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 community of hobby machine tool builders, 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 understood before design. Stability and correct balance are extremely important for the portal - this will reduce wear on the guides and gears, reduce the deflection of the beam under load, and reduce the likelihood of wedging during movement. To determine the correct layout, let's look at the forces applied to the portal during operation of the machine.
Take a good look at the diagram. The following dimensions are marked on it:
- D1 - distance from the cutting area to the center of the distance between the portal beam guides
- D2 - distance between the X-axis drive screw to the bottom guide beam
- D3 - distance between Y-axis guides
- D4 - distance between X-axis linear bearings
Now let's look at the actual efforts. In the picture, the portal moves from left to right due to the rotation of the X-axis drive screw (located at the bottom), which drives the nut fixed on the bottom of the portal. The spindle is lowered and mills the workpiece, and a counterforce appears directed towards the movement of the portal. This force depends on the portal acceleration, feed rate, spindle rotation and kickback force from the cutter. The latter depends on the cutter itself (type, sharpness, presence of lubrication, etc.), rotation speed, material and other factors. A lot of literature on the selection of cutting modes is devoted to determining the magnitude of kickback from a cutter; at present, it is enough for us to know that when the portal moves, a complex counterforce F arises. The force F applied to the fixed spindle is applied along the structural elements 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 can be seen from here, the forces acting on the guide beams decrease if D3, the distance between them, increases. Reducing the forces reduces wear on the guides 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 = D2 * Force A. Due to the large moment B, the sidewalls, being unable to bend strictly in the plane, will begin to curl and bend. Moment B must also be reduced because it is necessary to strive to ensure that the load is always distributed evenly across 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 -
- reduce force A.
- reduce leverage D3
The goal is to make the forces D and C as equal as possible. These forces consist of a pair of forces of moment B and the weight of the portal. For proper weight distribution, it is necessary to calculate the center of mass of the portal and place it 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 guides - i.e. minimize D2.
- If possible, reduce the spindle overhang relative to the beam, minimize the distance D1 from the cutting area to the guides. The optimal Z stroke 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 struts so that the center of mass is located exactly between the X-axis guide carriages and as close as possible to the X-axis lead screw.
- Space the portal guide beams farther away - maximize D3 to reduce the moment applied to the beam.
Z AXIS DESIGN
The next step is to select the structure of the most important part of the machine - the Z axis. Below are 2 design examples.
As already mentioned, when building a CNC machine, it is necessary to take into account the forces generated 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 following dimensions are marked on the diagram:
- 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 itself is mounted
- D4 = width of the entire structure
- D5 = distance between Z axis guides
- D6 = base plate thickness
- D7 = vertical distance from the point of application of cutting forces 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 down as possible, the cutter is recessed into the material and during milling a counterforce F arises, directed, naturally, opposite to the direction of movement. The magnitude of this force depends on the spindle speed, the number of cuts of the cutter, feed speed, material, sharpness of the cutter, etc. (we remind you that some preliminary calculations of what materials will be milled, and therefore an assessment of the cutting forces, must be made before the beginning 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 transverse forces to the guides. The force converted from the moment is inversely proportional to the distance between the points of application - therefore, 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 rotate 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 a constant length of the Z axis).
Hence the rule follows: all other things being equal, you should definitely try to space the Z-axis carriages further away from each other, especially vertically - this will significantly increase rigidity. Make it a rule to never make the distance 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 operating forces on the cutter and modeling the insert deflection in CAD.
Total, adhere to the following rules when designing the Z axis of a gantry machine:
- maximize D1 - this will reduce the moment (and therefore the force) acting on the gantry struts
- maximize D2 - this will reduce the moment acting on the portal beam and the Z axis
- minimize D3 (within a given Z stroke) - this will reduce the moment acting on the beam and the portal posts.
- maximize D4 (the distance between the Y-axis carriages) - this will reduce the moment acting on the portal beam.
And so, as part of this instructional article, I want you, together with the author of the project, a 21-year-old mechanic and designer, to make your own. The narration will be conducted in the first person, but know that, to my great regret, I am not sharing my experience, but only freely retelling the author of this project.
