By Dr. Jody Muelaner
Grooved pins are solid pins with grooves running axially along their surface. The grooves are swaged, which displaces material and increases the diameter of the pin. When the pin is forced into a hole, the grooves close — giving grooved pins more elasticity than dowel pins.
Knurled pins behave in a similar way, but grooved pins have higher pullout forces. Grooved pins are available in mild steel and stainless steel.
Typically there are three grooves, at equal spacings around the circumference of the pin. The grooves may run for all or part of the length of the pin. This can allow a hole of uniform diameter, drilled through a stack of components, to lock securely over one section of the pin while having clearance around another section. This can be useful when one component must be free to rotate around the pin.
Grooves running part-length may be at one end or in the middle, depending on the application. Where grooves are at an end, a “pilot” is sometimes included. This is a short length of plane pin before the grooves start. Since the grooves increase the diameter, this short length before the grooves start allows the pin to align with the hole before it is driven home.
Grooves may be parallel or tapered. Parallel grooves give a tighter fit. This means that pins are less likely to work loose when subjected to vibration but they require higher insertion forces.
Due to their rigidity, dowel pins often require a highly precise, reamed hole. The improved elasticity of grooved pins enables them to lock securely into holes with a wider range of diameters and greater circularity defects. This means that simple drilled holes can be used. Their elasticity also allows grooved pins to be removed and reused.
Compared to spring pins, grooved pins are less elastic but also considerably stronger due to their solid construction.