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The most common square, has a ruler with a groove running down the center of one face. The combination head uses this groove to lock onto the ruler at any point along its length. The combination head features faces at 45° and 90° to the rule, a level vial, and usually a scriber. The combo square is the most versatile, if not the most accurate, of the squares. It can be used to mark, measure, and set up ripping cuts, crosscuts, miters, dados, etc. Additional heads available for combo squares include a protractor head for measuring any angle or leveling any sloped surface, and a center finding head for finding the center of squares, circles, or octagons. Prices for combination squares range from less than $30 for a complete four piece set to over $80 for a Starrett square with combo head only. Needless to say, you get what you pay for, and only the more expensive squares will have accurate angles and precisely etched rules. I have found many inexpensive squares out of square by 1/16" over 10", and some even having only 15/16 in the last inch on the rule. YIKES!
The carpenter's square is simply an L-shaped piece of steel with rulers marked along its inside and outside edges. Carpenter's squares come in sizes from 9" to 24" along the longer edge. The scales on carpenters' squares are often graduated in 8ths, 16ths, 32nds, 10ths, and 12ths of an inch. Carpenters' squares are also useful for laying out stair stringers and drawing arcs.
Try squares are the traditional square of furniture and cabinet makers. The typically have a steel or sometimes brass blade fitted to a brass faced wooden stock. Most try squares have only the inner face of the stock faced in brass, so this is the accurate angle. The wooden back edge does not move evenly with changes in humidity due to the rivets securing the blade, so the outside angle is not trustworthy. Some modern try squares have wood covered brass bodies, so both angles are accurate, and some squares are even adjustable in case they should be dropped. Try squares come in blade lengths of 2" to 12".
This is essentially an all metal version of the try square, and comes in similar sizes. As with try squares, the blade is ground to ±.001" over its length.
Not generally thought of as a shop tool, the draftsman's square is still very useful in the shop. It costs little, but it is still accurate within .01" over its length, and dropping it will not cause it to go out of square. Available angles include 90°, 60°, 45°, and 30°.
Japanese Sashigane (Carpenter's Square)
This is very similar to the western carpenter's square. Sashigane are designed for use with ink, so the edges are slightly raised from the work surface so as not to smudge the ink. Also, the rulers are marked in either the metric or sun (traditional japanese) systems.
A specialty tool for accurately setting up and checking miters when a combination square is not accurate enough, as when the width of the miter exceeds a few inches. Looks like a bent T, with a wooden stock like a try square for the vertical part.
A specialized square shaped like a T, with a thick body for the vertical part. The blade is tapered on either side of the body, usually with a 1:8 taper and a 1:6 taper for marking hardwoods and softwoods, respectively. The square is set against the board with the blade flat against its face. The taper sets the angle for the tails.
Also called the adjustable bevel, has a movable blade that can be set to any angle from the body, also useful for laying out dovetails and setting up unusual miters.
A cutting gauge is the tool of choice for marking lines parallel to the edge of a board. It consists of a stock usually 4"-10" long with a blade set in the end, and a body through which the stock passes, and which sets the distance between the edge of the board and the marked line by clamping itself to the stock. The blade of the cutting gauge is beveled on one side only, with the bevel facing away from the body of the tool. This causes the blade to pull the body against the edge of the board as it is used. The blade usually has a double bevel on its one side, making a sharp, V-shaped cutting point that will cut when the tool is pushed or pulled. Some marking or cutting gauges use a sharp pin rather than a knife, however, a pin does not cut cleanly across the grain, and a knife also leaves a finer cutting line.
The mortise gauge is essentially a double bladed version of the cutting gauge designed for marking both sides of a mortise at the same time. Mortise gauges typically use pins rather than blades, but since they mark primarily along the grain, this is not a problem. The pins are independently controlled, with the space between them variable from about 1/4" to a couple inches.
The marking knife is the most accurate marking tool available to woodworkers. It consists of a skewed blade beveled on one side only, which allows the blade to mark exactly along a straightedge or try square blade. Marking knives come in left and right handed versions, beveled for use on the right or left side of the straightedge, and sometimes in left/right versions, sharpened with a spear point, but still on one side of the blade only.
The two best choices of pencils for accurate marking are carpenters' pencils and mechanical pencils. Carpenters' pencils have a rectangular lead which is sharpened to a chisel point. This allows the point to wear longer before it dulls, giving as fine a cutting line as can be had with any pencil. Mechanical pencils are the next best thing, offering ease of use and consistently fine lines.
Chalk / Lumber Crayon
These two are excellent for marking on rough lumber, or marking rough cuts on dark woods where pencil lines don't show well.
The chalk line is a simple way to mark a straight line for rough cutting, even on the uneven surface of a log. Chalk lines are mostly used where the surface marked will be removed or covered, as the chalk is permanent on porous surfaces.
Japanese Marking Tools:
Sumitsubo (Ink Line)
This is the same idea as the chalk line, only more refined. The line is actually silk thread, and leaves a fairly fine cutting line without the hassle of holding onto a straightedge while marking the line.
Sumisashi (Bamboo Pen)
The complement to the ink line, the bamboo pen is used for layout with the sashigane (carpenter's square) and for lettering pieces and joints for identification purposes.
Suji-keshiki (Marking Gauge)
Similar in design to the western cutting gauge, the main difference is that this version uses a wedge to secure the stock, and it is designed to be pulled along the board.
