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.
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.
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 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 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.
The way the marking gage is held in the hand and how it is placed on the wood have an important bearing on the successful use of this tool. The marking gage is held in the hand with the first finger in front of the head and the other three fingers in back of the head, around the beam. The thumb is placed as far out as possible on the side of the beam.
The corner of the beam is placed on the surface of the wood with the head pressed firmly against the adjacent side. The gage is revolved with a slight twisting motion of the arm, while the head of the gage is kept pressed firmly against the edge.
Marking gages with exceptionally long beams are known as panel gages. The mortise gage, another type of marking gage, differs from the other types only in that it has two pins on the same side of the beam, the inner one of which can be moved along the beam by means of a slide screw at the end. The purpose of the double pin is to scribe two parallel lines at the same time. The space between the movable pin and the head controls the distance from the edge of the stock that the lines are scribed.
To scribe a line, the marking gage is set by moving the head along the beam until the space between the head and the point of the pin is equal to the distance that the line is to be scribed from the face or edge. This is done by holding the beam in one hand, then releasing the pressure on the shoe by turning the thumbscrew 1/4 turn in a counter clockwise direction.
With the rule in the other hand, the head is moved in either direction by means of the thumb of the hand holding the beam or by a pressure on the end of the rule that is in contact with the head. When the correct space between the point of the pin and the head of the gage has been established, the head is secured by turning the thumbscrew in a clockwise direction.
After tightening the head in position, the setting should be rechecked with the rule. If the head has shifted, resulting in a slight error, it can be corrected by tapping the end of the beam on the bench. If the setting is undersized, the head can be moved down by tapping the stop-screw end of the beam; if it is oversized, it can be moved up toward the pin by tapping the pin end of the beam. This should be done without loosening the thumbscrew.
When setting a mortise gage to scribe two parallel lines, the thumbscrew should be loosened and the proper distance between the two pins set. This is done by turning the slide screw in either direction, thereby moving the inner piece toward or away from the fixed pin. After the setting between these two pins has been established, the head is set by moving the head in the required direction to obtain the correct distance between the movable pin and the head. This is done in the same manner as described for the setting of the marking gage.
The thumbscrew, which holds the head securely to the beam, also holds the movable pin in a fixed position by the pressure that is exerted on the beam, coming in contact with the slide to which the movable beam is attached.
Sometimes it is necessary to sharpen or reset the pin of a marking gage. The point of the pin should project no more than of an inch. The pin can be adjusted by first loosening the screw which clamps it in the beam, and then tapping the pin on the point to move it in, or on the opposite end to move it out. When the pin has been properly set, it is held securely by tightening the screw on the side of the beam.
The point of the pin can be sharpened with a small three-cornered file to produce a chisel point. The pin is sharpened by hand, working the file on opposite sides with the pin held securely in the beam. The sharp edge should be parallel to the head.
The divider, the trammel, and the compass
Some dividers are made so that hard, sharp points may be inserted as extensions of the legs. Sometimes in this type of divider only the points are made of steel, and the remainder is made of bronze, aluminium, or other suitable metal.
An improved form is the lock-joint type. By use of the lock nut the dividers can be locked at a given setting. This type of divider is useful when one dimension is to be laid off a number of times. Because of this special usefulness it is sometimes called the transfer divider. Other types are the spring divider (sometimes called the bow divider) and the split-nut divider. They are basically the same as those described here.
The trammel is a tool used to scribe circles when the distances involved are too great for the use of the divider. A trammel consists of two metal points fastened to any straightedge by means of thumbscrews. (B) Most trammel points provide a means of holding a pencil so that the trammel may be used for drawing large circles.
The compass also marks a line. (C) It consists of one steel leg with a sharp point and one leg with a holder for a pencil. The compass differs from the divider in that the divider scribes or cuts the line into the surface, and the compass marks the line with a pencil. A compass line can be removed readily, but the divider line is relatively permanent.
The divider, the trammel, and the compass are set in the same manner. In order to set any of these tools the legs should be free to move; this is made possible by releasing whatever device is employed to lock them in position. The actual setting of the tool is done by measuring the required distance from the point of one leg to the point of the other.
When placing a divider, compass, or trammel on the rule in order to set the points, it should be kept in mind that the setting should be made with one leg at the 1-inch mark rather than at the beginning of the rule. The reason for this is that the point cannot be accurately located at the beginning of the rule. The loss of the 1 inch must be made up by adding the 1 inch to the setting being made; for example, if the divider is to be set for 4 inches, one leg will be at the 1-inch mark and the other leg will be at the 5-inch mark on the rule.
One of the uses of the divider, compass, or trammel is scribing or drawing circles. The setting of the dividers determines the size of the circle the tool will draw. The divider must be set for the radius of the circle that is to be drawn. The radius is half the diameter; a divider set for 4 inches will scribe a circle 8 inches in diameter. When drawing a circle, one leg is forced into the work, forming the centre of the circle to be drawn. The divider or compass is revolved around this leg, and the outer leg marks the circle.
The only care required for the trammel, divider, or compass is keeping the steel points sharp. These may become dull or flattened after continued use or through misuse, making it necessary to sharpen the points again. This is done on a grindstone or a whetstone.