GENERAL CUTTING | Library builder

Tight trim joints require accurate layouts, sharp saws, and consistent methods.

Recuts are a fact of life. If you’re filling and painting trim, slight gaps are acceptable. But if you’re using a clear finish, joints must be tight. Before you start cutting trim, always check the accuracy of power-saw miter-stop settings by cutting a few joints from scrap. Then cut stock a hair long so that you can recut joints till they’re right.

Cut lines consistently. It doesn’t matter whether your sawblade cuts through the middle of a cut line or just past it. What matters is that your method is consistent. For example, moving the width of a saw kerf to one side of the line or the

Подпись: other can make the difference between tight and open joints. Some pros prefer to just “kiss” the inside of the cut-line with the saw kerf so that the line stays on the board.

Keep tools sharp. This applies to saws, chisels, planes, and utility knifes. Whenever a blade becomes fouled with resin or glue, wipe it clean immediately with solvent. A sharp tool is easier to push and thus less likely to move the stock you’re cutting. Likewise, a clean power-saw blade is less likely to bind or scorch wood.

Handsaws usually cut on the push stroke.

Start handsaw cuts with gentle pull strokes, but once the kerf is established along the cut-line, emphasize push strokes. (Western saw teeth are set so that they cut more on the push stroke, whereas Japanese saws cut more on the pull stroke.) As you continue the cut, keep your elbow behind the saw, which will help you push the saw straight and follow the cut-line.

Подпись: image848" Подпись: By raising the board's end and keeping the sawblade plumb, you create a back-cut joint whose surface edges can easily be shaved to create tight joints.

Подпись: CUTTING MITER JOINTS A miter splits a 90° corner in half, with a 45° cut on each board. With the sawblade set perpendicular to the stock (0° bevel), cut a 45° angle across the face of the trim. When the cut edges are closed together, the boards should form a right angle. Of course, if door or window frames aren't square, corners may be 89° or 91°, requiring that each miter be slightly more or less than 45°, though equal. That is, miter joints should bisect whatever angle is there. If you'll be painting the joints and the trim stock is relatively narrow (3 in. wide), you can fudge the joints and fill any gaps with spackling. But if you're installing stain-grade molding, espe-

Подпись: Back-Cutting Miters Ideally, miter cuts will meet perfectly, creating a tight joint. But back-cutting (also called undercutting) can improve the odds that joints will be tight even if corners aren't perfectly square and frame jambs aren't flush to the surrounding walls. In other words, the front faces of back-cut boards make contact before the backs, so the front edges can be finely shaved to fit. It's far less work to shave the leading edge of a back-cut board with a block plane than it is to recut the joint. The easiest way to back-cut trim is to shim under it slightly in the miter box or on the saw bed, as shown in the drawings at left. The sawblade is still set at 90 degrees (0 degree bevel), but the shimmed boards receive a slight bevel because they aren't lying flat. Even a Vim-thick sliver under the board is enough to give you a decent back cut. Fussing over a miter joint is probably not worthwhile if you plan to paint the trim because slight gaps can be filled with wood filler. But open joints are difficult to disguise when wood is to be stained and almost impossible when it is clear-sealed.

use an outfeed roller or a sawhorse to support the far end of long pieces so they don’t bow or flap as you try to cut them.

Подпись: Glued biscuit joints will keep butt joints or miter joints from spreading due to seasonal expansion and contraction. Here, a biscuit joins a mitered window-stool return. Biscuits can also join straight runs of crown molding or baseboard when a wall is too long for a single board. cially if it’s 5 in. or 6 in. wide, faking a miter joint will look terrible. So if a frame is out of square, take the time to cut and recut joints as necessary so that they bisect the frame’s angle.

There are two good reasons to use miters. First, mitering aligns the profiles of moldings so that bead lines and other details join neatly along the joint and sweep uninterrupted around the corner. Second, although flat trim allows you to butt or miter joints at corners, with butt joints you would see the rough end grain of one of the adjoining boards. Even if you sand down the roughness, end grain soaks up extra paint or stain and so often looks noticeably different from adjacent surfaces.

Two Ways to Splice Trim

SPLICING TRIM

When a wall is too long for a single piece of trim, you can splice pieces by beveling their ends at a 60° angle and overlapping them (called a scarf joint), or by butt joining them and using a biscuit to hold the joint together. If boards shrink, gaps will be less noticeable in a scarf joint because you’ll see wood, rather than space, as the overlap separates. In general, scarf joints are better suited to flat stock, whereas shaped molding will display a shorter joint line if butted together.

(Viewed head-on, the joint is a thin, straight line.)

Position splices over stud centers so you can nail board ends securely to prevent cupping. Where that’s not possible, say, where a baseboard butts to door casing, nail the bottom of the baseboard to the wall sole plate, and angle-nail the top of the baseboard to the edge of the casing. Predrill the trim or snip the nail points to minimize splits.

COPING A JOINT

All wood trim shrinks somewhat. Where beveled boards overlap, gaps aren’t as noticeable, but shrinkage on some joints—mitered inside corners, in particular—are glaringly obvious because you can see right into the joint. For this reason, carpenters cope such joints so that their meshing profiles disguise shrinkage. Basically, a coped joint is a butt joint, with the end of one board

A coped joint is first mitered, then back-cut along the profile left by the miter so that the leading edge of the trim hits the adjacent trim first. That thinner, leading edge can be easily shaved to fit tightly.

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