Today, an increasing number of “traditional” shops are considering this machining platform to, in some cases, produce complex parts complete, reducing setups, secondary operations and work-in-process. The goal in using this equipment is to minimize the number of times a part is touched during production.
• Learn the Swiss-type platform. Before operating a Swiss-type, it’s important that new personnel understand the sliding-headstock concept and how the machines differ from conventional turning centers. A Swiss-type uses a sliding headstock that feeds barstock through a guide bushing and past a tool during an OD turning operation. The guide bushing offers support for the barstock very near the point of the cut, preventing workpiece distortion. This makes Swiss-types particularly effective for producing long, slender parts.
• Know the difference between a headstock collet and a guide bushing. Swiss-types have a revolving collet in the headstock as well as a revolving or stationary guide bushing. The revolving collet must be adjusted tighter to enable it to grip the bar when the sliding headstock moves in or out. However, the guide bushing must be adjusted so it is loose enough to enable the bar to pass through, but not too loose to reduce the bar support needed near the point of the cut.To adjust the guide bushing on the Star machines, operators simply move the headstock back to access the bushing, then use a device similar in function to a spanner wrench with pins that are inserted into the bushing to enable it to be tightened or loosened.
• Measure each bar before installing. The guide bushing must be loosened each time a remnant is removed so as not to gall the bushing during removal. This means the guide bushing has to be re-adjusted each time a new bar is loaded. Most ground bars Vallorbs uses have a diameter accuracy of ±0.0005 inch, meaning the amount of adjustment can vary from bar to bar. However, Mr. Pitts says that’s not a problem, because an operator needs to re-adjust the guide bushing for each new bar anyway. What is problematic is if the diameter of a bar varies along its length.
• Mind the decimals. More often than not, simply zeroing offsets after changing an insert is all that’s required to start producing good parts again. In some cases though, an operator must input an offset value. New operators sometimes slip up by entering an offset value with the decimal in the wrong position.
• Take care when offsetting tools. Operators of Swiss-types must remember that a single tool might be used to perform a number of different operations. Therefore, adjusting the offset for a tool that’s currently producing an oversized diameter, for instance, might adversely affect subsequent operations the tool performs for that particular job.
• Get a feel for finishes. A turned feature looks different than a milled one. Both might have the same finish rating, but the milled surface includes witness marks that turning doesn’t produce.