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Old 01-12-2020, 07:44 PM
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Kartorbust Kartorbust is offline
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They are used to make a gear ratio more achievable, when say you cannot get a smaller engine sprocket or larger wheel/axle sprocket, or it's a matter of needing the clearance because of packaging. Meaning you don't have the room for say a 60 tooth #520 axle sprocket, but a 40 tooth #520 will fit. In the case of needing a deeper gear ratio for something heavy and using a large engine, but cannot get the sprockets needed to make the ratio with just 2 sprockets, for example 14 tooth on the engine and a 60 tooth on the axle only gives you a 4.2:1. It's a bit too high for a lot of larger projects. So you'd add a jackshaft. So 14 tooth to a 26 tooth (jackshaft input) to a 12 tooth (jackshaft output) to the 60 tooth axle sprocket gives you a 9.2:1 gear ratio.

Hopefully this helps. If you need a jackshaft ratio calculator here's one that'll help.
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