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How to pick the right drive rolls, liners, consumables and starter sets for a compact 200 amp class MIG welder.
The groove shape should suit the wire. A smooth V groove is the usual choice for solid steel and stainless wire. A knurled (toothed) V groove grips hollow cored wire without crushing it. A U groove is used for soft aluminium wire, because it keeps the wire round instead of marring or crushing it.Many rolls carry two groove sizes, one on each face, so read the markings on the roll. Using the wrong groove type can damage the wire or cause slipping and poor feeding, so check the wire type before you choose, and follow the feeder manual.
Set it just tight enough to feed the wire reliably without slipping. A common method is to release the tension completely, feed the wire against a block of wood, then raise the tension until the wire just stops slipping, and no further.Too much pressure can deform the wire, shave fragments into the liner and lead to arc instability or burnback. Too little lets the wire slip. Soft aluminium wire needs particular care. Re-set the tension every time you change the rolls, and follow the machine manual for how the adjuster works.
The liner should match the wire type and size. Steel liners are normally tightly coiled steel wire, while PTFE-based or similar low-friction liners are used for aluminium. One liner often covers two neighbouring wire sizes, and an oversized liner lets small wire wander and bird-nest.Length matters. A liner cut too short is a common cause of early wear, burnback and an erratic arc, and too long can kink. Trim carefully with the cable laid straight, avoid twisting the torch, deburr the cut end so it cannot shave the wire, and follow the torch manual for how the liner is secured.
The hole in the contact tip should match the wire diameter. An oversized bore gives poor current transfer, arcing inside the tip and burnback, while an undersized bore causes friction and erratic feeding. As a tip wears the hole stretches from round to oval, which makes the arc unstable and increases spatter, so tips are a regular replacement item.Replace a tip when the hole is no longer round or the wire has fused in it. Do not file the bore. Tips differ in thread and length between torch styles, so match the tip and nozzle to the torch.
Birdnesting is a tangle of wire at the drive rolls. It usually means the wire is being blocked further along the path while the rolls keep pushing it. Common causes are a liner cut too short or the wrong size for the wire, debris in the liner, a worn or spatter-blocked contact tip, too much roll tension and the wrong roll type for the wire.Work along the wire path. Release the tension and pull the wire through by hand to feel for drag, replace a worn tip, then clean or replace the liner and re-set the tension.
Typical signs are erratic or poor wire feeding, a loss of current at the arc and frequent burnback in the contact tip. Wear tends to concentrate where the cable bends sharply. Debris can build up inside, and can sometimes be cleared by removing the wire and blowing dry compressed air through the liner while wearing eye protection.A quick pull test helps: with the roll tension released, try pulling the wire through the torch cable by hand. If it drags, the liner is probably clogged or worn. Also look at the drive rolls and contact tip, as they can cause similar symptoms.