If you have ever dialed in a clean bead on 1/8-inch steel, switched to 20-gauge sheet, and watched the arc punch a hole straight through the workpiece, you are not alone. Thin metal punishes habits that work fine on thicker sections. The heat that a 1/8-inch plate absorbs and conducts away concentrates in a single spot on sheet metal, and within seconds the base metal melts past the weld pool and you are left with a hole, a wasted part, and the urge to throw your hood across the shop.
Burn-through is not a machine problem. It is a heat-input management problem. The machine can be adjusted. The welder needs to know which levers to pull and in what order. This article covers wire size selection, short-circuit transfer, machine-specific settings, stitch technique, travel speed, copper backing, fit-up preparation, and a systematic pre-weld checklist. Every number in a settings table is a starting point. Your machine manual and a test weld on the same material are the only final authority.
Why Thin Metal Is Different
Thin sheet metal (24 gauge through 16 gauge, 0.024–0.060 inches / 0.6–1.5mm) has significantly less thermal mass than the 1/8-inch (3mm) plate most intermediate welders learn on. Heat concentrates in the weld zone rather than being conducted away through the surrounding material. When the heat input per unit length of weld exceeds what the base metal can sink, the melting point is exceeded beyond the weld pool, and burn-through occurs (source: TWI Job Knowledge series).
MIG welding inherently delivers more heat input than TIG for the same material thickness. This is not a judgment against MIG. It means technique discipline matters more on thin metal. The same voltage, wire speed, and travel speed that produce a solid weld on 1/8-inch will burn a hole through 18 gauge (0.048 inch / 1.2mm) because the thin material cannot sink the heat fast enough.
You have five interdependent levers for controlling heat input on thin metal:
- Wire diameter – smaller wire allows lower minimum amperage
- Wire feed speed – lower feed speed reduces current
- Voltage – lower voltage reduces heat, but too low causes arc instability
- Travel speed – faster travel reduces heat per inch of weld
- Technique – stitch vs continuous welding, cooling intervals, tack sequence
These levers interact. Change one and you may need to adjust another. The goal of this article is to give you a systematic way to work through them.
Safety reminder – thin metal specific: Thin material reaches ignition temperature faster than thick plate. Maintain 35-foot clearance from combustibles per OSHA 1910.252(a). Standard MIG PPE applies: auto-darkening helmet (shade 10–13), leather gloves, long sleeves, adequate ventilation. Test coupons and scrap pieces get hot fast and stay hot – cool them before leaving the bench.
Wire Size Selection: The Foundation
Wire diameter is the first lever because it determines the minimum amperage range the machine can run while maintaining stable short-circuit transfer. Smaller wire has less cross-sectional area, so resistance heating is more efficient and the wire melts at lower current. This allows stable arcing at lower wire feed speeds, which means lower minimum current and less heat input.
0.023 inch (0.6mm)
Widely recommended by manufacturers for sheet metal 18 gauge (0.048 inch / 1.2mm) and thinner. Minimum stable short-circuit current is approximately 30–50 amps (source: Weldability Siff technical data). This enables the lowest heat input of any MIG wire size.
Caveat: 0.023-inch wire requires a proper feed system. Use a nylon or Teflon liner (not standard steel liner), U-groove drive rolls (V-groove can crush the wire), and a contact tip matched to 0.023-inch bore. Some machines, especially budget models or those with long (10-foot-plus) leads, cannot push 0.023-inch wire reliably. If that is your situation, 0.030-inch may be your practical minimum (source: Bernard/ITW Small Diameter Wire Guide).
0.030 inch (0.8mm)
Workable for 18–16 gauge (1.2–1.5mm). Minimum stable short-circuit current is approximately 50–80 amps. More tolerant of poor feed conditions and a good compromise if 0.023-inch feed is unreliable or you work across a range of thin-to-medium material. Many manufacturers (Lincoln, Miller, ESAB) list 0.030-inch as acceptable for 16 gauge with careful technique.
