Plumb Bobs, String and Chalkboxes
Working with string and the tools that hang from it.
Synopsis: An annotated tricks-of-the-trade for working with these very simple but effective layout tools. Good basic information, plus a few diagrams of useful knots like the clove hitch, twist knot, and bowline — all the ones that are easy to forget.
Building, it will surprise no one, is based on geometry and trigonometry. Points are established by measuring, these are connected to form lines, the lines are grouped to form planes, and these planes join to form a solid. Great — in theory. But this whole process relies on establishing straight lines with the right relationship to each other, and keeping them that way as you fill in the outline.
Levels and straightedges are good for short lines. But for long spans, a length of string, whether it is stretched between two nails, suspended by a weight on a plumb line, or coated with chalk and snapped against something, is indispensable. String can be used for many things: to plumb and level your work, to define points in midair, to tell you what’s straight and what isn’t, to establish grades, to align walls and floors, to make a circle or project its center up or down in space, and to mark your work for cutting or assembly. And if things aren’t going well, you can always use the first 100 feet or so to go fishing.
String
String, or twine, is thicker than thread and thinner than cord. Twine is made from natural hard-leaf fibers such as sisal and manila, or from cotton or synthetic fibers like nylon, Dacron and polypropylene. The fibers are drawn into slivers, counted, and spun into threads that are twisted or braided.
Coarse cotton line is ideal for chalk boxes and will do for a plumb bob. Cotton fibers stretch very little, but they rot and mildew around water and cement products, and are easily abraded. Nylon, on the other hand, doesn’t absorb water readily and is alkali resistant. Nylon string is also elastic, which is an advantage in stringing a line because you can get it very taut.
Nylon twine is either twisted or braided, and comes in twenty-some sizes ranging from a thin #3 to a thick #120. In carpentry and masonry, you’ll be fine with one of two sizes: #15, which measures a skinny 1/16 in. in diameter, and has a breaking strength of 120 lb.; and #18, which will withstand a 170-lb. force. The twisted version of either of these sizes of nylon line is pretty inexpensive, costing around $3 for a 350-ft. roll, and is adequate for laying out foundations and lining walls. It will stretch up to 8% of its length, and return to normal when released.
Braided nylon twine is a favorite with masons, because it’s more durable and easier to work with than twisted line. It costs about twice as much, but it stretches less. One kind of braided string is even heat set for minimum stretch.
Nylon string comes in three colors: white, yellow and green. Green is hard to spot in a background of grass or shrubs, but it is the best color if you’ve got fishing on your mind. White is very popular, but I like yellow for its high visibility. All three colors are sold in lengths of 250 ft., 350 ft., 500 ft. and 1,000 ft.
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