Tack Welding

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.

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.

Video of me tacking and laying a weld bead

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.

For more welding instructions see mig welding.