0.035 inch (0.9mm)
Generally too hot for material thinner than 16 gauge. Minimum stable short-circuit current is approximately 80–110 amps with a minimum feed speed around 150 IPM, which on most machines produces 110–140 amps. That is enough current to quickly cause burn-through on 18-gauge material if machine settings, wire feed, fit-up, backing, and travel technique are not controlled. On 16 gauge (0.060 inch / 1.5mm), 0.035-inch can be used with very careful technique and a copper backing bar, but it is usually not preferred for this gauge (source: ESAB Thin Materials Guide, Weldability Siff).
Wire classification
Both ER70S-3 and ER70S-6 are usable for thin carbon steel. ER70S-6 may provide slightly better arc stability at low amperages due to higher deoxidizer content (more manganese and silicon). This is a refinement, not a requirement – either classification works (source: AWS A5.18).
Wire Size by Material Thickness – Starting Recommendation
| Material Gauge | Decimal Thickness | 0.023 in (0.6mm) | 0.030 in (0.8mm) | 0.035 in (0.9mm) |
|---|---|---|---|---|
| 24 ga (0.024 in / 0.6mm) | 0.024 in | ✓ common starting choice | ✗ often difficult | ✗ often difficult |
| 22 ga (0.030 in / 0.8mm) | 0.030 in | ✓ common starting choice | ⚠ Marginal | ✗ often difficult |
| 20 ga (0.036 in / 0.9mm) | 0.036 in | ✓ common starting choice | ⚠ Use with care | ✗ often difficult |
| 18 ga (0.048 in / 1.2mm) | 0.048 in | ✓ common starting choice | ✓ Workable | ✗ usually not preferred for this gauge |
| 16 ga (0.060 in / 1.5mm) | 0.060 in | ✓ Good | ✓ Good | ⚠ Use with care, backing bar recommended |
*These are starting recommendations. Actual results depend on your specific machine, technique, joint type, and fit-up See our 5 basic welding joint types guide for more on this topic.. Test on scrap before welding the workpiece.*
Short-Circuit Transfer: The Standard Conventional MIG Mode for Thin Metal
Short-circuit transfer (sometimes called dip transfer or short-arc) is the standard conventional MIG mode for thin metal. Understanding what it is and how to recognize it matters more than memorizing voltage numbers.
What short-circuit transfer is
The wire physically touches the workpiece, creating a short circuit. Current flows, the wire melts at the point of contact, the molten metal “pops” off (transfers) to the puddle, the arc re-establishes, and the cycle repeats – typically 50 to 200-plus times per second. This produces the characteristic crackling sound often described as bacon frying. The periodic short-circuit gives the weld pool a fraction of a second to cool between each transfer cycle. That built-in cooling is what makes short-circuit suitable for thin metal (source: Miller, Lincoln, ESAB, TWI).
Why spray and globular transfer are usually poor choices for thin sheet
Spray transfer operates at higher current (typically 160-plus amps on steel) with a continuous stream of molten droplets and no periodic cooling. Globular transfer – the transition zone between short-circuit and spray – produces large, irregular drops that create uneven heat input and heavy spatter. Neither mode allows the periodic cooling that short-circuit provides. On thin sheet, the continuous heat input quickly exceeds what the material can sink, and burn-through follows (source: Miller Thin Metal Guide, Lincoln Sheet Metal Guide, ESAB Thin Materials Guide).
Listen for the crackle: A proper short-circuit arc produces a steady crackling sound like bacon frying. If you hear a smooth hissing sound (spray transfer) or irregular popping (globular), you are not in short-circuit mode. Reduce voltage and/or wire speed until the crackling returns. This is an observational technique – your ears are as useful as your eyes for dialing in thin metal settings.
Recognizing short-circuit
- Crackling or bacon-frying sound, steady and consistent
- Low to moderate spatter when parameters are correct
- Flat to slightly convex bead profile
- Voltage typically in the 14–18V range (machine-dependent – do not treat as universal)
- Current approximately 30–150 amps depending on wire diameter and machine settings
Pulse MIG on thin metal – a brief note
Modern pulse MIG machines (typically inverter-based) can weld thin material with pulsed spray transfer, which alternates between high current (spray transfer) and low background current (cooling). This is an advanced option and not the primary focus of this article. Most readers will be using conventional MIG machines with short-circuit transfer. If you have a pulse-capable machine, consult its manual for thin-metal pulse parameters.
