Modern Machine Shop

JUN 2017

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mmsonline.com June 2017 MMS 71 FEATURE W ithout a prior explanation, an observer of a live turning demonstration might declare that the tool in the demo lathe is cutting in the wrong direction, exactly opposite of the usual practice. Likewise, the viewer watching a video of this demo might strongly suspect that the recording was being played in reverse. That would account for what seems to be the "backward" motion of the turning tool. A rendering of the tool motion in these demos, as shown on the facing page, indicates that the direction of the cutting tool is actually following the yellow arrow. This dire ction is cle a r ly the opposite of a nor mal or traditional turning operation. What is going on here? Sandvik Coromant, the inventor of this process, calls this new turning concept PrimeTurning, which uses dedicated CoroTurn Prime tooling. In fact, the two current styles of inserts for PrimeTurning (o n e fo r l i g h t m a c h i n i n g a n d o n e fo r h e av y Turning Takes a New Direction A methodology for cutting in both directions on a CNC lathe promises to make turning a much more productive operation in certain applications. New types of inserts driven by new CAM tool paths are key enablers of this development, but implementing the whole multifaceted system as a system is essential. BY M A R K A LB E RT machining) are designed to cut in a direction that is opposite of the usual approach. In addition to moving toward the chuck in the Z axis as they cut, these tools can also "go in reverse" and move away from the chuck as they cut. Likewise, when needed, these tools can cut "up from" or "down to" the part centerline in the X axis for facing or shoulder cutting. Each insert is capable of rough- ing, finishing or profiling by cutting in either direc- tion when there is an advantage. For the right applications, the company claims that the results are astonishing: as much as an 80-percent boost in productivity. As much as twice the tool life for the inser ts. Significantly smoother surface finishes. How can cutting in the "wrong" direction be so right for certain operations in these applica- tions? A detailed answer to this question is worth- while, because it involves a number of insights into the nature of the basic turning process itself. Based on these insights, the concept of Prime- Turning seems to upend normal practice, and do so on several levels. Apparently, a turning capability like this has never been possible before. The geometry of the light-machining and heavy-machining insert styles a p p e a r s to b e e nti re l y n ew. B oth st y l e s a re highly specialized; the multi-angled nose of the A new method of turning enables an insert to cut away from the shoulder of a workpiece. Because the insert can travel toward the tailstock of the lathe instead of toward the chuck, there is no possibility of chips jamming in the corner as may occur in conventional turning. (All images from Sandvik Coromant, except as noted.)

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