The fourth axis for a cnc machine. Four-axis machining on a machine with a rotary axis

The rotary axis is designed to ensure the rotation of parts to the required angle. It is a rotary mechanism that allows you to rotate the workpiece in the required direction and at a certain angle. The 4 rotary axis can be used to process workpieces made of materials such as plastic and wood. In addition, the axis is also used for engraving metals. The rotary axis for the CNC milling machine allows you to create products of varying complexity: it can be used to make balusters, handles, engraved decor elements, various figurines and other complex shapes.

Exist rotary axes on a belt and harmonic gearbox. What is their difference? The first option is more suitable for processing plastic and wood, and the second is more suitable for working with hard materials, in particular, with metal. In addition, the axles are divided into 3 and 4 cam axles. The axis of the first type is designed for centering round workpieces, and the 4-jaw axis is for rectangular workpieces.

Benefits of rotary axis for milling machine,

What are the benefits rotary axis? This part significantly expands the capabilities of CNC machines: thanks to the positioning of the workpiece in space, the manufacture of complex products becomes available. The use of a rotary axis solves the problem of automation of the work performed: after its installation, the processing of workpieces begins to be carried out automatically. Besides, rotary axis cnc will significantly reduce the time for the manufacture of the product. And, of course, the rotary axis makes work on the CNC machine not only faster, but also more comfortable: after installing the axis, the need to rearrange the workpiece disappears, since it only needs to be clamped once for processing. It is important to note that the installation of a rotary axis is not difficult: as a rule, the axes are suitable for any machine, and standard programs allow the connection of these devices, so you do not need to reconfigure them.

Thus, CNC rotary axis for machine tools makes it possible to produce high-quality products that require high accuracy in the shortest possible time. Accordingly, the installation of a rotary axis will significantly increase productivity and increase profits.

In the three-dimensional coordinate system familiar to us, there are three mutually perpendicular axes (X, Y, Z), which form the basis.
Most of the CNC machines in the initial-basic version only do 3-axis machining.
However, for some products of complex shape, this is not enough. Due to the additional modification - the installation of a rotary axis, CNC engraving and milling machines are capable of performing 4-axis processing.
Four-axis machining on an engraving-milling machine on a CNC machine using a rotary axis is generally continuous machining of both symmetrical and non-symmetrical bodies.
Unlike conventional 3-axis machining of a 3D model, where the part must be attached on one side to the CNC machine table, 4-axis milling makes it possible to process the product from all sides continuously, without additional operations for rearranging the part on the desktop. This makes it possible to obtain products of complex shape. The manufacture of balusters, capitals, columns, pillars, legs of tables and chairs, chess pieces, as well as various figurines, rings of other jewelry and promotional souvenirs are the most common examples of such processing.
The variety of shapes, contours - any flight of fancy will be embodied in the processing of parts on an engraving and milling machine using the 4th rotary axis.
The main option for modifying, as mentioned earlier, a 3-axis machine to a 4-axis machine is the use of a rotary axis, figures 1 and 2.

Figure 1 shows a photograph of a rotary axis for a CNC machine, which allows for multi-sided processing.

Figure 1 Rotary axis for a CNC machine.

CNC milling modeler3040

Video of cutting a complex shape using a rotary axis using the example of a chess knight

Installation of a rotary axis on a 3-axis milling CNC cnc-3040al300

Figure 2 4 axis CNC milling machine

In addition, for continuous processing along 4 axes, the CNC system of the machine must still be able to control the repeated axis installed on it. Therefore, 4-axis machining implies not only the presence of a rotary axis, but also the use of an appropriate CNC system. Most often, a stepper motor controller with 4 control channels or, more simply, a 4-axis controller is used for this. An example of a controller is shown in Figure 3. Channel A of this controller can be used to control a rotary axis installed on the machine.

Figure 3

There are two types of 4-axis machining: the first is continuous and the second is positional machining (machining with indexing). Continuous processing - in this case, the cutter simultaneously moves through all degrees of freedom.
Positional processing - the rotary axis is used only to change the position of the workpiece, and the rest of the operations are performed in the three-dimensional processing mode.

To work with a rotary axis, it is necessary to configure the control program. Below are the settings for Mach3 for 6:1 and 4:1 rotary axes. Figure 4 shows the pin settings of the LPT port for the aluminum cased stepper motor controller shown in Figure 3.

Figure 4

Figure 5 - settings for a rotary axle with a ratio of 4:1.

Figure 5

Figure 6 - settings for a rotary axle with a ratio of 6:1.

Figure 6

Figure 7

Control programs for working with multi-sided processing are available in DeskProto, PowerMill, etc.

Figure 8 shows the result of multi-sided machining on a 4-axis milling CNC CNC-3040AL2

Figure 8. Multi-sided machining on a 4-axis desktop CNC using a rotary axis

After considering the design options for the long axis - X - we can move on to considering the Y axis. The Y axis in the form of a portal is the most popular solution in the hobby machine tool community, and for good reason. This is a simple and quite working, well-proven solution. However, it also has pitfalls and points that need to be clarified before designing. For the portal, stability and proper balance are extremely important - this will reduce wear on guides and gears, reduce beam deflection under load, and reduce the likelihood of wedging when moving. To determine the correct layout, let's look at the forces applied to the portal during the operation of the machine.

