[TowerTalk] Tack welding rebar, need howto

[Grant Saviers]

On 1/2/2014 2:27 PM, Richard (Rick) Karlquist wrote:
> On 1/2/2014 11:02 AM, Grant Saviers wrote:
>
>>
>> Tack weld the bolts together with #3 rebar when attached to the base so
>> they don't move when set without the base to make concrete work easier.
>>
>> Grant KZ1W
>>
>
> Can anyone refer me to a Dummy's guide to welding rebar?
>
> 1.  I have heard that I have to use special weldable rebar.
> What do I ask for?  I'm assuming that the common rebar
> at Home Depot, etc is not it.
That depends on your view of how strong the rebar in a tower foundation 
really needs to be.  All are weldable, it is how much the welding 
affects the heat treating and thus the yield strength.  HD rebar might 
be ungraded or grade 40, 40ksi yield and A706 is the official weldable 
rebar.  I think it is pretty common to weld up common rebar, and it 
might reduce the yield strength by 15 to 20%.
>
> 2.  Gas weld or arc weld?  How big of an arc welder needed?
> Can I get away with a MAPP gas torch?
A 120v 130amp MIG or bigger with flux core wire will work, these are 
tack welds not structural welds.  Could also use stick.  I'd stay away 
from gas as the heat will thoroughly anneal the rebar and it will take a 
lot of heat for size 7.
>
> 3.  What welding rods to use?
for mild steel, general purpose  ER70S-6 mig wire; E7018 stick
>
> 4.  What if the bolts happen to be galvanized?  Grind
> off the galvanizing near the weld?
Better to but not necessary as long as you don't inhale the zinc fumes.  
Been there, done that, never again.  (got very sick, but not too poisonous)
>
> 5.  Can this be done by a novice welder?  (I took a
> class on welding in college 40 years ago, so I know
> just enough to be dangerous).  Any stupid rookie
> mistakes to avoid?
Many.  Practice on some scraps.  Buy/borrow an auto-darkening helmet - 
that and MIG make it really easy!  (HF has an ok helmet for $40)
>
> 6.  Alternately, if I go to a welding shop, are they
> going to know what to do or do I need to go to a
> concrete company that makes rebar cages all the time?
Moving a built cage is a bit of a task, build it next to the hole.
>
> 7.  I am mainly interested in using tack welding to keep
> the bolts from moving.  The jury is still out on whether
> to weld or wire the rest of the cage.  I just don't
> trust wiring as being rigid enough to fix the bolts
> in place.
Agree for the bolts.  The rest can work if tied tightly, 
cross/diagonally braced, and not moved much.  Tie bolts to cage with 
rebar and you have a great Ufer ground for almost free.
>
> Thanks in advance.
>
> Rick N6RK
>
YMMV, etc

Grant KZ1W