5-1 Using_Marking_Tools_7612

Home > Critical Path > Using Marking Tools Using Marking Tools CHAPTER 5, LESSON 1 of 5 GOAL: To identify marking tools for joinery and understand how to use them correctly. Broadly speaking, solid wood joints come in three types: butt joints, mortise and tenon joints and dovetail joints. It is commonly believed that they are difficult to lay out, but there's actually an underlying simplicity to it. Furthermore, you need only five marking tools and they, too, are relatively simple: a pencil, a marking knife and three gauges - marking, cutting and mortise. You also need two measuring tools - try square and sliding bevel - to guide your pencil and marking knife. In this lesson, I'll introduce these tools and explain how to use them. Then I'll show you how to use them on the job, marking out the typical parts of a mortise and tenon joint and a through dovetail joint. Marks are divided into two categories: surface lines made by pencil and incised lines made by knife or gauge. Pencil The most universal marking tool is the pencil. The pencil makes two specific types of lines: orientation marks and cutting guidelines. Face side and face edge marks are orientation marks, which I discussed in a previous lesson (see Chapter 4, Lesson 1: Face Side, Face Edge and Width). Use a sharp B pencil to mark cutting guidelines on mortise and tenon or dovetail joints. Marking Knife The marking knife is essential for the exacting job of marking the shoulder lines of tenons and marking the dovetail pins from the tails. Because the marking knife cuts the outside fibers that form the visible part of the shoulder line, it determines the final fit and appearance of the joint. What's more, it does so at the marking out stage, not the joint Clockwise from top left, are: a cutting gauge, mortise gauge, marking gauge, pencil and marking knife - the tools author and master craftsman Ian Kirby uses to mark out precise joinery. cutting stage. The blade of a marking knife should be thin in section and sharpened to a slim V. In side elevation the end of the knife should be rounded rather than pointed. A pointed knife is liable to produce a ragged cut because of the pressure concentrated at the point. A rounded edge, with pressure distributed over a curved edge, will produce a smooth cut. A Swiss Army knife works perfectly. Gauges Gauges are simple tools that exist in all of the world's woodworking traditions. Their wide use underscores the fact that they perform an essential function that no other tool can: they cut a fine line parallel to a board's straight edge or squared end - quickly and accurately. Such a line precisely divides the waste from the work, which is one of several critical steps on the path to clean, accurate joints. All gauges have three major parts: fence, stock and knife or spur. A spur is designed to mark with the grain; a knife is designed to cut across the grain. Trying to make one gauge do work best done by the other results in poorly made lines and badly made joints. Marking Gauge The marking gauge has a steel spur sharpened like the point of a pencil. The spur incises a line by parting the fibers of the wood. It's a perfect shape for working with the grain but totally unsuitable for working across the grain because it tears the fibers. A rounded knife produces a smooth cut because pressure is distributed over a curved edge rather than concentrated at the point. A marking gauge cuts with the grain. Note the basic gauge grip - thumb behind the fence, index finger over the fence, three fingers grip the stock. A tti h k if The spur is made of steel that's too hard to sharpen or reshape with a file, so you have to use a small sharpening stone. The spur should stick out 3/16" from the stock. To adjust the spur, clamp the blunt end of the spur in a machinist's vise and tap the gauge up or down. Cutting Gauge The cutting gauge has a small steel knife, which is held in its mortise by a wedge of cast brass. The knife incises a line by cutting across the fibers of the wood. Don't use the cutting gauge to cut with the grain. The mark is difficult to see and difficult to keep straight because it tends to wander with the grain direction. The knife usually comes from the manufacturer with a sharp point, but it works better rounded. Grind and sharpen it like any other cutting edge. There's a flat side and a bevel side - just like a chisel. The bevel always faces the waste side of the line. Remove the wedge to change the orientation of the knife. Tighten the wedge when you replace it by tapping with a hammer. The knife must be parallel to the face of the fence. If necessary, re-align the square hole with a narrow chisel so that knife and wedge seat snugly and accurately. If the wedge is a rough casting, file it smooth for a better fit. If the wedge gets lost, make a new one out of hardwood. Mortise Gauge for cutting across the grain, held in place by a wedge. A mortise gauge incises both sides of the mortise and the tenon - with the grain. The setting is determined by the width of the mortise chisel. Marking Out a Mortise and Tenon Joint Knife the tenon's first shoulder. Use the face side and face edge to continue squaring round. For the second cut, rotate workpiece 90°. Mark the second set of shoulders