What is Centerlining

Many are familiar with something known as witness marks used on fasteners and equipment that you don't want to move. Witness marks serve as a quick way to see that everything is as it should be. Centerlining does the same thing, and more. A common place to start is the ruler with a pointer on points of adjustment on machines. It's a good place to start, but it is not the place to stop. Centerlining is a definite mark that is used for a specific set of inputs on a line that decreases setup time, and provides a visual indication that the line is indeed set up correctly at a glance.

The rulers are a good way to document setups with different inputs and how they perform. Imagine if the adjustable wrench above had lines for different sizes so it could be quickly set correctly for a bolt head or nut that it's used for repeatedly. These measurements can then be used in setup procedures to strengthen the data that those points are indeed the correct settings throughout the maintenance cycle of the line. This should be done for every adjustable part of the production line. If there's an adjustable part that shouldn't be adjusted, then the location for the centerlining mark is known.

This is where true centerlines are marked. If a production line only has one set of inputs then centerlining is the most straightforward. Permanently mark the location that's been established with the ruler and ensure the pointer is permanently marked. You keep the adjustability of the line while having a line that is quickly set up like a single product line. Going back to the wrench if it was only used for one size a mark to indicate where the wrench should be set would make using it faster and repeatable. Now lines with different sets on inputs are only slightly more complicated.

When setting up the centerlines of a multiple setup line it should be taken into consideration what the most frequent set up is. Generally the marks are numbered, colored, or both. What's important is that throughout the line it is consistent and that in a glance an incorrect setting is noticed. If there are change parts on the line they should match the way of indicating the setting i.e. if using numbers the change parts should have the same number on them. Returning to our wrench example, each bolt or nut size would have a mark and a number next to that mark that correlates to the mark on a bolt or nut.

With too many numbers and colors going on this can become a bit messy over an entire production line, depending on how many processes there are. This is why I prefer numbers and colors. If change parts are numbered for placement on the line, then putting a color on them makes it much easier. The centerlined adjustments can still be numbered, but also be color filled and match the color of the change parts.

Centerlining is not a complex process, and it shouldn't be. The goal of it is to reduce complication and thereby reduce time the line is not running optimally.