Striking In
An arc starts from a moving touch — scratch or tap — and lives at a gap about one rod diameter wide; hold the touch and the rod sticks, lift too far and the arc goes out. · 11 min
You know the loop, and you know the rod. Now the skill that makes beginners sweat: getting the arc lit and keeping it. The problem is narrow. With the rod touching the plate, current flows but there is no arc — a dead short, all heat and no light. With the rod too far away, the gap is wider than the voltage can jump, and the arc goes out. The arc lives in between, at a gap about equal to the rod's diameter. Striking is the move that finds that gap fast.
Guess before you learn
You touch the rod tip to the plate and simply hold it there. Two seconds pass. What is happening?
A held touch is a dead short: full current, no arc, and the tip melts itself onto the plate — welders call it sticking the rod. If you guessed 'nothing happens,' that is the intuitive read, and it is exactly backwards: touching is when the most current flows. The cure is motion, and motion is this folio.
9–12
3–5
The arc can only jump a small gap. Touching leaves no gap, so instead of an arc you get a stuck, glowing rod. Lifting too far makes a gap too wide for the electricity to cross, and the arc snaps out.
A moving touch works because the tip drags out a little melted metal as it lifts, and that hot trail becomes the arc's path. Then you hold the gap steady: about one rod thickness.
6–8
Why must the start be a moving touch? At contact, the short-circuit current spikes and the touch point flashes molten. Lift while moving, and that molten bridge stretches, vaporizes, and ionizes — it becomes the conducting path the arc runs on. Linger instead, and the same heat welds the rod to the plate.
Arc length — the gap from rod tip to puddle — is then your live control. One rod diameter is the working length. Shorter runs quieter but risks sticking; longer raises the voltage, throws spatter, and finally passes the distance the arc can sustain, and it snaps out.
9–12
The numbers behind the feel: the machine idles at 60 to 80 volts open-circuit — the most it can offer for starting — while a running arc needs only 20 to 30. A cold air gap will not ionize at either figure. The moving start works because hot metal vapor ionizes far more easily than cold air, so the stretched, vaporizing bridge lights where bare voltage cannot.
The flux helps. Coatings carry potassium and sodium compounds whose atoms give up electrons easily, seeding the gap with charge carriers so the arc re-lights readily. That is one reason a rod with a clean tip strikes more easily than one with a melted-over crater of flux.
K–2
If the stick touches the metal and stays, it gets stuck. If you lift it a tiny bit, a bright hot light jumps the gap. Lift too much and the light goes out.
So the trick is: touch while moving, then lift a little — about as high as the stick is thick.
Undergrad
This is short-circuit ignition: contact drives current toward the source's short-circuit limit; the constriction and vaporization of the molten bridge produce a metal-vapor plasma whose ionization energy sits well below nitrogen's. Arc stabilizers — low-ionization-potential alkali species from the coating — lower the column's effective re-ignition voltage.
The stable window follows from folio 5's source curve: arc voltage rises roughly linearly with length, and when the required voltage exceeds what the drooping source can deliver at any current, no operating point exists and the arc extinguishes. That is the circuit-level meaning of 'lift too far and it snaps out.'
Postgrad
At the cathode, emission is the gatekeeper. Steel is non-thermionic, so conduction relies on mobile cathode spots — micrometer-scale, field-enhanced emission sites cycling on microsecond timescales. Ignition succeeds when spot formation outpaces the cooling of the ruptured bridge, which is why contact velocity and the current at separation set striking reliability.
DC arcs, once lit, persist; AC arcs must re-ignite at every zero crossing, demanding either generous open-circuit voltage or coating chemistry that keeps the column conductive through the current zero. This is the design reason cellulosic rods specify high OCV, and why inverter machines superimpose hot-start current at ignition.
arc length
The gap between the rod tip and the molten puddle. Working value: about one rod diameter.
Two standard starts, one goal: touch already moving. The scratch start sweeps the tip across the plate in a short, light stroke — the motion you use to strike a match — and lifts as the arc flashes. The tap start descends, touches, and lifts straight back up in one motion. Scratch is more forgiving and is where beginners begin; tap is more precise and leaves no stray marks on the plate.
Every welder sticks rods; the skill is the calm exit. The instant you feel the rod grab, give the stinger a quick twist and pull — most sticks break free. If it holds, do not stand there while it glows: squeeze the stinger's release and take the stinger off the rod. That opens the circuit, the heating stops, and the rod cools in place, where a sharp sideways knock frees it. Then look at the tip — a melted-over crater of flux strikes poorly, so use a brisker scratch on the restart.
The first strike, narrated — the steps fade as you master them
About 90 A — one amp per thousandth of an inch
Safety glasses on, hood down
Scratch a light one-inch stroke; lift the instant it flashes
About 3/32 inch — one rod diameter
Striking is a reflex you build in a hundred repetitions, not a fact you memorize. Practice on scrap until the flash-and-lift feels automatic and stuck rods become rare, then boring. Next folio: keeping the arc you have lit moving in a straight, even bead — the four variables you will hold at once.
Practice — new ink and old, interleaved
1.Match each situation to its outcome.
2.Match each current setting to its working character.
3.Match each item to its identity.
4.Stick welding at 120 A — what suggested shade number?
5.Working arc length with a 1/8-inch rod, in inches?
6.From memory: name the two starts, the working arc length, and the first move when a rod sticks.
Scratch start and tap start; hold about one rod diameter; on a stick, twist and pull at once — and release the stinger from the rod if it holds.
How close were you? Grade yourself honestly — it sets your review date.
7.Your arc keeps snapping out a few seconds after each strike. Most likely cause?