Advanced Precision Machining

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CNC Grinding Technology and the Grinding vs. CNC Turning Debate

[February 17, 2014] In an effort to keep our readers informed of the many precision manufacturing techniques utilized at our Colorado machine shop, we thought we'd devote some time to what we feel is a time tested and highly effective method of high speed machining - that of grinding. At its core, grinding is a method of finishing a machined part using an abrasive form of cutting. Depending on the type of machine used however, CNC grinding systems can be adapted to manufacture precision machine components, especially when working with exotic materials requiring fine tolerances. At a typical CNC machining company, grinding is often used following more aggressive removal of material produced through traditional CNC milling or CNC turning methods. A power driven high-speed grinding wheel, often outfitted with diamond cutting heads, is mounted on a bed with a fixture to hold a workpiece in place. The grinding head either travels across a fixed workpiece to manufacture a part, or the head remains stationary while the piece travels, depending on the machine. Modern grinding systems rely on CNC for exacting control of the grinding head or table position, creating a finish on manufactured parts to exacting geometric tolerances, and they take on different forms and function.

As a somewhat generic term, grinding is used in a wide range of high speed machining applications. An introduction to CNC grinding in a milling and machining environment would not be completed without a basic overview of the most common systems utilized on a machine shop floor and their function. Surface, cylindrical and internal grinding make up the most common methods and account for most of the CNC grinding machines found in a modern machine shop. Surface grinding is the most basic finishing technique and involves smoothing a machined part's surface with a grinding wheel via abrasion producing a highly refined look. This results in a lot of friction-generated heat, and lubricants such as water-soluble chemicals and oils must be applied to the wheel and the workpiece during the process. Instead of finishing, cylindrical grinding machines are used to externally shape a work piece by removing material and are typically applied to rounded surfaces such as metal rods. A part is held in place on both ends and spun while a rotating grinding wheel is passed along its length. Internal CNC grinding essentially finishes a previously drilled or reamed hole on a workpiece to a high degree of accuracy with a small grinding wheel rotating at very high RPMs. This metal boring technique is typically applied mainly along the centerline to cylindrical work pieces. Instead of removing material externally, material is removed to exacting tolerances internally, producing a desired diameter and/or finish.

As new technology continues to advance and increase the capabilities of modern CNC turning machines, there is some debate in the precision machine community comparing the merits of grinding vs. hard turning for particular applications. Hard turning is an alternative method of grinding using a CNC turning machine. Parts can be manufactured with accuracies arguably comparable to the tolerances produced by CNC grinding machines. Therein lies the debate, hard turning methods hold the possibility of eliminating grinding operations altogether. "Why grind when you can hard turn?" Okuma, a manufacturer of CNC lathes, CNC grinders and machining centers offers some fresh perspective on reasons to grind rather than hard turn. Wherever your loyalties lie, there is no debate that accurately finishing a precision machined part is a crucial step in the high speed machining process. At Advanced Precision Machining, our certified machinists are happy to discuss any grinding, hard turning or other finishing project with you. Call us today at 303.776.1910 for a free consultation or quote, or learn more about our Longmont machine shop at:


About the Author


Gerry Dillon is a co-founder, current owner and certified CNC machinist at Advanced Precision Machining (APM), a full-service machine shop located in Longmont, Colorado. Before making his home in the United States in 2000, Gerry was born and raised on the emerald isle of Ireland and took an interest in milling and machining from an early age, ranking #1 in the Irish National Apprenticeship Program. In 2005, he partnered with his friend and colleague, Kirk Tuesburg, currently APM’s machine shop manager, together launching what’s grown into a leading Colorado machine shop. Gerry brings over 30 years of machining experience to the shop floor, and is certified in all aspects of geometric dimensioning and tolerancing.


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