Introduction
If you’ve spent time in conversations with packaging machine engineers, you’ve almost certainly heard both these terms: index and pitch. They’re closely related, but not identical. Understanding the distinction helps you read specs more accurately and ask better questions during the evaluation process.
Machine Index: The Motion Unit
Machine index refers to the distance a machine’s transport system advances in a single mechanical cycle. In other words, every time the machine completes one cycle of motion, how far does everything move?
On an intermittent-motion machine, the index is the length of each discrete advance. The machine stops, loads or performs an operation, then indexes forward. On a continuous-motion machine, the concept still applies but manifests differently as the machine maintains constant motion while the tooling moves with the product.
Pitch: The Repeating Unit
Pitch is the center-to-center distance between repeating elements in the machine (often called ‘flights’), while the distance each flight travels within a given cycle is the index.
In many machine designs, index and pitch are equal. The machine advances exactly one pitch per cycle. But they don’t have to be.
Some machines are designed to index multiple pitches per cycle, or use variable pitch configurations for different pack patterns. In those cases, confusing index with pitch leads to errors in speed calculations or format change expectations.
Often, when “pitch” is used distinctly from “index,” it means the required spacing between incoming products is different from the spacing of the cases those products will be loaded into.
Why This Matters Practically
Understanding index and pitch is important in several real-world scenarios:
Speed Calculations — Machine speed (cycles per minute) × pitch = throughput in linear terms. If you’re calculating CPM (cartons or cases per minute), you need to know how many products advance per cycle.
Format Changes — Changing pack count or product size often requires changing pitch, which may mean new tooling, a new flight bar, or reconfiguration of transport components.
Machine Matching — When integrating multiple machines in a line, pitch compatibility matters. Mismatched pitch between a cartoner and a downstream case packer can create accumulation or timing problems.
Packaging Material Specs — On some machines, pitch directly determines the repeat length of the substrate (such as labels, carton blanks and film). If pitch changes, material specs may need to change too.
The Takeaway
When reviewing machine specs or comparing OEM proposals, don’t assume index and pitch are the same unless it’s explicitly stated. Ask for both, and ask how they change when you change pack formats. That conversation will reveal a lot about how flexible the machine actually is across your product range.
Need to Discuss Machine Index and Pitch?
If you have questions about your equipment specs, give us a call. Douglas specialists are ready to help answer questions and point you to the solutions that make your operation simpler and more productive.