There will be quite a lot of drawings in this article., the notes to them are made in English, but I am sure that a real techie will understand everything without further ado. For ease of understanding, I will break the story into “steps”.
Preface from the author
Already at the age of 12, I dreamed of building a machine that would be capable of creating various things. A machine that will give me the ability to make any household item. Two years later I came across the phrase CNC or to be more precise, the phrase "CNC milling machine". After I found out that there are people who can make such a machine on their own for their own needs, in their own garage, I realized that I could do it too. I must do it! For three months I tried to collect suitable parts, but did not budge. So my obsession gradually faded away.
In August 2013, the idea of building a CNC milling machine captured me again. I had just finished my undergraduate degree in industrial design at university, so I was pretty confident in my abilities. Now I clearly understood the difference between me today and me five years ago. I learned how to work with metal, mastered techniques for working with manual metalworking machines, but most importantly, I learned how to use development tools. I hope this tutorial inspires you to build your own CNC machine!
Step 1: Design and CAD model
It all starts with thoughtful design. I made several sketches to get a better feel for the size and shape of the future machine. After that I created a CAD model using SolidWorks. After I modeled all the parts and components of the machine, I prepared technical drawings. I used these drawings to make parts on manual metalworking machines: and.
Frankly speaking, I love good, convenient tools. That is why I tried to make the maintenance and adjustment operations of the machine as simple as possible. I placed the bearings in special blocks in order to be able to quickly replace them. The guides are accessible for maintenance, so my car will always be clean when the work is completed.
Files for downloading “Step 1”
dimensions
Step 2: Bed
The bed provides the machine with the necessary rigidity. A moving portal, stepper motors, a Z axis and a spindle, and later a working surface will be installed on it. To create the supporting frame I used two 40x80mm Maytec aluminum profiles and two 10mm thick aluminum end plates. I connected all the elements together using aluminum corners. To strengthen the structure inside the main frame, I made an additional square frame from profiles of a smaller section.
In order to avoid dust getting on the guides in the future, I installed protective aluminum corners. The angle is mounted using T-nuts, which are installed in one of the profile grooves.
Both end plates have bearing blocks for mounting the drive screw.
Support frame assembly
Corners to protect guides
Files for downloading “Step 2”
Drawings of the main elements of the frame
Step 3: Portal
The movable portal is the executive element of your machine; it moves along the X axis and carries the milling spindle and Z axis support. The higher the portal, the thicker the workpiece that you can process. However, a high portal is less resistant to the loads that arise during processing. The high side posts of the portal act as levers relative to the linear rolling bearings.
The main task that I planned to solve on my CNC milling machine was the processing of aluminum parts. Since the maximum thickness of the aluminum blanks that suit me is 60 mm, I decided to make the portal clearance (the distance from the working surface to the upper cross beam) equal to 125 mm. I converted all my measurements into a model and technical drawings in SolidWorks. Due to the complexity of the parts, I processed them on an industrial CNC machining center; this additionally allowed me to process chamfers, which would be very difficult to do on a manual metal milling machine.
Files for downloading “Step 3”
Step 4: Z Axis Caliper
For the Z axis design, I used a front panel that attaches to the Y axis motion bearings, two plates to reinforce the assembly, a plate to mount the stepper motor, and a panel to mount the milling spindle. On the front panel I installed two profile guides along which the spindle will move along the Z axis. Please note that the Z axis screw does not have a counter support at the bottom.
Downloads “Step 4”
Step 5: Guides
Guides provide the ability to move in all directions, ensuring smooth and precise movements. Any play in one direction can cause inaccuracy in the processing of your products. I chose the most expensive option - profiled hardened steel rails. This will allow the structure to withstand high loads and provide the positioning accuracy I need. To ensure the guides were parallel, I used a special indicator while installing them. The maximum deviation relative to each other was no more than 0.01 mm.
