[TowerTalk] Be Careful With the Tolerance in Laser Levels (Tower base leveling.
patrick_g at windstream.net
Sun Jul 23 07:02:32 EDT 2017
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
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
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
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