Grooving

Also called: ploughing, trenching

Grooving is the cutting of a rectangular channel of even width into a piece of wood. What the groove is called, and how it is cut, depends mainly on which way it runs against the grain, the direction the wood's fibres lie in.

Ploughing and cross-grooving

A groove cut along the grain is called ploughing, named after the plough, the plane used to cut it. Cross grooving, also known as trenching, is the same operation but cut across the grain instead of along it. Rebating and grooving (or ploughing, the two names are used for the same thing) come up more often in joinery work than pit-sawing does. Trenching is put to work on jobs such as cutting the housings for stair stringboards, shaping raised panels, and forming rectangular or many-sided stair balusters.

Tools for the job

The dedicated tool for grooving with the grain is the plough plane; a metal-bodied version carrying eight or more cutters is often reckoned the best choice for this work. Woodworkers without a plough plane sometimes use another type of plane instead. A grooving plane's guide, called a skate, bears against both faces of the joint and keeps the cut accurate, and where the plane is wide enough it can also cut grooves sized to take loose tongues, thin strips of wood let into matching grooves in two boards to align and strengthen a joint between them. Cross-grooving is done with a dedicated trenching plane, also called a grooving plane; one design has a sole about three eighths of an inch across, with a double iron set at a skew so that it throws its shavings clear of the bench. The universal plane goes further still, carrying moulding cutters alongside its grooving and rebating cutters. Both grooving planes and rebate planes should start their cut from the far end of the work, not the near end. Cross-grooving can also be done without a plane at all, by first marking out the size of the groove with a marking knife. On machinery, a small-diameter grooving saw mounted on a spindle moulder or table saw can plunge straight into the work to cut an arched recess, and fitting a wooden plate in place of a saw table's metal one gives a wider opening for grooving with a circular saw.

Where grooves are used

A clamp joint grooves one board, the clamp, and fits the tongued ends of other boards into it, joining them across the grain. In a double-lap dovetail the groove can run right through both parts of the joint and still stay hidden once the joint is assembled. An angled rebate cut into the carcase, matched by an angled frame, can stand in for grooving in a joint of this kind. In one worked sequence for a moulded and mortised frame, the grooves for the lining tongues are ploughed after the mortises and tenons are cut, but before the beading is stuck and mitred; the wood is then pared flush to the tenon's face at a marked point on the rail before the ovolo, a rounded convex moulding profile, is scribed, its edge cut to follow the shape it meets, to fit.