Industrial-grade drive sizing calculator: V-belt section selection, exact belt length and center distance, wrap correction, catalog-anchored ratings and belt count; roller chain sprocket selection, chain length in pitches, ISO 10823-anchored ratings and full audit trail.
Decision:Run the stated engineering model, review its assumptions and warnings, then make the release decision against the governing standard and verified source data.
SectorCalc SC-025 sizes friction V-belt and positive roller-chain drives. The geometry is exact: belt length from pulley diameters and center distance, closed-form center distance from a standard belt length, wrap angle with the published cφ correction; chain length in pitches with the same closed-form inversion. Power ratings are interpolated from catalog-typical anchor values for narrow V-belt sections and ISO B roller chains — sufficient for feasibility and layout, but the final selection must be verified against the specific manufacturer's current rating tables, which differ 10–15 % between brands.
Design power and service factor
Pd = P · SF
The service factor absorbs shock, starts-per-hour and daily duration that the rating charts do not. Under-factoring is the main cause of short belt life on crushers and compressors; over-factoring wastes pulley width. Add 0.1–0.2 for >16 h/day or frequent starts, per catalog practice.
Belt length and center distance
Lw = 2C + (π/2)(d1+d2) + (d2−d1)²/(4C)
C = ¼ · [ B + √(B² − 2·Δ²) ], B = Lstd − (π/2)(d1+d2), Δ = d2−d1
Pick the desired center distance, compute the open-length, choose the next standard datum length, then solve back for the real center distance with the quadratic inverse. The drive still needs adjustment travel: typically −0.015·L for installation and +0.03·L for tensioning.
Wrap angle and the cφ correction
φ1 = 180° − 57.3° · (d2−d1)/C
Grip scales with wrap on the small pulley. Below 120° a belt drive is geometrically weak: increase center distance, reduce the ratio, or add an idler. The engine multiplies the per-belt rating by the published cφ table (0.69 at 90° … 1.00 at 180°) — ignoring cφ overstates capacity exactly where drives are tight.
Power ratings and belt count
z = Pd / (PN · cφ · cL) (rounded up)
PN is interpolated from catalog-typical anchors for SPZ/SPA/SPB/SPC at representative pulley sizes and speeds; cL corrects for belt length (short belts flex more often). Above 6 belts, load sharing degrades — jump one section instead of stacking belts.
Chain drive sizing
X [pitches] = 2C/p + (z1+z2)/2 + ((z2−z1)/2π)² · p/C
v [m/s] = z1 · p · n1 / 60000
Chain is a polygon, not a belt: tooth count sets the pitch diameter (D = p/sin(180°/z)), and chordal action produces speed fluctuation that shrinks as z1 grows — hence z1 ≥ 17, preferably 19–25. Round X UP to an even pitch count to avoid an offset (cranked) link, which halves fatigue life. Ratings follow ISO 10823 anchors at z1 = 19 with a tooth-count correction; duplex adds only ×1.7, not ×2.
Frequently asked questions
Belt or chain for this drive?
Belt: high speed, long centers, shock absorption, no lubrication, tolerance to misalignment. Chain: low speed, high torque, no slip (timing), dirty/hot environment, compact centers. Above ~20 m/s chain is out; below 1:1 torque-critical, belt slips.
Why does the calculated belt count differ from the catalog software?
Ratings are catalog-typical anchors, and manufacturers' tables differ 10–15 %. The geometry (length, center distance, wrap) is exact and brand-independent; verify the final count in the chosen brand's selector before ordering.
Can I reuse an existing pulley?
Enter its datum diameter as d1 — the engine re-solves everything else. Watch the minimum diameter per section warning: undersize pulleys kill belt life by bending stress even when power "fits".
Chain stretch — when is the chain worn out?
Elongation from pin/bushing wear: replace at 1.5 % (2 % with large sprockets) of nominal length. Measure over ≥ 20 pitches under light tension. If the drive jumps teeth before 1.5 %, the sprockets are worn too — replace as a set.
