How to choose a CNC router machine?
Check out the variety of 3D models on our website. You may be already thinking: “Isn’t it time for me to take the virtual stuff in my own hands?” “Where to begin? How? With what? This is so COMPLICATED!” – you say. Do not be afraid, you can handle it. The only thing needed is your willingness to learn and in this series of articles we will reveal many secrets of choosing a CNC router and working with it.
First, let’s decide which CNC router you want to start your milling career with. The vast majority of CNC router machines have similar design and differ only in size and specifications of the main elements. The mechanical subsystem of the machine consists of a bed, a working table with clamping devices for securing the workpiece, a movable portal with a spindle, a collet chuck and an collet for securing the tool, stepper motors for moving the spindle on the portal and moving the portal along the bed and a number of other auxiliary parts and optionally additional accessory. In small desktop CNC routers, the portal is made motionless relative to the bed; the table is movable relative to the bed. The operation of the engines is controlled by software that helps turn a virtual model into a real product.
When choosing a CNC milling machine for wood, pay attention to the following:
What typical products do you want to do on a CNC router? The number of products processed simultaneously. Processing speed.
What material do you plan to process? CNC router machines work with wood, plastic, wax, organic glass, rubber, acrylic, certain types of metal, composites, foams and etc.
3. The size of the working area.
Dimensions of the machine and its weight. Maximum product sizes? How many planes will be machined? Will there be processing of volumetric, cylindrical parts? CNC routers are usually capable of processing workpieces in three axes, however, this is not the limit. To obtain a high-quality complex contour surface, it is recommended to purchase four- or five-axis equipment, which provides more directions for moving the cutter. Thus, the three linear coordinates (X, Y, Z) indicate the machining space allowed by the machine. The size of the working field is selected based on the parameters of the workpiece. Remember to take into account the space required to install the clamp. One of the rules for high-quality manufacturing of a part is complete processing in one installation on a table, which eliminates multiple readjustments and a decrease in the accuracy and speed of processing on a machine. If you have a small souvenirs or decor elements production, a desktop milling machine will work for you.
The optimal size of the field of desktop machines starts from 300×300 mm. For processing complex and large-sized products, such as facades, doors, advertising structures, the size of the field starts from 1300×2500 mm. If we are talking about the production of large furniture, the best choice is large-format devices with a working area of 2000×3000 mm. A number of possible problems should also be considered, such as the permissible bearing capacity of the machine table. Does the workpiece interfere with the shift tool and whether the workpiece creates interference for other parts of the machine, for example: such as the protective housing of the machine. Is there enough space in your premises for the machine. Can you bring the machine into the premises? Can you move it if necessary?
To increase the speed and productivity of the machine, it can be equipped with additional elements:
- rotary spindle (4th rotary axis) for working with round facades;
- a rotary spindle with a 5th axis for working with complex three-dimensional forms;
- spindles with which you can produce several products at the same time;
- a table with an automatic feed of material, etc.
4. The bed of the milling machine.
The more powerful and stable the bed, the less vibration will be during operation and the higher will be the accuracy of the positioning of the cutter and the quality of work. The material used in the manufacture of the base of the machine affects the carrying capacity. The frame can be made of aluminum, steel pipes or cast iron. The latter is the most stable and allows handling especially massive workpieces.
5. Portal of the machine.
Plate steel should be used for its manufacture; it will serve as a guarantor of rigidity and vibration resistance of the machine. Cheaper machines have an aluminum structure. In the cheapest machines, portals are made of thick plywood or composites. Also, pay attention to the magnitude of the spindle stroke along the Z-axis in order to understand the maximum thickness of the workpiece that this machine can process. Several manufacturers of CNC machines cheapen the design by installing aluminum portals, which negatively affects the quality of products and machine life. It is especially important to take into account the magnitude of the spindle stroke along the Z-axis, since this value minus the length of the cutter and chuck shows how thick the workpiece can be milled. So, for example, if the spindle stroke is 300 mm, it may well be that when subtracting the length of the chuck and the length of the cutter, we get only 120-140 millimeters of the thickness of the workpiece, that is, about half the possible stroke along the Z-axis.
6. Spindle (speed and accuracy, power).
The spindle is considered to be the most important element of milling equipment. The milling accuracy, as well as the materials to be processed, the intensity of the processing modes and the service life of the machine depend on its power and quality. The greater the power of the spindle motor, the higher the rotational speed of the cutter and the greater the cutting force. Rotation speed, in turn, affects processing quality and productivity. The higher the number of spins, the higher the milling quality. There is a recommended speed range for different materials. For milling wood or plastic, power from 800W to 3,2kW is required, depending on the scope and depth of processing. At the same time, machines for the production of souvenirs often use spindles with a power of 120 watts or more.
The maximum speed is:
- up to 8000 rpm for entry-level machines;
- up to 28,000 rpm for professional machines.
