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Straight answers to the questions people ask most when choosing and looking after replacement feed rolls for a MIG wire feeder.
A V-groove roll is the usual choice for solid steel and stainless steel wire. The V shape grips the wire and feeds it without slipping or squashing it, so you get a steady wire speed at the tip.The groove must also be the right size for the wire diameter, so check the diameter printed on the spool and the size marked on the roll before you order. Your welder's manual will say which roll types suit your feeder.
Aluminium wire is soft and deforms easily if it is squeezed too hard. A smooth U-shaped groove cradles the wire and holds its round shape, so it feeds steadily without being flattened or shaved.A V-groove or knurled roll can mark or distort aluminium wire. Aluminium also usually feeds best with a plastic liner and a short, straight cable, so check those parts when you change over. A roll alone will not cure feeding trouble on a long torch.
Flux-cored and metal-cored wires usually need a V-groove roll with a knurled (toothed) surface. Cored wire is a thin tube filled with flux or metal powder, and a smooth roll needs a lot of pressure to grip it, which can crush the wire.The knurling bites into the outer shell, so the wire feeds with less tension and keeps its shape. Do not use a knurled roll on solid wire as a general rule, because the teeth can mark it and shave fine metal into the liner.
Many rolls have two grooves, one on each face, for two neighbouring wire sizes. The size is normally marked on the roll. The side facing outward or inward depends on your feeder, so follow the manual.Fitting the roll with the wrong size groove in the working position over-tightens or loosens the grip on the wire, which causes slipping, deformed wire and poor feeding. Always check the size marking against the wire diameter every time you change roll or wire.
Tighten only until the wire feeds without slipping. A common way to set it is to feed about 50 mm of wire past a cold torch tip, back the tension off until the rolls slip when you press the trigger, then add about half a turn at a time until the wire feeds smoothly. Wear gloves and keep the torch pointed away from you and from anything conductive.Too little tension lets the wire slip. Too much deforms the wire and can lead to birdnesting if anything restricts it further down. Your welder's manual may give a recommended setting.
Signs include the wire slipping or feeding unevenly even though the tension seems right, a polished or flattened groove, or knurling that has worn smooth. Worn rolls make it hard to reach the right pressure, and wear tempts people to keep tightening the tension, which deforms the wire.Inspect the rolls regularly, for example whenever you fit a new spool, and clean or replace any that are deformed. There is no fixed life, so replace them when feeding turns erratic with the right settings. Check the liner, guides and contact tip too, as they can cause the same symptoms.