TIG Welding Amperage: The Complete Settings Guide for 2026

A hobbyist welder once spent an entire afternoon fighting a 1/8-inch aluminum TIG joint that kept collapsing into a hole, convinced his machine was underpowered. The machine was fine — the amperage dial was simply turned down where it ‘felt’ safe instead of where the metal needed it. Almost every ugly TIG bead, every cold lap and every burn-through starts at the same place: the amperage setting on the front of the machine.

What TIG Welding Amperage Actually Controls (and Why It Comes First)

A hobbyist welder once spent an entire afternoon fighting a 1/8-inch aluminum TIG joint that kept collapsing into a hole, convinced his machine was underpowered. The machine was fine. The amperage dial was simply turned down where it “felt” safe instead of where the metal needed it. Almost every ugly TIG bead, every cold lap and every burn-through starts at the same place: the setting on the front of the machine.

TIG welding is formally known as Gas Tungsten Arc Welding, or GTAW. It uses a non-consumable tungsten electrode that reaches a melting point of about 3,422°C (6,192°F), which is why the electrode itself almost never melts into the puddle. An inert shielding gas, usually argon, blankets the arc, and filler metal is added by hand only if the joint needs it. As TWI’s technical overview of TIG welding describes it, the process is prized for control and cleanliness precisely because heat and filler are managed separately.

Amperage Is the Master Variable

Of all the knobs on a TIG machine, tig welding amperage is the single most influential one, because it sets heat input and penetration. Voltage and arc length shape the bead’s width and appearance, but the current flowing through the arc decides how deep the weld actually bites into the base metal. Get amperage wrong and no amount of hand speed, cup angle or filler technique will rescue the weld.

Physically, the arc concentrates heat into a small area on the workpiece. On DC electrode-negative, that heat lands in a tight spot called the cathode spot, and higher current enlarges and intensifies it. The result is a characteristic teardrop penetration profile: a narrow, deep root rather than a wide, shallow smear. Push the current up and the crater gets deeper; drop it down and the arc barely scratches the surface.

Amperage vs. Voltage: They Do Different Jobs

This distinction trips up a lot of beginners. In manual TIG, arc voltage is governed mainly by arc length — hold the tungsten closer and voltage falls, pull it away and voltage climbs. Amperage, by contrast, is what determines penetration depth. That is why a shaky hand that changes arc length by a millimeter mostly changes bead width, while a 10-amp mistake changes whether you fuse the root or burn through it.

Here is the reassuring part: TIG machines are constant-current power sources. The machine continuously adjusts output voltage to hold your selected amperage nearly steady as you move the torch up and down. Vary your arc length and the current stays essentially where you dialed it. Most quality machines and manufacturer guidance from Miller Welds and Lincoln Electric build on this constant-current behavior, which is exactly what makes TIG feel so predictable once the setting is right.

How TIG Differs From Stick and MIG

Orientation helps here. MIG runs on a constant-voltage power source, so amperage actually changes with wire stick-out and trigger time — the machine holds voltage, not current. Stick welding is closer to TIG in that it is a constant-current process, but the electrode is consumed, so arc length drifts as the rod burns and the operator is chasing two variables at once. TIG is the clean case: the tungsten does not shorten, so the current you set is the current you get.

One related term is worth clearing up. Open-circuit voltage (OCV) is the voltage present before the arc is struck — it exists only to get the arc started. Once welding begins, the voltage drops to a much lower arc voltage, and the current is limited by your amperage setting. A high OCV makes starts easier; it does not make a weld deeper. Penetration comes from welding current, not from the idle voltage sitting on the output terminals.

That is why every sensible setup routine begins the same way: identify the metal, estimate thickness, and calculate a starting amperage before striking the first arc. Whether you are working on precision aerospace assemblies or Aerospace TIG Welding: Standards, Techniques, and Training-level tolerances, the sequence never changes. Amperage comes first because it is the variable everything else in the puddle answers to.

The 1 Amp per 0.001 Inch Rule and Thickness Amperage Charts

Ask five experienced TIG welders how they set amperage and three will answer first with the same rule: one amp per one-thousandth of an inch of thickness. It is the most quoted starting point in the trade, and it works often enough that whole shop procedures still lean on it. But “often enough” is not “always,” and knowing where the rule comes from tells you when to trust it and when to overrule it.

Where the Rule Comes From

The logic is simple thermal arithmetic. Thicker metal has more mass, so more heat must go into the joint before both pieces reach fusion temperature together. On a square-edge butt joint in mild steel with decent fit-up, roughly one amp per 0.001 inch (one thou) of thickness lands close to full penetration at a normal manual travel speed. A 0.120-inch plate starts near 120 amps; a 0.060-inch sheet starts near 60. Both Miller and Lincoln Electric publish thickness charts built on this same baseline, with the same caveats we are about to walk through.

Notice the fine print: butt joint, mild steel, decent fit-up. Change the alloy, the joint geometry, the position, or the fit-up, and the number moves.

Mild Steel Butt Joint Starting Amperage

Sheet is usually sold in gauge rather than decimal thickness, so convert first: 16 ga = 0.0598 in, 14 ga = 0.0747 in, 12 ga = 0.1046 in, 10 ga = 0.1345 in.

