Spring-Loaded Pinch Roller Arm for Wire Feed

A spring-loaded pinch roller for a wire feeder stops the wire skating sideways the moment the drive roller starts pulling. A pivoting arm presses an idler down onto the wire directly over the drive roller, and the pivot, spring and preload screw all sit on the +X side so the -X side stays clear for the wire guide tube. It comes as three separate printed parts, laid out on the plate in their own print orientations: the motor frame, the pinch arm and the drive roller. The pieces are coloured separately in the file so you can tell them apart; print them all in black.

What prints, and how it lies

• Motor frame: lies on its back face so the plate prints flat. Carries the 31 mm NEMA 17 hole pattern and 24 mm boss hole, plus the pivot boss with the M6 nut pocket — 16 mm across, leaving roughly 2 mm of wall behind the pocket.
• Pinch arm: lies on one cheek so the 6 mm holes come out round. The nut boss on the opposite cheek is 16 mm across and 4 mm thick, with the M6 pocket facing up.
• Drive roller: stands on its end so it prints round. 24 mm diameter, 25 mm wide, plain — no groove. A 5 mm D-bore runs through a 10 mm hub that projects 2 mm each side, and the M3 grub screw now has a trapped hex nut you slide in through a slot open to the rim.

What it fits

• Idler: the arm carries an M6 × 35 bolt for your 30 mm × 25 mm bearing roller. Bolt head and washer on one side, trapped M6 nut in the cheek boss on the other, so the nut cannot spin while you tighten. Put a thin spacer each side of the roller so only the inner race is loaded — the cheek gap is 26 mm against a 25 mm roller.
• Spring: 14 mm long, 7 mm OD, 5 mm ID, sitting between the raised cross-bridge and the frame bracket. The M3 × 22 screw threads into an M3 nut trapped in the 5 mm thick bridge; turning it sets the preload.
• Pivot: 6.2 mm hole through the plate and boss, with a 5 mm deep hex pocket for an M6 nut on the back, so the arm is clamped by the bolt and nut rather than by the printed boss alone.

Hardware to have on the bench

Fit and force

The frame plate and pivot boss are set back so the arm cheeks clear the plate by about 4 mm and the drive roller hub by about 5.5 mm. The drive roller therefore sits further from the motor face — check the motor shaft actually reaches it before bolting anything down. The spring sits right over the idler shaft, so the ratio of spring distance to idler distance from the pivot is about 0.87: nearly all the spring force goes into pinch force. More pinch means a stiffer spring, not a longer screw.

Before you print

• The 24 mm drive roller and 30 mm idler meet exactly at their centres, so there is no gap for the wire until the arm lifts. There is no stop screw, so the arm can close completely with nothing in it — add one if you want a hard minimum gap.
• The idler bolt is deliberately M6 × 35, not 40, so it does not poke into the motor plate; the tip ends inside the trapped nut.
• PETG for the frame and arm. The NEMA 17 plate runs warm and PLA creeps near it. PETG, ASA or nylon for the drive roller; nylon wears best, and a thin rubber or TPU sleeve over the roller adds grip if the wire slips.
• Nut pockets and hole clearances are untested on your printer, so expect to open them up after a trial fit.