Machine Dependency: Why There Are No Universal Settings
Every machine brand uses a different voltage control scheme, different numbering scales, and different wire speed ranges. A Lincoln Power MIG 210 on voltage Tap 1 with wire speed 150 IPM is not the same as a Miller Millermatic 211 at voltage setting 1 and 150 IPM. Setting translations between brands do not exist. This is not a limitation – it is how these machines are designed.
Control scheme differences
| Machine Category | Voltage Control | Assisted Setup | Notes for Thin Metal |
|---|---|---|---|
| Lincoln (Power MIG series) | Voltage taps (fixed) or infinite voltage (inverter) | Smart MIG on some models | Thin metal typically uses lowest tap (Tap 1) with wire speed 100–250 IPM depending on thickness |
| Miller (Millermatic / Multimatic) | Voltage taps (transformer) or infinite (inverter) | Auto-Set on many models | Auto-Set provides pre-programmed settings by gauge; manual mode uses low-range voltage scale |
| ESAB (Rebel / EMP series) | Sync mode (integrated) or U/L manual (independent) | Sync adjusts voltage for wire speed automatically | Low-range Sync settings for thin material; model scales differ (215ic vs 235ic vs 285ic) |
| Generic / hobbyist (4–6 tap) | Fixed voltage taps (typically 4–6) | None or basic | May lack a low enough voltage for 24–22 gauge; stitch welding and backing bar become critical |
*Lincoln Smart MIG, Miller Auto-Set, and ESAB Sync mode all provide pre-programmed starting points by material thickness. These are helpful baselines but can always be manually overridden for fine-tuning. None of these features replaces a test weld on scrap.*
Synergic vs non-synergic control
In synergic mode, the machine adjusts one parameter (typically voltage) based on the other (wire speed). This means you set wire speed and the machine selects a matching voltage. In non-synergic mode, both are set independently. Neither is inherently better for thin metal – both require verification with a test weld. The Starting Point rule applies regardless of control scheme.
The Starting Point rule
Every settings table in this article is a starting point. Your machine’s manual is the first reference. A test weld on the same material, with the same wire and gas, is the verification step. No exception.
Stitch and Tack Welding Technique
Stitch welding – a series of short welds with cooling pauses between them – is one of the most effective techniques for controlling heat input on thin metal. The cooling interval allows the base material temperature to drop between weld segments, preventing the cumulative heat buildup that causes burn-through (source: Miller Thin Metal Guide, Lincoln Sheet Metal Guide, ESAB Thin Materials Guide).
Stitch length
A typical stitch length range is 3/8 to 3/4 inch (10–20mm). ESAB recommends 3/8–3/4 inch; Lincoln recommends 1/2–1 inch (12–25mm). Shorter stitches provide more cooling intervals but increase total welding time. Longer stitches reduce cooling effectiveness. Stay within this range for material 20 gauge and thinner.
Cooling interval
Weld time to pause time should be at least 1:1 (equal cooling time to weld time). Longer pauses – 2:1 or 3:1 pause-to-weld ratio – improve cooling on thinner material. The goal is to keep interpass temperature low enough that the base metal does not overheat visibly. If the metal around the previous stitch is still hot to the touch or glowing, wait longer.
Alternating stitch pattern
Do not weld stitches in sequential order along the joint. Distribute heat by welding in a skip sequence. For example:
Position 1 → skip to Position 4 → then Position 2 → then Position 5 → then Position 3 → then Position 6
This pattern allows each stitch zone to cool between passes. The further apart the stitches, the better the cooling.
Tack welding before the full weld
- Tack both ends of the joint first to hold alignment.
- Add intermediate tacks every 1–2 inches (25–50mm), alternating sides of the joint to balance heat distribution.