Thickness	Approx. Gauge	Starting Amperage (butt joint, DC)
0.040 in (1.0 mm)	~22 ga	40–50 A
0.0598 in (1.5 mm)	16 ga	55–70 A
0.0747 in (1.9 mm)	14 ga	70–85 A
0.1046 in (2.7 mm)	12 ga	90–110 A
0.1345 in (3.4 mm)	10 ga	115–135 A
0.1875 in (4.8 mm)	3/16 in plate	150–180 A
0.250 in (6.4 mm)	1/4 in plate	180–230 A

These are manual ranges on a constant-current machine with a pointed thoriated or lanthanated tungsten, argon shielding, and normal travel speed. If the arc starts easily but the puddle refuses to wet out and tie in at the toes, you are at the bottom of the range. If the puddle turns wide, flat and mirror-bright with a smooth wash into the plate, you have gone past the top.

Stainless Steel: Dial Back to About 75–80%

Stainless conducts heat roughly four to five times slower than mild steel, so heat stays concentrated at the arc instead of spreading outward. You need noticeably less current for the same thickness: the common shop adjustment is 75–80% of the mild-steel figure, sometimes closer to 70% on thin sheet where burn-through is the real enemy.

Thickness	Mild Steel Baseline	Stainless Starting Range (~75–80%)
0.0598 in (16 ga)	60 A	45–55 A
0.0747 in (14 ga)	75 A	55–65 A
0.1046 in (12 ga)	100 A	75–90 A
0.1345 in (10 ga)	125 A	95–115 A
0.1875 in	165 A	125–150 A

Stainless is also the alloy where “a little too hot” costs you the most. Excessive heat input drives chromium carbides out of solution along the grain boundaries — the classic sensitization problem that kills corrosion resistance — so erring slightly cool is metallurgically smarter, not just tidier.

Aluminum: Add 10–25% Over the Rule

Aluminum behaves like the opposite of stainless. It pulls heat away from the arc very quickly, so by the time a puddle builds on 1/8-inch 6061, the surrounding metal is already acting as a heat sink. Most welders end up 10–25% above the basic rule for AC work on aluminum, and higher still when the piece is clamped to a large fixture. The surface oxide layer is also roughly ten times thicker than the base metal’s nominal film and must be stripped by the electrode-positive half of the AC cycle, which is why a hesitant, underpowered arc on dirty aluminum feels far worse than the chart suggests. Good chemical prep before aluminum welding buys back some of that margin.

Thickness	Rule of Thumb (1 A/0.001 in)	Aluminum AC Starting Range (+10–25%)
0.0598 in (16 ga)	60 A	65–80 A
0.090 in	90 A	95–115 A
0.125 in (1/8 in)	125 A	130–155 A
0.190 in (3/16 in)	190 A	200–235 A
0.250 in (1/4 in)	250 A	265–300 A

If you have never set an AC balance and frequency before, our guide to aluminum welding processes covers how those controls shift the heat you actually deliver.

Adjusting for Joint Geometry and Position

The chart numbers describe the friendliest possible joint, and real work rarely is that friendly. Apply these multipliers:

• Fillet welds (T-joints): add roughly 25%. Two plates meeting at an angle double the heat-sinking mass around the arc, so a 1/8-inch fillet wants 150–160 A, not 125.
• Out-of-position welding (vertical, overhead): reduce 10–20%. Gravity pulls the puddle out of the joint, and excess current makes that worse. Our all-position welding reference covers the same principle across other processes.
• Edge and corner joints: reduce 10–20%. There is little metal to absorb heat at a corner, and it melts away faster than any chart assumes.
• Open roots and wide gaps: reduce further, often 15–25%, and shorten your arc. A gap is a shortcut for the arc to jump straight through.
• Copper backing bars, heavy clamping, or a large fixture: increase. That fixture steals heat, so you must replace it. Welding thin tube to thick plate is the classic case — set for the thick side and manage the thin side with travel speed and filler rod.

The real skill is not memorizing a chart. It is treating each number as a starting hypothesis, reading what the puddle tells you, and adjusting with confidence.

Why Base Metal Type Changes Everything: Thermal Conductivity vs Melting Point

Two numbers will dictate your TIG amperage setting more than any chart alone: thermal conductivity (how fast a metal pulls heat away from the arc) and its melting point (how hot it needs to become to liquify). If you only look at thickness, you will overheat metals that hold their heat, and you will burn right through metals that dump it into the surrounding plate. This is why setting the same amps for 1/8-inch aluminum and 1/8-inch mild steel will almost always end in one of the two TIG welding failures.

Thermal conductivity is measured in watts per meter-kelvin (W/m·K), a metric that directly translates to the amperage demand of a joint. As noted by The Welding Institute (TWI), the energy required to create a stable puddle is heavily influenced by how quickly heat is conducted away from the weld zone. The higher the conductivity, the harder the arc has to work, and the more amperage you will need to compensate.

Comparing the Common Alloys

The chart below breaks down the alloys you will encounter the most in a shop or garage, along with their starting implications for your TIG welding amperage settings.

Base Metal	Thermal Conductivity (W/m·K)	Melting Point (°C / °F)	TIG Amperage Tendency	Key Considerations
Mild Steel	~50	~1,370–1,510 / ~2,500–2,750	Baseline	The easiest to predict. Excellent starting point for charts.
Austenitic Stainless	~15	~1,400–1,450 / ~2,550–2,640	Lower than steel	Holds heat locally. Prone to sensitization if overheated.
Aluminum	~205	~660 / ~1,221	Much higher than steel	Oxide melts at ~2,072°C (~3,762°F). Requires AC cleaning action.
Copper/Bronze	~385 (pure Cu)	~1,085 / ~1,985 (Cu) & varies	Highest	Extremely conductive. Often needs preheat and high amps.
Titanium	~22	~1,668 / ~3,034	Slightly lower than steel	Reactive. Needs tight gas coverage and a clean purge.
Cast Iron	~55 (varies)	~1,150–1,200 / ~2,100–2,190	Lower than steel	Crack-prone. Small, short runs with lower amps are preferred.

