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+---
+title: MIG welding
+---
+
+Recently, I took a MIG welding class at [Artisan's
+Asylum](https://artisansasylum.com) in Somerville, MA. I wanted to document what
+I learned so that I can refer back to it in the future, so here it is!
+
+## Safety
+
+There are four primary hazards:
+
+1. **Burns.** You're dealing with liquid metal, so the work piece will remain
+   hot even after you finish a weld. Also, small balls of molten steel will fly
+   away from the work area and can burn through clothing and footwear, or ignite
+   flammable objects nearby. Precautions: welding jacket, welding gloves, face
+   mask, eye protection. Scan the surrounding area for fire hazards before
+   welding.
+2. **Electric shock.** MIG welding is an electrical process in which current is
+   passed between the welding wire and the ground clamp. Precautions: don't weld
+   in damp areas.
+3. **Radiation.** Ultraviolet light emitted from the arc can damage eyesight.
+   Precautions: welding face shield, preferably an auto-darkening one, though a
+   small amount of exposure will occur due to the delay between the arc flash
+   and the sensor activation, mostly a concern when you spend 40 hours a week
+   welding.
+4. **Asphyxiation.** MIG welding typically uses a gas mix called C25, a mix of
+   75% argon and 25% carbon dioxide, in order to displace oxygen from the work
+   area which would oxidize the molten steel and prevent a solid weld from
+   forming. As the gas mix displaces oxygen, welding in an enclosed area could
+   result in hypoxia. Precautions: weld in a well-ventilated area. The welding
+   shop at A^2 has an exhaust system.
+
+## Mechanics
+
+There are two primary controls on the welding machine: voltage (a proxy for
+temperature) and feed speed. There's a chart on the welding machine with
+recommended settings for types and thicknesses of sheet metal. Some machines
+have an "auto feed" setting which tends to work fairly well.
+
+Don't weld anything galvanized, as the zinc will vaporize and can cross the
+blood-brain barrier causing neurological damage.
+
+There are three common gauges of welding wire: 0.023", 0.030", and 0.035". 030
+is a good general purpose wire. When you switch out a reel, be sure that the
+feed rollers are fitted for the correct gauge. The number facing out on the reel
+is the groove in use, regardless of whether it's actually on the same side of
+the number or the opposite side.
+
+To reduce friction on the sleeve that holds the welding wire inside the gas
+cable, try to avoid sharp loops, similar to how a garden hose can kink.
+
+You want to keep the nozzle about 3/8" away from the work piece.
+
+After a weld, slag and ash may accumulate on the surface. This can be brushed
+off with a wire brush or ground down for a cleaner surface.
+
+The welding tip is where the current is transferred from the electrode running
+down the cable into the welding wire. It's relatively easy for the tip to become
+damaged and require replacement; it's a 15-cent consumable part so not a big
+deal. To replace, pull off (don't unscrew) the sheath from the end of the
+nozzle, unscrew the tip, and screw a new one in. The inner diameter of the
+sheath may also accumulate slag buildup over time which can easily be cleaned
+out using the tapered end of MIG welding pliers.
+
+To warn people nearby, announce "welding" before starting a weld.
+
+Two directions for welding: push and drag. Not much difference between them
+other than what you can see: drag allows you to see the bead you're laying while
+push allows you to see where you're going.
+
+## Tack Welds
+
+Useful for tacking a piece in place before laying a bead. With about 3/8" of
+wire protruding from the tip, place the tip against the work surface, and
+depress the trigger for about 1 second.
+
+## Beads
+
+A bead can be produced by dragging the end of the welding wire along the work
+piece. The bead should be about twice as wide as the work piece is thick; e.g.
+for 1/8" steel the bead should be about 1/4" wide. The width can be controlled
+by regulating the speed at which you drag the nozzle across the work surface.
+
+A nicer bead can be laid by using a circular motion, which also produces the
+aesthetically pleasing waves.
+
+The height of the bead should be fairly low, as the larger the angle between the
+sheet metal and the bead, the less sturdy the weld will be.
+
+## Fillets
+
+This is basically just a bead laid to join two pieces at a right angle. Use the
+same basic technique, but you'll be bumping then nozzle up against the side and
+bottom pieces in order to be close enough to the work area right at the join.
+
+## "Series of tacks"
+
+Can be useful when welding very thin stock that welding a bead might melt right
+through. This works by using the thermal capacity of the previously welded tack
+to help absorb some of the heat. Place the wire right up against the previous
+tack for optimal heat dissipation.
+
+## Fill-in
+
+You can fix a hole by placing a bunch of dots inside it. It won't look super
+pretty, you'll almost certainly need to grind it down afterwards, and it won't
+be very strong. You could use it as an aesthetic (rather than structural) fix
+e.g. if it'll be painted over afterwards.