All types of CNC machines according to use and characteristics

types of cnc machines

Future articles will detail types of cnc machines that exist according to their function, such as lathes, milling machines, router or cutting, engraving, drilling, etc. However, in this article we will focus on knowing the types according to the materials they can work with, and also according to the freedom of movement they have, that is, according to the axes. This is essential to know the uses and the possibilities that the rest of the types of machines will offer according to their function.

Types of CNC machines

types of CNC machines

As I have mentioned, these teams can be classified according to several factors. We will leave the analysis of the types according to their functions for future articles, since there will be a publication especially dedicated to each type in depth. Here we are going to focus on two ways of cataloging the types of CNC machines that are common to all types according to their function.

According to the materials

According to the materials that a CNC machine can use can be categorized into several groups. But it must be taken into account that the mechanical properties of metals can be very diverse, and not all allow all types of machining or in the same way.

Remember that the mechanical properties of a material can be: elasticity, plasticity, malleability, ductility, hardness, toughness and brittleness. The tool used, the cost and the machining time will depend on them. Also, many people confuse hardness and fragility with opposite things and it is not true. A material can be very hard and very brittle at the same time. For example, glass is hard since it is not as easy to scratch as wood would be, however wood is less brittle than glass since you can drop it and it will not break into pieces whereas glass will. will do.

CNC machine for metal

La cnc machine for metal It is the one whose tools can work with this type of materials and their alloys. The amount of metal materials a machine can work with will depend on the model and the tools it can handle. But they are usually materials widely used to manufacture all kinds of parts due to their mechanical properties. Metals and metal alloys suitable for CNC machining must have specific mechanical properties that include strength, flexibility, hardness, etc.

Between the most popular metals for CNC stand out:

  • Aluminum: it is a fairly profitable metal for CNC machining. It is light, easy to machine, strong, and can be used in a wide variety of applications, from windows, doors, vehicle structures, heat sinks, etc. Among the most used types of aluminum are:
    • Aluminum 6061: good resistance to weather conditions, although not so much to chemicals and salt water. Widely used for coatings, doors, windows, etc.
    • Aluminum 7075: very ductile, resistant, and resistant to fatigue, which is why it is often used for vehicles and the aerospace industry, although it is more complicated to machine (it is not easy to create such complex parts).
  • Stainless steel: it is less easy to machine, but it combines fantastic characteristics such as its low cost, its resistance, and its infinity of uses. We are certainly surrounded by pieces of steel if we look around us. In the CNC, the most common types are:
    • 304: it is very common, and can be used in multiple domestic applications, from coverings and structures of electrical appliances, to kitchen utensils, through pipes, etc. It has good weldability and formability.
    • 303: Due to its properties of corrosion resistance, hardness and durability, this sulfur-treated steel is used to create axles, gears, vehicle accessories of all kinds, etc.
    • 316: It is an incredibly strong and corrosion-resistant steel, so it is useful for some medical implants, for the aerospace industry, etc.
  • Maple: This iron-carbon alloy is very cheap, even more so than stainless steel. It does not offer the same corrosion resistance, but has similar properties in other respects. Among the most used types for CNC machining are:
    • 4140 steel: a steel with a lower carbon content, but alloyed with manganese, chromium and molybdenum. It stands out for its high resistance to fatigue, toughness, and resistance to impact. For this reason, it is very attractive for many industrial applications, such as the construction sector.
  • Titanium: it is a very expensive metal, but it has excellent properties, such as its low thermal conductivity, its high resistance, and its lightness, although it does not allow machining as easy as the previous ones. For example:
    • Ti6AI4V Grade 5: This alloy has an excellent strength-to-weight ratio, good resistance to chemicals and temperature. That is why it is used for applications exposed to extreme conditions, medical implants, in the aerospace sector, and in high-end or motorsport vehicles.
  • Brass: This copper and zinc alloy allows for very easy machining, even though it is not one of the cheapest metals. It has medium hardness and high tensile strength, making it good for electrical, medical, and automotive applications.
  • Copper: it is a metal that allows excellent machining, but has a high cost. Its properties make it fantastic for the electrical, electronic and thermal industries, as it is a great electrical and thermal conductor. For example, electrically conductive parts or heat sinks can be made, as was the case with aluminium.
  • Magnesium: It is one of the easiest metals to machine due to its mechanical properties. It also has high thermal conductivity, and is lightweight (35% lighter than aluminum), making it great for automotive and aerospace parts. The biggest drawback is that it is a flammable metal, so dust, chips, etc., can ignite and cause fires. Magnesium can be burned under water, CO2 and nitrogen. An example used for CNC is:
    • AZ31: excellent for machining and aerospace grade.
  • Others: Of course, there are many other pure metals and alloys that can be CNC machined, although these are the most popular.