The Aluminum Challenge

With roughly 4x the thermal conductivity of mild steel, aluminum will suck heat away from the arc at an alarming rate. Despite its low melting point of 660°C (1,221°F), this heat theft forces you to run significantly more amperage to establish and maintain a puddle. It is one of the biggest reasons that work on aluminum prep and repairs, from alloy wheels to marine hulls, can be so deceptive for first-timers.

The other hurdle lies on the surface. Aluminum forms a tenacious oxide layer that melts at about 2,072°C (3,762°F), which is far above the base metal itself. This is why TIG aluminum almost always relies on AC welding, as the electrode-positive portion of the cycle provides the necessary cleaning action to break that oxide free. This is a well-documented principle that Lincoln Electric and Miller Electric both stress when outlining AC TIG procedures.

Stainless, Reactive Metals and the Outliers

Austenitic stainless steel runs in the opposite direction. Its thermal conductivity of around 15 W/m·K is far lower than mild steel, meaning it will “stay hot locally” once it reaches temperature. For this reason, you can often run less current than you would for a comparable steel thickness. However, that trapped heat comes with a tradeoff: it increases the risk of sensitization, a loss of corrosion resistance. As the American Welding Society (AWS) notes, excessive heat input can negatively affect austenitic grades, so tighter amperage control is crucial.

When working with reactive metals, such as titanium, tight gas coverage is non-negotiable to prevent atmospheric contamination. These high-purity applications are common in aerospace TIG work, where even a slight draft can ruin a joint.

At the end of the day, amperage cannot exist in a vacuum. Aluminum will demand the most of it, stainless will punish you for too much of it, and outliers such as copper, titanium and cast iron will each rewrite the chart. By letting thermal conductivity and melting point lead your decision, your test bead will start far closer to correct than thickness ever could alone.

Joint Design, Fit-Up, Position and Heat Sinking

A thickness chart gives you a baseline: square butt joint, flat position, clean edges, tight fit-up. Almost nothing you weld matches all four at once. Joint geometry, fit-up, position, and whatever the part is clamped to all decide how much of the arc’s heat stays in the puddle and how much drains away, so your TIG welding amperage has to move with them. That adaptability is the point of the process: TIG welding is prized for precise heat control, but only when you change the setting as the joint changes.

Joint Geometry: Butt, Groove, Fillet, Lap and Edge

Start with the two extremes. A square-edge butt joint is the chart’s home turf: two members meet flush, the arc heats both evenly, and heat travels away along each plate. A fillet weld is a different animal. The arc sits in a corner, split across two members at an angle, and it must build a larger volume of weld metal than a butt of the same thickness. Rule of thumb: a fillet generally needs about 25% more amperage than a butt joint of the same material and thickness.

A 60-degree V-groove splits the difference. The root face is far thinner than the full plate, so set the root pass for the root thickness, not the plate’s nominal size. Fill passes then run in a narrow channel where previous beads are already holding heat, so they usually want the same current or slightly less with faster travel.

A lap joint behaves roughly like a fillet along the overlap, but the exposed edge of the top sheet is fragile and melts before the rest of the joint catches up. An edge joint or a corner joint is worse: two edges butted together with no backing mass behind them, so there is nowhere for heat to go. Both burn long before the chart says they should. Drop below the butt-joint number and let travel speed finish the job. This is exactly where thin aluminum repair jobs go wrong, whether you are fusion-welding a seam or doing careful alloy wheel welding on a thin rim section.

Fit-Up, Gaps and the Heat-Sink Effect

Fit-up changes the arithmetic more than most welders expect. An open root or a gap lowers the required amperage: the arc has to bridge air instead of metal, and there is less material behind the puddle to absorb heat. Set tight joints from the chart, then step down as the gap opens.

The opposite happens when your part is clamped to something massive. A copper or aluminum backing bar, a steel fixture plate, or even a heavy tack to a bracket conducts arc heat straight out of the joint. That is the heat-sink effect, and it forces you to raise the amperage noticeably to get the puddle to wet out. Jigs and strongbacks are routine in fabricating work like aluminum boat welding, where long hull seams are held against fixing plates. The upside is real: more current through a backed joint gives deeper penetration while the backing protects the back face from oxidation and blow-through.

Joining a thin tube to a thick plate is the classic mixed-mass problem. The plate acts as a heat sink on the tube side, so the tube needs more current than its thickness suggests while the plate pulls it back down. Set near the thin member’s requirement, bias the tungsten toward the heavy side, and raise the dial in small steps only if the puddle refuses to wet into the thick member.

Welding Position

Position is the quiet adjustment. In flat position the pool sits down and you can push it. Vertical-up, vertical-down and overhead all work against gravity, the pool wants to sag, and your travel speed naturally slows. Reduce amperage by roughly 10-15% compared with the flat setting, exactly as the parameter charts published by equipment makers such as Miller reflect, and expect to compensate with arc length and rod feeding. Positional work is its own skill set beyond the dial, which is why resources like the All Position Welding Rod Guide are worth reading alongside this one.

