Extreme accuracy: Drilling Performance

In many machine shops, the daily grind is brightened up by the stellar results they get from their jig grinding machines. The jig grinders in these shops are used to produce round holes and other shapes that meet the most stringent requirements for accuracy and finish. Jig grinders can be either computer controlled or manual, but CNC versions with advanced features are gaining in popularity as older manual machines are retired.

When it comes to position, form and finish accuracy, jig grinding takes things to another level compared to milling, according to Ian Slaughter, technical marketing manager for glass molding at Moore Nanotechnology Systems LLC, a manufacturer of jig grinders and other machine tools based in Swanzey, New Hampshire. “Milling is great for removing large stock quantities and gives an accuracy of 2 µm to 5 µm depending on your machines,” Slaughter said. “With jig grinding, you’re typically working from 2 µm down to 0.5 µm.”

The M600 jig grinder is designed to deliver repeatable sub-micron form and positional accuracy when grinding a variety of metals. Image courtesy of Moore Nanotechnology Systems

In many cases, Slaughter noted, jig grinders are used by the mold and tool industry to produce the forms needed to turn out accurate product shapes. In addition, he said, the machines are grinding components for the aerospace customers and others with high precision requirements.

Alternative Processes

As an alternative to jig grinding, Slaughter pointed out that similar results can sometimes be achieved by milling combined with a secondary operation. For example, a shop could mill and then polish to achieve similar surface finishes, he noted, but the entire process would be much more time-consuming than jig grinding.

Moreover, it would be “very difficult” to achieve comparable accuracy, he added. “Once you put in a manual operation, you will start to lose form very quickly. So customers looking to produce round holes or forms to sub-1 µm (accuracy) would be looking at a process such as jig grinding.”

Then there’s jig boring, which Slaughter described as a process done by a similar-looking machine that uses traditional cutting tools instead of a grinding wheel. Therefore, he said, jig boring can’t achieve the same levels of accuracy and surface finish as jig grinding. He also noted that a jig bore would only be used to produce round holes, whereas a jig grinder will produce other forms and contours.

Jig boring machines are very accurate when drilling, reaming and boring holes that need to be in a precise location, according to Andy White, president of White Jig Grinding Inc., a shop in South Elgin, Illinois, that offers a variety of jig grinding services. By contrast, White explained, jig grinders use a grinding wheel to finish existing holes or contour shapes with minimal stock to be removed. “Our customers usually leave a few thousandths of an inch of material to be removed to get the finished size,” he said.

An enhancement offered by the new M600 jig grinder is the integration of the conversational and customizable NanoSMART operating system.Image courtesy of Moore Nanotechnology Systems

For holding very tight tolerances, White said, wire EDM is often chosen as a faster and less expensive alternative to jig grinding, despite the fact that the wire will often leave a start/finish line on parts. There are no such flaws with jig grinding, he continued, noting that the process can generate a better surface finish because of the high speed (3,000 to 60,000 rpm) of the grinding head. “And with the many grinding wheel options, we are able to generate the surface finishes required for a specific job regardless of the type of material being worked on.”

Newer Machines

For shops that are tackling the jig grinding process, the latest machines are designed to deliver top-notch results while also making the job easier. One example is the M600, a state-of-the-art jig grinder co-developed by Moore Nanotechnology Systems and its sister firm, Moore Tool Co. Inc. in Bridgeport, Connecticut.

Officially introduced last year, the most recent version of the M600 includes a number of design elements aimed at boosting accuracy, repeatability and surface finish. According to Slaughter, these include increased rigidity at the wheel point where grinding takes place. Also new is a “counterbalance” for the machine’s Z axis. Thanks to this feature, “as the spindle motor, accelerates, decelerates and reverses in its reciprocation stroke, we have zero inertia, effectively putting no forces through the machine and giving us that ability to achieve greater accuracy and better surface finish,” he explained.