About this project
Parametric grooved plate cam with a translating pin follower: one turn of the knob runs a rise, dwell, return and dwell program. The pin rides in a closed groove, so the cam pushes the follower out and pulls it back with no return spring. Three separately printed parts: a base with the cam axle and the follower guide, the cam (grooved disc and knob) and the follower (a bar with a pin).
Geometry
The groove is built from the pitch curve, the path the pin centre has to follow. The Cam node generates it from the base radius, lift and program as a knife-edge profile with 720 segments; the curve is opened, stroked into a band as wide as the pin plus the clearance, and cut 6 mm deep above a 2.4 mm floor. The follower is in line with the axle and slides between two guide rails. At the defaults (25 mm base radius, 10 mm lift, 8 mm pin) the cam is 84.4 mm across and the base 130 mm long.
Cam program
Set the rise, high dwell and return angles; the low dwell takes the rest of the turn. Rise and return each get a motion law: cycloidal (the default: smooth, with zero acceleration at both ends), simple harmonic, 3-4-5 polynomial or linear. Readouts show the lift and pressure angle at the current cam angle, the peak pressure angle over the whole program, the low dwell, the cam diameter and the base length. Validators reject a program whose peak pressure angle goes over 30°, where a translating follower starts to bind in its guide, angles that add up to more than a full turn, and a base radius too small to leave room for the knob around the axle. The defaults peak at 17.8°.
Turning it
Cam angle 0° is the start of the rise, with the mark on the knob pointing at the follower. Increasing the angle turns the cam counterclockwise seen from above. Move the Cam angle slider or drag the handle on the knob, and the follower slides to the lift the program gives for that angle.
Verified
Clearance and overlap checks at eight cam angles through a full turn, with all four motion laws, and at the ends of the ranges (a fast 60° rise and return on a 40 mm base radius, 25 mm lift with a 12 mm pin, no high dwell, a tight 0.2 mm clearance): no overlap between any parts, and at the default 0.4 mm clearance the pin keeps 0.19 to 0.20 mm from each groove wall. Probed pitch radii match the motion-law formulas, and every part is one watertight solid.
Printing
All three parts print with no supports: base flat, cam knob up, follower flipped so its pin points up. The only bridge is the ceiling of the cam's blind axle bore (8.4 mm). About 52 g and 5 h 15 min in all (base 26 g, cam 23 g, follower 2.4 g). Default clearance 0.4 mm (0.2 mm per side in the groove and around the axle); raise it if your printer runs tight. The axle and the follower pin are short, thick pegs with light loads, so vertical layer lines are fine here. Assembly: drop the cam onto the axle, then lay the follower between the rails with its pin in the groove; gravity holds both.