Condition	Amperage vs. flat square butt	Why it changes
Square butt, flat, tight fit-up	Baseline (chart value)	Standard reference joint
60-degree V-groove	Set for root thickness; fill same or slightly lower	Root is thin, groove traps heat
Fillet weld	About +25%	Larger weld volume, arc split across two members
Lap joint	Near fillet range, edge caution	Overlap acts like a fillet; top edge burns first
Edge or corner joint	Below baseline	No backing mass; edges overheat fast
Gap or open root	Reduce	Arc bridges air; less metal absorbs heat
Copper/aluminum backing or heavy fixture	Increase noticeably	Fixture conducts heat out of the joint
Vertical or overhead	Reduce 10-15%	Gravity pulls the pool, travel slows

The habit worth building: look at the joint, ask what is drawing heat away, and adjust before you strike the arc. Geometry tells you where the dial starts, the puddle tells you where it ends.

Tungsten Electrode Size, Grind Geometry and Shielding Gas Flow

The tungsten is not just “a rod you strike an arc on.” Its diameter quietly sets the practical TIG amperage window you can comfortably work in, and getting it wrong is one of the most common reasons a welder blames a machine that is actually fine.

Tungsten Diameter Sets Your Amperage Window

A thin tungsten has a small cross-section, so it heats up fast and will erode, ball up uncontrollably or melt if you push too much current through it. An oversized tungsten does the opposite: it hogs the arc and makes it stiff and reluctant to start, effectively starving the arc of the constriction it needs. The practical ranges below are continuous-duty figures — momentary spikes above them are fine, sustained running is not.

Tungsten Diameter	Practical Amperage Range	Typical Use
1/16 in (1.6 mm)	Up to ~80 A	Thin sheet, small tube, detailed work
3/32 in (2.4 mm)	Roughly 80–200 A	The all-purpose size for most shop work
1/8 in (3.2 mm)	Roughly 150–300 A	Heavy plate, thick aluminum
5/32 in (4.0 mm)	250 A and up	Heavy sections, high-production AC

If you only buy one size, buy 3/32 in (2.4 mm). It covers the overwhelming majority of hobby and light-fabrication work, and it is the size most machines ship with. Step down to 1/16 in when you are welding under about 0.050 in material, and step up only when the workpiece is genuinely heavy — or when it is clamped to a big heat-sinking fixture, which as we covered earlier pushes the required amperage up.

Choosing the Electrode Alloy

Modern TIG electrodes are alloyed with small amounts of rare earths to improve electron emission and arc stability. The AWS classification tells you exactly what is inside, and the traditional colour bands on the tip make identification quick.

Type (Colour)	AWS Class	Best Suited To
2% Thoriated (Red)	EWTh-2	DC work on steel and stainless; starts easily, very popular
2% Lanthanated (Blue)	EWLa-2	Versatile all-position alternative to thoriated, DC or AC
Ceriated (Gray)	EWCe	DC at low amps; arc starters, thin work
2% Zirconiated (White)	EWZr-2	AC on aluminum and magnesium

Thoriated tungsten has been the industry standard for decades, but it contains radioactive thorium and its grinding dust is a documented hazard. Lanthanated (EWLa-2) electrodes are now widely offered as a non-radioactive, all-position substitute that performs almost identically on DC and holds up well on AC, which is why many shops have quietly standardised on them. Zirconiated remains the pick for AC aluminum work because it resists the balling and erosion that AC causes. And before any of that matters: aluminum needs proper chemical cleaning first, since no electrode will rescue a joint contaminated with oxide and oil.

Grind Geometry: How You Shape the Point Matters as Much as Size

Electrodes must be ground longitudinally, along the length of the point, so the grinding marks run in the same direction as the current flow. Circumferential grinding — spinning the tungsten against a wheel sideways — creates an arc that wanders and refuses to stay centred. Use a dedicated diamond wheel, keep the grind angle around 20–30 degrees for DC penetration work, and match the tip to the process: a sharp pointed tip for DC, and a balled or slightly truncated tip for AC on older sine-wave machines. Square-wave machines let you run a pointed or truncated tip on AC too, which gives a much more stable arc.

Shielding Gas Flow: 15–20 CFH of Argon

TIG shielding is normally 100% argon at about 15–20 CFH (roughly 7–9 L/min) for hand welding with a standard cup, which lines up with manufacturer guidance. Helium mixes exist for heavy aluminum where you want a hotter, deeper-penetrating arc, but they are a specialty choice, not a default.

Two things quietly ruin gas coverage: flow that is too high, which pulls air in through turbulence, and drafts. If your bead shows porosity or a sugared, frosty appearance on stainless, check the room before you check the machine. A gas lens is a worthwhile upgrade — it replaces the standard diffuser with a mesh that straightens the flow, giving laminar coverage that lets you drop flow rates and extend stickout. That extra reach is invaluable inside a boat hull, and it is one reason boat builders favour gas lens cups on awkward out-of-position joints.

Get the tungsten size, the grind and the gas right, and you will find the amperage you calculated suddenly behaves exactly as the chart promised.

Filler Metal, Travel Speed and Heat Input: The Other Half of the Equation

Setting the dial is only half the job. A welder can hit the textbook tig welding amperage for a given thickness and still produce a bead that sits on the surface like a caterpillar, or one that blows a hole straight through. What actually decides the outcome is total heat input: how many amps you push, how long the arc dwells over one spot, and how much of that energy the joint design and filler rod steal away before the base metal can melt.

