Accuracy Of Straight Lines Using Various Methods. - Building & Construction - DIY Chatroom Home Improvement Forum

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Old 04-14-2013, 08:00 AM   #1
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accuracy of straight lines using various methods.

When it comes to up and down leveling of any type, one can easily use a level, plumb bob, or laser to figure if the material is leveled. My question is simply this: nothing is 100% perfect, so I tend to use lasers and strings to get things plumb, but how does one get objects plumb that face each other in a mirror image? I have tried pulling strings and chalks so tight that I still cant get a straight line. I'm building a partition that combines two parallel walls. The final product if you were to view it from up high looking down should resemble an H. The walls being the vertical legs, and the partition being the horizontal leg. I would think that by putting a square on both walls and pulling a string, that would do the trick, and the line reference would be exactly 180 give or take a few degree due to wall imperfection. But I can't get this straight line to be straight. I've made it a mission to solve thiis issue without a laser. Does anyone know how to pull a straight line thats actually straight without dealing with measuring every aspect of the walls to find plumbness? The walls are prolly not square, and so I need to pull a string straight for a reference. The string will run parallel to the partition which will ensure that the partition is accurately straight from left to right AS VIEWED FROM THE GROUND STANDING IN FRONT OF THE UNIT LIKE STANDING IN FRONT OF A DOORWAY AND LOOKING AT THE THRESHOLD. That way, I can build the partition, and make sure all parts of it are lets say 3 inches from the string. It's embaressing if one stand on each edge where the partition meets the wall, and finds that the whole unit is crooked. Again, if you are creating a simple ceiling divider piece that breaks one big room into two, how can you pull a straight line so that the divider piece is 180% and in line? Horizontal leveling is easy where one can easily use a line level; bUT WHAT Good is that if the ends of the partition arent IN LINE WITH EACH OTHER CREATING A nice wall ; where the wall doesnt look like a wave as viewed at the ends looking up and a person is facing the opposite wall? The walls are not square to each other, but I'm guesing there somewhat close. I appreciate any help. Again; I PURPOSELY WISH TO SOLVE THIS LIKE THEY DID IN THE OLD TIMES WITHOUT LASERS. ONLY USING STRINGS AND SQUARES.


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Old 04-14-2013, 08:21 AM   #2
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The oldest technique I know of to get an almost perfectly straight horizontal and vertical line was used in tunneling up to at least 20 years ago. You get a straight vertical line by using a plumb bob attached to a thin wire, suspended in oil. For home use, you don't need the oil. To get a horizontal line, you can use an ordinary optical transit (not necessarily a laser).

You establish an offset from the plumb bob, say five feet. Set your transit five feet offset from the tip of the bob, make the mark on the ceiling 5 feet from the bob, and sight the transit onto the ceiling mark. Then turn 90 degrees. Accurate to whatever the accuracy of the transit is, which is often better than 5 seconds of arc. Of course, you can do this faster and easier with a laser, but you said you did not want to use a laser.


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Old 04-14-2013, 10:03 AM   #3
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that is quite the description! a 3-4-5 will give you a square corner if you have a straight line(wall) to work off of. measure 3' from inside of one wall and then 4' out onto wing wall and then 5' between those two points and that gives a true 90 degrees. find those points on floor and plumb up to transfer those points to ceiling or vise a versa , wa la- a plumb 90 degree wall/corner. a straight edge that is used in conjunction with a 4' level works to establish accuracy in the wall too.
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Old 04-14-2013, 11:26 AM   #4
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If you want to level two points over a large span or around corners or objects without a laser level, try a water level. Basically two clear tubes attached to the ends of a garden hose. $14 at the hardware store.
I use this method often for the leveling strip on forms for concrete. I sometimes build foundations under homes moved in place by Nicole Bros. A laser level is not practical because of the piers supporting the building. You can't get a line of sight to every point.
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