[TowerTalk] Be Careful With the Tolerance in Laser Levels (Tower base leveling.

Mon Jul 24 11:14:58 EDT 2017

That had been my experience as well, but one day one of the top builders 
in our EAA chapter reported a problem with a water level he had never 
head of, nor even seen a detectable difference. BTW: He had a degree in 
Aeronautical engineering.

I don't remember what he was measuring / building but the level was way 
off.
He was working in an unheated building, but I believe the temp was above 
freezing.
The water level is easy to check. just bring the ends together with the 
tubes vertical, side by side where you view the meniscus(sp?)

I can understand where the problem comes in when using  an antifreeze as 
with time and temperature, or plain water when the temperatures are 
different at the ends of the tubes. The specific gravity can end up 
different between the ends of even a "relatively" short tube. I have no 
idea as to what caused the problem he ran into.

Using the garden hose as you do (a temporary hook up), I'd expect no 
problems. I'm curious if used over time whether any volatils would leach 
into the water and how temp differential would then affect the readings. 
Still, if the water level is just checked (easily done) it's probably 
the easiest way to level things as long as the meniscus is viewed the same.

As cheap Chinese lasers, some of the stuff they build is pretty good, 
but the tolerances used in building houses doesn't require the close 
tolerances we are seeking.

I spent many years as an Instrument tech, before going to college full 
time. Every Monday was a calibration day, including RFI measurements 
with the old Singer metrics "portable" receiver. That thing was heavy!  
At any rare, I picked up a lot of experiences calibrating measurement 
equipment.

73, Roger (K8RI)

On 7/23/2017 Sunday 7:02 AM, Patrick Greenlee wrote:
> Roger, What did you use to measure the error in the water level. My 
> experience with water levels vs 4 ft and even 8 ft spirit levels shows 
> the water level to be as close as I could read it, essentially zero 
> instrument error.
>
> I second the disparaging comment posted here regarding cheap Chinese 
> laser levels.  I have a transit and find it no better than the water 
> level.
>
> For a water level I use garden hoses with clear plastic extensions.  
> The extensions are sold to use for filling RV water tanks.  A small 
> tipped  marker pen can scribe a narrow line on each when the water is 
> not disturbed.  Some of the plastic extensions have 90 degree ball 
> valves incorporated which makes it easier to move the hoses around 
> without spilling water.
>
> Patrick        NJ5G
>
>
> On 7/23/2017 1:25 AM, Roger (K8RI) on TT wrote:
>> I've never been able to successfully use a plumb bob for more than 
>> about 10 ft vertical outdoors.  The repeat ability just isn't there 
>> for here, at least not enough to trust it enough to make adjustments. 
>> It may be absolutely still on the ground, but above 30 or 40 feet a 
>> breeze so light you can hardly detect it can produce a substantial 
>> deflection of several inches at ground level.
>>
>> Be careful with water levels. I've seen as much as an inch or more in 
>> 3 feet and when the ends were paralled, there was still the same 
>> deflection.  This as in 1/4/, 3/8ths, and 1/2 inch Tygon. It was 
>> worse when antifreeze was mixed in the water (used in some unheated 
>> garages and sheds). Water levels are commonly used in building home 
>> built aircraft.  The big box store laser transits and levels for home 
>> construction were close enough for 18 to 20' fuselage construction, 
>> but on an 18 to 24" tower base?
>>
>> 73, Roger (K8RI)
>>
>> On 7/23/2017 Sunday 1:40 AM, Clay Autery wrote:
>>> I'll use a combination of plumb bobs and water tubes....  gravity is
>>> remarkably more consistent than laser levels made in China. ;)
>>>
>>> ______________________
>>> Clay Autery, KY5G
>>> MONTAC Enterprises
>>> (318) 518-1389
>>>
>>> On 7/23/2017 12:00 AM, Roger (K8RI) on TT wrote:
>>>> When using laser levels there is a tolerance of +/- Something per ft,
>>>> yard, 10 feet, etc.  It's often a lot more than acceptable for
>>>> leveling a tower base.
>>>>
>>>> I have two, a transit and a level.  Setup and calibration are
>>>> critical.  I have a plain old combination bubble and 3 digit, digital
>>>> level. Two digits to the right of the decimal is more than enough.
>>>> Calibration is easy. Find something close to level (level is not
>>>> necessary, but convenient) The two points should be about the same
>>>> distance apart as the bolts. You can even use those bolts, getting
>>>> them close with the bubble. Then you simply turn on the digital mode,
>>>> set the level on the nuts and push a button, swap ends with the level
>>>> and push a button.  The digital level is now zeroed.
>>>>
>>>> NOTE: The calibration points must be STABLE!  The nuts can not be
>>>> loose. The digital level properly zeroed is more accurate than the
>>>> laser transit or level you can purchase at the big box stores that
>>>> require much more care in calibrating.  A surveying laser transit (A
>>>> lot more money) is accurate, but still takes care in calibrating.
>>>>
>>>> Were I to go that route, I'd rent a surveying transit, but being
>>>> frugal (some would say cheap) and a bit lazy, I'd use my digital
>>>> level. I have it, know how to use it, and with a fresh 9V battery in
>>>> it being the only cost.
>>>>
>>>> I've seen manufacturer's suggestions to use a plumb bob. Now depending
>>>> on where you live, dead calm days may be rare. We might have 3 or 4
>>>> days a year where it's dead calm long enough to use a plumb bob on a
>>>> 60 - 100 ft tower and a plumb bob is far more work than these other
>>>> methods
>>>>
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-- 

73

Roger (K8RI)

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