Reprinted From: It differs from other cylindrical processes in that the workpiece is not mechanically constrained. On traditional OD machines, the work is held EMPHASIS: Grinding between centers or chucked and rotated against the faster spinning grinding wheel by an external motor usually located in a workhead. Unlike center-type or chucker-type grinding, parts made using a centerless process do not CenterlessCenterless require center holes, drivers or workhead fixtures. Instead, the workpiece is supported on its own outer diameter by a workblade located between Grinding:Grinding: a high speed grinding wheel and a slower speed regulating wheel with a smaller diameter. It’s the relationship among these three basic Not components—grinding wheel, regulating wheel and workblade—that makes the difference between a successful centerless grinding applica- Magic! tion and one that gives headaches and bad parts. Achieving consistent and quality results from the centerless grinding process Why Centerless Works requires an understanding of the basic In cylindrical grinding, understanding the fundamentals. Most application problems process is relatively straightforward. A workpiece, associated with centerless grinding derive supported by centers or a chuck, is rotated against from a misunderstanding of the basics. the grinding wheel, which is fed in a prescribed This article explains why the centerless distance radially (plunge grinding) or traversed process works and how to use it most axially across the workpiece to create the desired OD dimension. effectively in your shop. On the centerless grinder there are no centers, so it would appear that there is no means to control the workpiece size or roundness. However, quite the opposite is true. Centerless grinding, if set up properly, will achieve roundness, surface finish and dimensional tolerances that are among the best available in metalworking. Moreover, the process is able to improve the roundness of out-of-round workpiece blanks. Creating roundness from out-of-round condi-

Work Regulating Wheel

Grinding By Chris Koepfer Wheel Workblade It’s a good bet that grinding is the metalwork- So how does centerless grinding work, and ing process most associated with “black art” and what are essential components that need to be “smoke and mirrors.” Much of this mythology is understood to achieve successful part processing, perpetuated by a general lack of understanding consistently and predictably? We visited Cinetic of the basic fundamentals that make grinding Landis Grinding Corp.'s Milford, Ohio technical applications successful. center where it handles application development Of the grinding processes, centerless is and service of the Landis Cincinnati line of center- certainly among the least understood from a less grinding machines. We spoke with Greg Payne, fundamental perspective. On the surface it indeed the company’s bid and proposal manager, about the does tend to defy much of what we think we fundamentals of centerless grinding specifically, know about cutting metal. why the process works and how understanding that Setting the centerline of a workpiece on the centerlines of the Most obvious is the apparent lack of workhold- translates into successful part processing. grinding and regulating wheels will not produce rounding. In this ing. The part just lies between the regulating and setup, any high spot will create a diametrically opposite low spot. grinding wheel seemingly free to exit the cutting What Is Centerless Grinding? Over time, the workpiece will look like the exaggerated shape zone at will. Yet it doesn’t—usually. Centerless grinding is an OD grinding process. shown at the bottom.