Consider the diagram carefully. It has the following dimensions:

• D1 - distance from the cutting area to the center of the distance between the guide beams of the portal
• D2 is the distance between the X-axis drive screw to the lower guide beam
• D3 - distance between Y-axis guides
• D4 - distance between the linear bearings of the X axis

Now let's look at the current efforts. In the picture, the gantry moves from left to right by turning the X-axis drive screw (located at the bottom), which drives the nut fixed on the bottom of the gantry. The spindle is lowered and mills the workpiece, while there is a reaction force directed towards the movement of the portal. This force depends on the gantry acceleration, feed rate, spindle rotation and kickback force from the cutter. The latter depends on the cutter itself (type, sharpness, lubrication, etc.), rotation speed, material and other factors. A lot of literature on the selection of cutting conditions is devoted to determining the amount of recoil from the cutter, at present it is enough for us to know that when the portal moves, a complex reaction force F arises. The force F applied to the fixed spindle is applied to the portal beam in the form of a moment A = D1 * F. This moment can be decomposed into a pair of equal in magnitude, but oppositely directed forces A and B, applied to guides #1 and #2 of the portal beam. Modulo Force A = Force B = Moment A / D3. As you can see from here, the forces acting on the guide beams decrease if you increase D3 - the distance between them. Reducing forces reduces guideway wear and torsional deformation of the beam. Also, with a decrease in force A, the moment B applied to the sidewalls of the portal also decreases: Moment B \u003d D2 * Force A. Due to the large moment B, the sidewalls, being unable to bend strictly in a plane, will begin to twist and bend. The moment B must also be reduced because it is necessary to strive to ensure that the load is always distributed evenly over all linear bearings - this will reduce elastic deformations and vibrations of the machine, and, therefore, increase accuracy.

Moment B, as already mentioned, can be reduced in several ways -

1. reduce force a.
2. reduce leverage D3

The goal is to make the forces D and C as equal as possible. These forces are made up of a pair of moment B forces and the weight of the portal. For correct weight distribution, the center of mass of the gantry must be calculated and placed exactly between the linear bearings. This explains the common zigzag design of the sidewalls of the portal - this is done in order to move the guides back and bring the heavy spindle closer to the X-axis bearings.

In summary, when designing the Y axis, consider the following principles:

• Try to minimize the distance from the X-axis drive screw/rails to the Y-axis rails - i.e. minimize D2.
• If possible, reduce the spindle overhang relative to the beam, minimize the distance D1 from the cut area to the guides. The optimal Z travel is usually considered to be 80-150 mm.
• Reduce the height of the entire portal if possible - a high portal is prone to resonance.
• Calculate in advance the center of mass of the entire gantry, including the spindle, and design the gantry legs so that the center of mass is located exactly between the X-axis rail carriages and as close as possible to the X-axis lead screw.
• Extend the portal guide beams further - maximize D3 to reduce the moment applied to the beam.

The next step is to choose the structure of the most important part of the machine - the Z axis. Below are 2 examples of design.

As already mentioned, when building a CNC machine, it is necessary to take into account the forces that arise during operation. And the first step on this path is a clear understanding of the nature, magnitude and direction of these forces. Consider the diagram below:

Forces acting on the Z axis

The diagram shows the following dimensions:

• D1 = Distance between Y-axis guides
• D2 = distance along the guides between the Z-axis linear bearings
• D3 = length of the movable platform (base plate) on which the spindle is actually mounted
• D4 = width of the entire structure
• D5 = distance between Z-axis guides
• D6 = base plate thickness
• D7 = vertical distance from the point where the cutting forces are applied to the middle between the carriages along the Z axis

Let's look at the front view and note that the entire structure moves to the right along the Y-axis guides. The base plate is extended as far as possible down, the cutter is deepened into the material, and during milling, a reaction force F arises, directed, of course, opposite to the direction of movement. The magnitude of this force depends on the spindle speed, the number of cutter starts, feed speed, material, sharpness of the cutter, etc. start of machine design). How does this force affect the Z axis? When applied at a distance from the place where the base plate is fixed, this force creates a torque A = D7 * F. The moment applied to the base plate is transmitted through the Z-axis linear bearings in the form of pairs of shear forces to the guides. The force converted from the moment is inversely proportional to the distance between the points of application - therefore, in order to reduce the forces bending the guides, it is necessary to increase the distances D5 and D2.

Distance D2 is also involved in the case of milling along the X-axis - in this case, a similar picture arises, only the resulting moment is applied on a noticeably larger lever. This moment tries to turn the spindle and the base plate, and the resulting forces are perpendicular to the plane of the plate. In this case, the moment is equal to the cutting force F, multiplied by the distance from the cutting point to the first carriage - i.e. the larger D2, the smaller the moment (with the same length of the Z axis).

