What is a master drive point?

The master drive point (also known as the pacer or lead section) is the single drive point intended to control the overall speed of a web line. The master drive point (also called the pacer or lead section) sets the speed for the entire line through acceleration, steady speeds, and deceleration. If the master drive point slips, the web speed and tension control will be uncontrolled.

Each additional drive point beyond unwinding, master, and winding non-master are considered tensioning drive points or followers and create additional tension zones. Tensioning drive points will run near the master speed, but trim their speed or torque, as needed, to increase or decrease tension.

How is the master drive point selected?

Guideline to selecting a master drive point:

  1. No slip – The master drive point should have sufficient web-to-roller traction to ensure that you always know the relationship between the master’s speed and the web speed. (However, see my notes on measuring web speed.)
  2. Don’t bypass the master – The master is much good if you don’t use it.
  3. Select a master near your most speed-sensitive process – In coating lines, the coating backup roller or the closest driven roller to the coating process is usually the master. In extrusion processes, the extrusion nip rollers or casting drum are almost always the master. In both cases, speed variations directly translate into web or coating thickness variations. The master is the one driven point in a web line that isn’t trimming its speed to control tension.
  4. Make the highest inertia process element the master – High inertia components do not easily change their speed, so make them the master and control everything else relative to the ‘biggest animal’ in the room. In a tentering process, the tenter is always the master. If you have a high inertia driven roller, such as a roller of large diameter, thick steel walls, or filled with oil or water, consider making that roller the master. (Note: Be careful with large diameter master drive points, as larger diameter rollers will more easily lubricate, losing traction and failing guideline #1 – don’t slip.
master line speed ref to tension dps