Heat Input: The Formula Behind Every Bead

In plain terms, heat input is the energy delivered to the workpiece per inch of weld. For shop purposes it is commonly calculated as:

Heat input (kJ/in) = (amps × volts × 60) ÷ (travel speed in inches per minute × 1000)

The result comes out in kilojoules per inch. Double your travel speed and you cut heat input roughly in half, even though the machine never moved. Drop from 120 amps to 90 amps and heat input falls by a quarter. This is why two welders running identical settings can get completely different results: one is moving along at 8 inches per minute, the other creeping at 3. Arc voltage in TIG stays relatively stable and mostly tracks arc length, so amperage and travel speed are the two levers you actually control by hand. Standards bodies such as the American Welding Society treat heat input as a governed variable for exactly this reason — it drives penetration, grain growth and corrosion resistance in the heat-affected zone.

Matching Filler Rod Diameter to the Joint

The classic rule is simple: choose a filler rod diameter close to the thickness of the thinnest member being joined. A 1/16-inch (1.6 mm) rod for sheet metal, 3/32-inch (2.4 mm) for light plate, 1/8-inch (3.2 mm) once you get into 1/8-inch-and-heavier material. Oversized rod is one of the sneakiest causes of cold lap — the rod absorbs so much arc energy that the base metal never reaches fusion temperature, and you end up stacking material on top of a joint that never opened. Undersized rod forces you to feed constantly and often leads to starving the puddle. If rod selection is a gap in your kit, the sizing logic in our All Position Welding Rod Guide applies broadly across processes.

| Joint thickness | Suggested rod diameter | Typical amps (mild steel, butt) |
|—|—|—|
| 0.030–0.060 in (sheet) | 1/16 in (1.6 mm) | 30–60 A |
| 0.075–0.120 in (14–12 ga) | 3/32 in (2.4 mm) | 60–90 A |
| 0.125 in and heavier | 1/8 in (3.2 mm) | 90–130 A |

There is also a meaningful difference between autogenous welding — fusing the puddle with no filler at all — and welding with rod. Autogenous fusion keeps heat concentrated in the puddle and works well for butt joints with perfect fit-up, butting two clean edges together. Add filler and the rod becomes a heat sink the moment it touches the pool: it absorbs energy, builds the bead profile and lets you carry more current without increasing penetration as much. On a fillet weld, that extra metal is doing structural work; on a poorly fitted gap, it is acting as a bridge.

Travel Speed: The Fastest Adjustment You Have

When the amperage feels right but the bead is too wide or too shallow, resist the urge to turn the dial. Change how fast you move. Travel speed is the quickest lever you have, it takes effect instantly, and it does not risk the burn-through that another 10 amps can cause. If the bead is narrow, crowned and grey, slow down before you increase current. If the puddle is shiny, wide and following you like a shadow, speed up first.

One last discipline point: all of these variables interact. A change in amperage usually means a change in travel speed, rod diameter or arc length to compensate. Practitioners working to tight procedures, such as those in Aerospace TIG Welding, treat the whole system as one setting rather than a single number. Get in that habit early and your scrap pile shrinks fast.

Machine Controls: AC Balance, AC Frequency, Pulse and Downslope

The amperage dial is the headline number on a TIG machine, but on a modern inverter welder it is only the headline. Four secondary controls decide how those amps behave over time and across the AC cycle: balance, frequency, pulse, and downslope. Set them right and your base setting works harder; get them wrong and you keep chasing the dial without understanding why the bead looks the way it does.

AC Balance: Cleaning Versus Penetration

On DC, used for steel, stainless, and titanium, current flows one way and balance is not a variable. On AC, used for aluminum and magnesium, current reverses direction many times per second, and each half of the cycle does a different job:

– Electrode-positive (EP): the arc strips the aluminum oxide layer away. Oxide melts at roughly 3,700°F while the aluminum beneath it melts near 1,220°F, so the arc has to remove the oxide before the metal can fuse.
– Electrode-negative (EN): electrons flow from the tungsten into the work, producing the deep, narrow penetration you actually want.

AC balance is simply the ratio between those two halves. More EP gives a wider, brighter cleaning band but shallower penetration and a hotter tungsten. More EN gives deeper welds, a cooler electrode, and a narrower cleaned zone. Most welders start around 65 to 75 percent EN (some machines show it as 25 to 35 percent cleaning; check your manual’s scale). Haze and soot mean more cleaning; a frosted, over-etched surface or a wandering arc mean too much. Balance is pointless on dirty metal, so follow the degreasing and wire-brushing routine in Aluminum Cleaner for Welding: How to Prep Aluminum Right before blaming your settings.

AC Frequency: Focusing the Arc

Most modern inverter TIG machines default to an AC frequency near 100 to 120 Hz, which gives a soft, oval arc roughly the width of a pencil eraser. Raising the frequency does not change your amperage; it changes where those amps land. Higher frequency narrows and stiffens the arc cone, concentrating heat into a smaller spot for deeper penetration, a narrower cleaning band, and better control on corner joints and out-of-position welds. Lower frequency widens the arc into a broader, gentler heat spread that suits wide joints and faster travel. Manufacturers such as Lincoln Electric publish these ranges in their setup guides, and the trade-off is simple: a tighter arc is more precise but noticeably louder.

