For custom-built parts, many manufacturers turn to CNC routing and milling machines. But what is the difference between a CNC router and a CNC mill? They both perform similar functions but have very different characteristics. You won’t be able to use them with the same materials, and you’ll have to be mindful of their capabilities as you work with them.
Both machines are computer-controlled, hence the acronym CNC, which stands for computer numerical control. These computer-controlled machines gained popularity in the middle of the 20th century.
CNC refers to their abilities to run off of computer design programs, called computer-aided design (CAD) or computer-aided manufacturing (CAM). Both a router and a mill works by moving a cutting tool around the workpiece across several axes. The tool makes cuts into the workpiece, revealing the desired shape. These cuts can include sculpting or contouring in addition to complete cuts. Projects you can use them for run the gamut. From cozy kitchen chairs to tiny parts to help power electronics, CNC cutting machines are often involved in the process. Both routers and mills will use a cutting tool called an end mill or a router bit, which can vary significantly in capabilities. Many projects will require more than one end mill or router bit to achieve the right combination of cuts.
Each machine type works via subtractive manufacturing, which means they remove material from the piece instead of adding to it. An example of the opposite process, additive manufacturing, would be 3D printing — it takes an existing piece or starts from scratch and adds material to create the desired shape.
These are the standard tasks for both machines. How they perform them and what they perform them on can vary significantly. Keep reading to find out more about the difference between CNC milling and CNC routers.
The first thing you’ll probably notice about CNC router machining is the material it can handle. CNC Routers are not designed for hard materials, such as hard metals like steel and titanium. These machines are generally reserved for materials like wood, plastic and foam, but soft metals like aluminum may work as well. Because it is designed for lighter materials, the mass of a CNC router is significantly less than that of a milling machine, which needs to be larger to hold the hard metals steady.
Part of the reason CNC router machining can only handle the softer substances is because of the way it delivers power to the cutting tool. A CNC mill is the better choice for industrial-grade materials since a router doesn’t have the same amount of power. A router cuts much faster than a milling machine, but it has less torque, using rotational speed to drive the force to the tool. The RPM of a CNC router is much faster than the speed of a mill. As you would imagine, this makes it a quicker process, which is ideal if you need to make multiples of something. For manufacturing operations that need consistent products over and over, a router offers fast reproduction, keeping cutting time to a minimum.
The tradeoff for such fast processing is that a CNC router isn’t as accurate as a milling machine, so high-precision workpieces typically go to mills. This lower precision in routers is partially due to the stationary design of the workpiece. With a CNC router, the work usually stays on a table, and the spindle-head moves across the X, Y and Z axes. Three axes are common, but some routers have four to six for more complicated projects. In comparison, the mill moves the workpiece itself, as well as the cutting tool, providing better angles.
The cutting surface of a CNC router machine is often wide. That way, it can better accommodate the large size in which many of the softer materials come. For example, if you’re cutting into wood, you might have a slab or board that is several feet long. Though the cutting area is large, the clearance for the Z-axis often is not. This shallow depth can make it difficult for some workpieces to fit in the machine. For others, a CNC router makes for excellent 3D-cut results. You can find routers in a variety of sizes and configurations, with everything from small, DIY machines to massive industrial-sized ones.
The cutting tool of a router bit works like a drill bit. Some different shapes and sizes will influence the way your cut looks when finished. You can have straight bits, rabbeting bits, chamfer bits, beading bits and molding bits, among many others. They have different shanks and maximum speeds that can help increase stability and smoothness and decrease chatter. A router bit will dull over time, so you’ll have to keep an eye on them. Higher-quality bits may last longer due to better materials.
The CNC milling machine comes into play for heavy-duty jobs. Materials like steel, aluminum and even titanium will be right at home on a CNC mill. To show you just how tough some of these metals are, below are the tensile strengths of many common materials. Ultimate tensile strength is a measure of how well a material withstands being pulled apart, recording the maximum stress that it can take before it breaks:
You can see that there is a significant difference between the strength of traditional material like wood and a more heavy-duty metal such as stainless steel. The stronger metals need machines designed to handle their unique properties. These substances make milling a common approach for a wide variety of machine parts, especially those that require high levels of precision and accuracy.
