A worn-out OEM pivot bushing on a commercial abdominal machine, replaced with a redesigned 3D-printed part that fits straight off the printer — no machining or post-processing.
The challenge
The plastic bushing in the machine's main link-arm pivot had worn down and turned brittle, and its thin fins had broken off. The joint needed a replacement that would ride directly on the existing steel tube and press into the existing arm, with nothing else on the machine changed.
The approach
Reverse engineering: Measured the worn part, the 0.878" steel tube, and the arm, and researched the OEM parts lists to understand how the joint was built.
Redesign for strength: Replaced the original open, cantilevered fins with a closed outer shell and six supported spokes, removing the failure point that broke the original. Added filleted spoke roots and chamfered lead-ins.
Lubrication: Added three axial grease grooves that stop short of each end to hold grease in the joint, with relieved groove edges so the bore surface — not the groove edges — carries the load.
Material selection: Evaluated carbon-fiber nylon, bronze bushing inserts, and PETG for wear, creep, and abrasion against the steel tube. Chose PETG HF for clean, repeatable prints that won't wear the tube.
Parametric, print-calibrated model: Built the Fusion 360 model around named parameters for tube size, running clearance, press fit, and printer/material compensation. Each test print was measured and fed back into the model until the bore and outer diameter printed to size every time.
The result
A bushing that prints ready to install, slides onto the tube with a controlled running clearance, and presses into the arm — restoring the machine with a part that costs pennies and can be reprinted on demand.