Pulse Amperage: Peak, Background and Frequency

Pulsing alternates the machine between a peak current and a much lower background current. The practical rules are consistent across most welders:

– Set peak amperage exactly where you would set a constant-current weld for that thickness.
– Set background amperage commonly 40 to 60 percent below peak, or alternatively at 25 to 50 percent of peak. Either way it keeps the puddle alive without driving it forward.
– Use a low pulse rate of 1 to 10 Hz when you want a manual rhythm: dip the filler rod on one pulse, move on the next.
– Use a higher rate of 20 to 100-plus Hz for a finer, more cosmetic bead and reduced overall heat input. At the top of that range the pulses blend into a smooth, tightly rippled surface.

Downslope, Start Amps and Crater Control

Downslope ramps the current down over a set time when you release the trigger; start amps let the arc begin below your welding current. Both exist because aluminum cracks as it cools under restraint, and a puddle that shuts off instantly leaves a crater. Start at 50 to 70 percent of your welding amps, ramp up, then use a 2 to 5 second downslope so the puddle solidifies without a pinhole.

Practical Starting Settings

Control	Typical starting point	Adjust when…
AC balance	65-75% EN (25-35% cleaning)	Bead looks dirty (add cleaning) or over-etched (reduce)
AC frequency	100-120 Hz	Tighter arc on corners, softer on wide joints
Pulse peak	Your normal constant-current setting	Penetration is good but heat builds
Pulse background	40-60% below peak	Puddle freezes between pulses (raise) or heat creeps (lower)
Pulse frequency	1-10 Hz manual, 20-100+ Hz cosmetic	Rod dips to rhythm or refining bead look
Start amps	50-70% of welding amps	Arc blows metal on strike-on
Downslope	2-5 seconds	Craters or shrink marks at the stop

All four controls do the same job: they let you hold TIG welding amperage at what the joint needs, then shape when that heat arrives. Set balance and frequency once for the material, pulse when the joint is thin or appearance matters, and always finish with downslope.

Common Amperage Mistakes and How to Troubleshoot Them

Even experienced welders misread a bad bead. The instinct is almost always to reach for the amperage dial, and sometimes that is right. More often, the dial is fine and something else is off. Learning to read what the weld is telling you separates guesswork from diagnosis.

Reading a Bead That Is Too Cold

A bead that sits proud of the surface with wet edges and no visible fusion at the toes is the classic sign of insufficient amperage. The rod melted, the puddle never really bit into the base metal, and the result looks like a caterpillar laid carefully on top of the joint. Other cold-side symptoms include:

• A convex, ropey bead with a narrow width relative to the travel speed.
• Lack of penetration on the back side of an open-root joint.
• The tungsten sticking to the work when you try to start the arc, because the base metal never got hot enough to sustain it.
• Difficulty striking an arc at all on aluminum, where the oxide layer needs heat to break down.

The fix is usually 5 to 10 amps at a time, but first rule out the other culprits: an arc length that is too long (voltage goes up, penetration goes down), travel speed that is outrunning the puddle, or dirty metal. On aluminum, poor cleaning shows symptoms that look exactly like cold amps, which is why surface prep matters so much. Our aluminum cleaner for welding guide covers that prep step in detail.

Reading a Bead That Is Too Hot

Over-penetration on sheet shows up as burn-through or a very wide, flat, gray bead that has washed away the joint edges. Instead of a convex profile you get a concave one, sometimes with undercut along the toes. Additional hot-side signs include:

• Crater cracks at the end of a weld, especially on aluminum, which is why downslope and start-amps settings exist.
• Arc wander and a fuzzy, noisy arc as the tungsten tip erodes and deforms.
• “Sugaring” or heavy oxidation on the back side of stainless steel where shielding gas coverage was lost while the metal sat at excessive temperature.
• Heat tint ranging blue to straw on stainless, indicating the heat-affected zone has been pushed too hard.

Troubleshooting Table

Symptom	Likely cause	Fix
Bead sits proud, toes not fused	Amperage too low	Increase 5–10 amps, slow travel slightly
Arc hard to start, tungsten sticks	Cold workpiece, contaminated tungsten	Raise amps, regrind or replace tungsten
Burn-through on sheet	Amperage too high, travel too slow	Drop amps, speed up, add filler as heat sink
Wide flat gray bead, edges washed away	Excessive heat input	Reduce amps, check arc length
Sugaring on stainless back side	Too much heat, poor purge/coverage	Lower amps, improve trailing shielding and purge
Crater cracks at weld stop	No downslope, amps held to the end	Use downslope, add a final filler dab
Arc wanders, tungsten erodes	Too much current for the electrode, or AC balance wrong	Upsize tungsten, recheck balance
Penetration inconsistent run to run	Long extension cord, line-voltage drop	Use shorter, heavier cord; check supply voltage

Four Mistakes the Chart Cannot Fix

Setting amps from a chart and never adjusting. Charts give starting points, not finished settings. Material temperature rises as you weld, joints fit differently, and fixtures pull heat at varying rates.

Ignoring line-voltage drop. A long, thin extension cord can rob the machine of effective output, so the display says 90 amps and the arc delivers less. This one hides behind every other symptom.

Wrong tungsten size. A 1/16-inch electrode pushed to 150 amps will erode and contaminate the puddle, while a 5/32-inch tungsten on 40 amps of thin sheet work gives a clumsy, wandering arc. Match the electrode to the range you actually use.

Dialing up instead of improving technique. If the bead looks wrong, check arc length, travel speed, torch angle and cleanliness first. Amperage is the last resort, not the first reflex.

