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A welding tack is a spot or short seam. They are made for stationary fastening of parts before the main welding. But potholders also have their own rules, let's talk about that.
In the photo above, I show with the electrode rod that I will make a tack here. I was going to weld the flags to the hinges. Welding tacks should be done at a high current, that is, about a quarter more than the main welding current. What for?
The metal is cold before welding, it will be the temperature of the ambient air. The tack will be very short in time. In this short time, we need to melt this welding spot deep into the metal.
You see this table, it is clear here that the higher the welding current, the greater the penetration depth of the metal during welding. But when we cook, the metal is already hot enough from this process, it is already easier to penetrate the weld to a depth than with cold metal.
If we make tacks at the same current as we set for the main welding, then in the places of the tacks, the penetration depth will be less than the depth of the main seam. That is, at the place of the tacks, the seam will be weakened. Another moment.
Before the main welding, it is advisable to grind the tacks with a grinder, remove this bump, although at high currents the tacks can be obtained almost flush with the metal, then nothing needs to be done.
After grooving the tacks, we weld the product, if you do not remove part of the metal from the tacks before welding, then in this place the weld seam will turn out to be more convex and wider, since you will have to melt and weld the tack with the main metal.
But for a thin profile pipe of 1.5 mm or 2 mm, you can not particularly drive, the main thing here is not to burn even the tack itself when welding with an electrode. After all, there will not always be good small gaps, thin electrodes of a suitable diameter for the corresponding metal thickness.
But for metal thicker, well, conventionally thicker than 3 mm, this rule is better to apply. Even if everything is simpler in household welding, there is no rigid framework as in production. But it will just be faster and easier - at a high current, the tack welding time is much shorter, the tack welding itself is smaller, it can be sharpened faster with a grinder before welding. So it makes sense.