A drift pin is a device used to hold a pulley or gear on a shaft. The drift pin is a small and thick hollow tool grade steel pin. It is located in a hole through the pulley or gear flange and driven into a hole drilled through the crankshaft with a hammer.
Often, a drift punch is used to permanently locate the drift pin in place. The drift pin is typically hollow and divided on one side; this allows the pin to compress when guided into the hole of the well which is a fraction less than the diameter of the drift pin.
The drift pin is presented in the well and holds the gear or pulley in place by nothing more than interference. Nothing beyond the perfect adherence of the pin in the well to maintain the coupling. In many cases, the pin is doomed to fail if interference between the gear or pulley would occur. With the breakage of the drift pin, the machine is protected against further damage as a mechanical device can turn without interruption. By removing the obstruction and replacing the pin, the machine is allowed to take on normal operations.
The pin method derives from getting an object to a shaft is much more reliable than trying to get a gear wheel or pulley with a bolt. A tightening bolt against a drive shaft will ultimately result in a slip situation. Square face of the bolt is not a real round-shaped match of a tree and working a flat surface in the well removes some of the strength of the well.
Used extensively on agricultural machinery as well as production and transportation machine systems, the drift pin remains an effective and easy-to-maintain method of securing equipment and machinery components together. In the event that a gear swap is required, simply driving the pin out of position, removing the gear, placing a new gear on the shaft and installing a new pin is all that is required. The equipment is repaired with a minimal amount of long time.
From the huge harvesting machines found on the farm to the smallest fishing reel, drift pins are incorporated to ensure integral parts when they cannot be allowed to move. To require no adjustment or lubrication, the drift pins provide important service with a minimal amount of effort.