Xem Studiomeasured geometry

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Crane strap brake: steel strap round a drum, tightened by a lever

How does a strap (band) brake work? · Hardware · basis: Xem Studio design following Brown No. 242 (1868)

Also called: band brake, strap brake, crane brake, drum brake band, freno de cinta de grúa, Bandbremse (Kranbremse)

Exact dimensions. True size, with no printing tolerance added.

sizes
4 in table

Notes

  • A steel strap wraps most of the way round a drum on the hoist shaft. One end is anchored on the lever's fulcrum, the other on the lever close to it, so pressing the handle pulls the strap tight round the drum. Its grip grows along the wrap: the tension ratio between the ends is e^(μθ), 3.31 for μ = 0.3 over the 228.78° drawn, and the brake torque is (T1 − T2) × R.
  • Drum Ø60 × 20, strap 20 × 1.5 touching the drum over 228.78° with both legs tangent, pins 24 mm apart 48 mm below the axis, lever handle 142 mm from the fulcrum. Drawn snug, lever level.
  • Brown's No. 242 (strap brake used on cranes).
  • Parts (each has its own page): brake-drum-60x20-bore10, brake-strap-20x1-5-drum60-pins24, strap-brake-lever-130-pins24, dowel-pins-metric, linear-shafts-h6.
  • Brown's movement No. 242 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Crane strap brake: steel strap round a drum, tightened by a lever size chart

parametervalue
drumØ60
wrap228.78°
tension ratio (μ 0.3)3.31
lever ratio≈ 6 : 1

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Henry T. Brown (1868, public domain)Five Hundred and Seven Mechanical Movements — scan on archive.orgwebPublisher's page; dimensions are facts
507movements.comBrown's movement No. 242: figure, his text and an animationwebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

crane-strap-brake-mechanism-assemblyAssembled mechanism, all parts placed at one pose (STEP keeps each part separate)STEP · STL
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Plain text: sheet.txt · JSON: /api/geometry?object=crane-strap-brake-mechanism

Crane strap brake: steel strap round a drum, tightened by a lever, isometric render of a generated part
Render of crane-strap-brake-mechanism-assembly from the free STEP; not to scale.

Fits with

Brake drum Ø60 × 20, Ø10 bore, isometric render of a generated part
Brake drum Ø60 × 20, Ø10 bore60.0×60.0×20.0 mm★ 1 file
Brake strap 20 × 1.5 wrapped 228.78° round a Ø60 drum, eyes on Ø4 pins 24 mm apart, isometric render of a generated part
Brake strap 20 × 1.5 wrapped 228.78° round a Ø60 drum, eyes on Ø4 pins 24 mm apart63.0×83.0×20.0 mm★ 1 file
Strap-brake lever: fulcrum and strap pins Ø4 24 mm apart, handle to 142 mm, isometric render of a generated part
Strap-brake lever: fulcrum and strap pins Ø4 24 mm apart, handle to 142 mm153.0×12.0×5.0 mm★ 1 file
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325), isometric render of a generated part
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)5 sizes★ 23 files
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long, isometric render of a generated part
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long10 sizes★ 70 files

Questions

How does a strap (band) brake work?

A steel strap wraps most of the way round a drum on the hoist shaft. One end is anchored on the lever's fulcrum, the other on the lever close to it, so pressing the handle pulls the strap tight round the drum. Its grip grows along the wrap: the tension ratio between the ends is e^(μθ), 3.31 for μ = 0.3 over the 228.78° drawn, and the brake torque is (T1 − T2) × R.