Step 6: Screws and Pulleys
Screws convert rotary motion from stepper motors into linear motion. When designing your machine, you can choose several options for this unit: a screw-nut pair or a ball screw pair (ball screw). The screw-nut, as a rule, is subjected to more frictional forces during operation, and is also less accurate relative to the ball screw. If you need increased accuracy, then you definitely need to opt for a ball screw. But you should know that ball screws are quite expensive.
When choosing a CNC router decide:
1. what material are you going to work with? The requirements for the rigidity of the milling machine structure and its type depend on this.
For example, a CNC machine made of plywood will allow you to process only wood (including plywood) and plastics (including composite materials - plastic with foil).
Using an aluminum milling machine, you can also process blanks of non-ferrous metals, and the processing speed of wood products will also increase.
Aluminum milling machines are not suitable for processing steel; massive machines with a cast iron frame are needed here, while processing non-ferrous metals on such milling machines will be more efficient.
2. with the size of the workpieces and the size of the working field of the milling machine. This determines the mechanical requirements of a CNC machine.
When choosing a machine, pay attention to studying the mechanics of the machine; the capabilities of the machine depend on its choice, and it is impossible to replace it without significant alteration of the design!
The mechanics of a CNC milling machine made from plywood and aluminum are often the same. Read more below in the text.
But the larger the size of the working field of the machine, the more rigid and expensive linear movement guides will be required for its assembly.
When choosing machines for solving problems of manufacturing tall parts, with large differences in heights, there is a common misconception that it is enough to choose a machine with a large working stroke along the Z axis. But even with a large stroke along the Z axis, it is impossible to produce a part with steep slopes if the height of the part is greater than the working length of the cutter, that is, more than 50mm.
Let's look at the design of a milling machine and the selection options using the Modelist series CNC machines as an example.
A) Selection of CNC machine design
There are two options for constructing CNC machines:
1) designs with movable table, picture 1.
2) design with movable portal, Figure 2.
Picture 1Milling machine with movable table
Advantages The design of a machine with a movable table is ease of implementation, greater rigidity of the machine due to the fact that the portal is stationary and fixed to the frame (base) of the machine.
Flaw- large dimensions compared to a design with a movable portal, and the inability to process heavy parts due to the fact that the movable table carries the part. This design is quite suitable for processing wood and plastics, that is, lightweight materials.
figure 2 Milling machine with a movable portal (gantry machine)
Advantages designs of a milling machine with a movable portal:
Rigid table that can withstand heavy workpiece weight,
Unlimited workpiece length,
Compactness,
Possibility of making the machine without a table (for example, to install a rotary axis).
Flaws:
Less structural rigidity.
The need to use more rigid (and expensive) guides (due to the fact that the portal “hangs” on the guides, and is not fixed to the rigid frame of the machine, as in a design with a movable table).
B) Selection of CNC Router Mechanics
The mechanics are presented (see numbers in Fig. 1, Fig. 2 and Fig. 3):
3 - guide holders
4 - linear bearings or sliding bushings
5 - support bearings (for fastening the lead screws)
6 - lead screws
10 - coupling connecting the lead screw shaft to the shaft of stepper motors (SM)
12 - running nut
figure 3
Selecting a linear movement system for a milling machine (guides - linear bearings, lead screw - lead nut).
The following can be used as guides:
1) roller guides, Figure 4.5
Figure 4 
Figure 5
This type of guides found its way into the designs of amateur lasers and machines from the furniture industry, Figure 6
The disadvantage is low load capacity and low service life, since they were not originally intended for use in machines with a large number of movements and high loads, the low strength of the aluminum profile of the guides leads to collapse, Figure 5 and, as a result, irreparable play, which makes the further use of the machine unsuitable.
Another version of roller guides, Figure 7, is also not suitable for high loads and therefore is used only in laser machines.
Figure 7
2) round guides, are a steel shaft made of high-quality wear-resistant bearing steel with a ground surface, surface hardening and hard chrome plating, shown under number 2 in Figure 2.