- Allow all tacks to cool completely – until they are room-temperature-to-touch or at least no longer visibly glowing – before welding over them.
- If tacks are too large or too hot, they become sources of burn-through when the weld passes over them.
Alternating tacks distributes the thermal load, reducing distortion and the localized overheating that leads to burn-through (source: ESAB Thin Materials Guide, TWI Job Knowledge).
When continuous welding is possible
On thicker thin material (16 gauge) with good heat sinking such as a copper backing bar, continuous short welds may be acceptable for short joint lengths. Stitch welding is not always required – it is the safest technique for material 20 gauge and thinner.
Travel Speed as Heat Control
On thin metal, travel speed is your primary heat input control during welding. The faster you move, the less heat is delivered per inch of weld. Unlike thick material where you might slow down for penetration, thin metal demands a slightly faster travel speed than feels natural.
Correct travel speed
Steady motion with no hesitation. Bead width approximately 1.5 to 2.5 times wire diameter (a rough visual reference, not a specification). Consistent short-circuit crackling sound – no long pauses (which cause heat concentration) and no jerky acceleration (which causes lack of fusion). The goal is to deposit weld metal without dwelling in any one spot long enough to overheat the base material (source: ESAB Thin Materials Guide).
Too slow
The most common mistake on thin metal. Heat concentrates under the arc, the weld pool widens uncontrollably, the base metal melts through, and you get a hole. Also causes excessive melt-through on the back side and warpage. Miller states: “On thin metal, the tendency is to move too slowly – which concentrates heat and causes burn-through.”
Too fast
Wire burn-back (the arc climbs up the wire), erratic arc (short-circuit frequency drops), lack of fusion at weld toes, poor bead wetting, inconsistent bead profile. The wire feed speed outruns the melting capacity of the arc.
What correct travel speed looks and sounds like: Consistent bead width, steady crackling arc, no hesitation. Too slow – puddle widens, burn-through, hissing sound. Too fast – erratic arc, wire stubbing, lack of fusion, popping sound.
How to find the right travel speed
Run a test weld on scrap of the same material. Start at a speed that feels slightly fast (intentionally). Reduce speed gradually until you see consistent bead formation with no burn-through. That is your upper boundary. Then increase speed slightly until you see the first signs of lack of fusion or wire burn-back. Your target speed is between these two boundaries. Lincoln states: “On thin metal, travel speed is your primary heat control. Moving too slowly concentrates the arc in one spot, overheating and burning through.”
Relationship between travel speed, wire speed, and voltage
These three parameters interact. If you increase travel speed, you may need to increase wire speed to maintain adequate fill. If you increase voltage, you may need to increase travel speed to compensate for the added heat. Change one parameter at a time, observe the result, then adjust the next.
Copper Backing Bar Technique
A copper or brass backing bar clamped behind the joint serves three functions: it acts as a heat sink drawing heat away from the weld zone, it supports the back of the weld preventing melt-through, and it shapes the weld root for a clean back bead (source: Lincoln Sheet Metal Guide, Miller Thin Metal Guide, ESAB Thin Materials Guide).
Why copper works
Copper has a thermal conductivity roughly six times higher than steel. This makes it highly efficient at drawing heat away from the weld zone, preventing the base metal from reaching melting temperature underneath the arc (source: ESAB Thin Materials Guide).
Minimum thickness and clamping
A minimum thickness of approximately 1/4 inch (6mm) is recommended. Thinner bars can overheat themselves, losing their heat-sinking effectiveness. Thicker bars (3/8 to 1/2 inch) provide longer thermal capacity for longer welds.
The backing bar must be clamped firmly and evenly against the workpiece across the full joint length. Any gap between the bar and the workpiece creates an air gap that reduces heat transfer and allows melt-through. Use C-clamps, sheet metal clamps, or toggle clamps spaced every 4–6 inches for even pressure.
