Tool Grinding for the CNC Machine Tool Industry

Posted on Jul 21, 2021

Tool grinding

Tool grinding is a process to sharpen or recondition multi-point and single-point cutting bits such as drill bits, milling cutters, reamers, taps, etc. It is necessary as it ensures high-quality performances and accurate cutting results. Normally, tool and cutter grinders are used for this process.

A tool and cutter grinder is used to sharpen milling cutters, tool bits, and a host of other cutting tools. Tool grinding is a subspecialty of the larger field of grinding technology, which requires abrasives or custom grinding wheels to re-sharpen a machine tool. Tool and cutter grinders perform a variety of grinding operations: surfaces, cylinders, or complex shapes.
 

Construction


Fig. 1 General Configuration, Best Mechanical Engineering


The general configuration of a tool and cutter grinder is shown in Fig. 1 It has a basic structure similar to a lathe except the turning head is equipped with a grinding wheel instead of a jaw chuck. A fixture (usually a chuck or a vise) is mounted on the work table to clamp the cutting tool.
 

Cross-sliding Work Table

The work table is a cross-sliding table with grooves on the saddle. The grooves allow the fixture to move across the table to adjust the position of the cutting tool. The positioning of cutting tools is important in a tool grinding process as it affects the grinding results on every point and surface of the tool.

The grinding process can be manipulated in both the lengthwise and widthwise directions. Besides the work table, the wheel head on some models can swivel in the horizontal plane to provide more grinding dimension. With this additional clearance, the machine is able to process more types of cutters.
 

Tool Grinding Axes

A typical cross-slide work table is able to offer two axes: the lengthwise and widthwise axis (X- and Y-axis). A rotatable chuck stand provides an extra rotational axis (A-axis). These three axes cover the face and sides of a cutting tool. With the swivel wheel head, another grinding axis is enabled (C-axis).

On a manual tool and cutter grinder, the movements along these axes are controlled by the operator. On a CNC tool grinder, these movements are controlled by the computer. The manual tool grinding process (usually) only has three to five grinding axes while its CNC counterpart can have more than five axes.
 

Manual vs. Automatic

Performing a tool grinding process with a manually operated machine requires a high level of skill. Understanding the grinding wheel type and the cutting bit material is important because it affects the grinding process. Understanding the tool geometry is also necessary because it determines the feed angle and grinding axis.

On the other hand, the process performed on an automatic tool and cutter grinder is simpler. All the parameters that have to do with the process are pre-programmed with a CNC system. With a semi-auto machine, changing the grinding wheels, and loading the cutter bits are done by the operators. CNC tool grinding is conducted in shops that process a large number of tools with identical specs.
 

CNC Tool Grinder or Cutter Grinder

Modern tool and cutter grinders are usually equipped with a CNC system and multi-axis grinding features. CNC tool and cutter grinders enhance efficiency with other features such as automatic tool loading, the ability to support multiple grinding wheels, high-level automation, in-machine tool measurement, and compensation. Below is a video showcasing the features of a high-precision CNC tool and cutter grinder.
 


High-precision CNC Tool & Cutter Grinder, Makino Seiki Co


The in-machine tool measurement (1:19) using a touch probe or laser technology allows the cutting tools to be reconditioned. During normal use, cutting edges either wear and/or chip. The geometric features of cutting tools can be automatically measured within the CNC tool grinder.

With the CNC system, it is possible to simulate the process and the finished part with the software. It can also detect possible mechanical collisions. These features enable the optimization of the process. Cutting tools made of extremely hard and exotic materials are not a problem for today's CNC tool grinding machines, and multi-axis models are capable of grinding quite complex geometries.
 

Tool Grinding Types

There are various types of tools and cutters in the machining sector today. One machine is not able to process all these tools. Therefore, tool and cutter grinders have developed into types to recondition particular tools. Below are the common tool grinders.
 

Radius Grinder

The radius grinder (or radius tool grinder) is used to grind spherical surfaces. Here is another video showing how radius grinding works. The tool rotates on the tool pivot center so that the corner radius of the cutting tip can be ground.

 


Corner Radius & Ball Nose Grinding, Cuttermasters


During a radius grinding process, the wheel head is set still. The tool holder on the work table has a vertical rotational axis. As the tool is set to the pivot center, the process begins. While the grinding wheel is spinning, it grinds the tooltip. The tool rotates on the pivot center and has the corner radius ground.
 

D-bit Grinder

A D-bit cutter is a single-point cutting tool without teeth and flutes. The D-bit grinder is intended for the production of these single-point cutters. This type of cutter is used to create long straight holes and is replaced by CNC machining centers in the modern days. The machine is not capable of sharpening drill bits with standard profiles or any convex or spiral profiles.

 


Drill Sharpening: Universal Tool & Cutter Grinder AKA D Bit Grinder, Projects Down Under


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