Additional Strategies to Minimize Tool Deflection in CNC Machine Operations

Tool deflection is a common pain point in every machine shop. Not only does it cost money to replace your tool, but it can also result in machine chatter, extended leadtimes, and sub-par surface finish in your machined parts. Earlier this year, we covered the basics of tool deflection. In today’s blog, we explore some additional strategies to prevent tool deflection. Let’s get started! 

Recap – Tool Deflection Definition 

Tool deflection is the unwanted deviation of a tool from its expected alignment and tool path. During machining, the tool is held and moved by the chuck of the machine spindle, but the opposing force and vibration that arises from the contact of the rotating tool on the workpiece will result in the deflection of the tool from its set alignment. 

What Causes Tool Deflection?

As discussed above, tool deflection primarily occurs when there is a resisting force from the workpiece material against the action of the cutting tool, which is moving at high speed. There may be other causes of tool deflection. This may include loose tool fitting within the chuck, machine vibration, and even human factors. 

Effects of Tool Deflection 

Tool deflection is often detrimental to both the cutting tool, workpiece, and operator. The following errors may arise as a result of tool deflection: 

• Tool or workpiece failure 

Tool deflection can drastically reduce the lifespan of your end mills and cutting tools. In more severe cases, the deflection can break the tool and result in both tool and workpiece catastrophic failure. Once this occurs, the machinist will need to stock a new tool and re-machine a new block of material if the effects of the deflection cannot be corrected. 

• Safety issues 

The high speed involved in machining and the extent of opposing force from the workpiece means that tool deflection can be sudden and unexpected. Depending on how it occurs, tool deflection can constitute safety issues for the machinist, resulting in broken tools flying around at high speeds or chips of the material workpiece breaking out with high force. 

• Dimensional flaws 

Once tool deflection occurs, one can expect some level of dimensional inaccuracies around the workpiece. This may or may not be correctable. If you also experience tool deflection on the same tool frequently, the tool will become blunt and incapable of delivering sharp, precise cuts. 

• Bad surface finish or potential damage

Tool deflection can result in a bad, rough, and non-uniform surface finish or even damage the workpiece’s surface finish in its entirety. 

How To Minimize The Risk of Tool Deflection 

• Minimize overhang length 

The overhand length refers to the distance between the gripping or holding point of the cutting tool and its operating tip. When machining, the cutting tool is subjected to an array of stress from all directions. The length of the overhang plays a significant role in the impact of stress. Generally, the longer the length of the overhang, the more the bend stress impact, and higher bend stress will often result in tool deflection. 

To minimize the risk of deflection, ensure that you minimize the overhang length of your cutting tool. 

• Use carbide tools 

While HSS (High-speed steel) is the go-to solution for CNC machining tools, these options do not necessarily do well on exposure to high stress and load. HSS tools are three times more prone to deflection relative to carbide tools. If you have been experiencing tool deflection, you should consider using carbide tools. They are more brittle, more rigid, and less likely to deflect.

• Improve tool core strength 

A tool’s core strength is subject to the reach and length of its flute. If the core diameter is thicker, the tool will absorb and withstand more shear force, while thinner cores are more likely to deflect from the force of machining. Also, tools with shorter length of flutes are more rigid with longer tool life.  

Having a full grasp of the difference in rigidity between a long flute and long reach tool defines the core strength. When machining, opt to select the smallest reach and length of cut on a tool with the largest diameter. This will help prevent tool deflection and manage vibrations. 

• Long reach vs. Long flute 

Knowing when to use a long reach or long flute tool can be a tool saver. Use long reach tools when removing material with a gap where the shank would not fit in, but the non-cutting, extended portion of the tool would reach. Long flute tools are most appropriate when cutting with high-efficiency milling, cutting in deep slots, and finishing applications. They are, however, more likely to deflect or, in severe cases, break.