Precision, accuracy and feed-rate needs dictate CNC machinery upgrades

Figure 2: The OKK VM5 II table holds a dual-vise workholding with a workpiece.

"Before 1998, I didn't have very good equipment,” he explains. “I was using more inexpensive, economical-type machine tools."

He had just received a contract for four similar molds—a dream job for a state-of-the-art plastic and custom injection mold manufacturer like General Tool Specialties.

His shop was at full capacity, and, because his existing setup wasn’t up to par, he was missing deadlines.

Domici connected with a supplier of OKK machine tools, which is now represented in the U.S. by Methods Machine Tools and its dealer partners. He needed a 40-by-20-by-20-inch machine within a week, and the supplier delivered.

Figure 3: Custom workholding setups can be done on the OKK VP 9000.

In just two weeks, Domici had his first OKK VM5 II vertical machining center up and running (Figure 1). Compared to his previous machine, the difference was like night and day.

Domici needed that machine because his shop was at capacity. He was unfamiliar with the OKK brand at the time and spoke to his machine tool dealer.

“My surface finishes were incredible, my tool life was great, and the machine was so much stronger,” says Domici. “I had the ability to run larger cutters and take larger cuts. It was much more reliable and accurate.”

A lot of the benefits come from the machine’s construction and software. OKK’s proprietary algorithm, Software Scale, constantly monitors the movement and temperature of the spindle to compensate for thermal displacement. Counteracting thermal displacement eliminates inaccuracies in the workpiece, making Software Scale a unique machine tool component that solves a common problem and extends the life of the tool.

Figure 4: The VP 600 and 9000 have double-nut ballscrews. Having two points of contact on each ballscrew, instead of four, reduces friction, increases stiffness and generates more consistent torque.

The machine’s horsepower and torque enable it to remove larger amounts of material faster compared to other machines.

One OKK machine led to another and another and another at General Tool Specialties. Domici had a second VM5 II installed within a year (Figure 2).

In the mid-2000s, he was looking for a machine with better accuracy and feed rate than the machine on his shop floor. Once again, the current setup wasn’t reliable. While he never lost a contract, he was missing due dates.

One weak link could have massive ramifications, Domici says. You could, for example, have to run the parts on a different machine and put other jobs on the back burner. That creates one logistical problem after another.

Shifting jobs from one machine to another could result in additional overhead costs, such as overtime or paying a technician to fix the machine. It could also complicate shipping, logistics and work schedules. If you do miss a job, it could harm your shop’s reputation and therefore your ability to take on new contracts.

In addition to reliability, Domici needed a machine with incredible precision and accuracy. Naturally, the choice was an OKK VP600.

“The VP600, I could actually do work +/-  0.0002-inch  all day long without trying,” he says. “Those aren’t machine accuracies; those are accuracies I can produce in the work.”

Figure 5: The controls on both the VP 600 and the VP 9000 machines are largely the same, however the machines differ in many ways. An impeller ring is an example of a large part that can be machined on a VP 9000.

The results paired well with the price tag. “In my opinion, the OKK machines are the best machines for the price, they’re not expensive machines,” says Domici, who also was looking to replace an aging bridge mill. He grew accustomed to the reliability and performance of the OKK and soon had a VP 9000 three-axis machining center on the shop floor (Figure 3).

The VP 600 and 9000 have double-nut ballscrews, meaning there are two points of contact on each ballscrew, instead of four (Figure 4). This reduces friction, increases stiffness and generates more consistent torque, all of which contribute to accuracy, precision and longer tool life.

Those machines also have large linear-roller guideways and angular bearings in the spindle that improve accuracy. Both models' core-chilled ballscrews further minimize thermal displacement, excellent coolant sheltering that keep coolant and chips out of critical areas.

The controls on both the VP 600 and the VP 9000 machines are largely the same; however, the machines differ in many ways (Figure 5), including the feed rates, travels, max workpiece dimensions and designs

The VP 600 and VP 9000 are bridge-style machines. Since the spindle moves along a horizontal bridge, rather than hanging from the z-axis, bridge-style machines are more precise—meaning more repeatability—compared to other machine constructions.

More specific to OKK machines, the company uses a lot of heavy, cast-iron parts that absorb vibrations better than other platforms. OKK designs its machines so that internal sheet metal guides coolant and chips out of the machine more efficiently compared to some other builders, minimizing thermal distortion/growth and increasing precision. The ballscrews on OKK machines are generally larger and stronger compared to other builders, improving accuracy and thrust.

About the author

Bernie Otto is director, technical support, and product manager for Kiwa Japan and OKK Japan products at Methods Machine Tools. Contact him at [email protected].