So we know CNCs and we like CNCs because they can take our computer designs and make them a reality.
But what distinguishes CNC routers from CNC mills? What can each do and which one is right for you?
What Are the Main Differences Between CNC Mills and CNC Routers?
In short, CNC mills look vertical or horizontal while CNC routers look like flat (large) beds.
CNC mills are more rigid and more accurate. They are better at carving tough materials like steel, have a small working area, and work powerfully and slowly.
In contrast, CNC routers are better for working with large sheets of soft material like wood, MDF, and plastic. They have a large working area and work fast, but they are not as powerful.
In this article, we explain all their differences and characteristics. We describe how each looks, moves, and behaves and explain their technical features.
Their Looks: CNC Mill vs Router
Two things separate CNC routers from mills when you look at them: how the machine moves, and the shape of the machine (and the size of their workpiece).
Axis Movement: CNC Router vs Mill
CNC routers and milling machines move differently. In a regular CNC router, the workpiece remains immobile while the spindle moves around and works on it. This is also how laser cutters, 3D printers, PCB printers, and plasma cutters move.
On the other hand, in the most common CNC mill designs, the table bed that is holding the workpiece moves in the X and Y direction while the spindle moves up and down the Z-axis.
Therefore, a CNC router has a gantry design. The gantry is the moving part of the CNC router.
In this design, the Z-axis is mounted on the X-axis and the X-axis is installed on the Y-axis.
Meanwhile, in a CNC mill, the Z-axis is on a C-frame which is independent of the table that controls X and Y.
We just explained the common three-axis designs, but there are many other designs as well.
For example, there are 5-axis CNC machines that have a rotating bed while some 5-axis machines rotate the spindle around robot arms.
But for understanding the characteristics of router vs mill, consider the common design that we just explained.
Shape and Size of Workpiece: Router vs Mill
As we mentioned in the movement of the CNC router vs mill, you know that the whole table moves the workpiece around in a CNC mill. This is good for small X and Y movements.
So, the working area of a CNC mill is generally smaller than a CNC router.
The design of CNC routers does not limit their X and Y. So, the working area of a CNC router can be as small as 30⨯18cm or as large as 12ft⨯6ft in industrial CNC routers for wood-cutting.
In contrast, a CNC mill has a working area of a few square feet.
On the other hand, a CNC router has to move the X-axis above the workpiece. In turn, this design restrains the size of the Z-clearance (and the Z-axis travel) whereas the independent Z-axis of a mill can be large.
In other words, a CNC router has a small clearance between its bed and the X-axis above it. So, you can’t put a workpiece that stands tall or has a large Z dimension (thickness) in a CNC router.
For example, X-Carve has a Z-clearance of 67mm (2.6”) only. So you can’t put a material with a 3-inch thickness in it. For another example, Shapeoko’s Z clearance is 3”. In contrast, even small CNC mills have at least around 10” of Z-clearance.
So, the Z-axis (clearance) of a CNC mill is much larger than a CNC router.
To recap, CNC routers have large working areas (X and Y) which is good for large sheets of material, while CNC mills have a large Z clearance which is good for small materials that may be much taller than the thickness of sheets.
Capabilities of CNC Router vs Mill: What Can Each Do?
Now, we explain what the different designs of routers and mills bring to the table. Specifically, CNC routers are different from CNC mills in rigidity, materials they can handle, accuracy, power, and speed.
CNC mills are generally much more rigid than routers. This is a result of their design. Mills concentrate large weights in a small area to get very rigid.
A CNC router supports its gantry only through the linear movement mechanism. But in a CNC mill, the table moving mechanisms only have to support the weight of the table and workpiece while the C-frame independently supports the Z-axis rigidly.
It simply takes much more effort to make a CNC router more rigid.
Furthermore, the design of CNC routers makes them susceptible to bending.
For example, when a CNC router moves the spindle to the sides of the table (ends of the X-axis), it gets away from the center of mass of its gantry and creates a large rotating torque (shear force). But a CNC mill does not move the spindle away in these directions.
To sum up, CNC mills can stand much more cutting forces than CNC routers.
Materials: When you Need a CNC Mill vs When You Need a CNC Router
Since we know that CNC mills are rigid, they can stand larger cutting forces.
Cutting materials like wood, MDF, and plastic require small cutting forces. What’s more, these materials come in large sheets that just fit right with a CNC router.
Although aluminum is tougher than MDF, you can still cut aluminum with a CNC router since it is on the softer side of materials.
|Material||CNC Router||CNC Mill|
|Aluminum 6061||✓ (if the part is not tall)||✅|
|HSS (High-Speed Still)||❌||✅|
Materials like steel, cast iron, and titanium require a large cutting force and belong in a CNC mill. Compared to these tough materials, a CNC mill can cut aluminum very easily and precisely.
