Belts & chains
A V-belt round 100 and 200 mm pitch-diameter sheaves at 400 mm centres is 1277.5 mm long on its pitch line; an 80 (16A) chain on 19 and 57 tooth sprockets at 350 mm is 68.2 pitches, so 70 links. Enter the pulleys or sprockets and the centre distance for the length, or the length for the centre distance, with the ratio, the wrap and the sprockets’ pitch, outside and caliper diameters.
The drive is drawn to scale, the chain’s rollers in their seats, and the chain and belt pitches load from the table.
- Pitch length L
- Ratio D₂ / D₁
- Wrap on the small one
How it’s calculated
with R and r the pitch radii (half the sheaves' pitch Ø): exact, where the makers’ L ≈ 2C + 1.57(D + d) + (D − d)²/4C is within a hair of it. Here: L = 1277.50 mm at C = 400.00 mm.
Why round a chain up to an even number of links?
A roller chain alternates inner and outer links, so it closes only on an even count. An odd count needs an offset (cranked) link, which is weaker and wears faster, so round the length up to the next even number and move one shaft to take up the difference, or fit an idler on the slack span. Belts come in fixed lengths too: a timing belt in whole teeth, a V-belt in its maker’s pitch lengths, and the motor slides on its base to fit and tension it.