Knitting
Every needle is driven through every cam every revolution. Butt wear is a scheduled replacement with a computable date.
— h
At this load, speed and cam geometry
Archard describes steady mild wear and nothing else. It does not describe the transition to severe wear that follows once lubrication fails, and that transition is the thing that actually destroys a needle set - a machine running dry does not wear a little faster, it wears orders of magnitude faster and takes the cam with it. Read the interval as the life available while lubrication holds, and treat any observed life far below it as a lubrication or contamination finding rather than a reason to adjust the coefficient. The wear coefficient itself spans several orders of magnitude across lubrication regimes and is the input worth calibrating from the mill maintenance record rather than from a handbook; back it out of a known needle life on a known machine and the model becomes useful for comparing settings. Cam force is taken as constant through the profile, whereas the real load peaks sharply at the clearing cam where the needle is lifted against yarn tension and fabric take-down, so wear concentrates at one point on the butt rather than distributing evenly - which is why a worn butt is usually rounded on one flank. Nothing here covers latch and hook wear, which follow yarn abrasion rather than cam contact and have a completely different life.
Needle Butt Wear & Replacement Interval — free, with the formula and a worked example, at Textile School.