Hard Turn Without Leaving Feed Marks

Hard turning can reduce, and in some cases eliminate, finish grinding operations. Because it is a single-point turning process, however, it will produce feed marks on a part’s surface no matter how much the feed rate is reduced. This may be tolerable for non-finish-critical diameters, but is unacceptable for shaft

Article From: 9/19/2008 Modern Machine Shop
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Lead-Free Hard Turning Video

Hard turning can reduce, and in some cases eliminate, finish grinding operations. Because it is a single-point turning process, however, it will produce feed marks on a part’s surface no matter how much the feed rate is reduced. This may be tolerable for non-finish-critical diameters, but is unacceptable for shaft features such as seal bearing surfaces. Sumitomo Electric (Mount Prospect, Illinois) has developed a "lead-free" tooling system that, according to the company, hard turns critical diameters without leaving behind feed marks.

The keys to this lead-free turning process are tool design and feed direction. Single point turning feeds a cutting point along the lathe’s Z axis—longitudinally down the rotating part. Conversely, lead-free turning moves a wide, blade-like insert tangentially across the part in the X axis. A dedicated toolholder provides the proper lead angle for the insert as it traverses across the workpiece. The link to an online video of this turning process can be found in the Learn More box at the end of this article.

Two screws are used to secure the insert in the toolholder pocket for added rigidity, as the contact area in lead-free turning is greater than that of single-point turning. The polycrystalline cubic boron nitride (PCBN) inserts are available in cutting edge lengths from 22 mm to 48 mm.


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