Drive rolls pull wire from the spool and push it into the gun liner. The groove profile, the number of rolls and the roll pressure determine whether the wire feeds smoothly or birds-nests at the feeder.
Groove profile must match the wire. V-groove is for solid wire — it grips without deforming the round cross-section. U-groove is for soft wires like aluminium, where a V-groove would crush the wire. Knurled or serrated rolls are for flux-cored wire, which has a textured surface and needs more grip. Using a knurled roll on solid wire shaves metal off the wire and clogs the liner.
Two-roll setups suit light wire and short guns. Four-roll setups give twice the contact points and are needed for soft wires, long guns, and any application where feed consistency matters. The drive roll size and the wire diameter must match — a .030 roll will not feed .045 wire correctly.
Roll pressure is adjustable on most feeders and is a common cause of trouble. Too little pressure slips; too much crushes the wire and deforms it into an oval that will not feed through the tip.
