Almost every woodworking task starts with an accurate layout. Without these guidelines to follow, the table saw, drill press, band saw, and all your other cutting and shaping tools aren't of much value.
Often, the first tools you pick up when starting a project are the ones used to lay out the parts and joinery. So having a complete set of these essential tools is key to getting the job started down the right road. Here's a short list of the basic layout tools that I wouldn't want to be without.
Combination Square. A high-quality, 12" combination square is surely one of the most versatile layout tools you can own. Not only can it be used to mark accurate 90° and 45° lines, the sliding blade can be used for measuring, as a short straightedge, and as a layout gauge. Don't skimp on this one. Buy the best combination square you can afford. It'll get used every day and last a lifetime.
Tape Measure. For making large scale layout measurements quickly, a 12' or 16' steel tape measure can't be beat. The end of the tape hooks firmly over the end of a workpiece for easy outside measurements, but also adapts to inside readings.
Look for a tape with a 3/4"- or 1" wide blade that has fine, easy-to-read markings, then take good care of it. If the tape starts to wear or the hook gets damaged, replace it.
Ruler. A 6" steel ruler with etched graduations comes in handy for all sorts of precise layout tasks. The advantage over a bigger rule is in the compact size, thin blade, and the distinct, easy-to-read markings. You can use it lying flat or turn it on edge to get a better read when necessary.
My rule earns its keep when laying out dovetails, mortises, tenons, and any other joinery for which dead-on accuracy is a must. I keep it in my apron pocket at all times.
Straightedge. Project parts (and the layouts needed to cut them to shape) come in all different sizes. When working on a project that requires large panels, a 36" or 48" aluminum straightedge is invaluable.
The essential job of a long straightedge is to connect measured marks with a layout line. For this, you don't need an expensive "machinist's-quality" tool. Just find one that's straight and rigid.
Marking Knife. A pencil line is adequate for many layout tasks, but for more demanding work, the fine, incised line made by a marking knife is more accurate. A marking knife is my choice for scribing dovetail pins from the tails, or marking the shoulders of tenons and the cheeks of mortises.
The sharp line left by a marking knife leaves no doubt where to make a cut. The shallow "groove" created by the knife can even be used to position a chisel when cleaning up or fine-tuning a joint.
Compass. Not all woodworking is done along straight lines. It's often the graceful curves you add to a project that attract the most attention. To draw these arcs and circles easily and accurately on a workpiece, you need to keep a compass on hand.
The inexpensive compass shown here (my favorite) has spring-loaded arms and a screw adjustment that allows you to easily zero in on a radius up to 4 1/2 ". If your projects often have larger curves, consider adding a beam compass to your tool collection as well.
Bevel Gauge. Whenever a project layout calls for an angle other than 90°, you'll find that a sliding bevel gauge is indispensible. The slotted blade on a bevel gauge can be adjusted and locked at any angle, as well as extended or shortened as needed. I call on mine when laying out dovetails or other angled joinery, and to transfer angles from part to part or shop drawings.