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