止动螺钉与定位销完整指南：机械装配的类型、应用与选型

Set screw loosening on shafts is caused by: insufficient tightening torque — ensure you are using the correct socket size and applying adequate torque; a 3mm set screw requires only 0.5-1 N·m, while an M8 requires 5-10 N·m; vibration — specify cup point or knurled cup for vibration environments; consider adding a second set screw at 90 degrees to the first; soft shaft material — cup point set screws indent soft shafts over time; use a shaft with a drilled positioning hole (half-dog) or specify a harder shaft material; inadequate thread engagement — the set screw must thread fully into the component (minimum 1.5× diameter engagement); if the component is too thin, the set screw bottoms out before providing adequate clamping force.

Use taper pins for: permanent, high-accuracy positioning where the joint will not be disassembled; applications requiring very high positional accuracy (machine tool fixtures, precision instruments); joints where the pin must also transmit shear load. Use parallel dowel pins for: applications where components may need to be disassembled and reassembled; general precision alignment in machinery; where ease of assembly/disassembly is important. Taper pins require matching taper holes (reamed with a taper reamer) which are more expensive to produce than straight holes for parallel dowels.

Spring pins (tension pins) and roll pins (coiled spring pins) are both split longitudinally to allow compression during insertion, but they differ in manufacture and performance: Spring pins are a single piece of spring steel with a longitudinal slit; roll pins are a coiled strip of steel — essentially a spring wound into a pin shape. Roll pins are significantly stronger than spring pins (approximately 3× the shear strength) and resist jamming better. Roll pins are the preferred choice for most industrial applications; spring pins are used where very precise control of expansion force is needed.