This implies the rule: all other things being equal, you must try to space the carriages of the Z axis away from each other, especially vertically - this will significantly increase the rigidity. Make it a rule to never make D2 less than 1/2 the length of the base plate. Also make sure that the D6 platform is thick enough to provide the desired rigidity by calculating the maximum working forces on the cutter and simulating insert deflection in CAD.

Total, adhere to the following rules when designing the Z axis of the portal machine:

• maximize D1 - this will reduce the moment (and hence the forces) acting on the portal posts
• maximize D2 - this will reduce the moment acting on the gantry beam and the Z axis
• minimize D3 (within the given Z travel) - this will reduce the moment acting on the beam and gantry posts.
• maximize D4 (distance between y-axis carriages) - this will reduce the moment acting on the gantry beam.

Well, a separate plus is linear bearings immediately in the housing, since it is easier to install them on home-made structures. Simple LM08UU are cheaper, but you need to make a holder for them (you can print on a printer) - this is a separate conversation.

So, a few words about the set of components for the new Y-axis, then about the refinement. Received the parcel 3 weeks after ordering, in a postal bag and a narrow cardboard box for strength. This is a plus, it’s just that cylindrical shafts fall out of my package, for some reason the sellers don’t think about this on Ali. But in vain.


Each nomenclature from the set is packed separately in a bag. There are traces of oil in the bearings


To assess the scale, I attached a ruler to the guides and the screw. Ruler 30 cm, iron 40 cm


The ends of the screw and shafts are free of burrs. It seems that the shafts are cut into standard sizes from a large whip, as a little bit of soot is noticeable on the end. But processed after cutting. In principle, I can carry out the same operation on my own, so I try to take as long segments as possible.


The ends are chamfered. If you cut yourself (and I cut a little to size), then the bevel can be removed on a grinder / manually. It is mainly decorative so that there are no burrs and when installing the bearings it does not touch the balls.


I did not catch microns, the shaft diameter is quite 8 mm. There are no questions about the accuracy of manufacturing cylindrical shafts, the main thing is that they are not bent during delivery. I have more complaints about bearings. I took several lots of cheap LM08UUs on Ali, and so some are tight, and some are slightly loose. On bearings, this is noticeably strong, especially if installed on the same shaft.


SK8 calipers are handy. They are installed immediately on the profile (any), and the shaft is clamped. If desired, it can be used in amateur designs, for clamping anything with a diameter of 8mm (for example, a center for a machine tool).


Finding the overall and installation dimensions is not a problem, they are standard. If required - write in a personal or look in the first two topics, there were drawings.


Initially, when trying on the design and before ordering, I used 3D printed calipers. Now deleted due to uselessness. With metal it turns out much yo sche design


Calipers-bearings KP08 for fixing the lead screw. There are two 1.5 hex screws for clamping.
These calipers are very convenient to use in amateur designs: they are used in 3D printers for the Z axis, and you can also make homemade belt drives by clamping an 8mm shaft segment in this bearing and installing a gear on the shaft. Note: This copy of the CNC2417 uses KFL08 bearings in the form of a flange to install the T8 screw on the plate on the X axis.


And last but not least, the SC08UU housing linear bearing. It costs a little more (two times) than a simple LM08UU, but it has an M4 thread for installing mounting screws. It is also very convenient to use in amateur designs due to the ease of installation. There is a variant SC08LUU, extended, which I use in the z-axis slider.

Everything about the kit, now about the refinement.

I started the assembly with the X and Y axes, and the carriages, respectively.
First, we assemble the Y axis: engine, caliper, screw with nut and coupling.
We install the engine on the holder. It's simple: four M3 screws. The length is small, mainly depends on the plate used (thickness) and washers.


Engine with plate before installation on the profile.


Next, install KP08 opposite, keeping the distance from the center of the engine axis and from the center of the caliper axis the same




Next, install the SK8 shaft supports, four pieces, a pair per shaft. When installing the shafts, do not forget about the bearings.

Next, we assemble the plate with the X engine, as well as the plate with the KFL08 caliper


The plates are made symmetrical, and it is possible to assemble the screw on the KFL08 on both sides, having previously installed the engine on (M3 Brass Spacer - it is convenient to take in sets).


Initially, there was a 3D printed KFL08, but while I was collecting and testing, I managed to order and get a normal one)))

We assemble the X axis further. Install the plates on the frame


Install the second plate.
The plates provide additional structural rigidity, at the same time they are the holder of the X axis. 3 cylindrical shafts 8 mm are used for reinforcement.


Next, we install shafts (three pieces) plus SC08UU bearings (three pairs, respectively) into the holes of the plates




Closer photo. 10 mm cylindrical shaft on each side are clamped into the SHF08 caliper. And it is advisable to leave about 20 mm of the lead screw for installing the handle (manual movement of the carriage).


We install the plate-carriage X on the bearings. Don't forget the nut. I used a 3D printed nut holder. Buying a holder is quite problematic. Of the options to buy, there is either a flat plastic nut (POM) with holes for fastening right away (options and). I saw it for sale, but the money is expensive. So while the print holder…




We check the free play of the carriage from the beginning to the end of the axis, tighten the screws.


A Z-axis slider is already attached to the plate. You can make them from a section of the 2080 profile and SK8 supports, you can make it yourself,