This is a continuation of my series of posts about ancient tools, and the third of four posts about plumblines. If you have not read the previous posts, Scrolls 1 and 2, this one should still be interesting, but it will be more informative if you read them first.
弘法筆を不選 ”Master Kobo doesn’t select a brush.” (Japanese saying)
“The bad workman blames his tools” (Polish Proverb)
“A bad workman never finds a good tool” (French Proverb)
Ancient Tools - The Plumbline Stick
The Plumbline Stick is a simple but still relatively precision tool not to be confused with the improvised thingamajig frequently seen littering construction sites and known as the “plumb stick,” which is just a spirit level strapped to a 2x4 of some length, and which not only combines but actually magnifies the inaccuracies of the spirit level along with the defects inherent in the standard 2x4. The low-tech but utterly reliable plumbline stick is a better choice.
The Plumbline Stick is an ancient tool, with physical examples made thousands of years ago stored in Egypt’s museums.
This tool is simply a straight, stable board of the necessary length with an offset-block mounted at the top with a plumbline attached, and another offset block of the same thickness attached near the bottom, but above the plumb bob. Two more offset blocks are attached at the top and bottom of the board’s backside to bear against the wall or column. These back-blocks too must be the same thickness, but they can be thicker than the front 2 blocks if necessary to reach past/around braces.
It is pressed tightly against or secured to the wall/column to be checked. When the plumbline settles and is just kissing the front-facing bottom offset block, the wall/column is plumb (or at least the two points on the wall/column the backside offset blocks are touching are plumb). This tool is very accurate, and can be made as long as you can handle. 12ft is easy. This potential length and reliable accuracy, which no spirit level can duplicate, makes it very useful for checking the plumb of columns, tall walls, and curtainwalls unassisted and without a ladder or lift. These capabilities make this tool critical to my job.
The plumbline stick as I have described it can be made cheaply and quickly from materials found at any construction site, with nothing but a square, saw, knife, drill and scewdriver. Some careful saw work is required, so I usually borrow the use of a sub’s chop saw to make the offset-blocks, and then drill pilot holes and attach them with drywall screws, which makes it easy to shim with paper. I prefer softwood lumber, but light-gauge steel studs work just as well.
Unlike a delicate $250 Stablia 96” spirit level, or even more costly transit, it will never be stolen. Just detach the pretty brass plumb bob, lean the plumb stick in a corner, and walk away when it’s Miller Time.
The keys to making a precision plumb stick are twofold:
- The vertical board (I prefer a 2x4, but a 1x4 works just as well) is not twisted.
- The distance from the face of the back-block to the face of the front offset-block is the same for both upper and lower sets. (The back-blocks are not shown in the images above)
I like to sand the bottom offset-block’s face smooth and spraypaint it white to make it easier to see the string’s contact. There is usually a layout crew on the jobsite somewhere that has a can of white spraypaint.
I also like to tack a “U” shaped loop of wire over the front of the bottom offset block to retain the plumbline in place while moving the plumbline stick around. Without this, I end up looking like the proverbial amorous monkey with his coy football.
The Windproof Plumbline Stick aka “Boxed Plumbline”
I mentioned above that wind is the plumbline’s enemy. An ordinary plumbline exposed to wind is nearly useless, moreso as it’s length increases.There are ways to reduce wind’s nasty influence.
- Use a heavier bob;
- Use a streamlined, symmetrical bob;
- Use a thin, smooth line. High-tensile braided fishing line like Spectra’s HPME product James Waldron recommended for stringlines (I need to get some) would be perfect;
- Shield the bob from the wind with a bucket or a box. If you cut a hole in the bottom, you can see the target;
- Or, you can use a boxed plumbline that shields both line and bob from the wind.
What the heck is a boxed plumbline, you say? Take the plumbline stick described above, and add thin boards to the sides and face enclosing the plumbline in a long, skinny box. Cut a window at the front and sides so you can check that the bob is swinging free, and confirm that the plumbline is just lightly kissing the lower offset block. Add some clear plastic operable doors over these openings to let light in and keep the wind out until the last second. This too is an ancient tool (except for the plastic), and one I have used occasionally.
You would be surprised how often glass curtainwalls are installed out of tolerance because the only consistently performed check at the jobsite was Mark-1 Eyeball and spirit level.
Modern commercial versions of the plumbline box are available made of aluminum, and which telescope to become longer, have a graduated target installed for the bob’s point, use magnets to quickly dampen the bob’s swing, and have more magnets on the backside offset points for attaching to steel columns. Very slick indeed. Check out the URL below for Shinwa’s version.
http://www.shinwasokutei.co.jp/products/77524/
Notice the video and other pictures below the big picture.
This next URL shows another Shinwa product that is a plumbline with a dial readout. Digital plumblines can’t be far away!
http://www.shinwasokutei.co.jp/products/77549/
In the next and last post in this series, we will look at the Plumbline Level.
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