Your home center's tool rental division should have what you need...work
backwards from the hole size on the plate - it it is a little bigger
than 1/2" you need 1/2" anchoring...tyipically this is down with a
threaded rod - usually available from a nut and bolt house like a "House
of Threads" or "East Armpit Bolt & Screw" etc... they will also sell the
adhesive to set the bolts...opt for the best galvanizing option they
have - these will have lots of water streaming past them might as well
opt for hot dip galvanizing if available over a simple plating - and -
certainly do not get "black" or unplated t-rod.
If you are going to anchor the rods in construction epoxy make sure that
what you are drilling into is not just a thin slab - drilling a thin
layer like that usually just creates cracks starter holes... If the pour
is indeed deep then you can use the epoxy anchoring system... the
manufacturer of the anchors will have a chart where you cross reference
anchor bolt diameter, length and hole size and it will tell you how much
epoxy and how big around the hole you should drill is....
I would recommend that as soon as all the bolts are shoved into the
epoxy you lay the base plate on down - this will make sure that when the
epoxy sets the bolts are indeed where you want them to be and not off
center forcing you to drill out the plate and in so doing upsetting the
You may also wish to attach the first section of tower to that plate and
make sure that you are getting it started plumb - if the slab is typical
of most it is not perfectly level (they do need to shed water, ya know)
and just because that plate sits tight down on it does not mean that it
is going to provide you with the correct "take off angle" for you tower.
Some of the large drills [you will want a hammer drill and a masonry bit
of the appropriate diameter (see above)] have bubble levels built into
the housing to help you sight a plumb hole - otherwise have friends
watch you as you drill - someone a few feet away can detect
non-verticality better than you can when your on top of the hammer drill...
ALSO - make sure that you know just where to put the base - you
mentioned a bracket up 20 feet - that will move the tower out and away
from the wall it is on - make sure you have calculated that in - again
you may wish to bolt a few of these pieces of the tower and the bracket
together and lean them up - this can be very revealing - plumbing the
tower and then marking the slab is far easier than the option of
re-inventing the base later!
Again, try and use the holes on the manufacturer's base - they will have
galvanizing on them.
Have fun and wait for about 50 other e-mails from the Towertalkians!!!!
Yup, just 51 days until the Florida QSO Party
Kenneth E. Harker wrote:
> I am helping a university ham radio club with a tower installation
>on an already-poured level concrete slab. It will probably be a 40' Rohn
>45G tower bracketed once at about 20'. We would like to put three or four
>bolts in the slab and drill holes in a Rohn 45G base plate to match.
> Can someone recommend a particular concrete anchor bolt and
> What needs to be done to drill the holes properly? What kind of
>drill and bit are needed, how do you keep the hole vertical, etc?