During the CAD design process of these metal parts, the characteristics of these metals must be taken into account. In addition, the CNC machines to work them must have the appropriate tools and the necessary power to do so. On the other hand, when machining a metal by CNC some factors must be taken into account: intended use/necessary properties and total cost (material cost + machining cost). On the other hand, the goal of many CNC machines is to produce a high quantity of parts at the lowest possible cost and in the shortest possible time. The easier the metal is to machine, the less time and cost it will take, although this will also depend on the complexity of the part.

Finally, I would like to stress that it is also important finishing and post-processing that can be given to metals after CNC machining. For example, some parts will need polishing to remove marks produced by CNC tools, remove burrs after cutting, surface treatments (galvanized, painted,...) to prevent corrosion or for aesthetic reasons, etc.

CNC machine for wood

There is a lots of wood available in the market, including particle board, MDF, plywood, etc. Wood, in general, allows quite easy machining, so it is widely used for milling, cutting and turning. In addition, it is a relatively cheap material, and abundant. On the other hand, it is usually one of the most used materials also for domestic CNC machines used by some makers and DIY enthusiasts.

Some examples of wood to work with CNC are:

  • hard woods: they are usually exotic woods with great durability and quality. They are expensive, but their tight grain makes them very resistant for many applications. These need more rigid and hard tools to work it, and can take a longer time. However, they can be better than soft ones when it comes to complex carvings or intricate shapes. Some common examples are:
    • Fresno: Light-colored, heavy wood with excellent mechanical properties such as stiffness and hardness. Can be used for chairs, tables, hockey sticks, baseball bats, tennis rackets, etc.
    • Haya: similar to the previous one in terms of resistance, but it is more flexible. Therefore, you can build pieces of furniture with curved shapes without splintering. Being odourless, it can also be used for spoons, plates, glasses, cutting boards, etc. Of course, this wood is not recommended for carving.
    • Abedul: it is very hard, similar to that of oak or walnut. Its color is clear, it does not dent easily, it has good strength, and it holds screws well. Therefore, it can be used for reinforcement of furniture structures.
    • Cerezo: It has a light reddish brown color, good strength, is not easily deformed, easy to carve, and is hard. Therefore, it can be used for carved ornaments, furniture, musical instruments, etc. But care must be taken when working with blunt tools, as they could generate burn marks due to friction.
    • Olmo: Light to medium reddish brown, high hardness, and great for cutting boards, furniture, decorative panels, hockey bats and sticks, etc. Of course, it can be damaged if a low power spindle is used to cut it by its fibers.
    • Mahogany: It is very popular for its appearance and solidity, with a deep reddish-brown hue. It is highly resistant to water damage and is suitable for building boats, chalices, furniture, musical instruments, flooring (parquet), etc.
    • Arce: it is one of the hardest and most durable, and does not need too much treatment after machining. Ideal for desks, work tables, floors, butcher cutting boards, and other instruments that need to withstand "rough treatment."
    • Roble : a wood resistant to breakage, resistant to moisture and weather, and heavy, as well as interesting from an aesthetic point of view. That is why it can be used for outdoor furniture, shipbuilding, etc. Due to its cross-grain characteristics, you will want to make shallow passes for its cut, and better use carbide-tipped cutters.
    • Nogal: It is an expensive wood, with a strong brown color. But it is shock resistant, it is hard, it does not burn easily during machining, although shallow passes should be made for the cuts to avoid breaking. The applications for this material can be from gun stocks, to sculptures and relief carvings, through turned bowls, furniture and musical instruments.
  • Soft woods: They are a good choice for beginners or types of CNC machines that are not too powerful. In addition, being cheaper and easier to find, they can be recommended for low-cost carpentry. They even have another positive aspect, and that is that they do not cause so much wear on the tools. However, they do not have the same properties as the hard ones. Some common examples are:
    • Cedar: It has a pleasant aroma, and a quite nice reddish-brown tone, with knots that can make milling difficult. It is weather resistant, so you will be able to make outdoor furniture, boats, fences, posts, etc. Does not burn easily at slow machining speeds like hard ones.
    • Cypress: it has good resistance to decomposition, it is soft, easy to work with, although it has knots that can make it difficult to work with large blocks. It can be used for cabinets, furniture, windows, trim, and paneling.
    • Abeto: easy to work wood, with a consistent pattern, soft, and durable. Despite not being among the hardwoods, it can also be used for floors.
    • Pine: It is a cheap wood, with a pale color and light weight. Holds its shape well and doesn't shrink too much. It is hard enough to make carving machining difficult. Cut lengths should be reduced to prevent chipping, and faster spindle speeds should be used to prevent damage.
    • Redwood: wood with a red hue, very resistant to decay and sunlight. It is easy to machine and the result is very smooth. It can be a good choice for carving, creating intricate details, or for objects that will be outdoors. Of course, very sharp tools must be used to avoid chipping and tearing.
    • Abeto: It is one of the hardest within the spectrum of softwoods. It is light, but susceptible to decay. It's easy to work with, and it's affordable. It can be good as panels, musical instruments, furniture, etc.
    • MDF: This acronym refers to medium-density fiberboard, a type of engineered (man-made) wood used for furniture, doors, etc. It is very cheap as it is made from hard and soft wood waste combined with wax and resins. It is denser than plywood and works easily, without chipping or breaking easily (feed and spindle speeds must be adequate, as they heat up fairly quickly and can burn), and will have a smooth finish. However, it can have better resistance in one direction than another, something that is not positive for parts that must be robust or for structures. Another important detail is the aesthetic, since it does not offer the grain of natural wood, so it requires painting, or the use of decorative sheets. As a precaution, say that the fine particles that are inhaled during the processes with MDF are harmful to health, since it is not just wood. Wear a mask.
    • Plywood: It is made of multiple thin sheets of wood that are glued together. It weighs less than other solid woods, and may be suitable for hanging cabinets, and other low cost, low cost things. You have to take precautions when working it with any type of CNC machines, as it tends to chip

