Max Unbraced Drum Length

Notes & Use

Calculates the maximum distance between internal braces in a helical cable drum.

  • The drum must be of constant pitch diameter

Figure

Terms

ν = Poisson’s ratio for drum material

Material Poisson’s ratio
Steel, mild 0.303
Steel, high carbon 0.295
Steel, Cold-rolled 0.287
Aluminum 0.334
Aluminum, 6061-T6 0.35

$E$ = Modulus of elasticity for drum material, psi

Material E
Steel 29,000,000 psi
Aluminum 10,000,000 psi

$t$ = Drum wall thickness, after machining, inches

$D$ = Internal diameter of drum, inches

$\gamma$ = Design factor, typically 8

$T$ = tension in line, pounds force

$d$ = Cable diameter, inches

$L$ = Max unbrace length, inches

Equations

$$ \left[ \left( \frac {1}{( 1 - \nu^2)} \right) ^3 \frac {t^2}{D^2} \right] ^ \frac {1}{4} \left( \frac{0.807 E t^2}{\gamma T D} \right) \frac{d (2D + 2t)}{2} $$

Sources

Mechanical Design for the Stage