Lap Joints and Carpentry Tips

by Albert Binoka
(Ireland)


Lap Joints and Carpentry Tips. Easy to cut but somewhat weak, lap joints connect two boards at an angle, usually at 90'. End lap joints, at the ends of boards, are made with wide, flat cuts; cross lap joints, formed by two notches, join boards at any point between the ends. A third type, called a middle lap, has an end lap and an intersecting cross lap and forms a T-shape. Middle laps that have to endure tensile (pulling) stress are best dovetailed. You can make a lap joint with boards of equal or of unequal thickness. With equally thick boards, cur half their thickness; otherwise, cur no more than half the thickness of the thinner piece. Because the grains of the pieces cross, keep the lap width under 4 inches, or the wood may split when it shrinks and swells as its moisture content changes. Mark the cutting lines on the board edges with a square or

a marking gauge. Mark the shoulders of the dovetail lap with a square; use a marking gauge on the cheek. With a I-bevel, mark the dovetail angle between 8 and 12° (a 1:5 to 1:8 ratio of to length). Although end laps are most easily cut with a table saw equipped with a dado head, you can make repeated curs with a standard blade. Or use hand tools: after marking the joint on the wood, saw the shoulder (cross-grain cut) with a - dovetail saw; then remove the waste by turning the piece on :- end and sawing along the grain with the same saw. To cut accurate cross laps, first score the shoulder lines on the waste side with a wide chisel held vertically. Then, with the chisel held bevel-up at an angle, remove a sliver on the waste side of the line to Form a groove in which to start the saw cut.

Set height of standard blade using mark on board edge as reference. Screw backer to miter gauge to prevent tearout as blade exits. Fine-tune depth of cut on scrap. Start at end and work toward shoulder. overlapping passes. Pare rough cut with chisel. You can also use a dado head, or make an initial shoulder cut with a standard blade, then clamp work in tenoning jig and remove waist

For straight cut when cutting sides of notch, press saw again wood depth guide, which should be just thick enough so that the rib atop the saw hits the guide when cut is right depth. Make a cut at each side. then score the waste at 1-in, intervals with dove-tail saw. Remove waste with a mallet and chisel, held bevel-up, and working from edges toward center. Trim corners with chisel held bevel-down.

Mark pin's shoulders, cheek, and dovetail angle. Saw dovetail shoulders. cheek. and angle, in that order, with dovetail saw. For an accurate fit. use the finished dovetail as the template to mark the housing on mating piece. Saw and chisel the housing as you did for the cross lap joint. Thanks for reading this page on lap joints and Basic Carpentry Tips

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