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MoreCowbell 04-12-2012 09:00 PM

Spirit Level Accuracy
 
I am doing a project that involves pouring new concrete footings for several steel columns in my basement. I want as good a bearing surface between the concrete and the column base plate that I can get, which is why I am trying to think through how I will get the footing surface as level as I can get it.

The thing that I never had to consider before is that every spirit level out there, from cheap to high end, all have a gap between the edge of the bubble and the lines on the vial. When using it you need to estimate how centered the bubble is. :confused:

Does anyone know why levels are not made where the lines are spaced so that the bubble touches each one when the tool is level? That would seem to improve accuracy a great deal. Also, does anyone know of a trick to make precision leveling easier with a spirit level? Thanks.

nealtw 04-12-2012 10:30 PM

Have you ever been accused of being to anle about the details?

oldognewtrick 04-13-2012 06:01 AM

Get a laser level. No bubble, just a red optical line.

MoreCowbell 04-13-2012 09:28 AM

Quote:

Originally Posted by oldog/newtrick (Post 71388)
Get a laser level. No bubble, just a red optical line.

Interesting point. I have a rotating laser that I can try using for this. I never thought about using it over such a short distance but it is worth a try.


Quote:

Originally Posted by nealtw (Post 71384)
Have you ever been accused of being to anle about the details?

Yes. I've been accused of being anal with details exactly 23 times. ;)


Seriously, I know I am probably overthinking this but I keep thinking that it's just not a good thing to have all the weight on one edge of the steel pipe. I probably would not worry about it as much if they were filled with concrete (buckling resistance), but they are not. I thought about filling them myself but I'm concerned about excess moisture being trapped in the column after I weld the plates on. There I go again overthinking ...

nealtw 04-13-2012 10:15 AM

Fill them with concrete, moisture is not a problem without air, so tap the sides while filling it to get the air out.

notmrjohn 10-17-2012 11:03 AM

2 Attachment(s)
The reason the bubble doesn't line up with lines perfectly is because the bubble is not always the same size. The liquid and gas do not expand and contract due to temperature changes same amount or at constant ratio to each other.

In addition manufacturing process is just not that precise, temperature and air pressure variations cause different amts of liquid and gas. I have six foot level with 12 vials, Few bubbles match in size. Not a big variation, but detectable.

I dunno the size of your footings but I'd say a person with average eye sight and "guesstimating" skills isn't gonna be off by more than you can accurately build forms and pour concrete. At any rate you are going to be well within tolerances, as long as your level is accurate, have you checked it with end for end top to bottom flip test?

There are digital read out levels available.

Or use what the extra-terrestrials used when they made the pyramids.

Wuzzat? 10-17-2012 11:13 AM

Quote:

Originally Posted by MoreCowbell (Post 71383)
The thing that I never had to consider before is that every spirit level out there, from cheap to high end, all have a gap between the edge of the bubble and the lines on the vial. When using it you need to estimate how centered the bubble is. :confused:

The Grainger paper catalog publishes level accuracies in minutes of arc and maybe the online catalog does the same. You will need to convert between rise:run and arc angle using the tangent function on your computer.

For large distances I use a garden hose and the water level attachment at each end which probably gives me an accuracy of +/- 1/16" in 100'.
Experienced construction workers can tell you what's achievable using ordinary diligence and what kind of accuracy is not worth pursuing.

As far as your own eyeball accuracy, using small drill bits or bits of tinfoil or copy paper (thickness = 0.004") under one end of your level, have you and others make readings and see how you all do. You already know the error in level because you know the thickness of your shim.

Regarding anal, how bad do you have it? If you do the handwashing thing or tapping on things, that's pretty bad.
I've also heard that things have to be done in multiples of two; the first puts a curse on someone and the second takes it away.
And even Prozac is getting some bad press. :(

nealtw 10-17-2012 12:40 PM

The best way is to get prefection out of your head.
When a new house being built everyone trys to get foundation and curb wall as close to level as possible. Then you can cut each stud to length and make sure all walls coming out of the basement are level. Then you get different loads in some area with more or less crush facter. lumber with different amount of moisture drying to different sizes and crowns in floor joists and headers or beams. By the time you get to the third floor you have more waves than a wading pool.
Anything technicle being placed on a block of concrete like elevator gear, it is always done with shims.

Wuzzat? 10-17-2012 03:17 PM

And with more than 3 shims for a triangle or rectangle footprint the load sharing almost certainly is not equal.

To the OP, if you are happy with your own house check the level and straightness at different places over given distances and post your results. This survey may help future OPs.

notmrjohn 10-18-2012 08:09 AM

"different loads in some area with more or less crush facter."

Depending on temperature extremes, length and diameter of pipe, you may get expansion and contraction of metal that makes accuracy of your level moot.


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