Such was the case for Sturges DesignWorks, a company in Portland, Ore., that provides automation and design engineering solutions in a variety of industries, including medical products, electronics, fixturing and tooling, and research and development. The company was working with a client who needed a special machine built that required substantial CNC lathe work. But Sturges didn’t have a lathe. “CNC lathes are expensive, take up much needed floor space, and have a steep learning curve,” explains Dan Sturges, company CEO. He considered a CNC mini lathe, but found that it would not be precise, rigid or accurate enough for the work required.
To address the issue, the company developed what it calls the Sturges Turning Head system to bridge the gap between traditional, full-featured CNC lathes and low-productivity, small CNC mini lathes. “I had always wondered why we couldn’t somehow do precision CNC lathe work on a CNC milling machine,” Mr. Sturges says. “The problem is, even if you attach a lathe tool to the mill spindle and lock it, there’s still a tiny bit of play that makes it impossible to maintain a standard of precision. So we developed a turning bar toolholder that places the tip of the tool at the spindle’s center of rotation, eliminating the slight play in the tool tip and providing the precision and accuracy needed for professional, high-quality swis type automatic lathe work on a mill.” Based on this principle, the company built the prototype for the Turning Head system, which is capable of external turning, facing and contouring operations. An optional cross slide accessory bolts onto the table, allowing for plunge operations such as parting and grooving.
The Turning Head spindle—the equivalent of a lathe headstock—is made of steel and cast iron and uses premier Grade 7 pre-loaded ball bearings that are lubricated for life. The standard model has less than 50 millionths of an inch runout, and the super-precision model has less than 20 millionths. It has a large, through-bore 5C spindle with a 4-degree taper mount nose.
The system comes with a set of three turning bars, each with an R8 or 3/4-inch straight. The universal design allows left-hand, right-hand and center cutting operations simply by rotating the tool. Tool changes between different turning operations are eliminated. The toolholders are available in three sizes (1/32 radius, 1/64 radius and 1/128 radius) and maintain cutter concentricity to less than 0.001-inch TIR.
Operating the system is straightforward. The operator places a piece of stock in the spindle, tightens the collet, turns on the unit, and hits “Go” on the CNC interface. The system allows the machinist to set up a job on a mill and crank out smooth, accurate parts in a repetitive way. Operating on the existing milling machine’s software, the CNC program provides fast, efficient operation without the need to learn new software.
