Ancient Tools - The Plumbline - Scroll 1 一ノ巻
“There was a time when nails were high-tech” (Tom Clancy)
https://lh3.googleusercontent.com/jr...UFS8FyaPii6eAc
This begins a series of posts about the Plumbline, the third in my continuing series here on Sawmillcreek titled “Ancient Tools.”
A single post containing all the information I plan to share would be too long for Sawmillcreek, so I have divided it into four parts. Since the subject is a truly ancient tool, and because I am writing this without remuneration and don't have to worry about lice-ridden editors objecting, I am using the archaic designation "Scroll" called “maki” 巻 in Japanese. The first in this series (“Ichi no Maki” or “Scroll 1”) will be about the definition of the Plumbline, and how to use it to create a vertical wall or column. The second post will be about using the plumbline to transfer layout lines overhead, and creating a vertical layout line on a wall or column. The third post will be about the venerable plumbline stick. The fourth post will be about the plumbline level. I will post them at approximately one-week intervals. I hope you find these scribblings interesting, and maybe even useful.
What is the Plumbline?
No definitive physical records exist, and no one living knows who originally invented the plumbline or when, but we know it was already an ancient tool when King Gilgamesh of Ur was knee-high to a grasshopper. Many old traditions suggest the basic tools and techniques for working wood, stone, metal and making things were among God’s original gifts to mankind. God is a builder, after all.
But let’s look at what we do know. The Plumbline is simply a line from which is suspended a weight. The force of gravity pulls this weight directly towards the earth’s center of mass making the line taut and straight forming a reliable vertical reference line.
The weight is called a “plumb bob,” and can be any stable mass that can be connected to the line. A round lump of lead makes a good plumb bob because of this metal’s high density, but it is very soft, so if the bob’s dimensions are important, it may not be the best choice.
In Japanese, the word for vertical is “enchoku” 鉛直 which translates directly to “lead straight.” Merriam Webster says the English-language word “plumb” comes from the Latin word “plumbum” meaning the metal “lead.” Nay, ladies and germs, Sawmill Creek is not all tedious sharpening threads and garage sale reports but is awash with international, historical, cultural, engineering and physics references, and worth every penny you pay.
But I digress. Let us examine the lowly lump further. Wind is the plumbline’s greatest weakness. The less the bob’s surface area, and more streamlined and symmetrical its shape, the less the wind will push it and twist it around. Indeed, stone, lead, copper, brass, hammers, chalk boxes and inkline pots have all served as plumb weights. I have used keys very frequently, and even pieces of cinder block in a pinch. Some people even use golf clubs. But cats simply won’t cooperate.
https://timelineauctions.com/upload/...ll/38967-s.jpg
A Roman cast-bronze plumb bob, 1-3 century.
Somewhere back in the mists of time, a clever fellow, probably named Robert, thought to shape a point on his plumbline's weight’s end making it easier to locate the centerline of the plumbline on a target surface below. Combine this with a tapered conical shape, and you have the classic plumb bob.
Looking back at more recent history, plumb bobs were installed during the construction of tall buildings and domes from the highest current level to the ground floor to act as datum line for both vertical and horizontal measurements. Many cathedral spires, domes and towers from medieval times still have brass datum plates embedded in their ground-floor floor to serve as plumb bob targets during construction. A remnant of this practice are the decorative floor inlays found in high-ceiling ground-floor spaces of more elegant buildings even today. As the building went higher, the plumbline was extended upwards with it. The bobs used for towers and cathedrals were very heavy, and were often set into a bucket of viscous oil to dampen the plumbline’s movement.
http://jsah.ucpress.edu/content/ucpj...?download=true
https://lh4.googleusercontent.com/qv...WrGaIIBH5xRztg
Do you see the plumbline in the photo above? Oops. Won't be able to fix that with spackle and paint.
Let’s look at some examples of how to use a plumbline/bob.
Plumbing a Wall
http://www.medievalists.net/wp-conte...on-425x268.jpg
https://lh3.googleusercontent.com/Qe...NgA9xzuyEs5iUg
https://fthmb.tqn.com/KSggWTH2eJk71O...f772b48f28.jpg
One of this tool’s oldest uses is constructing straight, plumb walls, columns, fences, retaining walls, etc. from masonry, stone, wood or concrete. This technique is still commonly used today.
The plumb bob must be symmetrical in the vertical axis in this case, usually round, but sometimes square. Round bobs with a flat top and bottom are the traditional shape for this ancient mason’s tool, but a pointed end is handier.
While the mortar is still soft, the horizontal leg of an L-shaped right-angle wooden hook is placed over the top surface of the brick or stone being laid with the vertical leg hanging down. This downward leg is the same thickness as the radius of the plumb bob minus ½ the string’s thickness.
A common and very convenient mason's tool used even nowadays is a plumbline and bob with the line passing through a block of wood or metal plate which serves as a handy dandy offset block/plate. Quick to use, but it takes two hands.
The bob is lowered down the wall’s face until it almost touches the foundation. If a line is drawn on the foundation the same distance as the leg’s thickness away from the wall’s face (called an “offset”), the position of the brick or stone being set above is adjusted until the bob’s point is right above this line. If no offset line has been prepared, the bob’s belly should just kiss the face of the lowest brick/stone course. Indexing off the bottom course of brick or stone instead of an offset line may be a bit less precise, but it is much easier since you don’t have to bend down and squint at the bob’s point.
In the case of high walls or breezes, the bob is lowered only partway down the wall and the brick or stone being laid is adjusted until the bob’s belly just kisses the face of a lower course of brick or stone. If this check is repeated every few courses, even a very tall wall will be plumb. Optical tools cannot do a more accurate job, although they may be quicker.
So next time you see some block mason use a 6ft spirit level to build a 14ft wall without bothering to hang a plumbline, you will know he is either ignorant of the techniques that made masons the most honored of the building professions throughout much of human history, or he is more concerned about speed and convenience than performing quality work.
And despite what your local surveyor with his $5,000 Leica Total Station and $350 hourly crew fee may tell you, this technique is still the most precise way to plumb stud walls and structural posts, or for setting formwork for concrete walls. Optical transits, theodolites, and stations are excellent tools, but if you own the simple and venerable plumbline and know how to use it, your wall and column work will be more accurate. Take it from someone that was trained in using such expensive tools and frequently has to deal with the consequences of operator error.
I will post Scroll 2 in a week or so, God willing and the creek don't rise.
Stan
