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As customer demands continue to increase, the need to deliver parts with unmatched precision and a sharp finish are becoming increasingly important. To achieve this result, professional CNC companies must minimize tool deflection. As the name implies, tool deflection is the result of cutting forces that exceed the stiffness of the tool material and cause it to bend. Tool deflection wears down the tool and puts it at risk of breaking. For these reasons, minimizing tool deflection is critical to ensuring part repeatability and high-quality finishes. It is additionally worth noting that minimizing tool distortion is economical because it reduces machine downtime. What affects machining accuracy? How do you minimize the chance of tool damage? What should you pay attention to in CNC machines? We write about it below!

How tool deflection affects the workpiece

Tool deflection is defined as the bending of a tool. The deformation of tools and workpieces occurs due to the load on the tool or workpiece, which can cause it to change significantly. It happens when cutting forces can overcome the stiffness of the tool, resulting in tool deflection. CNC machining tools have two ends. One end of the CNC machining tool can be held freely, while the other is fixed in the tool holder. During CNC machining, the device can exert force on the workpiece. When the CNC machining tool exerts an influence on the workpiece, the workpiece also exerts an opposite resistance to the tool. Several other working forces and resistances also act on the CNC machining tool. If the external force applied to the tool becomes more significant than the tool’s force, it can cause the tool to deflect. The deflection and bending of the tool considerably impact CNC machining. 

CNC tool damage and machining accuracy

Deflection, or tool damage, causes the following complications in CNC machining: 

  • Tool deflection can damage the workpiece or tool.
  • A deflected tool shortens the CNC machining life cycle. It destroys dimensional accuracy and causes numerous errors in CNC machining systems.
  • In addition, it gives a rough CNC machined surface.
  • Tool deflection can lead to severe dimensional errors – This significantly impacts the CNC machined surface and leads to potential surface damage.
  • It shortens tool life and causes tool breakage – If not properly considered, tool deflection can cause parts to scratch.
  • Tool wear can increase, and manufactured parts with tool deflection can be subject to variation, out of tolerance, or vibration of surface finishes.

Suppose you want to reduce tool deflection and achieve high-quality surface finishes without sacrificing part quality. In that case, you need high-quality CNC lathes, tools, and experienced engineers to operate these machines. Tool deflection can be minimized by minimizing the distance from the tool holder to the tooltip.

How do you reduce CNC tool deflection? 

Tool deflection in CNC machining is very common and can be catastrophic with minimal impact on part quality. Knife overhang cannot be avoided entirely or prevented, but there are ways to reduce it. Depth of cut, proper endpoint, and proper programming of the CNC machine – are a few aspects of caring for your CNC machine. Here are some tips to help you reduce tool bevel during CNC machining. 

Increase tool core strength by changing the cutter diameter

Diameter is an important factor when considering deflection and bending, especially core diameter. The strength of a tool’s core depends on its span and groove length, and the difference between the span and groove length can be referred to as core stiffness. Using the resulting tool, the diameter of the core can be used for calculations; the diameter of the center then becomes the diameter of the neck. By changing these values, the deflection of the final tool can be reduced. This can have a significant impact on the size of long groove tools.

Learn the difference between long grooves and long distances

Tool deflection can be minimized by understanding the key differences between long grooves and long-pitch tools. The core diameter is primarily responsible for the difference in stiffness between long-groove and long-stroke tools. A tool with more material is relatively stiffer than a tool with less material. In addition, tools with shorter grooves are more complex and have a longer life. Each type of tool has its strengths. To reduce deflection during a specific operation, use the right tool.

Use a reach tool to avoid deflection

Long-reach tools are often used to remove material from crevices where the tool holder does not fit and cannot remove material. Material is removed by inserting a non-cutting extension of the tool diameter. Tilting can be prevented by reducing the reach behind the cutting edge to the tool diameter.

Application of the long groove tool

Long groove tools mainly have long cutting lengths. Long groove tools are primarily used to create slots in seamless walls. The core diameter size does not change and remains the same over the entire length of the cut. The larger the core diameter, the more likely the part is to skew. In addition, some cutting edges can cause tapered edges at high feed rates.

Reduce throat cutting length

The overhang is the length between the end of the CNC tool and the connection point. The tool must withstand bending stresses and horizontal and vertical forces when mounted as a cantilever beam. According to the theory of loading stresses, shorter overhangs lead to a lower impact of bending stresses.

Increase tool stiffness to avoid deflection

Tool deflection in CNC machining can be reduced by increasing tool stiffness. CNC machining tools typically consist of high-speed steel. High-speed steel is often helpful in machining operations, but exposure to high loads can cause the tool to deform. An alternative high-speed steel tool is a carbide, three times stiffer than a high-speed tool. Carbide tools can reduce the deformation due to their brittle properties in CNC machine tools.


Generally speaking, tool deflection and bending stress is a major cause of failure or spoilage of a workpiece product. Deformation of the tool during operation can be minimized by using specific strategies, such as reducing the distance of the tool holder from the tooltip and increasing the stiffness and core strength of the tool. Reducing the overhang also minimizes the deflection of the CNC machining tool. To reduce failures and inaccuracies, it is advisable to use the best equipment and constantly participate in training to be knowledgeable about CNC machines and get the most out of the tools. Proper programming methods (using the best program for machining or milling) and training the operator in this area will undoubtedly improve the function and quality of the CNC machine. Other problems and questions related to tool too much deflection will become irrelevant.