from the first set. The mortise gauge has a fixed top spur and a moving bottom spur. If the moving mechanism is binding, disassemble the gauge and clean the parts. That usually solves the problem. When you disassemble the mortise gauge, look out for a little metal disc that sits under the stock's locking screw. It keeps the screw from damaging the brass strip. If you lose the disc, you must replace it. Some mortise gauges have a third spur on the back side of the stock. The idea is that by using this spur like a regular marking gauge, you get two tools for the price of one. The economy is false because regular marking just wears out the fence of the expensive mortise gauge sooner than necessary. What's worse, you will likely one day puncture your thumb on one of the spurs. Using the Gauges Despite the nuances of each gauge, all require the same grip and operate much the same way. The following instructions assume you are right- handed. Practice the basic gauge movements first without the added complication of making a mark. Set the fence of the marking gauge 3/4" from the spur. Hold one end of the practice workpiece in your left hand, trapping the ends between your chest and a bench stop or vise. Press the gauge against the face side and rotate it forward, like a throttle on a motorcycle, raising the spur above the workpiece. Press the fence against the face edge and push the gauge down the workpiece. Apply pressure Set the mortise gauge with the chisel you'll use to chop the mortise (top right), then mark the tenon edges and end with your mortise gauge (above). Turn to the marking gauge (bottom right) to mark the tenon sides and end. Marking Out a Typical Dovetail Joint Set the cutting gauge 1/32" less than the thickness of the pin piece (left). Knife all the shoulder lines with the cutting gauge (right). Lay out the tails by squaring across the top with pencil. Mark the slope with pencil and sliding bevel. Extend the pencil guidelines well below the shoulder lines to help guide the dovetail saw (left). Mark the pins from the tails with a marking knife (right). inward at 90° to the edge of the workpiece and forward down its length parallel to the edge. Once the movements become fluid, rotate the gauge backward until the spur touches the workpiece. Initially, especially if the wood is hard, make several passes, strengthening the mark by increasing the rotation with each pass. Once proficient, you will make a crisp mark in a single pass. Once you get the hang of it, avoid clamping the stock you are marking to a bench or table, in order to save time and fuss. It's possible to do this even when you must mark the workpiece's full length. Tilt short workpieces slightly on edge so the gauge rides on the high side and clears the bench at the end of the cut. Long boards hung over the edge of a table or your workbench are usually heavy enough so that clamping them is unnecessary. When marking out joints, you often need to stop the gauge line at a given point. Before marking the line, position the gauge so that you can drive the spur deeply into the workpiece about 1/8" from the stop point. When you mark the line, the spur will drop into the hole and stop the travel of the gauge. Mortise and Tenon Joint With these simple steps in mind, now you're ready to start marking up joints on an actual project (see photo series on previous page). You mark the shoulder lines of a tenon with marking knife and try square. First measure the length of the tenon from the end of the rail. Register the stock of the try square against the face edge and lay the blade on the face side. Hold the try square in place by pressing down with the index finger and squeezing it between your thumb on the stock and three fingers on the far edge of the workpiece. Hold the knife vertical to the try square blade and incise the line. Before making the second cut, rotate the workpiece 90°. It doesn't matter whether you mark the face edge next or the opposite edge. It does matter that you reference the stock of the try square against the face side. Insert the knife in the nick of the first line and slide the try square to it. Using the knife to position the try square is much easier and more accurate than guessing the try square position by eye and then moving the knife to it. Dovetail Joint A dovetail joint has two parts, a tail piece and a pin piece. The tail piece is made first and the pin piece is marked from it. Knife the shoulder lines on both pieces with a cutting gauge (see photo series at right). Set the cutting gauge to just less than 1/32" of the Square down cutting guidelines from the pin marks with pencil and try square. thickness of the stock. Knife around the pieces with the cutting gauge fence riding on the end grain. For a downloadable PDF of this lesson, click here. Designed for a 3-ring binder, the lessons are printer-friendly and available for 99 cents each. Next Lesson: Mortise and Tenon Joints Click Here to Return to the Top of the Page Related Articles - Arts and Crafts Movement - More Dovetail Lore - Making a Single-Lap Dovetail - Perfect Dovetails - Gluing and Clamping - Your First Veneering Experience - Frame-and-Panel Variations - Frame-and-Panel Doors - Final Construction Stages - Initial Construction Stages Advertisement