This is the optimal solution for amateur designs, because... cylindrical guides have sufficient rigidity for processing soft materials with small CNC machine sizes at a relatively low cost. Below is a table for choosing the diameter of cylindrical guides depending on the maximum length and minimum deflection.
Some Chinese Manufacturers of cheap machines I install guides of insufficient diameter, which leads to a decrease in accuracy, for example, when using an aluminum machine at a working length of 400 mm, guides with a diameter of 16 mm will lead to deflection in the center under its own weight by 0.3..0.5 mm (depending on the weight of the portal).
With the correct choice of shaft diameter, the design of machines using them is quite strong; the large weight of the shafts gives the structure good stability and overall structural rigidity. On machines larger than a meter, the use of round guides requires a significant increase in diameter to maintain minimal deflection, which makes the use of round guides an unreasonably expensive and heavy solution.
| Axial length | Plywood machine | Aluminum machine for woodworking | Aluminum machine for aluminum work | |
| 200mm | 12 | 12 | 16 | 12 |
| 300mm | 16 | 16 | 20 | 16 |
| 400mm | 16 | 20 | 20 | 16 |
| 600mm | 20 | 25 | 30 | 16 |
| 900mm | 25 | 30 | 35 | 16 |
3) profile rail guides
Polished shafts on large machines are being replaced by profile guides. The use of support along the entire length of the guide allows the use of guides of significantly smaller diameters. But the use of this type of guides imposes high demands on the rigidity of the supporting frame of the machine, since beds made of sheet duralumin or sheet steel themselves are not rigid. The small diameter of the rail guides requires the use of a thick-walled steel professional pipe or a large-section structural aluminum profile in the design of the machine to obtain the necessary rigidity and load-bearing capacity of the machine frame.
The use of a special shape of the profile rail allows for better wear resistance compared to other types of guides.
Figure 8
4) Cylindrical guides on a support
Cylindrical guides on a support are a cheaper analogue of profile guides.
Just like profile ones, they require the use of large-section professional pipes in the machine frame rather than sheet materials.
Advantages - no deflection and no spring effect. The price is twice as high as cylindrical guides. Their use is justified for travel lengths above 500mm.
figure 9 Cylindrical guides on a support
The movement can be done as follows: bushings(sliding friction) - Fig. 10 on the left, and using linear bearings(rolling friction)- rice. 10 on the right.
figure 10 Bushings and Linear Bearings
The disadvantage of sliding bushings is the wear of the bushings, leading to the appearance of backlash, and increased effort to overcome sliding friction, requiring the use of more powerful and expensive stepper motors (SM). Their advantage is low price.
Recently, the price of linear bearings has dropped so much that their choice is economically feasible even in inexpensive hobby designs. The advantage of linear bearings is a lower coefficient of friction compared to sliding bushings, and, accordingly, most of the power of stepper motors goes to useful movements, and not to combat friction, which makes it possible to use motors of lower power.
To convert rotational motion into translational motion on a CNC machine, it is necessary to use a screw drive ( lead screw ). Due to the rotation of the screw, the nut moves forward. Can be used in milling and engraving machines helical sliding gears And helical rolling gears .
The disadvantage of the sliding screw transmission is the rather high friction, which limits its use at high speeds and leads to wear of the nut.
Sliding helical gears:
1) metric screw. The advantage of a metric screw is its low price. Disadvantages - low accuracy, small pitch and low speed of movement. Maximum speed of propeller movement (velocity mm`s per min) based on the maximum motor speed (600 rpm). The best drivers will maintain torque up to 900 rpm. At this rotation speed, linear movement can be obtained:
For M8 screw (thread pitch 1.25mm) - no more than 750mm/min,
For M10 screw (thread pitch 1.5mm) - 900mm/min,
For M12 screw (thread pitch 1.75mm) - 1050mm/min,
For M14 screw (thread pitch 2.00mm) - 1200mm/min.
At maximum speed, the motor will have about 30-40% of its initially specified torque, and this mode is used exclusively for idle movements.
When working at such a low feed rate, the consumption of cutters increases; after just a few hours of operation, carbon deposits form on the cutters.
