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An all-digital control package will soon be standard on many machining center models from Cincinnati Machine (Cincinnati, Ohio). For now, the technology is standard on the "Arrow" line of vertical machining centers. Cincinnati didn't begin the upgrade with its high-end machines, but instead with its lowest-cost VMC family.
Part of what the company means by "all-digital" is digital axis drives and digital scale positioning. Digital drives permit improved precision at high feed rates. And digital linear scales make precision more consistent than previous position-measurement devices because they can provide accuracy unaffected by wear or temperature changes. Completing the all-digital package is a digital vector-drive integral-motor spindle. This lets the Arrow put more peak spindle power into the cut, the company says.
Why make the digital improvements to the Arrow machines first? The answer comes from Jim Spearman, Cincinnati's product manager for VMCs. He says the company is starting with the low-end machines because "this is where the biggest number of machines are bought, and where accuracy improvements will have the greatest impact."
Job shops, for example, can benefit from improved precision on a low-end machine by being able to bid on higher-value work.
Meanwhile, the same improved precision can let mold shops bring some of their high speed machining disciplines down to a low-cost machine.
In fact, fast, precise contouring is where the accuracy improvements from digital technology are particularly apparent, Mr. Spearman says. Dynamic contouring accuracy for the Arrow machines is now 0.0006 inch maximum total true position error at 40 ipm. Each machine is tested at this feed rate through ball-bar plotting.
"Look at an Arrow's ball-bar plot, and you see that spikes at axis crossovers have been almost eliminated," says Mr. Spearman. In practice, this means that circular interpolation is more precise, and round-offs and overshoots that once resulted from sudden changes in tool path direction may now be eliminated.