Rigging and moving machinery

Why it matters

Millwrights and machinery mechanics install, move and remove heavy equipment: motors, gearboxes, pumps, whole machines. Lifting is where small mistakes become fatal ones: a sling cut on a sharp edge, a hook loaded on its tip, a load that weighs twice what someone guessed. This lesson is awareness only. Before you rig or signal a lift for real, your employer must train you and, for many lifts, certify you as a qualified rigger under OSHA rules.

The lift plan

Every lift, even a routine one, follows the same thinking. Complex or critical lifts get a written plan signed by a competent person.

1. Know the weight. Use the nameplate, drawings or manufacturer data. If you must estimate, calculate volume × density and round up. Add the weight of rigging hardware.
2. Find the center of gravity (CG). The hook must be directly above the CG or the load will tilt or swing when it lifts.
3. Choose the hitch and slings, accounting for the sling angle.
4. Check every capacity: hoist or crane, hook, slings, shackles, eyebolts, beam or gantry.
5. Plan the path and landing: overhead obstructions, floor loading, blocking at the landing spot.
6. Control the area: barricades, a single designated signal person, nobody under the load.
7. Inspect all rigging before use and remove anything damaged from service.

Weight estimates

Steel weighs about 490 lb per cubic foot (about 7,850 kg per cubic meter). A solid steel plate 4 ft × 2 ft × 2 in is 4 × 2 × (2/12) = 1.33 ft³, so about 650 lb. Machines are mostly air and castings, so use the nameplate or shipping weight when you can.

Hitches

• Vertical: one sling straight down. Full rated capacity, but the load can spin.
• Choker: the sling wraps around the load and through itself. Capacity drops, typically to about 75 to 80 percent of vertical for a standard choke.
• Basket: the sling goes under the load with both eyes on the hook. Capacity can be up to twice vertical when the legs are vertical, but only if the load is balanced and cannot slip out.

Always use the manufacturer's tag on the sling, which lists capacity for each hitch.

Sling angle: the critical calculation

When two sling legs spread out from the hook, each leg carries more than half the load. The flatter the angle, the higher the tension.

tension per leg = (load / number of legs) / sin(angle from horizontal)

Angle from horizontal   Load multiplier per leg
90 degrees (vertical)   1.000
60 degrees              1.155
45 degrees              1.414
30 degrees              2.000

Worked example. A 2,000 lb gearbox is lifted with a two-leg bridle at 45 degrees.

tension per leg = (2,000 / 2) / sin(45°) = 1,000 / 0.707 ≈ 1,414 lb

Each leg needs a working load limit (WLL) of at least 1,414 lb, not 1,000 lb. At 30 degrees each leg would see 2,000 lb, the full load. Many sites forbid angles below 30 degrees; aim for 60 degrees or steeper. You can estimate the angle from the sling length and the vertical height: sin(angle) = height / sling length.

Hardware

• Slings: wire rope, alloy chain (only grade 80 or higher for overhead lifting), synthetic web and round slings. Every sling must carry a legible capacity tag.
• Shackles: the pin must be fully seated; load the bow in line, not sideways.
• Eyebolts: shouldered eyebolts lose much of their capacity when loaded at an angle; use them in line with the shank or use swivel hoist rings.
• Hooks: load in the bowl, never on the tip; the latch must work.

Inspecting rigging

Remove from service: slings without a tag; web slings with cuts, burns, holes or exposed red warning yarns; wire rope with broken wires, kinks, birdcaging or crushing; chain with stretched, nicked or bent links; hooks with a throat opening that has grown or a twisted tip. Protect slings from sharp edges with softeners.

Moving machinery without a crane

Mechanics also use machinery skates, toe jacks, pry bars, come-alongs and gantries. The same rules apply: know the weight, keep below rated capacity, keep hands and feet out from under the load, and crib (block) a raised load before anyone reaches under it.

Common mistakes

• Guessing the weight.
• Ignoring sling angle, so each leg is overloaded.
• Standing under or beside a suspended load, or riding a load.
• Using a sling with a missing tag "because it looks fine".
• More than one person giving signals.

Rules and training

OSHA covers slings in 1910.184 (general industry) and rigging equipment in 1926.251 (construction), with crane rules in 1926 Subpart CC: https://www.osha.gov/cranes-derricks. ASME B30.9 covers slings: https://www.asme.org/codes-standards/find-codes-standards/b30-9-slings. Rigger and signal person certifications are offered by bodies such as NCCCO: https://www.nccco.org/ (Checked on 2026-10-23.)

Recap

• Know the weight and CG, choose the hitch, then check every capacity.
• Tension per leg = (load / legs) / sin(angle); 30 degrees doubles the load on each leg.
• Inspect and tag; protect from edges; one signal person; nobody under the load.
• Real lifts require employer training and, for many, a qualified rigger.

Try it

Open the Do tab and plan a lift on paper.