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

Clay Autery cautery at montac.com
Sun Jul 23 09:46:07 EDT 2017

I built my own extensions...  I adapted 500 ml graduated cylinders onto
short extensions with control valving...  I have a special hose that I
use in the middle... actually, several in differing lengths.
I'm OCD, so I have a whole procedure for setup, use, teardown, and
storage.  It involves minimizing anything that can screw with the
accuracy....  like differing temps along water column, purging for 100%
fill, reading the water level using basic chemistry skills (reading the
low point of the meniscus, etc, etc.  I have stands that hold the grad
cylinders vertical (tri-pods with center sleeves).  Can measure to
within 4" of surface.  If I need it lower, I translate it with a metal
ruler marked in 64ths, or 100ths.... depending on which readers I have
on.  <big grin>

I've never had cause to use a plumb bob from a pendulum fix point above
about 38 feet... and that was a non critical measurement.  My lightest
plumb bob is 16 ounces of brass...  And I suspend them using the
thinnest kevlar fishing string appropriate to the weight of the plumb bob.
Air mass movement IS a factor to consider, but you can control for it
most times....  measuring in the early morning works for me as it is
usually dead calm.... BEFORE the sun can start local airmass heating. 
Alternatively, here in the south in summer, you can almost always
measure in the afternoon on a clear day....  hot as blazes, but the air
is typically VERY, VERY still...


Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389

On 7/23/2017 6:02 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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