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    Ancient Tools - The Stringline

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    The stringline is simply a string. Sometimes it is called a dryline because chalk or ink are not applied, and it does not leave a mark. The humble stringline has been an important tool in construction and woodworking long before Himiunu was pacing off Cheops' resurrection pile.

    Do you own a really precise steel straightedge a meter or yard long? Most woodworkers don't. They are horribly expensive, a pain to store and haul around, and don't tend to stay straight. But in the horizontal direction, a taught stringline is perfectly straight over its entire distance, be that 1 yard or 100 yards. Think about it. I hope you can see the power of this inexpensive tool.

    One common and ancient application of the stringline is to check the straightness of a board, wall, concrete form, doorframe, cabinet carcass, etc.. For this you need a good stringline, hooks or pins, and three small blocks of wood perhaps 1/2" square and 2" long. Hooks can be made from wire, pins can be made from nails, and you already know how to make the small blocks of wood. I use 2 of the plastic widgets in the attached picture which combines pins (for pushing into wood) and a hook into a single tool with a cap. They can also be secured with a nail.

    To use the stringline, hook, pin, or nail one end on the board, wall, concrete formwork, doorframe, floor, ceiling, cabinet carcase, etc. to be checked (the "Thing"). Stretch the stringline very tight, and hook/pin/nail the stringline to the opposite edge of the Thing. Insert one of the blocks of wood you prepared under the stringline at each end. The stringline is now stretched more-or-less 1/2" away from the Thing's surface. Now, place your third block of wood between the stringline and Thing's surface, and move it the length of the stringline. Wherever the block lightly kisses the stringline without making it deflect, the surface is "in line" with both of its ends. Where there is a gap, the surface has a depression or "swamp" relative to its ends. Where the traveling block makes the string bow out, the surface has a "belly." Use a pencil, lumber crayon, or chalk to mark the swamps with a circle, and the bellys with a + mark.

    Note there are limits to the accuracy of this method when the string is stretched over the top of or underneath a Thing because gravity makes it sag in the middle. The longer the distance, the greater the sag. It can be reduced by stretching the stringline tighter. But you can easily account for the sag if you pay attention.

    I don't layout buildings or walls anymore, but I find myself using a stringline frequently when conducting quality inspections of jobsites and factory inspections of construction materials and assemblies. In many cases, it is the only tool for the job.

    More times than I can count I have asked a contractor on the jobsite if his stud/gypboard walls, concrete forms/walls, block walls, or ceilings are straight. "Yassir," he always says, "straight as a frikin arrow." He'll pull out a 1-meter straightedge, press it against the surface, and say "See?" It looks pretty good, dagnabit. Then I stretch my stringline, fiddle with my blocks and pencil, and show him the truth. I take pictures, and leave the stringline in place so he and his layout crew, framing crew, drywall crew, and their QC dude, can check for themselves. More frequently than I like, I have to show them how its done. Embarrassing for them, but its my yob. I usually need to do this only two or three times before the contractor gets the hint and starts making his walls/ceilings straight, but if his work product is still sub-standard, I make him tear it out and redo. Ouch.

    A similar situation occurs regularly when I inspect curtainwall frames (sash) or tall doorframes, especially stainless steel doors and doorframes. These expensive products have specified tolerances. During an inspection at the jobsite or factory, the manufacturer and installer always respond to my polite questions about tolerances with "Yassir, straight as frikin arrow," and with great dignity press their $20 scratched and dinged straightedge against the beautifully polished stainless steel surface while they smile at me indulgently as if I was a small schoolboy with a snot bubble coming out my nose. But 6 times out of 10, my unpretentious stringline and little blocks of wood, combined with feeler gauges, send them beetling away in a panic to find their QC dude.

    This ancient tools works well in the woodshop too when you need to check for the flatness of a board or tabletop or workbench, or the alignment of cabinet frames.

    Another common but more elegant application is testing for wind or flatness. Let's say, for example, that you need to install an h84" x w72" double door frame in a wall. Do you own 2 ten foot straightedges or winding sticks to check for twist in the assembly? How would you even using winding sticks on a doorframe in a wall? This job has been handled by stringlines forever, and the technique has applications everywhere in woodworking and construction. Sadly, most craftsmen settle for using a spirit level nowadays, and the resulting quality is quite poor.

    First, plane the sides and top of the doorframe's edges straight and square. Your stringline, used as in the example above, can help with this. Then assemble the doorframe with all 3 members square and properly aligned. Then mount one side in the opening, plumb it in both axis (a plumbline is better, but I will save plumblines for another post in this series about ancient tools), and tack it into place. I assume you know how to use wedge shims to ensure it is installed straight without bending, bowing, or "doing the wave."

    You need to have a temporary spreader board attached between the two uprights to keep the bottom of the doorframe opening the precise width.

    Second, pin one end of your stringline at one corner, pull it across the opening (not too taut), and pin it to the diagonal corner. Let's call this the "inside string." Now pin a stringline across the other diagonal. Let's call this the "outside string." The two diagonals form an "X" which is a name given to this technique. Wrap the same stringline 5 to 8 times around each end of the outside string where it rides over the frame's corners. The string must be wrapped very neatly so there is only one layer of string between it and the wood. No doubling up. This wrapping will elevate the outside string precisely the thickness of the string away from the inside string when the doorframe's edges are in plane. A slicker and quicker method is to make two shims the same thickness as the string and slip them under the outside string's ends instead of wrapping with string.

    Now, adjust the position of the unmounted vertical doorframe member so the two strings just kiss and bounce, and then kiss and bounce. If you paid attention, the doorframe is now in a single plane and free of twist. Check the doorframe during and after installation to make sure it stays free of wind.

    Do you have a workbench top or tabletop or countertop or large cabinet assembly that you need to make flat and free of wind, but is too big for your straightedges or winding sticks? Give this technique a try. It never fails. Combine it with wooden blocks and a pencil, and you will be master of all you survey.

    The precision of this tool is improved in manufacturing by using thin, kink-free steel wires stretched tightly and given an electrical charge. When the two wires touch, a circuit is closed and a light goes on or a buzzer sounds.

    A stringline must be a balance of thin and strong. A good stringline will be tightly wound, with a smooth-ish surface, versus being corrugated like a manila-rope hawser, and not hairy with frayed threads. A fuzzy stringline is absolutely useless for this job. I have never seen a usable stringline being sold at a big-box home center, BTW. The old woven nylon fishing lines were pretty good. Good stringlines can still be found in Japan.

    A bright flashlight can be useful in seeing swamps, bellys, and stringline contact.

    The world's best craftsmen have used stringlines for thousands of years. Give it a try.

    Please add your experiences and techniques to this thread.

    Stan
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    Last edited by Stanley Covington; 09-26-2017 at 11:09 PM.

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