Another common question: “Should I chase penetration by raising amps until I see full fusion on the back side?” On thin material, no. By the time full penetration is visible from the front, you are usually past the point of a clean bead. Control penetration with heat input as a whole, which is the subject of the filler, travel speed and pulse controls covered elsewhere in this guide. For welders working to tight cosmetic or structural tolerances, such as aerospace TIG welding, procedure qualification and documented settings replace the trial-and-error approach entirely.

The practical habit that fixes most of this is simple: run a bead, read it honestly, change one variable, run another. Amperage troubleshooting works when it is treated like a diagnosis, not a knee-jerk turn of the dial.

Safety, Ventilation and the Standards Behind Your Settings

Amperage is usually framed as a quality decision, but it is also a safety decision. Every amp you dial up produces heat that does not end up in the weld pool. Some radiates outward as visible light, ultraviolet and infrared. Some volatilizes metal into fume. Some leaves the surrounding plate hot enough to ignite whatever is underneath it. A TIG arc at 150 amps creates a dramatically different working environment than the same arc at 60 amps, and the fix for many shop safety problems is simply putting the arc in the right current range in the first place.

What Higher Amperage Actually Changes

Push the current beyond what the joint needs and three things happen at once. Heat input climbs, so the heat-affected zone grows and stays hot longer. Fume generation increases because more metal is vaporized at higher arc temperatures. The arc itself becomes harsher to control, which leads to spatter, arc wander and long arc lengths that throw UV radiation across the bench. A stable arc sitting in the correct amperage band is not just a prettier weld, it is a cleaner one, with less fume and less stray radiation.

This is why the troubleshooting fixes in the previous section double as safety measures. Correcting a too-hot setting reduces oxidation, fume, spatter and the chance of setting your workspace on fire.

Personal Protective Equipment: The Non-Negotiables

TIG produces some of the most intense UV radiation of any welding process. Because there is no flux coating or spatter cloud shielding nearby workers, that radiation travels. Minimum PPE for TIG work includes:

• A welding helmet with the correct filter shade. Most TIG work at moderate currents calls for shade 10 to 13. Auto-darkening helmets are fine as long as the lens is ANSI Z87.1-rated and the shade range suits your amperage.
• Welding gloves rated for TIG. They are thinner and more dexterous than stick gloves because you need finger control for rod feeding, but they still have to block UV. Do not substitute shop gloves.
• Leathers or flame-resistant clothing. Long sleeves, closed collar, no cuffs that catch sparks, and no synthetic fabrics that melt against skin.
• Safety glasses under the helmet, steel-toe boots, and ear protection where grinding or heavy material handling is involved.

Anyone working within roughly 35 feet of an open arc needs eye protection too, not just the welder. If you use air acetylene or brazing equipment alongside TIG work, the same eye protection rules apply to those torches.

Ventilation: What OSHA Actually Requires

Welding fume is a legal exposure issue, not just an inconvenience. OSHA’s general industry welding standard, 1910.252, requires ventilation sufficient to keep airborne contaminants below the applicable permissible exposure limits, and it prohibits welding, cutting or brazing where adequate ventilation is unavailable and protection is not provided. On construction sites, OSHA construction standard 1926.353 sets out the same logic: use natural ventilation where it works, and mechanical ventilation where it does not.

The rule of thumb behind both standards is that natural ventilation is generally adequate only in open, well-mixed spaces where the welder is not working inside an enclosure. The moment you are welding inside a tank, vessel, bin or badly enclosed shop corner, mechanical exhaust or supplied air is expected.

Stainless Steel, Hex Chromium and Manganese

Welding stainless steel generates fume containing hexavalent chromium, which OSHA regulates with a permissible exposure limit of 5 micrograms per cubic meter of air averaged over eight hours. Mild steel welding can also expose you to manganese, which affects the nervous system at chronic exposure levels. Amperage ties in directly again: excessive current on stainless accelerates oxidation and fume generation, and the sugary oxide scale on an overheated stainless backside is visible proof of metal that entered the air instead of the joint.

For a deeper look at the pre-weld prep side, see our guide to aluminum cleaner for welding, since contaminated joints are one of the avoidable sources of excess fume.

The Consensus Standard: AWS Z49.1

Beyond OSHA, the welding industry’s own consensus reference is AWS Z49.1, Safety in Welding, Cutting and Allied Processes, which most fabricators, apprenticeship programs and employer safety manuals adopt directly. Z49.1 covers ventilation design, PPE selection, electrical safety, fire prevention and compressed gas handling, and it is the document behind most shop safety certifications. If your employer sends you to formal training or qualification, the safety curriculum will be built on it.

Note: If you are heading toward professional or certified work, from structural fabrication to aerospace welding school programs, expect the safety and qualification standards to be tested as rigorously as the welding itself. Skills get you the job; documented safety knowledge keeps it.

The short version: pick the correct amperage for the metal, keep the arc stable, ventilate the space, wear the right gear and treat OSHA and AWS Z49.1 as the floor rather than the ceiling. That combination protects the weld and the welder at the same time.

A Practical Step-by-Step Setup Routine and Final Amperage Chart

Charts and rules of thumb only pay off when they’re turned into a habit. Consistent TIG results come from a short, repeatable setup routine, not constantly guessing at the dial. A few minutes of prep will save hours of grinding and rework, whether you’re on a garage bench or in a production booth.

