Shaft Hole

Shaft Hole is the socket that mounts a printed part on a shaft — a knob on a potentiometer, a pulley on a motor, a lever on a spindle, a wheel on an axle. Pick the face, pick the shaft profile, and it cuts a through bore shaped to match: round, D-shaft with one flat, double-D with two, hex, square or splined. Both openings get a 45-degree chamfer, which is a self-supporting print-friendly lead-in that also helps the shaft start into the hole instead of catching on the rim. Diameter and Fit clearance size the bore together, so you set the nominal shaft size once and tune the fit separately rather than doing the arithmetic in your head every time. Flat depth positions the flat for D and double-D profiles, which is the parameter people usually get wrong when they draw these by hand — a D-socket that is right in diameter but wrong in flat depth will either not go on or will spin under torque. Rotate the part and the socket goes with it; change the shaft size later and the bore and both chamfers rebuild together. Set Fit clearance to the joint you want: around 0.1 mm for a press fit that needs no grub screw, around 0.3 mm for a slip fit you can pull off by hand. Orient the part so the bore axis is vertical for the cleanest walls and the most accurate profile. One honest limitation: round, hex and square profiles are geometrically exact, while D, double-D and splined currently approximate their curved arc as a fine polyline, so the arc reads very slightly faceted — dimensionally sound, and a true-arc profile is on the way.