Copying / Scribing Tools:
A copy gauge commonly uses steel pins held semi-rigidly in a body to copy the profile of an object, a molding for example, so it can be traced onto another object or pattern. It is used by first flattening the pins against a flat surface, then pressing them into the profile to be copied. The size of the pins determines the amount of detail that can be copied by this method, and the length of the tool limits the length of profile that can be captured.
Very similar to a hermaphrodite caliper, the log scriber has an "outside" caliper leg and a straight leg for scribing. Sometimes the straight leg is replaced by a pencil, but the idea is the same: set the legs apart as required by the shape being scribed, and hold the tool level while following the contour with the "outside" caliper leg to scribe the object to be fitted. Some log scribers come with level vials to assist in holding the tool level, but with a little practice, good results can be had without leveling aids.
This is basically a narrow lead bar with a plastic casing around it, available from most drafting and art supply stores. The rule can be bent to any curve not less than about 2" in diameter. Flexible rules come with inch, metric, and no markings, and lengths range from 12" to 24".
Used for measuring inside closed areas such as turned hollow forms or drilled holes. Has two legs bent apart at the tips, and often has a fine adjustment / locking nut to help it hold accurate measurements.
Has two legs bent inwards, used mostly for measuring the diameters of cylinders. Commonly has a fine adjustment / locking nut to help it hold accurate measurements.
A combination between dividers and outside calipers, used for scribing and sometimes for marking parallel to an edge.
Inside/Outside Bowl Calipers
This is a double ended caliper, with an inside caliper at one end, and an outside caliper at the other. It is designed such that on end can be set on the work while the measurement is taken at the other end. This makes it possible to measure the wall thickness in turnings such as hollowforms, where removing the caliper would lose the measurement.
Dial & Vernier Calipers
These are used for very fine measurements, when thousandths of an inch count. Common uses include differentiating between fractional, letter, number, and metric size drills; and setting up stack-type dado blades on a tablesaw. Dial calipers are easier to read, featuring a large dial which is read directly for the hundredths and thousandths. Vernier calipers require some familiarity with reading a vernier scale, and a little math to obtain the measurement. Both types of caliper can make inside, outside, and depth measurements.
The straightedge is an often misunderstood tool, and its name is frequently applied to the common ruler, which is rarely as accurate for setup work. A true straightedge is a piece of finely ground and tempered tool steel, straight and flat to ±0.001" over tis length, without any graduations or index marks. It can be used for aligning tables on jointers, tablesaws, planers, etc. and can be used when checking sharpening stones and plane soles for flatness.
Hook rules are handy for quickly measuring from an edge, as they have a built-in hook that lines up the zero point on the ruler with the edge of the material. The hook rule is a similar idea to the hook on a tape measure, only much more accurate. On most hook rules, the hook can be detached for use as a regular rule and for adjusting, if necessary.
Center Finding Rule
The center finding rule features a scale starting at zero in the center and counting upwards toward either end. The measurements on either side are matched, and zero marks the center. Some center finding rules feature a full size scale on one edge and a half size scale on the other. The reading from the full size side is marked off the half size side to mark the center of the board.
Zig-Zag or Folding Rule
Not popular, but still made and still handy, folding rules can do a few tricks that combo squares and tape measures have yet to fully match. Many folding rules have a thin, retractable metal strip at one end for depth measurements in small holes or mortises. A folding rule can be opened partway such that one or both ends stand perpendicular to the work surface, allowing both hands to be used for setting up machinery, and unlike the combo square, a folding rule fits in a pocket yet opens to six feet in length. Folding rules come in wood and metal versions, some with calipers at one end, and in lengths from two to six feet.
The tape measure became popular in the fifties, and has since become an indispensable tool for measuring anything over a few feet. Tape lengths range from 3'to 30', and up to 100' in reel type measures. The most popular sizes for shop use are 10' to 15', with a 1" wide tape. The hook on the end of the tape slides by exactly its own thickness enabling accurate inside and outside measuring. Magnetic "clips" are available for convenient carrying on a belt without fumbling to reattach the tape to the belt after use.
Compasses, Trammels, Dividers, Etc.
There are many varieties of compass, here I'll describe the three most common types found in the shop. The first two are transplanted drafting tools: the draftsman's compass and drop compass. Both use a standard 2mm drafting lead, which is sharpened to a chisel point. The drop compass is used for small circles under 1/2" in diameter, and is less commonly found in the shop. The advantage to using these compasses is the qualities that make them good for drafting also suit them well to layout on projects: points designed not to mar the wood more than necessary, fine adjustment for accuracy, and high quality, fine lines. The other type of compass uses one sharp point and clips a wood pencil to the other leg for marking. These are less expensive, but not quite as nice as the beteer quality drafting tools.
Trammel Points / Beam Compass
Trammels are points or a point and a pencil holder that clamp to a wooden beam for marking circles with radii exceeding 6". A smaller trammel is typically called a beam compass, and comes as a complete unit. Larger trammels come with the points only and the user supplies the necessary length of beam. Higher quality trammels feature interchangeable points and pencil holders, and a screw adjuster on one point for fine adjustments.
A pair of dividers is similar to a compass, but with two sharp points for scribing arcs or stepping off equal measurements. A loose leg divider is able to replace one leg with a pencil for added versatility.
Links / Points