Whitepaper: Timing Screws

Timing screws, often just called screws, worms or helices, have applications in virtually every operation that can occur on a packaging line. Metering containers into a starwheel on a capper or other machine is one of the most common. It is certainly not the only application for this versatile device. This article will discuss the different types and applications of screws as well as design concepts and troubleshooting.

Like a fastening screw, a timing screw is straight rod with threads. Unlike fastening screw, the thread pitch is frequently not uniform. Another important difference is that in use timing screws are rotating rather than stationary.

The nomenclature of both types of screws is similar. The key dimensions of the timing screw are:

Outside Diameter – The maximum outer diameter of the screw. This is generally constant for the length of the screw though it may taper at the infeed in some designs.
Root Diameter – The root diameter, sometimes called the barrel diameter or inner diameter, is the diameter of the screw at the bottom of the pockets. It is normally constant for the length of the screw though can vary in some applications.
Pocket – The pocket is the space formed between the threads by the difference between root and outside diameters. The shape or profile of the pocket is generally cut to conform to the shape of the container.
Pitch – The pitch of the screw is the distance between the leading edge of one pocket to the leading edge of the previous pocket. The timing screw shown has a variable pitch as if often the case. The pitch is usually critical only at one point, such as the discharge and it is at this point that it needs to be clearly defined.

Download the complete Timing Screws Whitepaper to continue learning how these simple devices are the packaging line workhorse.