Centerless grinding is critical to manufacturing many high-volume automotive components. These include valve spools, control rods, camshafts, crankshafts, pistons, sleeves and rollers. In addition, centerless grinding is applied to produce parts for the hydraulics and fluid control, medical and aerospace industries—indeed, any industry where roundness and extreme accuracy of cylindrical surfaces is needed.
For those “making chips” every day, centerless grinding may seem mysterious, but it’s a fairly straightforward process. This article will discuss how it works, where and when it should be used, and offer advice on how to apply this well-established technology.
Before the development of centerless grinding, round parts were either ground between centers or by gripping them with a chuck or fixture. Centerless grinding requires no such workholding methods. Parts are fed between a grinding wheel and a smaller regulating wheel while resting on an angled workpiece support—a blade-like device that sits between the opposing wheels.
During grinding, the force of the grinding wheel pushes the workpiece into the regulating wheel and against the support. The regulating wheel determines the workpiece’s rotational speed. Tilt it a few degrees and the workpiece will be pulled through the wheels and out the back of the machine, a technique known as through-feed grinding. Infeed grinding is the second technology available for centerless grinding. The regulating wheel pulls the part against a dead stop placed at the work-rest blade. The grinding wheel, which often contains a profile, is then fed into the part until the final part size is achieved.
There will always be a need for cylindrical grinding, but centerless offers several advantages. Because there’s no need to locate the part between centers or clamp it in a chuck, parts can be loaded quickly into a grinding machine, increasing throughput. The workpiece is securely held between the wheels and support rail, allowing long, thin workpieces to be ground. (Entire lengths of bar stock are often centerlessly ground for use in Swiss-style CNC lathes.) And because the wheel adjustment is diametral as opposed to radial—as is the case with cylindrical grinders—any infeed errors are halved, enhancing precision.
Less grind stock for finishing is generally needed on centerless parts, as the workpiece tends to find its own center upon initial contact with the wheels. Unfortunately, this means concentricity with previously machined holes and other features can be a problem, which is one of the main disadvantages of centerless grinding. Increased setup time is another, because of the need to handle and dial-in large wheels, and special work supports might be required.
Read more: Basics of centerless grinding