—— To enable the centerless grinding process to and regulating wheels. So, for a 1 inch diameter Grinding create rounding action on the workpiece, it Work Regulating workpiece, the height should be a half inch above Wheel must be placed above the centerline of the Wheel the wheel’s centerline. “This is the primary start- wheels. In this setup, high spots no longer create ing point for most centerless grinding setups,” diametrically opposed low spots. Instead, the says Mr. Payne. high spots are ground and a gradual rounding Most centerless grinding machines give the of the workpiece takes place. distance from the top of the lower slide to the centerline of the grinding wheel and regulating wheel as one of the specifications. For example on Cincinnati’s DE model centerless grinders, this distance is 9.875 inches. Mr. Payne points out that this measurement varies among machine Workrest manufacturers and models. Workblade With this known dimension, the next step to Shims get the correct blade height calculation is to add the workpiece height above center to the tions is the claim to fame of the centerless grinding blade or the regulating wheel, it does not create distance between the slide and wheel centerline. process. It does this by virtue of the relationship a directly opposite low spot because of the angle For a 1 inch diameter workpiece on a Cincinnati among the grinding wheel, regulating wheel and created between the centerlines of the wheels DE model, the workpiece center height needs the workblade. and workpiece. to be 10.375 inches measured from the lower Side-viewed, from the operator’s perspective, Instead of grinding a lobe shape in the slide. the centerless grinder has the grinding wheel on workpiece, the high spot is gradually reduced “There are numerous ways to get this measure- the left, workblade in the middle and the smaller by the action of the grinding wheel. So rather ment,” says Mr. Payne. “Ultimately though, the diameter regulating wheel on the right. For most than creating a low spot on the periphery of the machinist needs to end up with one half of the applications, the centerline of the grinding wheel work equal to the high spot, the grinding wheel workpiece above the centerline of the wheels, and regulating wheel are in the same plane, at generates a proportionally smaller low spot at its resting one-third of the way down from the top equal heights above the machine bed. contact with the workpiece. To achieve rounding action, the workblade To better visualize this rounding action, must be set so that the centerline of the workpiece imagine a workpiece with several high spots. Now is above the centerline of the grinding and imagine that part being ground with only a single regulating wheels. This is a critical relationship rotation. When the part is removed, it would show for successful centerless grinding. only the high spots had been touched. If the workpiece rests on a flat workblade that The angle of the workblade helps keep the is on center with the regulating and grinding workpiece in contact with and under the control wheels, the contact points form three sides of a of the slower rotating regulating wheel to resist square. As the part is ground in this setup, any any tendency to “spin up” to the speed of the high spot on the workpiece will shift the work grinding wheel. In some cases, a spin-up can slightly on the blade, allowing the grinding take a workpiece from 850 rpm to near 60,000 wheel to cut a directly opposite low spot. Over rpm in the blink of an eye. This is not something time this setup will create three lobes on the you want to have happen. workpiece that may be dimensionally accurate but far from round. Setup Keys Infeed centerless grinding is analogous to plunge grinding on a Setting an angled workblade so it slopes toward To get the centerless grinding operation started, center-type machine. The work is placed on the blade, and the regulating the regulating wheel and supports the workpiece the workblade height must be set. This will con- wheel moves into a programmed feed to begin the grind. The work does centerline above the centerline of the regulating trol the workpiece centerline, the height above not move axially in this type of centerless grinding. and grinding wheels is how the centerless opera- the centerline of the two wheels that determines tion is able to generate roundness. In this setup the rounding action of the centerless grinding of an angled workblade and against the regulating if a high spot comes in contact with either the operation. wheel. This will provide good rounding action and “One of the most common setup stable grinding conditions.” Grinding mistakes we see,” says Mr. Payne, “is Centerless grinding workblade angles range Wheel incorrect measurement of the work- from 0 to 45 degrees. For most centerless grinding piece height. This is a critical dimen- applications, a top blade angle of 30 degrees sion and should not be guessed.” seems to provide the best results. “The basic rule Workrest A rule of thumb for setting the is the steeper the angle of the blade the faster Guides correct height for a workpiece that the rounding action,” says Mr. Payne. “There are is up to 1 inch in diameter is to have limits, however. For larger diameter and longer one half of the workpiece diameter work, a shallower blade angle is best. Choosing above the centerline of the grinding 30 degrees is a good general starting point for Work top blade angle.” Thrufeed grinding is generally applied to continuous, Also, setting the regulating wheel slow, at about volume production applications. The wheels are 30 rpm, is a point to begin optimizing the center- dressed in such a way that the workpiece is driven less grinding process. Obviously, this regulating Regulating through the cutting zone, across the face of the wheel rotation speed is dependent on work diameter Wheel grinding wheel. Often a single pass is sufficient to and stock removal rates required. But 30 rpm is a finish the workpiece. good place to start.

—— tact between the workpiece, grinding wheel and Grinding Wheel regulating wheel must be maintained. Therefore, the regulating wheel must be trued with a diamond block located on the truing attachment. The dia- mond block is a device that adjusts the diamond contact relative to the workpiece height above the 12r 7r Above grinding and regulating wheel centerline. Center Below “A quick check to see if the thrufeed setup is 31/ 64 Center running correctly,” says Mr. Payne, “is to look Regulating Wheel at the wear line across the top of the workblade. 1r This line should be parallel to the top of the blade. If it runs uphill, from front to back, there is too much diamond block offset. It’s the opposite 1 /2 if the line runs downhill.”