You should also consider other aspects important when choosing the right wood for your project:

  • Grain size: fine grain belongs to softwoods, coarse grain to hardwoods. The fine-grained one is easier to mill, but the coarse-grained one offers greater smoothness and a better finish.
  • moisture content: Interferes with the flex and durability of the wood, as well as the finish during carving and the feed rates you can achieve. The ideal for carving is wood between 6-8% humidity. The humidity will also determine the temperature of the tool during the process, and for every 1% humidity that goes up, the temperature will increase by about 21ºC. Also, low humidity can cause the surface to tear excessively and too much humidity can cause more fuzzy surfaces.
  • Knots: these are areas where the branches join the trunk, and they usually have fibers in different directions and are harder and darker. When working with a CNC machine, the sudden change in hardness could cause shock loading, so you should use proper parameters or use directions that avoid these knots.
  • advance rate: is the feedrate at which the tool passes over the part surface. If it is too low it can cause burns on the surface of the wood, and if it is too high it can cause splinters. Most machine models usually have different settings to work with multiple materials, others will need you to adjust them manually.
  • ToolsNote: In addition to choosing CNC machines with spindles rated at least 1 to 1.5 hp (0.75 to 1.11 kW) to achieve proper machining speeds for wood, the tool used (and replacement when worn or dull) is also important:
    • rising cut: They remove chips in an upward direction, and can tear the top edge of the workpiece.
    • downward cut: They push the cut wood down, giving a smooth top edge, but can cause tearing on the bottom edge.
    • straight cut: They are not at an angle to the cutting surface, so they offer a balance between the previous two. On the contrary, they have that the speed of removal of the material is not as fast and they tend to heat up more.
    • Compression: It is a kind of tool that has a length of a few millimeters and can achieve cutting up or down by controlling the depth of cut. This allows for smooth top and bottom edge finishes.

