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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