: when drilling for fixings such as bed bolts or small screws, boring all the way through the wood is usually unnecessary.

Aligning and matching holes

Some holes have to match another part exactly. With a steady hand, both halves of a simple through-dowel joint can be freehand-drilled while clamped together, and clamping matching posts side by side lets both be marked and drilled at once. Where one part is already drilled, dowel centers, small transfer pins, or squared pencil marks can carry the position of its hole onto the part it must match. A jig with an adjustable fence can position a workpiece for drilling into its end grain, the surface left where the fibres are cut across, and boring horizontally into a workpiece held on a dedicated boring post, an upright fixture the work is clamped against, may be easier and more accurate than other methods. On chair or stool posts, a mortise can also be bored so that it runs tangent to the line marking the seat plane. To match a bit to a brace, a wooden collar, a bushing sized to a particular bit, can be shop-made by boring matching shank and stem holes into a cylinder of wood.

Boring by machine

Drill-bit makers publish tables recommending rotation speeds by bit size and by the material being drilled. Purpose-built horizontal mortising machines exist specifically to bore out mortises, and a multi-purpose woodworking machine's optional attachments can include a drilling head and mortiser alongside saws, a planer and sanders. Boring can also serve a smaller role within hand work, removing some of a mortise's waste material before it is finished by other means such as chiselling.