[TowerTalk] Be Careful With the Tolerance in Laser Levels (Tower base leveling.
w3ea at hotmail.com
Sun Jul 23 19:30:30 EDT 2017
I have two 6 ft. Aluminum bubble levels... I use cheap black electrical tape ( not Scotch 33 or 88 ) to attach them to the first section @ 90 degree angles on one leg.... this method has served me well on quite a few tower install .
I then walk back a far distance and use a 3 ft aluminum level held vertically by the shank of a round screw driver as a SITE-BOB @ 90 degree sightings.
guy tensioning and a Loose gage and your in business .
From: TowerTalk <towertalk-bounces at contesting.com> on behalf of Grant Saviers <grants2 at pacbell.net>
Sent: Sunday, July 23, 2017 1:07 PM
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Be Careful With the Tolerance in Laser Levels (Tower base leveling.
IMO, straight is more important than plumb (assuming reasonable) for
guyed towers. Otherwise the tower is being bent and has stresses not in
the load calcs. Pro tower installers use a level-transit at each
anchor (two is enough) for tall towers to insure the guys are keeping it
plumb and straight when guys are being tensioned. A decent one is
better than +/- 3/16" at 150'. Easy to rent. Pretty hard to eyeball
that or keep a plumb bob unaffected by wind or thermals.
I think a 6' carpenters level properly used is good enough to get the
bottom section plumb and they are certainly cheap and easy to check,
even if made in China. (Stanley 6' spec 0.036" over 6', $43) It's easy
to see 0.1" error. At 100' that is 1.7". I think I measured my R65
bottom section 4 times all around before pouring and at least 2 times
afterwards. One trick is to use offsets at both ends of the level so
interference from galvanizing imperfections can be minimized. For
towers <80' a level and eyeball check of straight are probably good
enough. Laser levels - nice for drop ceilings, setting forms, and
grading. (the coolest is the dozer blade that follows the laser).
For fun, one could use a 3D mems accelerometer to measure tilt, even
cheap ones (new cars have lots of them) have sub 1 milliG resolution for
+/- 1G range. 1 deg of tilt is 0.983G Z axis output, so dynamically
measuring your tower's sway in strong winds is not so hard. Use X & Y
to measure direction of tilt. 1 deg tilt at 150' is 2.6'
Now that is REALLY gilding the lily.
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