2) trapezoidal screw. In the twentieth century, it occupied a leading position in metalworking machines, before the advent of ball screws. The advantage is high accuracy, large thread pitch, and therefore high speed of movement. You should pay attention to the type of processing; the smoother and more even the surface of the screw, the longer the service life of the screw-nut transmission. Rolled screws have an advantage over threaded screws. The disadvantages of the trapezoidal screw-nut transmission are that the price is quite high compared to a metric screw; sliding friction requires the use of stepper motors of fairly high power. The most widely used screws are TR10x2 (diameter 10mm, thread pitch 2mm), TR12x3 (diameter 12mm, thread pitch 3mm) and TR16x4 (diameter 16mm, thread pitch 4mm). In machines, the marking of such gear is TR10x2,TR12x3,TR12x4,TR16x4
Helical rolling gears:
Ball screw drive (ballscrew). In the Ball Screw, sliding friction is replaced by rolling friction. To achieve this, in a ball screw, the screw and nut are separated by balls that roll in the recesses of the screw thread. Recirculation of the balls is ensured using return channels that run parallel to the screw axis.
Figure 12
The ball screw provides the ability to operate under heavy loads, good smooth running, significantly increased service life (durability) due to reduced friction and lubrication, increased efficiency (up to 90%) due to less friction. It is capable of operating at high speeds, provides high positioning accuracy, high rigidity and no backlash. That is, machines using ball screws have a significantly longer service life, but have a higher price. The machines are marked SFU1605, SFU1610, SFU2005, SFU2010, where SFU is a single nut, DFU is a double nut, the first two numbers are the screw diameter, the second two are the thread pitch.
Lead screw The milling machine can be mounted as follows:
1) Single support bearing design. Fastening is carried out on one side of the screw with a nut to the support bearing. The second side of the screw is attached to the stepper motor shaft through a rigid coupling. Advantages - simplicity of design, disadvantage - increased load on the bearing of the stepper motor.
2) Design with two thrust bearings. The design uses two support bearings in the inner sides of the portal. The disadvantage of the design is that the implementation is more complex compared to option 1). The advantage is less vibration if the screw is not perfectly straight.
3) Design with two support bearings in tension. The design uses two support bearings on the outer sides of the portal. Advantages - the screw does not deform, unlike the second option. The disadvantage is that the implementation of the design is more complex compared to the first and second options.
Running nuts there are:
Bronze backlash-free. The advantage of such nuts is durability. Disadvantages - they are difficult to manufacture (as a result - high price) and have a high coefficient of friction compared to caprolon nuts.
Caprolon backlash-free. Currently, caprolon has become widespread and is increasingly replacing metal in professional structures. A running nut made of graphite-filled caprolon has a significantly lower coefficient of friction compared to the same bronze.
figure 14 Running nut made of graphite-filled caprolon
In a ball screw nut, sliding friction is replaced by rolling friction. Advantages: low friction, ability to operate at high rotation speeds. The disadvantage is the high price.
Coupling selection
1) connection using a rigid coupling. Advantages: rigid couplings transmit more torque from shaft to shaft, there is no backlash under heavy loads. Disadvantages: require precise installation, since this coupling does not compensate for misalignment and misalignment of the shafts.
2) connection using a bellows (split) coupling. The advantage of using a bellows coupling is that its use allows you to compensate for misalignment of the drive shaft and the axis of the stepper motor up to 0.2 mm and misalignment up to 2.5 degrees, resulting in less load on the stepper motor bearing and a longer service life of the stepper motor. It also allows you to dampen the resulting vibrations.
3) connection using a jaw coupling. Advantages: allows you to dampen vibrations, transmit more torque from shaft to shaft, compared to a split type. Disadvantages: less misalignment compensation, misalignment of the drive shaft and the stepper motor axis up to 0.1 mm and misalignment up to 1.0 degrees.