The Seven-Step Setup Routine

1. Measure the actual thickness. Use digital calipers or a sheet metal gauge. Nominal sizes can vary, and beveled or cleaned edges can be thinner than the plate itself.
2. Identify the alloy and polarity. Mild steel, stainless, and aluminum all conduct heat differently. Confirm if you’re running DC electrode-negative or AC before moving to any settings.
3. Pick tungsten and filler. A 3/32 in (2.4 mm) lanthanated tungsten will cover most shop work, with 1/16 in for thin sheet and 1/8 in for heavy plate. Match your filler to the joint thickness, leaning slightly smaller over larger.
4. Calculate a base amperage. A solid starting point for mild steel butt joints is 1 amp per 0.001 inch. From there, adjust for alloy (less for stainless, more for aluminum), joint type (about +25% for a fillet), position, or any heat-sinking fixtures.
5. Cut scrap to match. Use a coupon of the same alloy, thickness, and fit-up as the real joint, clamped to the same table. A loose piece on a cold bench will never reflect true heat absorption.
6. Test and adjust in small steps. Strike the arc and run a 2 to 3 inch bead. Make adjustments in 5–10 amp increments. Large jumps tend to create one defect only to introduce another.
7. Lock it in and refine. Once the bead looks correct, don’t chase the knob. Focus on travel speed and arc length to dial in the weld from there.

Consolidated Starting Amperage Chart

These are hand-TIG starting ranges for typical butt joints with good fit-up. Treat them as a place to set your dial before testing, not a guaranteed final setting.

Material	Thickness	Process	Starting Range
Mild steel	1/16 in (0.062)	DCEN	40–70 A
Mild steel	1/8 in (0.125)	DCEN	80–110 A
Mild steel	3/16 in (0.187)	DCEN	110–160 A
Stainless steel	16 ga (0.060)	DCEN	35–55 A
Stainless steel	1/8 in (0.125)	DCEN	60–90 A
Aluminum sheet	1/16 in (0.062)	AC	50–80 A
Aluminum sheet/plate	1/8 in (0.125)	AC	120–140 A
Aluminum	3/16 in (0.187)	AC	140–180 A
Aluminum tube	1/8 in wall	AC	110–140 A

Three Practical Scenarios

0.040 in 4130 chromoly tube: While the rule suggests around 40 A, fixtures tend to pull heat away from thin tube. Start between 45–55 A on DCEN with 1/16 in tungsten and 1/16 in filler, keep a tight arc, and rely heavily on travel speed. This level of heat control is the same kind of discipline seen in aerospace TIG welding.

1/8 in 6061 plate: The chart places this at roughly 125 A, so aim for 120–140 A on AC. Thorough oxide removal is non-negotiable, a modest cleaning balance goes a long way, and you’ll need more current for aluminum than steel of the same thickness.

16 ga stainless steel: Stainless holds heat very locally, so its 35–55 A window is easy to overshoot. Drop towards the lower end, back off at the tail of your bead, and watch for heavy straw heat tint as your first sign of excess heat input.

Bringing It All Together

Amperage is the foundation for every other adjustment. Thickness gives you your base, the alloy and joint design modify it, and travel speed and arc length fine-tune the result. For aluminum-heavy work especially, cleanliness is just as critical, so it’s worth learning how to prep aluminum right before striking an arc.

When the work becomes structural or commercial, procedure control matters. The American Welding Society publishes the certification pathways and performance standards that many inspectors expect. For supervised practice on real joints, a structured aluminium welding course can build that discipline far faster than trial and error alone. Measure, test on scrap, adjust in 5–10 amp steps, and let your scrap pile do most of the teaching.

Frequently Asked Questions

What is a good starting amperage for TIG welding?

For mild steel, start at about 1 amp per 0.001 inch of thickness for a butt joint — so a 0.125 in plate begins near 110-125 A. Reduce about 20% for stainless and increase 10-25% for aluminum, then test on scrap and adjust in small steps.

Can you TIG weld too hot?

Yes. Excessive amperage washes out the joint edges, causes burn-through in thin material, flattens the bead, and can create craters and cracks at the end of a weld. Back the amperage off and control heat with travel speed, pulsing, or preheating where appropriate.

Why does my TIG arc keep going out?

Usually the amperage is too low for the thickness, the tungsten is contaminated or ground wrong, or the arc length is too long. Check the setting first, then regrind the electrode to a clean point and keep the tip close to the work.

Does AC or DC change the amperage I need?

The mode changes how the heat behaves, not the basic rule. DC electrode-negative gives deep penetration for steel and stainless, while AC is required for aluminum because the electrode-positive half cleans away the oxide layer — which is why aluminum generally needs more current than steel of the same thickness.

How do I choose tungsten size for a given amperage?

Pick the smallest tungsten that comfortably carries your current: roughly 1/16 in for thin sheet work up to about 80-100 A, 3/32 in as the all-purpose choice around 80-200 A, and 1/8 in or larger for heavier plate. An oversized electrode gives a weak, wandering arc.

What is the difference between amperage and heat input in TIG welding?

Amperage is the current flowing through the arc; heat input is the total energy delivered to the joint, which also depends on arc voltage, travel speed, and duty cycle. Two welds at the same amperage can have very different heat inputs if travel speed differs.

Does pulsing let me weld thinner material?

Yes. Pulsing drops the background current below the peak, so the workpiece spends part of each cycle cooling while the peak amps still provide good penetration. This lets you hold a stable arc on thin stock that would otherwise require a lower, less stable constant current.

How do I avoid craters at the end of an aluminum TIG weld?

Use the downslope control to taper the current at the end of the bead and hold the torch over the crater while post-flow gas protects it. If the machine lacks downslope, reduce the amperage by hand in the last second of the weld.