How to weld square tubing without blowing holes

Free guide · The Welder's Forge · updated September 2026

Square tubing is the raw material for gates, railings, workbenches, shelving and trailers. The catch is the thin wall: the tube is hollow, the heat has nowhere to go and it is easy to blow a hole, especially at the corners.

Quick answer

Measure the wall, then start low: a 5/64 in (2.0 mm) rod at 45–70 A or a 3/32 in (2.4 mm) rod at 60–90 A for stick, or .030 in (0.8 mm) wire at 15–19 V for MIG. Tack first, weld one face at a time and move quickly over the corners, which is where tubing burns through.

What is the wall thickness?

The outside size (1 in, 1-1/2 in, 2 in) says nothing about the wall. Wall thickness is often given as a gauge number: the higher the number, the thinner the wall. Rather than guess, measure with calipers at the end of the tube. The wall, not the tube size, decides your settings.

Starting settings by wall thickness

Wall	Stick	MIG/MAG
Thinner than 16 ga (.060 in, 1.52 mm)	Very difficult; use MIG	.023–.030 in wire, lowest settings that fuse
16 ga (.060 in, 1.52 mm)	5/64 in (2.0 mm), low end of 45–70 A	.030 in, 15–19 V, 160–275 IPM (4–7 m/min)
14 ga (.075 in, 1.90 mm)	5/64 in at 45–70 A, or 3/32 in (2.4 mm) at 60–90 A	.030 in, 15–19 V, 160–275 IPM (4–7 m/min)
11 ga (.120 in, 3.04 mm)	3/32 in, upper part of 60–90 A	.035 in (0.9 mm), 18–24 V, 160–355 IPM (4–9 m/min)

Currents from Table 3.2 and MIG settings from Table 4.2 of the e-book The Welder's Forge (carbon steel, flat position). Reduce stick current 10 to 15% for vertical or overhead. Starting points: confirm with the package and the machine manual.

Always test on an offcut of the same tubing. The full rod table, with signs of too much or too little current, is in the stick welding amperage chart. On very thin walls the logic is the same as for body panels: spaced tacks and patience, as in welding thin sheet metal.

Where tubing burns through: the corners

The flat faces take heat well. The corners and cut ends have little metal and heat up fast, so the puddle drops through. To avoid it:

Start the bead on a flat face, never on the corner.
Pass the corner without stopping, a little faster, and do not weave there.
Weld one face at a time, with pauses. Do not go all the way around in one pass.
Keep a short arc and aim the heat at the heavier side of the joint (on a T-joint, the piece that receives the tube).
Keep the gap minimal. A big gap forces extra filler and extra heat.

Burned a hole?

Stop and let it cool. Close it with short tacks around the edge, working from the outside toward the center. Holding the arc on the hole only makes it bigger.

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Squaring up and 45° miter cuts

At frame corners, a 45° miter gives a clean look and closes the tube. The rules:

Cut every piece with the same saw or grinder setup so the angles match.
Deburr each cut before assembly.
Assemble on a flat surface with clamps and a 90° square.
Tack opposite faces of each corner first, measure the diagonals and only then run the final beads.

A complete frame, step by step, is in how to weld a gate.

Clean before you weld

Tubing often ships with oil, mill scale or paint. All of it causes porosity and spatter. Grind to bright metal on both sides of the joint and where the work clamp attaches.

Galvanized tubing

If the tube is galvanized, remove the zinc from the weld zone. Zinc oxide fume causes metal fume fever (chills, fever, malaise). Grind the coating off, use local exhaust and wear a NIOSH-approved respirator with P100 filters. Never weld a tube that is sealed at both ends: trapped air expands and can blow out.

Cap the ends

Open tubing on a gate or railing fills with water and rusts from the inside. Close the ends with a welded plate or plastic caps, and finish with primer and paint.

Frequently asked questions

What amps should I use to weld 1/8 in square tubing?

For a wall near 1/8 in (3.2 mm), a 3/32 in (2.4 mm) rod in the upper part of 60–90 A or a 1/8 in (3.2 mm) rod near the low end of 90–130 A are starting points. Test on an offcut.

Why does square tubing burn through at the corners?

Corners and cut ends have little metal and heat up very fast. Start the bead on a flat face and run over the corner without stopping.

Is MIG or stick better for square tubing?

MIG with .030 in (0.8 mm) wire is easier to control on thin walls. With stick, use a small rod and low current, and below 16 gauge switch to MIG.

What rod works best for square tubing?

E6013 is a common choice for home fabrication: it strikes easily and gives a clean bead. On thin walls use the small 5/64 in (2.0 mm) size.

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