C) Electronics selection
The electronics are presented (see Fig. 1 and 2):
7 - stepper motor controller
8 - power supply unit for the SD controller
11 - stepper motors
There are 4-wire, 6-wire and 8-wire stepper motors . All of them can be used. In most modern controllers, the connection is made using a four-wire circuit. The remaining conductors are not used.
When choosing a machine, it is important that the stepper motor has sufficient power to move the working tool without losing steps, that is, without skipping. The larger the screw thread pitch, the more powerful motors will be required. Typically, the greater the motor current, the greater its torque (power).
Many motors have 8 terminals for each half-winding separately - this allows you to connect a motor with windings connected in series or in parallel. With parallel-connected windings, you will need a driver with twice the current than with series-connected windings, but half the voltage will be enough.
In case of series, on the contrary, to achieve the rated torque, half the current will be required, but to achieve maximum speed, twice the voltage will be required.
The amount of movement per step is usually 1.8 degrees.
For 1.8 it turns out 200 steps per full revolution. Accordingly, to calculate the value, the number of steps per mm ( “Steps per mm” (Step per mm)) we use the formula: number of steps per revolution / screw pitch. For a screw with a pitch of 2mm we get: 200/2=100 steps/mm.
Controller selection
1) DSP controllers. Advantages - the ability to select ports (LPT, USB, Ethernet) and the independence of the frequencies of the STEP and DIR signals from the operation of the operating system. Disadvantages - high price (from 10,000 rubles).
2) Controllers from Chinese manufacturers for amateur machines. Advantages - low price (from 2500 rubles). Disadvantage - increased requirements for the stability of the operating system, requires compliance with certain configuration rules, it is preferable to use a dedicated computer, only LPT versions are available.
3) Amateur designs of controllers based on discrete elements. The low price of Chinese controllers is displacing amateur designs.
Chinese controllers are the most widely used in amateur machine designs.
Selecting a power supply
Nema17 motors require a power supply of at least 150W
Nema23 motors require a power supply of at least 200W
Knowing that this is a complex technical and electronic device, many craftsmen think that it is simply impossible to make it with their own hands. However, this opinion is wrong: you can make such equipment yourself, but to do this you need to have not only its detailed drawing, but also a set of necessary tools and relevant components.
Processing a duralumin blank on a homemade desktop milling machine
When deciding to make your own CNC machine, keep in mind that it can take a significant amount of time. In addition, certain financial costs will be required. However, by not being afraid of such difficulties and by correctly approaching all issues, you can become the owner of affordable, efficient and productive equipment that allows you to process workpieces from various materials with a high degree of accuracy.
To make a milling machine equipped with a CNC system, you can use two options: buy a ready-made kit, from which such equipment is assembled from specially selected elements, or find all the components and assemble a device with your own hands that fully meets all your requirements.
Instructions for assembling a homemade CNC milling machine
Below in the photo you can see a one made with your own hands, which is accompanied by detailed instructions for manufacturing and assembly indicating the materials and components used, exact “patterns” of machine parts and approximate costs. The only negative is the instructions are in English, but it is quite possible to understand the detailed drawings without knowing the language.
Download free instructions for making the machine:
The CNC milling machine is assembled and ready to go. Below are some illustrations from the assembly instructions for this machine.
“Patterns” of machine parts (reduced view) Beginning of machine assembly Intermediate stage Final stage of assembly
Preparatory work
If you decide that you will construct a CNC machine with your own hands, without using a ready-made kit, then the first thing you will need to do is to choose a circuit diagram according to which such mini-equipment will work.
As a basis for CNC milling equipment, you can take an old drilling machine, in which the working head with a drill is replaced with a milling one. The most difficult thing that will have to be designed in such equipment is the mechanism that ensures the movement of the tool in three independent planes. This mechanism can be assembled using carriages from a non-working printer; it will ensure the movement of the tool in two planes.
It is easy to connect software control to a device assembled according to this concept. However, its main disadvantage is that only workpieces made of plastic, wood and thin sheet metal can be processed on such a CNC machine. This is explained by the fact that the carriages from the old printer, which will ensure the movement of the cutting tool, do not have a sufficient degree of rigidity.