Is Centerless Grinding For You? Traditionally, centerless grinding is found in The drawing above illustrates how the diamond block can be set to Wear Line shops involved in high volume production runs. obtain true line contact on the regulating wheel. The drawing on the That’s still an important segment for the technology. right illustrates a quick check to determine if the thrufeed setup is Increasingly, though, the advantages of correct. The wear line on the workblade should be parallel to the centerless grinding, such as rapid rounding top of the blade edge. and accuracy, are finding application in shops that run relatively shorter job lot sizes. The Kinds Of Centerless Grinding enabler for this is the application of CNC and Like center-type cylindrical grinding, which servomotor technology to the centerless grinding can use plunge or traverse motions to grind a machine. workpiece, centerless grinding too has different With electromechanical actuation of slides, ways to get the job done. The two most common dressers and truing attachments, setup of the centerless grinding techniques are infeed and centerless machine is a much less daunting thrufeed. and time consuming exercise. Moreover, the Setting up for infeed is the less complicated of ability to program grinding and regulating wheel the two. Although workpiece height is important, The work is driven axially between the wheels contours using CNC actuated truing attachments proper workblade and wheel profiles are a must by inclination of the regulating wheel relative to eliminates the need for profile cams, which to obtain the required step relationship of the the grinding wheel. Because all of the points to take time to manufacture and are usually less finished workpiece. be ground on the workpiece contact all the points accurate. The workpiece is placed between the wheels, on the wheels, this centerless grinding method is Centerless grinding is successfully applied to and the grinding cycle begins. After spark-out, the best applied to straight cylindrical parts without manufacture of parts ranging from hypodermic finished part is removed and the next one goes in. shoulders or other interfering features. needles to bowling balls. The principles of the Infeed centerless grinding is analogous to plunge In thrufeed grinding, the regulating wheel process remain the same regardless of the work- grinding on a center-type machine in that the is inclined, creating a feed angle relative to piece. Like most metalworking processes, center- workpiece is static in the axial direction. the grinding wheel. This feed angle allows the less grinding is not magic, if you understand the For continuous, production-type centerless regulating wheel to perform the dual purpose fundamentals. grinding, the thrufeed method is very effective. of rotating the workpiece against the grinding ■ Thrufeed grinding is accomplished by passing the wheel and driving the workpiece across the face For more information about centerless grind- workpiece between the grinding and regulating of the grinding wheel. ing from Cinetic Landis Grinding Corp., call wheel. Basically, raw material goes in one side The regulating wheel can be swiveled relative (513) 707-1712, visit the company's web site at of the grinding zone, and finished workpieces to the grinding wheel. However, to do its job and www.landis-us.com or visit the Online Showroom come out. use the full width of the grinding wheel, line con- at www.mmsonline.com

Originally published in the December 2000 MODERN MACHINE SHOP Magazine and revised with permission of the author in January 2007 to update the information. Copyright © 2007 by Gardner Publications, Inc., 6915 Valley Ave., Cincinnati, Ohio 45244-3029.

—— Cinetic Landis Grinding offers the most comprehensive line of precision centerless grinders and centerless grinding expertise in the industry

Our product range and aftermarket VIKING SUPERSERIES II® support are the result of the marriage of The Best Value In Precision Processing Cincinnati, Landis and Giustina centerless grinders. Today’s Landis Cincinnati centerless • Superabrasive Capable • 0.1 Micron Machine Resolution grinders are respected the world over for • Extremely Stiff Composite Filled Cast Iron Base their accuracy, reliability and ease of use. It is • Quick Change Twin Grip™ Spindles Bottom Line important to note that we not only sell and • Super-Precise CNC Dressing Of Both Wheels Centerless service centerless grinders, we support you • 20 Or 40 Horsepower Grinding Wheel Drive Grinding Solutions with expert application development and • Speeds Up To 16,000 sfpm system integration not available elsewhere. • Multi-axis Servo Machine Motions • Servomotor Regulating Wheel Drive Making the right choice for your optimum • Very Fast Set-Up And Wheel Change process solution is easy when you consult • All Electric Machine With NO Hydraulics • Landis 6400 PC-based, open-architecture with a Cinetic Landis Grinding application CNC control system specialist. We take into consideration the type of parts you’ll be grinding and the LANDIS CINCINNATI RK SERIES required tolerances, the production A Precise, Reliable, Wide-Wheel Workhorse requirements, where the process needs • For Workpiece Diameters Up To 6” to be driven, and how the machine will fit • Grinding And Regulating Wheel Widths Up To 20” into your existing process. Then we calculate • 50 Horsepower Main Drive the metal removal rate and select the • 0.1 Micron Machine Resolution right grinder model to meet the process • Stable Epoxy Granite Base requirements. • Easily Handles “Old Style DE” Tooling • Twin Grip™ Grinding Wheel Spindle With Landis Cincinnati Centerless Grinders are Hydrodynamic, Self-Centering Support field-proven in hundreds of installations • Servo-Driven, Twin-Support worldwide. And, every grinder backed by Regulating Wheel Spindle • Anti-Friction Slideways Cinetic Landis Grinding’s industry-leading • Landis 6400 PC-based, open-architecture service and support. CNC control system

For more information, contact Greg Payne by phone at 513-707-1712 or by e-mail at: [email protected] or visit our web site at www.landis-us.com

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