Material options
| Material | Thermal Conductivity vs Steel | Notes |
|---|---|---|
| Copper | ~6x steel | Best heat sink. Weld metal does not fuse to it. Most commonly recommended. |
| Brass | ~3x steel | Good alternative. Lower cost, easier to machine. |
| Aluminum | ~2.5x steel | Lighter, less effective. Can work for light-duty use but prone to overheating. |
| Steel | 1x (same) | Not recommended as a heat sink – similar conductivity means no benefit. Can support root if gap is small and heat is controlled. |
DIY options
Split and flattened copper pipe, copper bar stock from scrap yards, or brass bar stock. The surface must be flat and mate cleanly to the workpiece. Clean the bar before use – contaminated copper can cause porosity in the weld.
When a backing bar is most useful
- Butt joints in 16 gauge and thinner
- Full-penetration single-pass welds
- Joints with unavoidable small gaps
- Thin metal with 0.030-inch or larger wire
When a backing bar is less needed
- Lap joints (the overlapping sheet provides some heat sinking)
- Edge joints (no back side to protect)
- Stitch-welded joints with good fit-up
- Joints using 0.023-inch wire with well-controlled technique
Fit-Up and Joint Preparation
Joint selection and preparation matter as much as settings on thin metal. A gap that would be acceptable on 1/4-inch plate guarantees burn-through on 18 gauge.
Joint selection (in order of difficulty)
- Edge joint – Easiest. No back side to protect, no gap to control, lowest burn-through risk. Preferred when the application allows.
- Lap joint – Moderate. The overlapping sheets provide some heat sinking. Gap between sheets is less critical because the arc does not “see through.” Typically acceptable with minimal gap.
- Butt joint – Most challenging. Requires tight fit-up because the arc can burn through the gap.
Gap control for butt joints
A general guideline for butt joints in thin sheet metal is to keep the gap less than half the material thickness. For 18 gauge (0.048 inch / 1.2mm), the gap must be less than 0.024 inch (0.6mm). Gaps larger than this significantly increase burn-through risk because the arc can “see” through the gap and melt the backing surface or blow through entirely (source: Lincoln, AWS D1.3, TWI).
Edge preparation
- Laser-cut edges – Cleanest fit, minimal gap, best for thin metal butt joints.
- Sheared edges – May have burrs that create local gaps. Deburr with a file or sandpaper before fitting.
- Ground or abraded edges – Can produce acceptable fit if done carefully. Over-grinding can thin the edge and increase burn-through risk at the joint interface.
Cleaning
Remove oil, grease, paint, rust, and mill scale from both sides of the joint (top and back side). Contaminants concentrate arc heat locally, increasing burn-through risk (source: TWI). Clean at least one inch on each side of the joint.
Clamping and fixturing
Use magnets, C-clamps, sheet metal clamps, corner clamps, or toggle clamps to hold parts tightly and prevent gap movement from thermal expansion during welding. Clamping also acts as a secondary heat sink – metal clamps draw some heat away from the joint.
Additional heat sinks
- Heavy steel or aluminum blocks clamped behind or beside the joint absorb heat.
- Fixturing tables with aluminum or steel tooling – the table mass acts as a heat sink.
- Water-based improvised heat sinks (wet rags, sponges): Not recommended. Water plus electricity near welding equipment creates a serious shock hazard. Even well-grounded low-voltage situations present risk of electrocution if the rag contacts the torch, wire, or any electrical component. This general guide does not recommend the use of wet rags or sponges as heat sinks. Use dry copper or steel backup blocks instead.
Back-purging for tubular thin metal
Back-purging thin-walled tube or pipe with inert gas (typically argon) on the root side can shield the weld root from oxidation. However, C25 (75% argon / 25% CO2) contains carbon dioxide, which is not an inert gas — using C25 as a back-purge gas for tubular thin metal introduces carbon into the weld root and is not standard practice. If back-purging is needed for thin-wall tube, use pure argon or another inert gas per the applicable welding procedure specification. This is an advanced technique that requires a qualified welding procedure and is beyond the scope of this general guide.
Heat Control Strategies Summary
The five-lever model is a practical mental framework for approaching any thin metal job. None of these levers operates independently.