Other materials

Of course, there are CNC machines that can work with multiple materials by interchanging the tools. Also other types of CNC machines ranging beyond wood and metal. Some other examples of materials suitable for CNC are:

  • Nylon: A low-friction thermoplastic polymer that can be used as an alternative to metal in some cases. It is a rigid, strong, impact resistant material with good chemical resistance and surprisingly elastic. It can be used for tanks, electronic parts, gears, etc.
  • Foams: a material that can have different stiffness values ​​and is very light and durable.
  • other plastics: such as POM, PMMA, acrylic, ABS, polycarbonate or PC, and polypropylene or PP, polyurethane, PVC, rubber, vinyl, rubber…
  • ceramics and glass: alumina, SiO2, tempered glass, clay, feldspar, porcelain, stoneware, etc.
  • Fibers: fiberglass, carbon fiber…
  • multi-material: ACM or sandwich panels.
  • Paper and cardboard
  • marble, granite, stone, silicon,…
  • Leather and other fabrics

According to their axes

The types of CNC machines according to their axes will determine the number of degrees of freedom of movement and the complexity of the pieces that can work The most prominent are:

3-axis CNC machine

xyz

machining 3 axis, or 3-axis CNC machines, allows the work tool to operate in three dimensions or directions called X, Y and Z. These types of machines are often used for machining 2D, 2.5D, and 3D geometry. Many of the cheap CNC machines usually have this axis configuration, and also many industrial ones, since it is one of the most common configurations.

  • X and Y axis: these two axes will work the part horizontally.
  • Z axis: Allows the tool vertical degrees of freedom.

3-axis CNC machining was an evolution from rotary turning. The part will occupy a stationary position while the cutting tool moves along these three axes. Ideal for parts without intricate detail or depth.

4-axis CNC machine

cnc machines 4 axis they are similar to the previous ones, but an additional axis is added for the rotation of the piece. The fourth axis is called axis A and will rotate while the machine is not working the material. Once the part is in the correct position, a brake is applied to that axis and the XYZ axes continue to machine the part. There are some machines that allow XYZA to be moved simultaneously, and they are known as continuous machining CNC machines.

This type of CNC machines can create a greater degree of detail than the previous ones, and can be suitable for parts with cavities, arches, cylinders, etc.. These types of machines usually have two problems, such as the wear of the worm gear if it is used intensely, and there may be play in the shaft that can affect the precision or reliability of the machine due to vibrations.

5-axis CNC machine

5 axis cnc

a cnc machine 5 axis it is based on a tool with 5 degrees of freedom or different directions. In addition to X, Y, and Z, you have to add the rotation with the A axis as in the four axis, and another additional axis called the B axis. This ensures that the tools can approach the part in all directions in a single operation, without the need to manually re-position the part between operations. The a and b axis they will be intended to bring the workpiece closer to the tool that will move in XYZ.

These types of machines were introduced in the XNUMXst century, allowing higher degree of complexity and high precision. They are often widely used in medical applications, research and development, architecture, the military industry, in the automotive sector, etc. The biggest drawback is that CAD/CAM design can be complicated, plus they are often expensive machines and require highly skilled operators.

Others (up to 12 axes)

12 axis CNC, kinds of CNC machines

Source: www.engineering.com

In addition to 3, 4 and 5 axis, there are types of CNC machines with more axes, even up to 12. These are more advanced and expensive machines, although not as common. Some examples are:

  • 7 axes: Allows you to create long, thin parts with a lot of detail. In these types of CNC machines we have the axes for right-left, up-down, back-forward motion, tool rotation, workpiece rotation, tool head rotation, and work clamp motion.
  • 9 axes: This type combines a lathe with 5-axis machining. The result is that you can turn and mill along multiple planes with a single setup, and with great precision. In addition, it does not need secondary accessories or manual loading.
  • 12 axes: they have two VMC and HMC heads, each one of them allowing movements in the X, Y, Z, A, B and C axes. These types of machines offer improved productivity and precision.

Depending on the tool

Depending on the tool that mounts the CNC machine, we can differentiate between:

  • just a tool: are those that only mount a single tool, be it a drill bit, a milling cutter, a blade, etc. Some of these machines can only perform one type of task, and cannot be tool swapped for another. Others it is possible to change the tool, but it has to be done manually.
  • automatic multitool: They have a head with several tools, and they themselves can switch from one to another automatically as needed.

