Newbie advice needed - running over tack welds

[trewjohn2001]

Been practicing for a couple of months now mainly 1.5/1.0mm steel as I will be mostly using this for car body repair work. I´m reasonably happy with my welds now - they seem to pass the hammer test and don´t look too shabby. I have a question regarding tack welding before running beads. At the moment I tack each end of the joint before running a bead. Should I grind back the tack on each end before running the bead? At the moment if I start the arc on the tac weld I get an ugly lump at the beginning of the weld and the end. If I start the weld just at the edge of the tack I get a small gap - see picture. Whats the accepted method of doing this - any other criticism or suggestions welcome.

Cheers

 

[chevy2]

Snip back the mig wire so that theres no blob of wire left over from the last weld,
that way you'll get a cleaner start to the weld so forming less of a lump at the start of the weld before the heat builds up.

 

[trewjohn2001]

Hi,

Thanks for the reply. Yes I've been doing that every time. Problem is the tack weld is quite a bit bigger than the surrounding metal. Only issue is starting the arc on top of the tack or should I start it a little bit ahead of the tack and run over it?

 

[chevy2]

Start the weld just in front of the tack or you'll only make it bigger,
once the new weld pool bonds with the tack then run the torch away and continue the bead.

 

[trewjohn2001]

Great thanks, I also have a pit that appears at the end of every weld (you can see it on the left hand side in the photo). It happens when I take my finger off the trigger- any way to stop it?

 

[chunkolini]

The little pit?
let go of the trigger then flick it for a fraction of a second while the weld it still really hot it will drop a tiny spec of weld into the pit. Hard to describe, easy to do and almost impossible to remember to do.

 

[spaf4]

Make your tacks smaller by increasing your rate of travel, or, failing that, grind them down before you begin your actual welding. If possible tack weld on the opposite side of the plate leaving the side you're going to weld free of tacks. Once that side is done, grind off, completely, the tacks on the backside and you'll end up with a finished work piece with no visible signs of tacks.

Tacks at the beginning and end of work piece are never a good idea as they often make the start and finish look untidy. Like I say, make your tacks smaller with one of the above methods and your finished welds will look all the better. No-matter what you're doing always make tacks smaller than the weld. And never ever tack in any corner you intend to weld around.