The five levers
| Lever | Action for Less Heat | Warning |
|---|---|---|
| Wire diameter | Use 0.023 inch for 24–18 gauge | Some machines cannot feed 0.023 inch reliably |
| Wire feed speed | Reduce to lower current | Too low causes arc instability and stubbing |
| Voltage | Reduce within short-circuit range | Too low causes erratic arc and lack of fusion |
| Travel speed | Increase to reduce heat per inch | Too fast causes lack of fusion and burn-back |
| Technique | Switch to stitch welding with cooling intervals | Continuous possible on 16 gauge with good heat sinking |
Interdependence
If you change wire speed, the stable voltage range shifts. If you change travel speed, you may need to adjust wire speed to maintain fill rate. Change one variable at a time, test, observe, then adjust the next.
Testing on scrap – the essential step
Before every thin metal job, run a test weld on a piece of the same material (same gauge, same joint type, same fit-up). This is how you verify settings without risking the workpiece. Miller labels all settings in their guides as starting points – the machine manual and test welds are the final authority. Every manufacturer source says the same thing.
Recognizing the sweet spot
- Steady short-circuit crackling sound (consistent frequency, not erratic)
- Consistent bead width (approximately 1.5–2.5 times wire diameter)
- No burn-through (visual inspection of front and back side)
- Full fusion at weld toes (no undercut, no cold lap)
- Flat to slightly convex bead profile
- Minimal spatter
Passive heat sinks
Copper or brass backing bars, steel or aluminum backup blocks, and fixturing table mass are passive heat controls. They work continuously without requiring technique adjustment. If you are struggling with burn-through and have adjusted all five levers, add a heat sink.
Starting Point Settings Tables
STARTING POINTS ONLY. These settings are derived from manufacturer manuals. Your specific machine, joint configuration, fit-up, wire brand, and technique will require adjustment. Always verify settings with a test weld on the same material before welding the workpiece. Your machine’s manual is the final authority.
All tables assume C25 shielding gas (75% argon / 25% CO2) unless noted.
Table 1: Lincoln Power MIG Series – Starting Points
| Material | Wire Dia | Voltage Tap (PM 210) | Wire Speed (IPM) | Notes |
|---|---|---|---|---|
| 24 ga (0.024 in) | 0.023 in | Tap 1 | 80–120 | Lowest heat. Stitch weld. Backing bar recommended. |
| 22 ga (0.030 in) | 0.023 in | Tap 1 | 90–140 | Stitch weld. Minimize gaps. |
| 20 ga (0.036 in) | 0.023 in | Tap 1 | 120–160 | Stitch or short continuous. |
| 18 ga (0.048 in) | 0.023 or 0.030 in | Tap 1–2 | 130–200 | 0.023 in preferred; 0.030 in on Tap 1. |
| 16 ga (0.060 in) | 0.030 in | Tap 1–2 | 150–250 | 0.030 in on Tap 1. Shorter stitch OK. |
*Power MIG 210 uses 4 voltage taps. Other Power MIG models (260, 350) may have different tap numbering. Consult your manual.*
Table 2: Miller Millermatic / Multimatic Series – Starting Points
| Material | Wire Dia | Voltage Setting | Wire Speed (IPM) | Notes |
|---|---|---|---|---|
| 24 ga (0.024 in) | 0.023 in | Low ~1 (or Auto-Set 24 ga) | 80–130 | Auto-Set recommended if available. Stitch weld. |
| 22 ga (0.030 in) | 0.023 in | Low ~1 | 100–150 | Stitch weld. Backing bar helpful. |
| 20 ga (0.036 in) | 0.023 in | Low ~1–2 | 120–180 | Short continuous on short joints. |
| 18 ga (0.048 in) | 0.023 or 0.030 in | Low ~2 | 150–220 | 0.023 in on thinner end; 0.030 in toward 18 ga. |
| 16 ga (0.060 in) | 0.030 in | Low ~2–3 | 180–280 | 0.030 in works well here. Shorter continuous OK. |
