CNC machining has revolutionised manufacturing across the world. With the right CNC tools, these machines can deliver intricate results and unrivalled accuracy. The trade off is that commercial CNC machines rely on fine tolerances and high-precision tools. When you’re working to tolerances measured in thousandths, even the slightest imperfection in the tool can impact the quality of your workpiece.
The most common issue is tool deflection. Deflection refers to the bending that occurs as tools pass through a workpiece. While it’s impossible to eliminate deflection entirely, excessive deflection reduces the quality of your work, shortens tool lifespans and can even create safety issues on the shop floor. In this article we’ll go over the 4 most effective things you can do to manage deflection in your CNC tools.
- Use Tools with the Right Diameter
Tool deflection is a normal part of CNC operations. As the cutting tool passes through the workpiece, it’s exerting force on the material you’re cutting. Just the same, the workpiece pushes back with equal force, which can result in tool deflection (e.g. bending, or the tool being pushed off its true centerpoint). The biggest factor in tool deflection is the rigidity of the tool. This is affected by things like overhang, your choice of chuck, tooling material and tool diameter.
Of these, tool diameter is the easiest variable to control. The greater the diameter, the more rigid a tool tends to be. The trick here is to use the tool’s core diameter when calculating the correct size. The core diameter is a measure of the tool’s widest point in the flute valleys. This gives a much truer indication of a tool’s rigidity and allows you to select the right CNC tooling to minimise deflection.
- Invest in Long Reach CNC Tools
Long reach tools allow you to get further into a workpiece and complete complex machining processes. This adds lots of value to each product, but it’s a serious challenge for your tools. You can improve tool life and reduce deflection by investing in the right types of long reach tools for each application.
When talking about long reach CNC tools, we’re typically referring to two different types of extended tools:
- Long reach tools – Long reach tools combine a fluted tip with a non-cutting extension to the shank. This means the tool can be used to access gaps that a long tool wouldn’t fit through. To avoid rubbing the non-cutting surface on the workpiece, long reach tools typically use a reduced diameter extension that’s smaller than the fluted part of the tool.
- Long flute tools – Long flute tools have cutting flutes along more of the tool’s length. This type of tool is best suited to finishing deep surfaces, such as slots and bores. The additional length of long flute tools can make deflection more pronounced if too little of the tool’s cutting length is engaged during a cut.
- Minimise Tool Overhang
Tool overhang is a measure of how much the tool extends past the end of the chuck. While a large overhang can allow tools to reach further into a workpiece, it also increases deflection.
Large overhangs increase the amount of leverage that a workpiece can exert on a tool. The bigger the overhang, the more the tool bends. In extreme cases this can even cause tools to break. Remember that most CNC tools are produced from high carbon steels or highly rigid tungsten carbide. The hardness of these materials makes them brittle under lateral loads, which can dramatically shorten tool lifespan.
The best way to get around this issue is to minimise tool overhang wherever possible. Aside from investing in long reach CNC tools, you can also purchase specialty chucks or collets that provide additional support beyond the end of the spindle. Combined with programming that reduces your reliance on long reach tools, this dramatically reduces deflection and improves the quality of final products.
- Increase Tool Rigidity
Finally, we reach the question of tooling materials. Most CNC tools are available in a mix of high carbon steels and tungsten carbide. These materials are highly rigid and very well-suited to CNC applications. But, steel tooling is much cheaper, and it can be tempting to reduce your expenses by avoiding full carbide tools. This may be okay for some applications – such as machining softwood or plastic – but it severely limits your CNC machining capabilities.
Increasing tool rigidity is usually a question of buying the right tools. If you’re working with hard materials, long reach programs or demanding carving processes, paying extra for carbide tooling is the way to go. Carbide tools offer the rigidity you need to manage deflection and improve the quality of each cut. That lowers your overall cost, reduces waste and allows you to increase the speed of your machines. Ultimately, these additional efficiencies mean that high quality carbide tooling is the cheaper option for most CNC manufacturers.