• MMS Youtube
  • MMS Facebook
  • MMS Linkedin
  • MMS Twitter
10/20/2007 | 4 MINUTE READ

Creep-feed Grinding Is A Milling Process

Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

Because creep-feed grinding is essentially a milling process, why not use a VMC? A grinding machine supplier describes how a VMC platform can make creep-feed grinding more effective.

Related Suppliers

Creep-feed grinding is an abrasive machining process, but beyond that, it doesn’t resemble other forms of grinding. Nelson Beaulieu, grinding product manager with Hardinge Inc., says it makes more sense to characterize creep-feed grinding as a milling process.

After all, creep-feed grinding employs a deep cut and a high metal removal rate, and it features a low feed rate in place of fast reciprocating motion. The “tool” in creep-feed grinding—the grinding wheel—gets buried in the material like a milling cutter.

In fact, that tool gets more effective as its diameter shrinks down closer to the dimensions of the largest milling cutter on a typical machining center. And if the machine itself is designed like a vertical machining center, he says, then a tool such as this becomes more practical.

Mr. Beaulieu says these points summarize the thinking behind his company’s VMC-based grinder. The FGC 2 “flexible grinding center” from Bridgeport (a Hardinge company) represents a departure from traditional creep-feed grinder designs—and the orientation of the spindle is perhaps the most fundamental difference.

Up Out Of The Way

When creep-feed grinding was first developed, Mr. Beaulieu says, practically all grinding machines had horizontal spindles. Creep-feed grinding naturally built on this platform. However, one of the basic requirements of this horizontal design is a big wheel. The wheel diameter has to be large enough for the edge of the wheel to clear the spindle housing and reach the table.

This requirement imposes limitations, he says. Coolant penetration is essential to effective creep-feed grinding, but the wide arc of the big wheel results in a tighter space for this coolant to try to reach. In addition, the big wheel makes it impractical to interpolate along complex machining paths. Instead, parts are often held on complex fixtures, and the part may be moved from fixture to fixture on one creep-feed machine after another as different features of the part are ground.

By contrast, lifting the spindle housing out of the way of the work zone makes it easy to apply a smaller wheel. Coolant can thus be delivered to the cut more effectively, and the part can be fed through rotary axes to let the small-diameter wheel use tool paths like those of a five-axis machining center.

The FGC machine essentially is a five-axis machining center. However, because the work is grinding instead of milling (milling in the conventional sense, that is), the machine had to deliver the sort of stiffness that is a key strength of the traditional horizontal platform. Unlike a typical VMC, the rigid cast iron base of this machine weighs 30,100 pounds. Also unlike a VMC, the machine is used in conjunction with a special coolant system able to deliver the 1,000 psi or 50 gallons per minute that creep-feed grinding requires.

These changes mean the vertical machine is not necessarily less expensive initially. Mr. Beaulieu says the savings come once the machine is applied. Sources of savings include:

  • Fewer fixtures or fewer machines. Instead of multiple setups, it may be that all of the grinding can be performed in one setup.
  • Reduced setup time, because the need for complex fixturing can be eliminated.
  • Fewer machining operations, because the ability to reorient the part within the cycle can make it possible to machine separate features with the same wheel.
  • Faster machining (over and above the setup time savings), because the smaller wheel can be moved more nimbly. Mr. Beaulieu says the user can take a lighter depth of cut on this machine and still achieve a higher metal removal rate because the potential feed rate is that much higher.

Conventional Machining

Further savings come when the machine is used exactly as a conventional VMC. Its spindle uses a machining center’s standard BT interface for the tooling, and grinding wheels are delivered to the spindle via a standard machining center toolchanger. The same system can therefore be used to apply more typical machining center tooling within the same cycle. That is, mills or drills can wait in the tool magazine alongside the wheels. If some milled or drilled feature needs to locate with respect to a ground surface, then it makes sense to let the machine produce those additional features while the part is still set up.

One other way the VMC platform makes creep-feed grinding easier to apply relates to resources outside the work zone. With the machine so similar to a standard machining center, it becomes possible for machining center personnel to program and run the creep-feed process effectively. The pool of available talent therefore increases. As Mr. Beaulieu points out, “There are a lot more milling operators out there than there are grinding operators.”

Hand holding a crystal ball

We’d rather send you $15 than rely on our crystal ball…

It’s Capital Spending Survey season and the manufacturing industry is counting on you to participate! Odds are that you received our 5-minute Metalworking survey from Modern Machine Shop in your mail or email. Fill it out and we’ll email you $15 to exchange for your choice of gift card or charitable donation. Are you in the U.S. and not sure you received the survey? Contact us to access it.

Help us inform the industry and everybody benefits.


  • The Anatomy Of An End Mill For Aluminum

    By using specialized cutter geometry and incorporating smooth finishes with tough coatings, Toolmex Corp., created an end mill well suited to cut aluminum aggressively. This tool called the "Mako" is part of the SharC line of specialized tools from the same company.

  • How To Machine Aircraft Titanium: The 8-To-1 Rule For Finishing Walls And Ribs

    Part of a series of articles on more efficient machining of pockets in titanium parts, this article makes the case for a tool with many cutting edges, and describes how best to apply it.  

  • Bringing Anodizing In-House

    What’s it going to cost? How much space do I need? What environmental hassles will I encounter? How steep is the learning curve? Exactly what is anodizing? Here are answers to preliminary questions shops have about bringing anodizing in-house.