Mills Or CNC Routers for Stones?
This is a tricky one. Cutting a stone requires large forces so you might be thinking mill. But if we are talking about stones that come in large sheets, then they fit in CNC routers.
So for engraving purposes, you will need a rigid CNC router which is heavy.
Accuracy: Mill vs Router
The accuracy of a CNC machine comes down to its rigidity. So, mills are more accurate than CNC routers.
The accuracy of most CNC mills is around 0.01mm no matter what material they work on.
Many CNC routers claim a 0.01mm accuracy as well but that totally depends on the material. There are no figures but if you forced a CNC router to carve steel, supposing it can labor through the job you can’t expect a better tolerance than 0.2mm.
So, most machine parts in cars, aerospace, ships, and generally all metallic stuff are manufactured by CNC mills with great precision.
Power and Speed: CNC Mill vs CNC Router
We already know that a CNC mill is suitable for tough materials that demand more power for cutting them.
On the other hand, CNC routers are faster for three reasons.
- CNC routers work at higher feed rates than Mills: The appropriate feed rate for cutting wood is much higher than for cutting steel. For this reason, CNC routers work faster than mills because of the nature of the material.
- Higher RPM: In agreement with the feed rate, CNC routers also employ a higher spindle speed (RPM).
- Repeatability: CNC routers can cut the same item several times out of one large sheet. But a CNC mill works one item at a time. That means clamping down and defining its position for every product.
Suppose you want to cut five of the same product with a mill. Since the working area is small, you have to remove your item after cutting it and attach another piece of material to the mill again to cut the same item.
So, CNC mills are generally more powerful while CNC routers are faster.
Technical Differences: CNC Router vs Mill
CNC mills and routers have different spindles, stepper motors, cooling systems, and linear mechanisms.
Spindle Differences: CNC Router vs Mill
We already have discussed the power and speed differences between CNC routers and mills. As a result, the spindle of CNC mills must provide enormous power at low ranges of speed.
To get a better sense of this, let’s give some example numbers. A machinist may decide to cut wood at 20000 RPM with their CNC router while a machinist may cut steel at 1500 RPM with their mill.
Plus, cutting steel is more difficult, so the spindles of CNC mills have large torque at low speeds while the spindles of CNC routers spin very fast.
We can also use routers instead of spindles in CNC routers. That is probably where the name comes from.
Routers yield high RPMs, less power than spindles, and more noise. CNC mills, however, always employ spindles – never routers.
Stepper Motors in CNC Router vs CNC Mill
High-end industrial CNC machines usually have servo motors. But stepper motors are also a nice and affordable option for machine movement.
Stepper motors have a high holding torque, but they lose their torque steeply with speed. If you are choosing a stepper motor for a CNC machine, here is the best advice.
For a CNC mill, the holding torque is more important while for a CNC router strength at high speeds is more important.
Because of the hardness of materials that a CNC mill engages in, it demands a lot of thrust force from the stepper motors for cutting. But the good news is that it doesn’t matter if the stepper motor loses its torque with speed since the mill works at low feed rates anyway.
On the other hand, the stepper motor of a CNC router may not need to provide huge torque, but it is best if it retained a lot of its muscles up to 400 RPM.
We have introduced the best stepper motors for CNC in this article. We have introduced several that have amazing high-speed performance.
Coolants in Mill vs Router
Cutting metals creates more heat than cutting wood, for example. That is why CNC mills have a cooling system that mists coolant on the bit and working area at times.
Cutting wood and plastic does not require a coolant. But if you have a CNC router for stone engraving, you should use a consistent flow of water on the working area.
Linear Axis: CNC Router vs Mill
Ball screws are effective and powerful actuators of linear axes. But they are only good for short travels. You should never use ball screws for axes over 4 feet long.
For this reason, we usually see rack and pinion or timing belts in CNC routers X and Y-axes. But we usually see ball screws or lead screws in CNC mills.
To summarize, CNC routers and mills are different in a number of ways. CNC mills are tall but CNC routers look like big beds.
CNC routers have a gantry design like lasers and 3D printers, but CNC mills move the workpiece with the table while carrying the spindle on a C-frame.
CNC mills are more rigid and more accurate. They are better for tough materials like steel, cast iron, and titanium that come in small sizes (though they may stand tall on the table).
CNC routers are faster and can perform repeated operations. They are best for softer materials like wood, MDF, and plastic. These materials are mostly in large sheets that lie flat on the table bed.
Finally, CNC mills have more powerful spindles and stepper motors that turn slowly. CNC routers have faster spindles and stepper motors that retain their strength at higher speeds.
Check out our other CNC mill and router articles: