A Cheat Sheet for the Unwritten Rules

As experienced manufacturing people, we often take for granted at least some of the knowledge we possess. We tend to forget just how long it took—and how much effort we expended—to acquire our knowledge.

Since much of what we know seems so very basic to us (now), we often mistakenly assume that others in manufacturing know what we know as well. This leads us to unwittingly implement certain unwritten rules in our operations.

Every company I’ve visited has them. They seem to infiltrate every aspect of CNC machine tool usage. And while workers will eventually learn the unwritten rules, newcomers often struggle. This can lead to confusion and costly mistakes.

At the very least, you should explain your shop’s unwritten rules to a new hire during his or her orientation period.

The problem is, it may be difficult for your experienced people to come up with a good list of your company’s unwritten rules. Again, these include a lot of information that you take for granted. If possible, enlist the help of a relative newcomer to the shop to compile such information. Surprises they encountered shortly after starting work for your company will be fresher in their minds. 

Most importantly, don’t let unwritten rules continue to be unwritten. Every time you discover one, write it down. These rules may not warrant inclusion in setup sheets and production run documentation, so create a supplemental document that can be explained during orientation and posted for all to see.

The following are some example categories of unwritten rules I have uncovered when visiting CNC-using companies:

Rules related to making sizing adjustments. Companies often assume that setup people and operators know how—and when—to make sizing adjustments. But if you don’t explicitly spell it out, technique and frequency may vary depending on who’s doing the work.

When do you expect operators to make a sizing adjustment? Is it when a measured workpiece attribute is growing or shrinking within 10 percent of its tolerance limit? 15 percent? 20 percent? If a sizing adjustment is necessary, what will the operator be shooting for? That is, what is the target value for the adjustment? Is it the mean value of the tolerance band? Is it something closer to the opposite tolerance limit that allows a longer period of unattended operation?

Again, if you leave it up to your operators to figure out the answers to these questions, each will likely come up with different answers. Write down exactly what you expect people to do and when you expect them to do it.

Rules related to offset selection. For each cutting tool’s primary offset, most programmers will in some way relate the tool station number to the offset number. For example, tool No. 1 will use offset No. 1, tool No. 5 will use offset No. 5, and so on. While this is a pretty good unwritten rule, operators must be in sync with programmers, so spell it out.

What happens if a cutting tool requires a secondary offset (often helpful when tool pressure issues affect sizing adjustments)? Maybe you add 30, 40 or 50 to the offset number to come up with the secondary offset. Or what if your machining center has but one table of offsets? How do you determine which offset number will be used for tool length compensation and which will be used for cutter radius compensation? It’s likely that you have developed a great (unwritten) rule for this application—so write it down.

Rules related to tightening fasteners. How tight are setup people and operators expected to tighten the various fasteners used for clamping workholding devices and workpieces? Left on their own, they will likely apply as much clamping force as they can. You probably don’t provide torque wrenches for all clamping applications, so newcomers should be shown how much force you expect them to apply in various clamping applications. 

Rules related to dull tool replacement. When do you expect operators to replace worn tools? Left on their own, it’s likely that they will do so at the beginning of each shift (regardless of whether it is necessary). If this is what you want, write it down. If it’s not, be sure newcomers know  exactly how to determine when worn tools must be replaced.

All of the knowledge we’ve accumulated over the course of our careers seems very elemental to us, but those just starting out don’t usually have that breadth of experience. Documenting our unwritten rules can help get them up to speed a lot faster.