What is a CNC router or CNC router

cnc router

Un router or cnc router uses a tool head similar to CNC milling machines. However, they have some differences from these. This sometimes generates great confusion, and many confuse them with the CNC cutting machines themselves, or use the term as a synonym for CNC milling.

Differences with other CNC machines

A CNC router works very safely.similar to a CNC machine such as a lathe or milling machine. Routers are widely used for door manufacturing in the woodworking industry, among others. They can do many things, from the carving of the door, the decoration of the panels, engravings such as signs, moldings, cabinetry, etc. Some of the most notable differences with milling machines are:

  • A router is perfect for creating profiles and sheets at high speed. This is another important difference, since CNC milling machines are not designed to work so fast.
  • Generally, CNC milling machines are used to mill/cut harder materials (titanium, steel,…), and CNC routers for softer materials (wood, foam, plastic,…).
  • CNC routers are usually less precise than CNC milling machines, but will allow you to create more parts in less time.
  • A CNC routing machine is significantly cheaper than a milling machine. Some advanced routing machines can cost around €2000, while a CNC milling machine of the same quality would cost around €10.000.
  • CNC routers are often used for machining and cutting large parts (doors, plates,...).
  • As for the difference between CNC router cutting, and cutting by another type of CNC cutting machine, there is the fact that the router uses the rotational speed of its tool to make the cut.
  • One problem with the router for cutting is that it will waste more surface area than other types of cutting, since the entire diameter of the drill bit or milling cutter will be lost.
  • A CNC router makes it easy to cut in 3D.

On the other hand, it also has some similarities, such as milling cutters used as tools, which can also be found with several axes, for different materials (foams, wood, plastic,...), etc.

Types of tools for CNC machines

CNC tools

Source: Fictive

There are also various types of tools for CNC that can be mounted on the work heads. The type of machining that the CNC machine can perform will depend on them, as well as the depth, radius of action, working speed, etc. Some of the most important are:

  • Face or shell strawberry: It is quite common, and they are good for removing material from a wide area. For example, for the initial roughing of a piece.

flat end mill

  • flat end mill: another standard tool that can be seen in different sizes (diameters), and can be used to work the sides and top of a piece, as well as cut. It can also be used to drill cavities.

round end mill

  • Round end mill: it is another type of cutter with a rounded tip, similar to the previous one, but with a slightly rounded edge, for some types of engravings.

 

round bur

  • ball bur: It is completely round at the tip, similar to the round end, but with a more perfect shape. It is ideal for 3D contoured surfaces, and will not leave sharp corners like square ends.

drill

  • Drill: They are the same as drills, a tool for drilling, making tapped holes, precision adjustments, etc. These brushes can be of many different sizes.

male and thread

  • males: if you know the dies, to make threads on the external surface of a piece, the males do the same but inside. That is, while the dies could be used to create a screw, the taps can create nuts.

chamfer milling cutter

  • chamfer milling cutter: It is similar to the face milling cutter, but it is usually shorter and somewhat sharper (they have an angled tip, depending on the desired chamfer, 30º, 45º, 60º, etc.). This type of milling cutter is used to create chamfers in the corners. It can also be used to machine countersinks.

toothed cutter

  • serrated blade: it is a type of cutter in the form of a cutting disk that can be used to make undercuts or grooves, even T-shaped notches passing through the piece.

sierra

  • Longitudinal saw: It is similar to the previous one, but it has a difference, and that is that the disc is usually thinner to cut deep grooves or divide pieces. They also usually have a larger diameter.

reamer

  • Reamer: is a type of tool used to widen existing holes to give them an exact diameter. In addition, they leave a good finish, and have better tolerance than drill bits.

fly cutter

  • fly cutter: It is a type of milling cutter that only has a cutting blade mounted on a bar. That bar can be moved to create a larger or smaller cutting diameter.

radius cutter

  • External radius cutter: is another special tool to add a radius on an outer edge.

engraving tool

  • engraving tool: They are used to engrave images, text or outlines on the surface of a piece.