*Low ~1–2 refers to low-range voltage scale on manual-mode Millermatic/Multimatic. Auto-Set users: select material gauge and adjust wire speed from the Auto-Set baseline. Consult your manual for your specific model.*
Table 3: ESAB Rebel / EMP Series – Starting Points
| Material | Wire Dia | Sync Setting | Wire Speed (IPM) | Notes |
|---|---|---|---|---|
| 24 ga (0.024 in) | 0.023 in | Low 1 / Min | 80–120 | Use Sync mode low end. Stitch weld. |
| 22 ga (0.030 in) | 0.023 in | Low 1–2 | 100–150 | Stitch weld. Backing bar if butt joint. |
| 20 ga (0.036 in) | 0.023 in | Low 2 | 120–180 | Short continuous on lap joints. |
| 18 ga (0.048 in) | 0.023 or 0.030 in | Low 2–3 | 150–220 | 0.023 in on thinner end. |
| 16 ga (0.060 in) | 0.030 in | Low 3–4 | 180–280 | 0.030 in preferred. Short continuous OK. |
*Sync mode adjusts voltage automatically based on wire speed. In manual (U/L) mode, set voltage low and adjust as needed. EMP 215ic, 235ic, and 285ic have different Sync scales – consult your manual.*
Table 4: Generic 4-Tap / 6-Tap Hobbyist Machines – Starting Points
| Material | Wire Dia | Tap Selection | Wire Speed (IPM) | Notes |
|---|---|---|---|---|
| 24 ga (0.024 in) | 0.023 in | Lowest tap (1 of 4 or 1 of 6) | 80–100 | These machines may lack low enough voltage for 24 ga. Stitch weld essential. |
| 22 ga (0.030 in) | 0.023 in | Lowest tap | 90–130 | Test on scrap first. Copper backing strongly recommended. |
| 20 ga (0.036 in) | 0.023 in | Tap 1–2 (low) | 110–160 | Stitch weld on butt joints. Lap joints more forgiving. |
| 18 ga (0.048 in) | 0.023 or 0.030 in | Tap 2 (low) | 140–200 | 0.030 in may work better if 0.023 in feed is unreliable. |
| 16 ga (0.060 in) | 0.030 in | Tap 2–3 | 170–250 | Most hobbyist machines can handle 16 ga with 0.030 in. |
*Generic machines vary widely. These are approximate ranges. If the lowest tap still produces burn-through, switch to 0.023-inch wire, add copper backing, or use stitch welding exclusively. Some machines cannot weld 24–22 gauge reliably – consider borrowing or upgrading, or use a different process such as TIG.*
Remember: All settings are starting points. Your machine’s manual and a test weld on the same material are the only final authority. Settings that work on one welder’s machine may not transfer to another brand or even a different model from the same manufacturer.
Troubleshooting Common Thin Metal Problems
Burn-through
Causes: Wire speed too high (too much current), voltage too high, travel speed too slow, stitch spacing too tight (no cooling), fit-up gap too large, no backing bar on butt joint, wire too large for thickness.
Immediate fixes: Reduce wire speed to lower current. Increase travel speed to reduce heat per inch. Switch to stitch welding if running continuous. Add copper backing bar. Switch to 0.023-inch wire if using 0.030 or 0.035 inch. Reduce voltage if possible while maintaining short-circuit stability.
*(For spatter that accompanies burn-through, see the MIG spatter troubleshooting guide.)*
Warpage / distortion
Causes: Heat input too high for material thickness. Continuous welding instead of stitch. No cooling intervals. Unrestrained parts (no clamping or fixturing). Uneven heat distribution.
Mitigation: Stitch weld with adequate cooling intervals. Alternate stitch positions to balance heat. Clamp and fixture parts securely. Use copper backing bar as a heat sink. Allow parts to cool completely between weld segments.
*(See the MIG troubleshooting articles for general warpage guidance.)*
Lack of fusion / cold lap
Causes: Travel speed too fast (arc moves ahead of puddle), voltage too low for wire speed (cold arc), wire speed too low for thickness, incorrect wire diameter.
