Making a Chalk Line

When a “chalk line” is used for marking, the string having been chalked and stretched tight between the marks t the ends of the proposed lines it must be raised in a direction at right angles to the surface of the board upon which the line is to be marked, and then dropped; the line thus struck should be sighted in order to see that it is straight.

A slight curve can also be struck with a chalk line; for instance, suppose it be desired to strike a line down the middle of a board 10 feet long, this line not to be straight, but to be a curve deviating 1 inch from the straight line; to do this, the ends of the line having been marked upon the board, a straight line is first struck, from which the deviation (1 inch) of the proposed line is marked at the middle of the length of the board.

The board is then supported upon two places near the ends (a pair of trestles will do, or two pieces of wood upon the floor) in such a way that, instead of lying flat, it droops a little in the middle; the chalked string is then put to the marks at the ends of the board, and the string, being held by the finger and thumb at the middle of its length, is raised, not vertically, but at an angle, away from the required line; if, when the string is dropped, it strikes the mark for the required line, at the middle of the length of the board, the line will most probably be found, upon sighting it, to be a true curve.

It requires practice to learn to judge the angle at which the String should be raised, but when an error occurs, it is easy to wipe out the line, and try again. The chalked string is always called a chalk line, or line, and it is used to strike a line.