Starting the Arc

Arc welders don't have a button to start the arc. Unlike MIG welders the rod (electrode) will become live as soon as the machine is switched on.

The arc is started by touching the electrode momentarily against the work to complete the electrical circuit before raising the electrode to establish the arc. This needs to happen quickly to avoid welding the rod to the work. "Tap Starting" and "Scratch Starting" are the two common methods of starting the arc.

Because the rod is live at all times it needs to be kept insulated from the earth when not in use. In the photo the welding bench is earthed, and a piece of wood is being used to isolate the rod from the bench. After welding the rod is returned to the piece of wood.

Tap Starting

A sharp tap of the rod against the work will remove excess flux from the end of the rod and create the electrical contact needed to start the arc.

A sharp wrist action should allow a momentary contact with the work before quickly pulling the rod a short distance away. Too heavy a contact or too slow an action can cause the rod to stick.

In the video the auto-darkening helmet darkens as soon as the arc is started. The light is bright at first because the arc length is initially too long. The arc length is quickly reduced to the correct distance for welding.

Rods start much more easily on the second attempt. It is good practice to first start the arc on some scrap material before starting the arc at the beginning of a weld.

Scratch Starting

An alternative starting method is to lightly scratch the rod against the work. Moving the rod against the work removes excess flux from the rod and allows electrical contact from the steel in the middle. As soon as the rod starts to spark it is lifted from the work to start the arc.

In the video a backwards and forwards scratching motion is used to remove the flux coating. A limited movement should mean the arc will start somewhere close to where you want to start welding. When the first spark is seen the rod is pulled away from the work to prevent sticking, and then it is returned to the normal arc length for welding.

The scratch start technique is more prone to sticking as it relies on human reaction times. It can be a useful technique for difficult to start rods, or for AC machines and those with low open circuit voltage which make Tap Starting more difficult.

Excessive pressure on the rod while scratching will increase it's chances of sticking.

Rods Sticking to the Work

If you are new to arc welding you will frequently stick the rod to the work when trying to start the arc. The rod welds itself to the work and it won't be possible to remove it just by pulling. Moving the rod backwards and forwards, or twisting the rod should fatigue the joint allowing you to remove the rod. If you have a crocodile clip type electrode holder you can just release the rod from the holder.

There's no need to panic when the rod sticks. It's normal for rods to stick occasionally, so arc welders are designed to cope with it for a short time. Inverter welders will reduce voltage automatically, and transformer welders should only go up in smoke if the rod is stuck for a prolonged period.

For interest, the photo shows the electrode of a 7018 rod recessed into the flux coating after welding - it illustrates why the flux coating needs to be removed before the arc will start.