Fixes: Slow travel speed slightly – but watch for burn-through as the window is narrow. Increase voltage slightly while maintaining short-circuit transfer. Increase wire speed slightly. This is a fine balance – make small adjustments.
*(See the MIG troubleshooting guide for lack of fusion.)*
Wire feed problems with 0.023-inch wire
Causes: Wrong liner type (steel liner instead of nylon or Teflon), V-groove drive rolls crushing the wire, push distance too long (over 12 feet / 3.5m), worn or oversized contact tip, bird-nesting at drive rolls.
Fixes: Install nylon or Teflon liner for 0.023-inch wire. Switch to U-groove drive rolls. Reduce push distance if possible. Replace contact tip with correct 0.023-inch bore. Check drive roll tension.
*(See the MIG wire feed troubleshooting guide.)*
Erratic arc / excessive spatter on thin metal
Causes: Voltage too low for wire speed (arc instability), contact tip worn or oversized, wire feed speed too low (stuttering short-circuit), gas flow too low (turbulence), dirty base metal (contaminants cause arc wandering).
Fixes: Increase voltage slightly. Replace contact tip. Increase wire speed to stabilize short-circuit frequency. Verify gas flow (15–20 CFH). Clean base metal thoroughly.
*(See the MIG spatter troubleshooting guide.)*
Burn-back when traveling fast on thin metal
Causes: Travel speed outruns wire burn-off rate, wire feed speed too low for travel speed, voltage too low, contact tip-to-work distance too long.
Fixes: Slow travel speed slightly. Increase wire feed speed. Increase voltage slightly. Reduce stick-out to 3/8–1/2 inch. Ensure correct polarity (DCEP for steel).
*(See the MIG burnback troubleshooting guide.)*
Putting It All Together: Pre-Weld Checklist
If you have time to weld it once, you have time to test it on scrap first.
Step 1: Verify wire size and feed system. Confirm wire diameter matches the job (0.023 inch for 18 gauge and thinner, 0.030 inch for 16 gauge). Check liner, drive rolls, and contact tip are correct for the wire diameter.
Step 2: Set machine to starting point. Consult the machine-category table (Lincoln, Miller, ESAB, or generic) for your material gauge and wire size. Set voltage and wire speed to the starting point.
Step 3: Clean and prepare the joint. Degrease, remove mill scale, deburr sheared edges. Verify gap is less than half material thickness for butt joints. Clamp and fixture parts tightly.
Step 4: Set up copper backing bar (if needed). For butt joints in 18 gauge and thinner, or any joint where burn-through risk is high. Clamp firmly with even pressure across full joint length.
Step 5: Tack the joint. Tack both ends first, then intermediate tacks every 1–2 inches (25–50mm), alternating sides. Allow all tacks to cool completely before welding.
Step 6: Run a test weld on scrap. Use the same material, same wire, same settings, same joint type. Adjust settings if the test shows burn-through, lack of fusion, or excessive spatter. Repeat until the test weld is clean and sound.
Step 7: Weld the joint using stitch technique. Run short stitches (3/8–3/4 inch / 10–20mm) with cooling pauses at least equal to weld time. Alternate stitch positions to distribute heat.
Step 8: Inspect the weld. Check for burn-through (visible holes or excessive melt-through on back side), distortion (warping of the workpiece), undercut, lack of fusion, excessive spatter.
Step 9: Adjust and retest if needed. If burn-through occurs on the workpiece, stop. Re-assess wire size, settings, travel speed, stitch pattern, or backing. Run another test on scrap before continuing.
*This article is part of the Weldsmartly MIG welding series. For thin aluminum MIG, see our MIG Welding Aluminum guide. For shielding gas selection, see the MIG Shielding Gas Guide and Argon vs CO2 vs C25 comparison. For wire feed, spatter, or burnback troubleshooting, see the corresponding MIG troubleshooting articles. For welding shop fire prevention, see the Welding Shop Fire Prevention guide. Gas regulator setup is covered in How to Read a MIG Gas Regulator and Flow Meter.*
