Lift Cable & Drum Systems
Cable wrapping geometry, drum sizing, drum set screws, cable seating verification, and cable replacement criteria.
- Describe cable wrapping geometry and correct drum orientation
- Select correct drum size based on door height rating
- Verify cable seating and routing for safe operation
- Identify cable replacement criteria and inspection points
Lección 1
Cable Wrapping Geometry & Drum Orientation
How Lift Cables Work
The lift cables connect the bottom brackets of the door to the cable drums mounted on the torsion shaft. As the torsion spring unwinds and rotates the shaft, the drums wind the cables, lifting the door. Each cable wraps around its drum in a specific groove pattern.
Cable wrapping geometry refers to the spiral groove pattern on the drum. The groove starts with a small diameter at the inside and spirals outward. This increasing diameter compensates for the changing mechanical advantage as the door transitions from vertical travel to horizontal travel. The first wraps (door fully open) have a smaller effective radius than the last wraps (door fully closed).
Drum Orientation
Cable drums are left-hand and right-hand specific. The left drum mounts on the left side and the right drum on the right side (viewed from inside the garage). Installing a drum on the wrong side reverses the cable wrapping direction and the cable will not seat in the grooves properly.
Each drum has a cable stop (a small hole or slot) where the cable end is secured. The cable must be threaded through this stop and tightened before winding begins.
Cable drums are side-specific - left drum on left, right drum on right. The spiral groove geometry changes effective radius to compensate for the door's transition from vertical to horizontal travel.