  • countersink tool: used for countersinking or for chamfers.

dovetail

  • dovetail cutter: it is a tool with a somewhat special shape and that can make an undercut in a material.

CNC control parameters

cnc lathe

Finally, it is also important cknow the machining parameters that interfere with the control of these CNC machines. If you want to perform calculations, you should know that there are many resources that can help you, from apps for mobile devices, to software for PC, through some online calculators. Some examples that you can use for the proper settings of your CNC tools are:

Important machining parameters

As for the the parameters you should know when controlling a CNC machine are:

Parameter Definition Units
n Number of revolutions, that is, the turns per minute during the machining process. In professional machines it is usually between 6000 and 24000 RPM. It is calculated with the formula:

n = (Vc 1000) / (π D)

RPM
D Cutting diameter, that is, the largest diameter of the tool that is in contact with the part at the moment of cutting. mm
Vc Cutting speed. It is the speed with which the machine (lathe, drill, milling...) cuts the chip during machining (the higher D, higher Vc). It is calculated using the formula:

vc = (π D n) / 1000

The maximum speed specified by the tool manufacturer should not be exceeded. Besides:

  • Speed ​​too high:
    • Increased tool wear
    • Poor machining quality
    • Defects in certain materials
  • Speed ​​too low:
    • Poor chip evacuation
    • Excessive heating or tempering of the bur
    • Low productivity and increased cost
    • Defects in certain materials

For example, depending on the material it could be:

  • Aluminum: 350
  • Hardwood: 400
  • Softwood and plywood: 600
  • Plastics: 250 – 600
m / min

(WHO)

Fz Feed per tooth or Chip Load (also known as cl or Chip load). That is to say, it is the amount or thickness of the material that starts each tooth, edge or lip of the tool.
  • To increase Fz, Vc must be increased, RPM must be decreased or a milling cutter with fewer teeth must be used.
  • To decrease Fz you must decrease Vf, increase RPM or use more teeth.

To calculate Fz, you can use the formula:

Fz = Vf / (z n)

And if you want to calculate the feed per revolution:

F = Fz z

mm
Vf Forward speed. It is the length traveled by the tool on the part per unit of time. The formula is:

Vf = F n

Feedrate should be controlled to:

  • Excessive speed:
    • Better chip control
    • Minor cutting time
    • Less tool wear
    • Increased risk of tool breakage
    • Rougher machined surface
  • Speed ​​too slow:
    • older chips
    • Better machining surface quality
    • Longer machining time and higher cost
    • Accelerated tool wear
mm / min

(om/min)

Z Number of teeth of the cutter or tool. -
ap
Depth of cut, axial depth, or pass depth (may also appear as wc). It refers to the depth that the tool achieves with each pass. A shallower depth will force more passes.

It depends on the maximum height of cut (LC or I), the diameter of the cutter (S or D). And it can be controlled, for example, to double the depth of cut you have to reduce the chip load by 25%.

mm
ae Width of cut, or radial cut depth. Similar to above. mm

These are the values that you can obtain from the CNC machine manufacturer's manual, software, or calculators, in order to adjust the parameters for the type of machining (according to the limits of the model and technical characteristics), the material of the tool itself (they can break, bend , overheating,... if they are not suitable), and the material used (it could generate poor machining, defects in the part,...). And all these parameters are also included in the G-Code, such as S commands to modify RPM, forward speed using G-Code F commands, etc.

Manufacturer information

CNC machine manufacturers provide data on cutting speed, chip load, etc., everything is usually in the manual that came with the machine, in the digital version of the manual that you can find on the official website of the brand of the CNC. machine, or also your data sheets. Make sure it is for your specific model, as it could vary between models, despite being from the same machine.

From these data it is possible to calculations manually, using the formulas in the table above, or using online calculators, apps, or software. In case you do not have the manufacturer's data, then you have several options:

  • Use experience to guide you, always starting with more conservative parameter values ​​so as not to force. That is, a kind of trial and error. In the guild it is usually called the listen and measure method, that is, checking that the machine is doing the job properly in terms of cutting and finishing, and adjusting the parameters to make the necessary corrections.
  • Use the manual or table of values ​​from another manufacturer that has similar characteristics (D, number of teeth, material,...).

Learn More


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