Roller Chain Drive Calculator — Selection, Geometry & Wear Life (ISO 606 / ANSI B29.1)

The design power is the nominal transmitted power multiplied by the service factor Ks, which accounts for shock loading (smooth Ks = 1.0, moderate 1.25, heavy 1.75). Lubrication is a prerequisite for achieving the tabulated power rating — it does not reduce the design power. The chain speed at each candidate pitch is computed from the driver tooth count and speed, and the required minimum breaking load (MBL) follows from the tangential force and the speed-dependent safety factor. The algorithm iterates to a fixed point so the selected chain satisfies its own MBL requirement at its own chain speed.

Multi-strand drives multiply the effective breaking load by the number of strands and the ISO 10823 efficiency: a duplex drive gives 2 × MBL_single × 0.95 = 1.9 × MBL, not 2.0 ×, because unequal load-sharing reduces the fully-loaded strand capacity slightly.

The sprocket pitch-circle diameter is derived exactly from the chain pitch and tooth count. Tip and root diameters follow ISO 606: the tip (outer) diameter uses the standard coefficient 0.6 + cot(π/z), and the root diameter is the pitch-circle diameter minus the roller diameter. Chain length in links is calculated from the standard formula and rounded up to the nearest even number (to avoid an offset link), then the actual centre distance is back-calculated exactly from the even link count.

The wrap angle on the driver sprocket must exceed 120° for reliable engagement. It depends on the tooth-count ratio z₂/z₁ and the centre distance; increasing either the tooth count or the centre distance improves the wrap angle. The polygonal (chordal) effect — the speed ripple due to the polygon geometry of the sprocket — is characterised by the speed-variation ratio δv = (1/cos(π/z₁) − 1) × 100 %. Using ≥ 17 teeth and an odd driver count distributes roller wear evenly.

Roller-chain elongation is caused by abrasive and adhesive wear at the pin-bushing contact, governed by Archard's law: wear rate is proportional to bearing pressure (tangential force divided by pin-bushing projected area) and inversely proportional to hardness. The model scales the wear rate by lubrication quality (forced spray ≈ 3× life vs. unlubricated) and contamination level. Replacement is triggered at the ANSI criterion of 1.5 % elongation for standard chain.

The required lubrication type rises with chain speed: Type A (manual) for slow, lightly-loaded drives; Type B (drip) for moderate speeds; Type C (bath/disc) above 4 m/s; and Type D (forced/spray) above 8 m/s or above 15 kW, as specified in ISO 606 and ANSI B29.1. Providing insufficient lubrication for the computed speed triggers a warning — it does not change the selected chain size, but it will shorten service life.