In many companies, CNC machinists do not work directly from workpiece drawings because those types of drawings show only the finished workpiece. Instead, a manufacturing engineer will create other drawings from which the shop personnel can work.
In last month’s column I stated that one of the most common causes of wasted setup time is improper trial machining to make the first workpiece pass inspection. Trial machining involves taking each tool in the program and making it cut to size prior to going on to the next tool.
When teaching setup reduction, one of the first principles I try to explain is related to what I call the “core tasks” required to make a setup. Core tasks are the physical tasks a setup person must perform in order to get the machine ready to run production.
When hiring new people to run CNC machines, most managers want it all. They want a person who has run the same machine they will be running for the company.
In past columns, I’ve addressed how you can program trial machining operations. It seems obvious to me that if a setup person or operator can recognize a workpiece tolerance that is so tight that trial machining is required, then a programmer should be able to recognize it as well.
Most turning centers are equipped with some helpful canned cycles. Fanuc, for example, has three simple, one-pass canned cycles (G90 for turning and boring; G92 for threading; and G94 for facing).
CNC machining centers provide users with three compensation types: tool length compensation, cutter radius compensation and fixture offsets. Similarly, CNC turning centers provide wear offsets, geometry offsets and tool nose radius compensation.
Custom macro B provides many tools to help users with CNC programming, including variable capabilities, arithmetic calculations and program flow control. One of the most powerful functions allowed by this custom macro (and for that matter, any computer programming language) is looping.
I’ve written about task simplification in several of my previous columns. Task simplification lowers the skill level required of a person performing a task, minimizes the potential for mistakes and shortens the time required to perform the task.
Should you program at the machine or should you program off-line? This debate has been going on for more than thirty years, since the first conversational control was introduced. I thought most of the main considerations for making a wise decision were pretty well understood, but a visit to any of the manufacturing forums on the Internet quickly illustrates that the debate is still raging—and there are still many misconceptions.
All machining center controls come with a set of helpful hole-machining canned cycles. Most control manufacturers use G codes from G81 through G89 to name them (G81 for drilling, G82 for counter-boring, G83 for peck drilling and so on).