Fine-Tuning SMAW amperage by observation

Once you have decided on a rough, approximate starting amperage by consulting with product literature, asking welding supply shop personnel, or using the formula that calculates amperage by the thickness of the stick electrode, you will still need to fine-tune and adjust the amperage until the welder starts performing properly on the specific job in hand. There is the remote possibility that you will have chosen exactly the necessary amperage through these means, but the overwhelming likelihood is that a bit of trial and error will be necessary.

You can tell whether or not your amperage is drastically too low or too high by observing the behavior of the equipment and metal while you are doing a test weld. Feeble amperage impedes striking an arc, so if you are unable to strike an arc with the workpiece or if it takes a long time to do so, then you know that your amperage needs to be adjusted upwards. Another symptom of excessively low amperage is a measly welding pool without much molten metal in it. 

Conversely, if you have a very large, loose welding pool that is difficult to control (or cannot be controlled), if the metal in the welding pool starts to visibly boil, or if the flux coating on the outside of the stick electrode begins to burn, then the amperage is set too high for the metals you are welding and the electrodes you are using, and you should tone the current down a few amps.

There are several special considerations in choosing what amperage to run on your portable SMAW welding machine as well. Amperage needs to be adjusted to account for the thickness of the metal you are welding, since the more physical material there is in the workpiece, the more metal there is to absorb and distribute the heat away from the welding site. Thinner metals require a reduction in amps to avoid making them too hot and warping or holing them, while thick metals need the amperage to be dialed up a bit to compensate for their “heat sink” tendencies.

Vertical welds need less amperage than welds in any other position, so another slight downward adjustment is appropriate in their case. Corner joints and butt joints are also situations where a lesser amperage is appropriate, while lap joints and T-joints require higher amps. Once all of these fine adjustments have been made, however, there is still the physical evidence of an actual weld to consider.

A weld made at proper amperage will have an oval stopping point almost as wide as it is long, and a series of thin, even, curving ripples along its length. The cross-section should be a very even, flattened lens shape with edges that slope down smoothly to the base metal.

If amperage was too low, the weld will be tall, and almost round in cross section, jutting up above the surface more than a proper weld; the ripple will be large and uneven, the weld bead narrow, and the end point elongated. A high amperage weld is wide, slumped in cross-section and possibly even slightly sagging at the center, with deformed-looking ripples, and a large, porous end point. There is also likely to be a lot of spattering of globules of filler metal across the surface.