Boy, I thought I was the only one who had problems with bolt alignment after
the pour! I was too embarassed to report it because I thought you all would
think I was stupid...
I used the plywood template provided by U.S. Tower for my MA770. They no
longer supply J-bolts. Instead, they supply 2-foot anchor bolts with nuts
welded on the ends. I was concerned that the template and bolts would get
roughed up if they were in place during the pour, so I gently and slowly
pushed the whole assembly down after the pour, making sure the bolts went in
straight. But, after the concrete cured and I removed the template, I found
that it wouldn't go back on easily. Sure enough, one of the bolts had
shifted between 1/16" and 1/8". Examination of the template showed a bit of
flexing in that corner, caused by some separation of the plywood layers. I
think this might have been caused by overtightening the nuts above and below
the template (a real dilemma -- you have to tighten them enough so the bolts
won't slip, but not so much that the template cracks.)
I figured that U.S. Towers drills out the holes in the base a bit more to
compensate for this potential problem, so I wasn't too worried. My installer
said if we did have a problem, we could ream out the holes a little more, or
we could put nuts on the bolt, slip a piece of pipe over them, and "tap" it
into alignment with a hammer (as mentioned, this is the "pro" solution.) I
decided to give it a try anyway, so I slipped a piece of PVC conduit over
the bolt and gave it a few "taps" with a hand sledge hammer. This worked
surprisingly well. I also corrected some minor errors in the alignement of
the other bolts. Again, very little force was required to do this, so I'm
not concerned that the bolts or concrete were weakened.
When the tower base arrived, it was a tight fit over the bolts. The base
specs indicate that the holes are supposed to be 1 1/8" (1/8" more than the
holes in the template) but they didn't look that big to me. However, the
base did go down with a little jogging back and forth and some light taps
with a hammer. The fit was tight enough, though, that it probably would be
tough to remove it (not something I'm planning on doing anytime soon.) On
the other hand, I had no problem running the nuts up and down to level the
base, so the fit must be within tolerance. In any event, after seeing that
1" steel base plate, I think reaming out the bolt holes would have been a
*big* job.
My advice to anyone placing bolts like this is to measure the
center-to-center distances very carefully after the concrete has been poured
and the bolts have been set. I think they should be corrected to at least
1/16" or better while the 'crete is still wet. I suppose that the template
could still flex as the concrete sets, but at least you will have done the
best you can.
Also, I think a piece of 1/8" steel plate would make a much better template
than plywood...
73, Dick, WC1M
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