CNC mills are capable of much more delicate cuts than a router, and they can make cuts within 1,000th of an inch. This precision makes mills the go-to choice for detailed pieces. Soft materials can benefit from this precision as well, despite the CNC mill’s capability for strong metals. If the work is intricate or delicate, a mill may still be the way to go for a softer material.
One reason for the precision of a CNC milling machine is the configuration of the axes. While a CNC router moves the spindle around a stationary table, a CNC milling machine typically moves the workpiece itself along a linear axis. Here’s how:
This axis design provides more clearance along the Z-axis, allowing for much thicker cuts and intricate designs. A benefit to this configuration is that the workpiece can be flipped, eliminating the need for operators to reposition the piece to reach other sides. One drawback is that the cutting area is smaller, but if you work with higher-value metals, you likely will have less excess.
A milling machine is much more precise but takes more time to complete a job. To make up for the slower speed, the mill uses more torque. It can handle much tougher jobs with this power to remove materials from the hardest of metals. To cut hard metals, the machine itself is much more substantial than routers and more expensive. They are typically made of die-cast iron or another incredibly hard material. This construction provides stability and enough structure to handle the high torque.
A milling machine uses an end mill as its cutting tool. This piece is similar to a drill bit in that there are many different shapes and configurations that offer various cuts. Some end mills are better for creating specific shapes than others. Scalloping, for instance, takes on a very different quality when performed with a flat end mill vs. a ball end mill. The shape of the flute, or the direction the spiral goes, will also influence your machining. A flute influences aspects like your chip load, feed rate and surface finish. Using the correct end mill for your project can make a big difference in how it turns out. Working with metal is very different from working with wood or other soft materials, so you’ll need to have someone who knows the subtleties of this practice.
These versatile machines can get a lot done, but you have to use the right one. Some of the key differences between CNC milling and a router are as follows:
In both cases, you get the benefit of a computer-controlled device. By using CAD software, you eliminate human error from the physical cutting process. You can recreate the same piece over and over again. Or, if you only need one part, you know that it will be made exactly to the specifications you put in. Measurements are accurate, and cuts are sharp and defined. CNC machining turns a rendering in software to a completed piece in whatever material you’ve designated. CAD software requires skilled workers to execute the designs in an efficient and effective way.
For either machine, the process is typically loud and dirty. Unless you have an enclosed router or mill and an installed vacuuming system, the dust from the device will end up all over the shop and potentially cause health and safety problems. Though the machines are relatively simple to use, the operator needs to use standard best practices and wear the appropriate personal protective equipment as is necessary to prevent noise or respiratory issues. A skilled operator should also know the signs of a project that is having problems. If the piece starts burning or shaking or the tip jumps, there may be an issue with the design or the equipment.
Both machines can create consistent results that often cannot be performed by hand. Whether you need to make parts for a wooden chair or a gear for an aircraft, CNC machines can get it done.
For cutting-edge custom machining, American Micro Industries creates custom-built parts for a wide variety of industries. We’ve made tiny parts for electronics, precise pieces for aerospace applications and much more. Other fields we’ve worked with include the military, automotive and medical industries.
Many companies in these fields and others turn to AMI for more than just a part. They turn to us for unbeatable customer service. We will work with you to develop the part you need. From material selection to the manufacturing process, we can help you find the right approach for even the most unique applications.
We’ve been working with custom components since 1995, and quality is one of our top priorities. We inspect each part thoroughly before we ship it out, and we strive to provide the best customer service we can. If you need a part machined via a CNC router or mill, don’t hesitate to reach out to an AMI representative. We can discuss the process and get started creating the custom parts you require for your application.