Gear train
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![An Agricola illustration from 1580 showing a toothed wheel that engages a slotted cylinder to form a gear train that transmits power from a human-powered treadmill to mining pump.](/Images/godic/202501/19/Fotothek_df_tg_0000387_Bergwerk_^_Bergbau_^_Tretrad_^_Entwässerung_^_Taschen5101.jpg")
![](/Images/godic/202501/19/Gears_animation5101.gif")
![2 gears and an idler gear on a piece of farm equipment, with a ratio of 42/13 = 3.23:1](/Images/godic/202501/19/Gears_large5101.jpg")
A gear train is a mechanical system formed by mounting gears on a frame so that the teeth of the gears engage.
Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission of rotation from one gear to the next.