Tuesday, March 29, 2011

Chain Drives Design (Part 3)

Let's take a look at the formulas related to chain design.
The pitch diameter of a sprocket with N teeth for a chain with a pitch of p is determined by

Note: the angle of sine function must be degree (not radian)

The center distance, C, is the distance between the center of the driver and the driven sprockets. It's the distance between the two shafts coupled by the chain drive. In typical applications, the center distance should be in the following range:

The chain length, L, is the total length of the chain. Because the chain is comprised of interconnected links, the chain length must be an integral multiple of the pitch.
"It's preferable to have and odd number of teeth on the driving sprocket and an even number of pitches (links) in the chain to avoid a special link"
The chain length is expressed in number of links, or pitches (not in mm or inches!), can be computed as

The center distance for a given chain length can be computed as

Please note that the computed center distance assumes no sag in either the tight or the slack side of the chain, and thus it is the maximum center distance. Negative adjustment and adjustment for wear must be provided.

The angle of contact, θ, is a measure of the angular engagement of the chain on each sprocket. The arc of contact θ1 is for the chain on the smaller sprocket and it should be greater than 120o. It can be computed as

And the angle of contact of the chain on the larger sprocket, θ2, can be computed using


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