Metalworking's Butterfly Effect

Forecasting the weather accurately more than two weeks out is almost impossible, because that span of time leaves the chance for small disturbances to have big results. Meteorologists refer to the "butterfly effect"—the idea that a butterfly flapping its wings could, in theory, set off an atmospheric chain reaction that ultimately would lead to a weather change.

Columns From: 2/5/2001 Modern Machine Shop, ,

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Peter Zelinski

Forecasting the weather accurately more than two weeks out is almost impossible, because that span of time leaves the chance for small disturbances to have big results. Meteorologists refer to the "butterfly effect"—the idea that a butterfly flapping its wings could, in theory, set off an atmospheric chain reaction that ultimately would lead to a weather change.

I think something like this effect can also happen in a machine shop, particularly one in which some aspect of the process has gone unchanged for too long.

A friend relayed the following anecdote. In the shop where he once worked (he owns his own shop now), a debate started over whether to use coated tools in place of some uncoated tools being used at the time. Proponents pointed to the longer tool life the coating would deliver. Skeptics said the existing tool life was fine, so why incur the extra expense?

On an experimental basis, the shop began using the coated tools.

And then something happened.

Shop personnel realized that it now made sense to increase the number of parts they machined in one setup. The shop typically changed out tools at the same time that it changed out workpieces, but the coated tools were now outlasting the typical batch size. In response, the shop added fixturing and revised its programs to let the machine run many more parts in a single cycle.

And then something happened.

With the machine now running so much longer without the operator having to intervene, suddenly it became attractive to let the machine just keep on running after everyone had gone home. Soon, it became standard practice to leave the machine running unattended at the end of the second shift, producing one more large batch of parts per day for the first-shift operators to find in the morning. Thus, what started with a small tooling change ultimately led to higher productivity.

CNC machining processes are complex. Not only are there important decisions to make related to the machine tool, cutting tool, tool path, clamping and other process factors . . . but there is also the chance that any one of those decisions might affect other parts of the process.

That's why it may be impossible to forecast just how significant any one small change might be.

So don't focus on just the immediate results of any change you may be contemplating. Bigger results may come. Sometimes, it's important to keep an open mind about the power of small disturbances.

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