Cut Lines

A sharp pencil and straight edge are just the beginning to cutting in the right place. Click image to enlarge

Little Errors = Big Problems

Text and Photos by Tom Hintz

   We begin each project by marking and cutting wood. Seemingly minor errors, even this early in the process, can lead to ill-fitting joints, out-of-square conditions or a myriad of other problems.

   Logic suggests we should use a tool that makes a mark the exact width of our saw blade. That way we could precisely indicate the intended path of the blade. Unfortunately, logic and reality have not converged on this portion of woodworking just yet.

Measuring Tools

   How we use tools to lay out cut lines can be partially responsible for errors in finished size. A case in point is the metal tape measure, notorious for loosening tips. Most tape measures come with tips that are loose - but with a reason. The tips are designed to slide in and out to compensate for the thickness of the tip itself. When holding the end of the tape against an object, like when measuring the inside of a box, the tip slides in so the markings are correct.When the tip is hooked over the end of a board, the tip slides out a specific amount (equal to it's thickness) so the markings are again correct.The problem comes when the user lets the end piece impact the case when retracting the blade. That damages the little slots that control the amount of travel the tip is supposed to have and the tape becomes less than accurate.

   To eliminate these errors, some start their measurement at the one-inch mark, and then add an inch to the reading at the other end. Sound easy to get confused? You bet.

   The "start at one, add one" system has another drawback. If the piece being measured is more than several inches long, keeping the one-inch mark at the beginning of the board while trying to mark a cut line farther down the piece accurately is all but impossible. You may be able to do this accurately, every time--I can't. Whenever possible, I use combination squares or metal rules and yardsticks to lay out cut lines.

Learn to identify the good and waste sides of your cut lines to avoid expensive mistakes. Click image to enlarge

Cut Line Indicators

   One way to help prevent cutting errors is to incorporate an indicator into your cut line that identifies the good and remnant sides of the mark. This is not a new trick, but a valuable one if applied consistently.

   I always add a short wavy line just to the remnant side of my cut lines. Some woodworkers finish their cut lines with a small "tail" that always runs toward the good side of the cut line, others towards the remnant side. Whatever method you use, whichever way you point it, learn to do it the same way every time.

   When marking angle cuts, many woodworkers make a small mark indicating where the cut is to be made, but add another indicating how the angle should be cut. Adding this second mark will save time and wood. I promise, if you do not indicate the direction of the angle, you will make a mistake. It happens to everyone.

Line Decisions

   After the cut line is placed correctly, there remains ample opportunity to mess things up. Do you cut on the line? To the left of the line? The right? Split the line? Picking the wrong option for the situation may be only slightly worse than settling for hitting the line at random. To insure the best results in our projects, we have to make all of our cuts accurately, and the same way each time.

(Top) Learning to place the edge of the blade at the right spot, and do it consistently is very important. (Bottom) This is the total error possible while keeping a standard 1/8-inch-wide blade in contact with the cut line. Click image to enlarge

   Let's say you lay out a pencil line 30 inches from the end of a board. If hitting the line with some portion of a standard 1/8-inch-wide blade is close enough, you have nearly ¼-inch of possible error. In this case, I try to split the line (assuming the good side is to the left, the waste to the right of the line) with the left edge of the blade. If my cut line was made at the correct measurement, this technique produces an accurately sized board. By using this procedure each time, the variance from piece to piece is minimized.

   Another common practice is using one piece of wood as a gauge to mark others meant to be identical in length. In this case, we know the entire line is actually in the waste portion. To get the most accurate cut we need to take the whole line, running the edge of the blade down the edge of the line.

No Cut Line

   When making a number of identical pieces, the easiest cut line to hit is one we do not make at all. Using a stop block (see our story on this technique) takes just a little longer to set up, but makes this operation much faster, and very accurate. The down side is that this technique is usually used on a radial arm saw or power miter box.

   Some lengths can be safely cut on a table saw by installing an extended miter fence with a stop block attached at the correct place. The overall length of the work piece must be large enough to be cut safely. If the work piece is too large, they can be hard to handle on the table saw, making the operation dangerous.

A zero-clearance insert helps give a tighter "site picture" when trying to align the blade with the cut line. Click image to enlarge

Cutting Aides

   There are few effective devices that make hitting the cut line accurately easier. The radial arm saw is ideal because we can bring the blade forward and touch the wood to be sure we have the alignment correct. The miter saw is a close second.

   Using the miter gauge on the table saw is probably the most difficult because of the blade meeting the wood from the underside, essentially out of sight. Zero clearance inserts help by providing a better "sight picture." With a little practice, you can align your cut line to the edge of the blade slot in the insert and produce surprisingly accurate cuts.

   Learning to cut on marking lines accurately takes practice and discipline. If you can teach yourself to use the same techniques every time you make a cut this skill improves rapidly. As this skill improves, the fit and finish of your projects gets better as well.

Related Story

Accuracy In Woodworking

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