Troubleshooting Differences in Programming Methods, Machine Usage

For years, differences in CNC machines and controls have wreaked havoc on the shop floors of CNC-using companies. Differences come in at least two categories: programming methods and usage techniques. Companies with unlike machines must often maintain separate programs for the same component. This multiplies the number of required programs by the number of dissimilar machines. More severely, CNC people on the shop floor must learn multiple ways of performing common tasks. This is especially troublesome when the company is staffed by newcomers — and when CNC people are expected to run multiple machines and/or work in multiple departments.

The related challenges are so severe that many companies tend to limit their machine purchases to machines made by one machine builder and one control manufacturer. While this eliminates many (but not necessarily all) inconsistencies, these companies may not be purchasing the best machine(s) for a given application. Additionally, companies that traditionally purchase from one machine builder/control manufacturer are eventually confronted by other issues. For example, their machine builder could update their machine(s) to a degree that newer machines are not compatible with older machines. The machine builder may go out of business, or maybe they have nothing to offer for a given application. In these cases, a company will have no choice but to purchase something that is out of their comfort zone.

Regardless of the level of consistency among machines owned by your company, you probably have experienced consistency-related issues. I offer two general suggestions: First, don’t give up on making dissimilar machines more compatible. And second, find ways to simplify what it takes for CNC people to go from one machine style to another. Resources to accomplish machine consistency include your knowledge of parameters and parametric programming, your understanding of machine functions, your ability to get machine builders involved and your persistence to stick with it until a solution or improvement is found.

With programming inconsistencies, the goal is to be able to make one program run properly on multiple machines. If there are just a few programming differences, it may be possible to modify parameter settings or create custom macro programs that change the way one or more of the dissimilar machines behave.

For example, one CNC (as currently utilized) may require the specification of directional vectors for circular commands with the distance and direction from the motion start point to the arc center. Another may require the specification of the arc center absolute position. This by itself means a different program must be created for each machine. But with a little digging, you may discover that for one or all of the related machines, a parameter controls how directional vectors are specified. Modifying the related parameter will eliminate the programming inconsistency. This is but one of countless times that machine functions can be adjusted by parameter settings.

Another example is related to M codes. For machines that use different M codes, parametric programming techniques can be used to change the M-code number for a given function. Doing so will for differing M codes will eliminate M-code inconsistencies.

As the number of programming inconsistencies grows, however, so does the likelihood that you must maintain a separate program for each machine. In this case, of course, you must develop a simple way for operators to easily distinguish which program(s) are needed for each individual machine.

Machine usage inconsistencies are more serious because they can cause downtime and because CNC operators must deal with them on a continuous basis. You must strive to either eliminate them or simplify what must be done to deal with them. Again, knowing your available resources will help.

You may, for instance, have some machines that require diameter entry for cutter compensation offsets and others that require radius entry. This confuses operators and has been the source of countless offset entry mistakes that have led to scrap parts. Most current controls enable you to specify, by parameter settings, how cutter compensation offsets are entered — in radius or diameter. Setting all machines the same will eliminate the inconsistency.

Don’t be afraid to ask machine builders and their distributors for help. You may find that your particular consistency issue is a common problem for which they have already found a solution.

Concentrate most on times when operators struggle, when mishaps occur, or when machines are down. Prioritize your machine consistency improvements based on the issues that cause the most severe problems. You may find, for example, that machining center operators measure a cutting tool’s length each time they use it on a different machine. That is, a given cutting tool has a different tool length compensation value depending on which machine is being used. With FANUC CNCs (and probably many others) this issue can be easily overcome using the common work shift offset. The Z-axis register of this offset can specify the deviation for each machine. This eliminates the tool length inconsistency among the machines.

If you cannot eliminate an inconsistency, do your best to simplify what must be done to deal with it. CNC displays — with all their button layouts and switches — for example, vary dramatically among CNC manufacturers. Operators often struggle to determine or remember how to perform simple tasks, like program loading, offset entry, tool length measurement and program zero assignment. Be sure to provide a set of procedures for each machine (which I call an operation handbook) that guides them through the various tasks they must perform.

Admittedly, the time when you need to know the most about a machine is when you first purchase it. This is when you determine basic processes for how the machine is to be used. Do not rush through this process. Many a CNC user has lamented some action taken early on that had a terrible consistency-related impact on the machine’s performance.