I once asked Karl Tashjian (Engineer and owner of Tashjian Towers, ex
Triex) how vertical was vertical enough and his reply was that +/-
1degree was the tolerance.
Digital or spirit (bubble) level, you should read the instrument, turn
it around, and read it again. If the readings differ, the truth is close
to half way between the readings. This is most likely not applicable to
your laser level.
I have never seen a "water level" that had an error great enough to
read. Further I believe a properly constructed/used water level is
incapable of having an error. The only error is in reading it. I
suppose theoretically a long enough water level could have a different
extant barometric pressure at the two ends but I have never used a water
level longer than 300 feet and haven't encountered that or any "spatial
anomalies" or ruptures in subspace. A strong wind blowing over the open
end of a water level could, by means of the Bernoulli principal, cause
an error in the reading. Placing scraps of cloth over the open ends of
the water level (Secure with tape or???) would eliminate the error at
moderate wind speeds. It is easy to check to see if wind matters. Just
place your hand next to the open end of the water level and move it
around. If there is no change in the level reading you can ignore the wind.
Not everyone has faith and confidence in gravity and therefore some
avoid using a water level. I had a neighbor offer to assist me in
leveling a pad for a house I was building for my mom. I had a water
level set up but the neighbor and his friend/helper couldn't be
persuaded that it could work and they insisted on using a small bubble
level to which I added a straight board for a better "average" reading.
Of course out here in our very rural setting anything more complicated
to understand than slip-joint pliers is considered high tech.
You can lead a horse to water and you can hold his head under but
whether or not he drinks is another matter.
Patrick NJ5G
On 7/23/2017 6:49 AM, Dave Sublette wrote:
OH DEAR…. Now you have me thinking. What bad things do you have to say about
the digital levels available in the big box stores? I am using one to check the plumb
of a Rohn 55 tower I am putting up. It is on a rotating joint and the guys can be
used to adjust the plumb. When I put it up the first time I used a bubble level and
it operated flawlessly for 28 years. So now do I have to be worried about the new
digital level I just bought?
Really, guys, aren’t we gilding the lily just a bit? Even on a self supporting base, which has less adjustment
that a rotating bearing, I would think that you can get it “straight enough”. We have been putting these
things up for years and I haven’t seen any news reports of “leaning towers”.
Just a bit of tongue in cheek here — 73,
Dave, K4TO
ps— my Rohn 55 is already at 55 feet, including the rotating base. It is on its way to 153 +/- feet
and is looking “straight as an arrow”. The extra odd footage is due to the short base
section with the rotary joint and rotator on it, plus the top section is only 7 or 8 feet. I forget
which.. At my age (75), the doctors (and my wife) would like me to quit climbing, so I reconfigured my 200
ft Rohn 55 with the rotary joint at 50 to this configuration with the rotary down where I can stand on the
ground and service it. I figure it will be easier to get volunteers to climb to 150 than it would be to
200 feet. I still climb to 60 feet or so. I’m feeling great.
On Jul 23, 2017, at 7:02 AM, Patrick Greenlee <patrick_g@windstream.net> 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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