Line Levels

Tscarborough

On another forum, a non-construction one, to a request for the proper usage of a line level:


******X, here are the complete instructions on how to use a line level. Follow them very, very carefully or else you will have unlevel projects:

Face the lake.
Take your line level in your right hand (left if you are a lefty).
Cock your arm back like you are going to throw a football.
Bring your arm forward in a rapid motion.
Release the line level at a point that will ensure that the line level flys far enough into the lake that it is gone forever.

Now you know how to use a line level!


Was that just mean?

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master mason

or if it's football season,you can punt it into the lake.

tgeb

Yeah, that was mean, if it was asked by a Harry Homeowner type.

I caught one of my guys using a line level to layout a level line for a slab. I asked him what he was doing then let him finish, and checked it with both a 4 foot level and then again with the laser, his layout was more than an 1 1/2" out over about 10 feet.

I do agree it is best just to toss it, I have never seen accuracy from those things, but then I have never been trained in their proper usage.

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Tscarborough

You can use them in the same way as you use a water level. A line stretched between 2 points with the line level in the center will tell you if the ends of the line are equal, to the accuracy of the bubble. It can not account for the sag of the stringline, however, which is multiplied if the level is left on the line after leveling.

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Railman

The simple way to check the level is to set it up level, & then rotate 180°. It should read the same. If not, level will be 1/2 the difference. This works for any kind of level, including dumpy/field levels. Some vials are adjustable, & that's how you calibrate them.
Joe

neolitic

Someone else knows what
"dumpy level" is?

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reveivl

My experience is that you use a line level at the ENDS of the line, not the middle.

If you use it at the middle, the levels own weight will tend to distort the reading. (This distortion is towards reading true so one wants to believe it, but look out!)

If you use it at each end and it reads the same at each end (assuming the level is true), then the end points of the line are level.

I've used this occasionally over the years and have never had an issue with it.

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wesmartyn

I always place it in the center. I prefer a water level however.

Tscarborough

If the line level is in the center, it does not really matter how much sag there is in the line. Both ends will be level to the accuracy of the bubble. Using the line level anywhere other than the center is inaccurate, and the further from the center the more inaccurate it will be. After getting a good bubble, mark the ends, remove the level and re-tighten the stringline.

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master mason

just spend some $ and buy a Hilti hand held lazer.There accurate,and cheap enough to own.Over longer distances though,the red dot gets big, so transfer your marks.

Tscarborough

A peice of tubing and two glass vials are still more accurate than a laser.

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TOthe16th

a tubing water level is the most accurate thing you can use, this is correct. However its hardly as practical as a laser. They're small (about the size of a digicam), and can plumb and square. Much more practical, sophisticated, and efficient, than carrying around a garden hose and a homemade tubing contraption. But for a very long range leveling plane I cannot deny the water tubes have the lasers beat in accuracy, even the beacons and rodeyes, just not in practicality. MasterMason is right about the laser being a very handy, somewhat inexpensive, device. The beacons are excellent for larger scale as well as small scale elevation plotting. But they're pretty pricey. But back to the line levels, it would seem to me, placing it on the end of the line would eliminate most of the sag, combined with pulling the string very tight. This would seem to be superior to placing it in the middle.
Although I do agree about throwing them in the lake.

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Tscarborough

Tothe16th, your reasoning is the exact reason why line levels should be thrown in the lake. Used correctly within their limits of accuracy they are workable. Used incorrectly they simply do not work.

Below is a quick graphic to illustrate the principles.

A shows the best use. The ends are level, the line level is centered. This gives you the best possible reading for a bubble.

B shows the ends level, the line level at one side. Accuracy is reduced, both because the natural arc of the line is deformed by the weight of the level, and because the the bubble has less caternary (the distance from the line to the gray line) to work with.

C shows the ends not level, and illustrates the reduction of the catenary even more.

D shows the ends not level and illustrates the amount of catenary that is available to read the bubble is greater.

Technically, when leveling two points with a stringline, there is no need to stretch the line at all, as shown in E. The more the catenary, the more accurate a reading is possible. And on anything over very short runs, there Will be line sag.

Attached Thumbnails

 

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Tscarborough

Here is another way to look at it. When the line level is in the center of the line, the effective length of the level is the entire line. When it is at one side, the effective length of the level is the distance from the end times 2 (actually, it is worse than that, but close enough).

So on a 20' run, centered, you have a 20' long level. On a 20' run with the level 2' from one end, you have a 4' level. Which is more accurate?

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TOthe16th

yea i got yah, but i was thinking more along the lines of the level being placed completely at the end, creating a fixed point. So then the line would only have to support half the weight of a level instead of the weight of an entire level. but i see now that that would be distorted because like you said, there will always be sag. So if you put it in the center, it would have to be DEAD center to equalize the sag to create level. If it was off center it would lean slightly one way or the other wouldnt it?

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Tscarborough

Just remember that the purpose of the line level is to create two points that are level to each other using string. They are not used to set a line to level directly.

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Stewy

I dont think you give the line level enough credit. I can see your point on longer distances but for shorter distances like say 20' for setting level or slopes on decks or slabs i have used them with no issues with an accurate bubble and a tight line. I dont think you should rely on them entirely but for a quick and easy check they have a place and I would trust them more than some of the cheapo laser levels I have seen out there. The water level will not lie and are great for going around a corner etc. but are more work to use and set up to check 1 level or grade. My choice would be an optical level for accuracy but requires 2 people. Just my 2 cents.

CJKarl

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CJKarl

I HIGHLY recommend these guys. I have a PLS-5. One of the best tools I've ever bought.
http://www.plslaser.com/

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TOthe16th

cjkarl, the pls 5 on that page is almost identical to the hilti pm24 shown here.
im not too familliar with the pls tools..which would you say is more accurate?

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