Rotate a board or small piece between the fingers and it might look identical from all sides. Now angle the light, and a streak becomes evident; slide a finger along one edge and it feels rougher; slide it in another direction and the same edge feels smoother. This is the direction of the grain. While you might not have given it much thought, the grain can make a difference in the way a hand saw performs, in the way sandpaper feels and works, or in the appearance of your final finish coat.
Unlike sheet goods or many other materials you might work with, wood is not just a featureless plane to work. Wood is made of grain which can either help you or hinder you with your tools. With a good hold and a sharp saw, cutting with the grain can be quite rewarding. It can be frustrating, however, to tear small splinters on an unsupported edge while sawing against the grain. This does not mean you must study wood like an expert carpenter. It only means that it pays to take a moment to observe the board, or workpiece, you are planning to work on before beginning.
You can observe the direction of grain more clearly when you are sanding. If sanding across the grain with too much pressure, you can make scratches more visible when the finish is applied; sanding with the grain can sometimes hide these scratches on the surface. Using a sanding block is great, as long as it is done with care; if you tilt the sanding block too much at one of the corners, you may round the edge before the body of the workpiece is smoothed. Sanding at the same angle or with too much force can result in dips and scratches, not a smooth finish.
A simple experiment to do as part of any mid-way sanding session is to divide an offcut into two separate areas, and sand one side along the grain with the lightest pressure. Sand the other side carelessly with the same sandpaper. Wipe away the dust and examine each area in the slant of the light. While the results may be subtle, you will begin to understand the effect sanding in the direction of the grain has on the feel of the wood. You can try the experiment again on another board by switching to a finer grit of sandpaper.
The direction of the grain is also important during the finishing process. Any dust that fills up the open grain may make the surface feel slightly rough despite careful sanding, so make sure to dust the board before applying your first finish coat. If you finish a test area of the board before completing the entire project, it will become clear whether sand scratches and tear-out remain visible. The grain may not be as noticeable during the sanding process as it is after finishing; this difference can be much better understood on an offcut than the main project piece.
Edges, and in particular end grain, require patience. You may notice that the finish soaks into the surface differently and feels rougher after it is sanded. When sanding the end grain of a project piece, keep your sandpaper under control. Applying too much force may deform the edges and corners, especially when you are sanding smaller projects such as boxes, trays, or shelf parts. Check the sanding progress on each project edge after you apply pressure with the sandpaper in order to ensure the edges and corners are well smoothed. Your goal is to have a smooth, even surface you can touch and hold comfortably, not a blank surface where there is no trace of the wood.
Before cutting and sanding, you should briefly observe the grain on the board to determine the direction you are working and where to begin testing. Checking the board before you start, you can see the grain direction, lightly feel its surface, observe any fragile edges, and decide what to try first. Taking a moment to understand the direction of grain can prevent tear-out, visible scratches, and an uneven surface finish, and can save you from many unnecessary frustrations. Learning to observe the direction of the wood grain doesn’t add time to the project, it simply allows you to learn how the workpieces wants to be sanded.