The purpose of a tack weld is so that for
example if you were making up a square or rectangular frame out of some box section
steel.
You would lay it out on the floor or the
welding table and just tack weld all the corners together first so that you could then recheck it
for square.
If you were to
just go ahead and weld it all up first without tack welding it together, the heat from the
welding process would twist and buckle the job out of square.
And by that time it's too late to make a last
minute adjustment because you would have just fully welded it up.
Video of me tacking and laying a weld
bead
The tack weld is a little small weld, that is not designed to be of any
structural value.
See the picture above for an example of some
tack welding.Note:A tack weld is relative to the size of the work you are doing. So if you needed
to tack weld up a ship, those tack welds would be much larger as you are working with thicker
steel.
Having the welds on the inside corners will allow the
frame to be able to move left and right so that you can adjust it into square.If you welded up the outside corners, or the
outer most edge it is a lot harder to adjust left and
right.
The way to make a rectangle
or square equal in all corners at ninety degrees (square) is to either use a large metal builders
square. Or the other way for larger projects is to use a tape measure.To do this, simply measure the two diagonal
corners form the longest point to the longest point.To be square both distances must be equal. They never
will be when you first lay out your work, so that's why you tack weld the job and fiddle and
adjust until each diagonal measurement is the same length. Then you will have a square
job.Once square you can tack
some more, and then finally fully weld up. The use of welding clamps is highly recommended as
the heat from the welds will pull you work out of square.
The tack weld is just a one
second squeeze on the trigger. As you can see in the photo above, if this was out of square. It
would be much easier for me to only grind off these small tack welds instead of a big long weld
bead.So you can see here what tack
welding is and what it would be used for.
