This high-volume shop produces parts on both mechanical and Swiss CNC machines, but which machine is right for which job? #workforce development
The first sign that Precision Plus is different from other machine shops is a slight click. The sound comes from a dozen mechanically operated Swiss-type lathes in the center of the workshop. The machines are neatly built and serviced by what appear to be newer bar feeders, which are not closed off and do not have the sonic shrouds typical of shop floor CNC machines. Closer examination shows that as the cam rotates, about half a dozen tools are pushed and inserted into the workpiece at the same time.
Here Mike Reader is standing next to a Miyano BNX duplex CNC lathe. Mike runs the store’s training program, teaching new employees how to use Swiss-style screw machines. Image credit: Precision Plus
By the time the company moved to its current location in Elkhorn, Wisconsin in 2000, some of these machines had been making parts for years. Under the leadership of company president Mike J. Reeder, the company has added a variety of new CNC equipment, including Miyano ABX and BNX twin-spindle lathes, as well as several Star and Tsugami Swiss-style CNC lathes. However, Precision Plus still relies heavily on the same equipment that Reader’s father, Phil, first bought the company in 1988, using physical cams rather than CNC to plan cuts in time and depth. Why?
This is my first question to Michael P. Reeder, VP of Engineering (also son of Mike Reeder). His answer was simple: “Cam-driven machines, when available, are cheaper to run,” he said.
Small precision parts such as screws for oboes and bassoons are ideal for cam-driven machines. The grooves are cut with a saw blade attached to the pick-up head. Image credit: Precision Plus
“Swiss cam machines are very economical for small cylindrical parts with high annual volumes,” Rieder said. Tornos’ swiss-style machine-driven lathe fleet requires less energy costs and, most importantly, often cuts parts faster.
This last factor may surprise some, as it seems that computer-controlled machine tools should have no problem competing with machines without any processing power. However, cam-driven machines can use multiple cutting tools at the same time with very short strokes. “The tools all sit motionless within two inches of the part,” Reeder says, pointing to semi-circular cutting tools that frantically carve a striker out of a thin rod. “That makes it much faster than a CNC controller.”
Five cutting tools surround the workpiece on this Swiss cam-driven screw machine. When the camshaft rotates, various cutting tools perform their operations and cut the finished part in one revolution of the shaft. The tight position of the cutting tool relative to the workpiece makes it an excellent choice for fast production of parts with a small number of features. Image credit: Precision Plus
How much faster can it be? “We have parts that take 8 seconds each on a Swiss CNC machine,” Rieder said. “On a cam machine, it takes three seconds.” More than doubling production speed is an important difference, especially when dealing with high production volumes. “If we had to use CNC on this part,” he said, “we wouldn’t even break even.”
Another benefit of Tornos cam driven machines? Visual effects. “The Swiss video camera is readily available so you can see what’s going on,” Rieder said. This makes them suitable for the company’s apprenticeship program, which Reeder believes provides a workforce. Image credit: Precision Plus
“It really depends on the demand for that part,” Rieder said. “Some parts require more precision and that’s what Swiss CNC delivers.” Take, for example, factory-produced dental components. First, the diameter is only 0.01″ and the aspect ratio is quite large, so extra support was needed to eliminate vibration and prevent the part from breaking off in the machine. These characteristics of the part make CNC necessary due to its higher precision and greater rigidity. In addition, the surface roughness must be close to ideal, as minor imperfections can have catastrophic consequences. “We had to make sure that we kept the tolerances exactly,” Rieder said. “If this dental component has any surface imperfections, it could lead to crack propagation and failure during use.”
I think anyone sitting in the dentist’s chair will appreciate the increased precision of a CNC machine.
This dental component must meet tight tolerances and have a large length to diameter ratio, requiring the use of a Swiss-type CNC lathe rather than a cam-driven lathe. Image credit: Precision Plus
Factors other than tolerances can also influence the choice of CNC machine. For starters, they can process larger parts – 12, 20 or 32mm, depending on the machine. In addition, parts such as dental components require high pressure coolant, which is not possible on Swiss cam driven lathes. Coolant can also be a major cause of sticky or viscous chip materials and valve components with o-ring grooves that require high pressure to clear chips.
Finally, headstock lathes can machine larger and more complex parts up to 2.5 inches in diameter. “Typically, when we need to remove a lot of material or a higher level of complexity, we use our Miyano platform,” Rieder said. The Miyano ABX is used for aggressive and precise machining, thanks in part to the hydraulic chucks and rugged machine design offered by the platform. One part used in semiconductor manufacturing involved extensive removal of ID material, off-center drilling, tapping, and OD turning of high-strength, high-yield stainless steel. On a twin spindle lathe with three turrets, parts can be machined in one operation at very competitive speeds.
Used in semiconductor manufacturing, this part is more suitable for conventional lathes. It involved several eccentric drilling operations, removal of heavy ID material, and several external features, all from a difficult-to-machine stainless alloy. Image credit: Precision Plus
Another lathe is the Miyano BNX, mainly because of its efficiency. “BNX offers better performance than ABX while still allowing five decimal places,” Rieder said. Precision Plus machines plus or minus 1 thousandth of an inch for OD turning and a total of 30,000ths of an inch for ID holes. When such precision is not required, a single turret can be used to machine both the main and sub spindles at the same time, increasing productivity on many parts. Both stages are equipped with the Hainbuch quick change chuck system, which reduces spindle to spindle changeover time and part alignment.
As with many other machining applications, it all comes down to the details. “In general, the larger and more complex the part, the more likely it is to be machined on a fixed headstock lathe,” Rieder said. “Smaller cylindrical parts that have very tight tolerances or require high pressure coolant are machined on Swiss CNC machines. But if we could make them on a CAM machine in Switzerland, it might be faster to produce them there and with such same precision.”
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Post time: Jan-12-2023