It is also worth considering the spindle stroke length along the Z-axis, because the thickness of the workpiece, which the milling machine can process, depends on it. To obtain an accurate value, the length of the cutter and chuck (ISO30 or collet) must be subtracted from the stroke length. The final result will be the maximum allowable thickness of the workpiece. The temperature of the spindle with the cutter rises during operation. Therefore, air or water cooling is used. There are modifications of industrial CNC routers with 2 spindles to increase efficiency and processing speed.
7. Working table.
When choosing a CNC router, you should decide on the size of its working field. For house works and small parts, there is no need in large table. The fact is that the larger the table, the longer the guides. Making long guides is expensive, which raises the price of the machine. Extendable table increases the working area. In some models, the moving parts increase the area to 3 meters. It is a hard table that can withstand the weight of a long and heavy workpiece. If you plan to work with large parts, you should choose a CNC routers with a sliding carriage.
8. The engine for moving the portal or table (speed and accuracy).
The power and the quality of the engine determine the accuracy of positioning, moving and ensuring high-speed processing modes. Modern CNC routers processing are equipped with two types of motors: stepper or servo drives. Steppers are reasonably priced but are poorly suited for precision machining. They are characterized by skipping steps, shuttle motions and no coupling with the electronics of the equipment, so there is a likelihood of failure. The servo drives are much more expensive, however, they are characterized by a smooth ride, exceptional accuracy and are equipped with an encoder that informs the controller about all stages of milling and allows timely correction of errors in case of their occurrence.
If you plan to purchase an inexpensive machine with today’s most popular rack and pinion gear or ball screw gears, then a stepper motor is for you. If maximum speed and accuracy are required, then servo drives should be preferred.
9. Cutters. The principle of replacing the cutters.
Before buying equipment, it makes sense to determine the nature of the work and the necessary cutters for its implementation. To carry out the same type of processing with its infrequent replacement, models with manual change will fit in perfectly. If it is necessary to regularly select cutters, it would be practical to purchase a machine with automatic change or a semi-automatic change mechanism. This will not only reduce the time required to complete the work but also increase the accuracy. You have to determine how many units of equipment you need to produce the needed quantity of parts. If it is more than 3 units and their frequent replacement is required, then a machine with a semi-automatic or automatic cutter change is justified from the economic point of view.
In woodworking CNC routers with manual replacement of the cutter, technological stops are provided during which the operator replaces the tool. This is not critical if most of the work is performed by some type of milling cutter alone, since the total temporary downtime is negligible.
Mills of various shapes are used as an executive cutting tool in milling machines:
- disk milling cutter;
- corner milling cutter;
- end mill;
- shaped milling cutter;
- cylindrical cutters.
Due to a wide variety of cutters, the machine is a universal device. Before choosing a milling machine, you need to decide which cutters you will use. Pay attention to whether the dimensions of the shank of the cutter correspond to the dimensions of the chuck, i.e. whether you can fix the desired type of cutters in a particular machine.
10. Rack control.
There are two types of control of CNC routers: using a computer with special software installed or a specialized stand-alone stand. The rack is essentially a standalone CNC control unit with a display or remote control (DSP controller). When using a computer, the software is used both for modeling and for work, it is possible to emulate the process and display it graphically. Stand-alone racks provide better integration and stability since they are directly connected to the control board of the CNC machine and are also protected from dust. That is why the rack is installed in most professional machines.
Check out the software that comes with the machine. As a rule, these are obsolete programs, such as Type3 or UcanCam, which are inconvenient to use, especially for 3D processing. One of the best solutions available on the market today is ARtCam, which provides clear and intuitive access to all the necessary functions. The task setting for all CNC systems occurs using a universal programming language in the form of a control program code, which is called the G-code. The control program consists of a sequential set of frames, each of which is responsible for one step in the operation of the machine.
The type of equipment and the list of tasks necessary to perform the tasks affect the choice of the program for controlling the CNC machine. Different types of software differ in their functionality and PC requirements. However, there are universal solutions that are compatible with all types of CNC devices and modern computers. The most common are LinuxCNC, Mach3 and 4, MeshCAM, SimplyCam, CutViewer, CadStd, Cut2D, Cut3D, VCarve, PhotoVCarve, Aspire, ArtCAM. To work with flat forms, you can use any graphic (CorelDraw, Photoshop) or drawing (AutoCAD) software packages. You can use 3ds Max, Solidworks, AutoCAD, or other similar products for 3D modeling.
12. Machine maintenance.
One of the most important factors that you should pay attention to is the availability of a service department that will carry out installation supervision, commissioning and subsequent maintenance of the equipment you purchased.
What can you afford? The price of entry-level CNC routers ranges from $150 to $500 including delivery. Professional machines cost from $10,000.