The pencil and knife

Lines are made on wood with a pencil or a knife. Pencil lines are temporary lines and can be readily removed. Knife lines are cut into the wood and are therefore permanent; they are removed only with difficulty.

A pencil should be used for temporary layout lines. There are various types of pencils of varying degrees of hardness.

Pencils that are used for laying out lines on wood should be fairly hard in order to hold a sharp point, but not so hard as to scratch deeply into the surface to produce a permanent line. The point of a pencil should be kept sharp at all times so that fine lines can be drawn.

To draw long lines with a pencil, sharpen the pencil point to a wedge shape. The wedge-shaped point will not wear away so quickly, and a more uniform line will be produced. Dull pencils that produce exceptionally wide lines result in inaccuracy of layout. Lines of a permanent nature or where great accuracy of layout is required should be drawn with a knife. The sloyd knife is designed for such work.

Rules

A rule is a tool consisting of a straight-edged strip of metal, wood, or some other material, graduated in some units of measurement. Today there are but two universally accepted standards: the English system, based on the inch, and the French or metric system, based on the meter. All scales in common use are graduated or calibrated in either metric or English units; on some scales both metric and English units appear.

The graduations on a rule calibrated by the English system are actual measurements of inches and fractions of inches. These fractions of an inch on a woodworker's rule are usually in 8ths or 16ths of an inch; that is, each inch is broken up into 8 or 16 equal parts. If the inch is divided into 8 parts, each part is equal to 1/8 of an inch; if the inch is broken up into 16 parts, each part is equal to 1/16 of an inch. For greater accuracy in measuring, there are rules with graduations in 32nds and 64ths of an inch.

Figure shows a steel rule which is graduated in centimetres, millimetres, and half-millimetres on one edge, and in inches divided into 32nds on the other. In making a part whose dimensions are given in millimetres, use the metric side of the scale; and if the dimensions are given in inches and fractions of inches, use the inch side.

Sometimes it is necessary to duplicate a part dimensioned in millimetres to the nearest inch measurements, or vice versa. In drawings, metric measurements are nearly always given in millimetres.

To convert a metric measurement to inches, multiply the number of millimetres by .03937. For example, if a dimension on a drawing is given as 100 millimetres, multiply 100 by .03937 and get 3.937 inches. Using Table 1, Decimal Equivalents, in Appendix, we would find that the nearest decimal to .937 is .921875. Since .921875 is the decimal equivalent to our measurement is 364 inches. This is not exact, but when working with a scale do not attempt to come closer than firth of an inch to a given measurement. When more accurate work is required, other measuring tools are used. When working with a metric scale from a drawing dimensioned in inches we should reverse the process.

There are many kinds of rules, but the function of each is basically the same — to measure distances. Certain types of rules may be used to draw straight lines or to test a surface in order to determine whether it is straight. Folding rules, zigzag rules, and flexible-steel-tape rules, ranging from 2 feet to 6 feet in length, are designed so that they may be closed to form a relatively small compact instrument which can be easily carried or stored.

The folding and zigzag rules have their various sections held together by means of a swivel or folding joint made of metal. This permits the opening of the rule to its maximum length without loss of accuracy.

The calliper rule is similar to the folding rule, but in addition it has a brass calliper slide graduated in fractions of an inch, usually 16ths and 32nds. The straightedge rule has a straight edge along its entire length. These rules are usually made from a single piece of material, 1 foot to 6 feet in length. When new, or if kept in good condition, they can be used for drawing straight lines and for testing a surface to see if it is straight or flat.

The trysquare

Most of the dimensions on drawings appear on lines drawn at right angles to each other. When work is laid out corresponding lines must be drawn or scribed (scratched). For locating these lines and for testing the trueness of the work as it progresses, the square is used. A commonly used type is the try-square.

The trysquare is a layout tool consisting of a blade, calibrated in inches, and a handle; the blade and handle form an angle of exactly 90 degrees. The blade is set into the handle and is riveted securely in place. It must be treated with great care in use and carefully protected from damage when not in use. Before being replaced in its box after use, it should be wiped off with an oily cloth.

As a testing tool, the try-square is used to test the squareness of any corner; as a layout tool, it is used in drawing lines at right angles to an edge, face, or end of the work. When testing a corner for squareness — that is, to see if it is 90 degrees — the try-square should be held by the handle, the handle placed tightly against one surface, and the blade brought down until with the adjacent side as shown. If the corner being tested is exactly 90 degrees, no light will be seen under the blade of the trysquare. If this corner is more or less than 90 degrees, light will be seen under the blade of the trysquare.

The framing square

The framing square is a tool used for laying out various angles. It can also be used in the same manner as the trysquare for testing the squareness of a corner. This square consists of two parts, the tongue and the body or blade, which form an angle of 90 degrees. The tongue is the shorter and narrower part, and the body is the wider and longer member. The tongue and blade are both marked in inches and fractions of an inch, so that the tool can be used to lay out any size of angle. The framing square will be considered in more detail in Unit IV.

The T-bevel

The T-bevel is a tool that is used to lay out and test angles other than 90 degrees. It consists of a handle, a movable blade, and a clamping screw. The blade can be moved by loosening the clamping screw; when the blade is set, it is held securely by tightening the screw. The clamping device is designed so that the pressure of the fingers against the lever is sufficient to loosen or tighten the blade.

The bevel can be set at any angle with the aid of a protractor or a framing square, as shown. When the protractor is used for setting the bevel, the centre reference mark on the protractor must coincide with the corner formed by the blade and the handle of the bevel. With the bevel in this position, the blade is then brought in line with the graduations on the outer edge of the protractor. Check back carefully on the centre reference mark, because any movement will shift the blade at this point.

A framing square equipped with a fence is used for setting the bevel. The fence is adjusted to the required angle by means of the graduations on the tongue and body; then the handle of the bevel is placed against the body and the blade adjusted so that it is flush against the fence. The clamping device which secures the blade in any set position should be tightened as soon as the blade is set. After tightening, the setting of the bevel must be checked by placing it on the protractor or against the fence and the body of the frame square.

The marking gage

The marking gage is a tool that is used for scribing lines parallel to the edge or the face of a piece of wood. Sometimes it is used to scribe lines across the grain or parallel to an end, but this practice is not advisable because the pin which does the marking will tear the wood fibres rather than cut them. The lines are scribed by a pin with a wedge-shaped point.

A marking gage consists of the beam, head, thumbscrew, shoe, faceplate, pin, and stop screw. The beam holds the pin and carries the head. The thumbscrew is used to apply pressure to the shoe, thereby securing the head at any point along the beam. The faceplate is a piece of metal set into the head to prevent excessive wear. The stop screw prevents the head from sliding off the beam.

Sometimes it is necessary or convenient to lay off a given distance from some point, to repeat a given dimension a number of times, or to divide a line into parts. The tools used for this purpose are the divider, the compass, and the trammel.

The divider is a tool which scribes a line. It consists of two steel legs hinged at one end and sharpened to a point at the other end, a wing, a lock screw, an adjustment screw, and a spring. (A) The legs can be moved toward or away from one another by turning the lock screw in a counter clockwise direction, thereby releasing the pressure on the wing. Fine adjustments between the points of the divider can be made by means of the adjusting screw.