In order for your homemade CNC machine to be able to perform full-fledged milling operations with workpieces made of various materials, a sufficiently powerful stepper motor must be responsible for moving the working tool. It is absolutely not necessary to look for a stepper type motor; it can be made from a conventional electric motor, subjecting the latter to minor modifications.
The use of a stepper motor in yours will make it possible to avoid the use of a screw drive, and the functionality and characteristics of home-made equipment will not become worse. If you still decide to use carriages from a printer for your mini-machine, then it is advisable to select them from a larger model of the printing device. To transfer force to the shaft of milling equipment, it is better to use not ordinary, but toothed belts that will not slip on the pulleys.
One of the most important components of any such machine is the milling mechanism. It is its production that needs to be given special attention. To properly make such a mechanism, you will need detailed drawings, which will need to be strictly followed.
CNC milling machine drawings
Let's start assembling the equipment
The basis of homemade CNC milling equipment can be a rectangular beam, which must be securely fixed on guides.
The supporting structure of the machine must have high rigidity; when installing it, it is better not to use welded joints, and all elements should be connected only with screws.
This requirement is explained by the fact that welds very poorly withstand vibration loads, to which the supporting structure of the equipment will necessarily be subjected. Such loads will ultimately lead to the machine frame beginning to deteriorate over time, and changes in geometric dimensions will occur in it, which will affect the accuracy of the equipment settings and its performance.
Welds when installing the frame of a homemade milling machine often provoke the development of play in its components, as well as deflection of the guides, which occurs under heavy loads.
The milling machine that you will assemble with your own hands must have a mechanism that ensures the movement of the working tool in the vertical direction. It is best to use a screw gear for this, the rotation of which will be transmitted using a toothed belt.
An important part of a milling machine is its vertical axis, which for a homemade device can be made from an aluminum plate. It is very important that the dimensions of this axis are precisely adjusted to the dimensions of the assembled device. If you have a muffle furnace at your disposal, then you can make the vertical axis of the machine yourself by casting it from aluminum according to the dimensions indicated in the finished drawing.
Once all the components of your homemade milling machine are prepared, you can begin assembling it. This process begins with the installation of two stepper motors, which are mounted on the equipment body behind its vertical axis. One of these electric motors will be responsible for moving the milling head in the horizontal plane, and the second will be responsible for moving the head, respectively, in the vertical plane. After this, the remaining components and assemblies of home-made equipment are installed.
Rotation to all components of homemade CNC equipment should be transmitted only through belt drives. Before connecting a program control system to the assembled machine, you should check its functionality in manual mode and immediately eliminate all identified deficiencies in its operation.
You can watch the assembly process in the video, which is easy to find on the Internet.
Stepper motors
The design of any CNC-equipped milling machine necessarily contains stepper motors that ensure the movement of the tool in three planes: 3D. When designing a homemade machine for this purpose, you can use electric motors installed in a dot matrix printer. Most older models of dot matrix printing devices were equipped with electric motors with fairly high power. In addition to stepper motors, it is worth taking strong steel rods from an old printer, which can also be used in the design of your homemade machine.
To make your own CNC milling machine, you will need three stepper motors. Since there are only two of them in the dot matrix printer, it will be necessary to find and disassemble another old printing device.
It will be a big plus if the motors you find have five control wires: this will significantly increase the functionality of your future mini-machine. It is also important to find out the following parameters of the stepper motors you have found: how many degrees are rotated in one step, what is the supply voltage, as well as the value of the winding resistance.
The drive design of a homemade CNC milling machine is assembled from a nut and a stud, the dimensions of which should be pre-selected according to the drawing of your equipment. To fix the motor shaft and connect it to the stud, it is convenient to use a thick rubber winding from an electric cable. Parts of your CNC machine, such as clamps, can be made in the form of a nylon sleeve into which a screw is inserted. In order to make such simple structural elements, you will need a regular file and a drill.
Electronic equipment
Your DIY CNC machine will be controlled by software, and it needs to be selected correctly. When choosing such software (you can write it yourself), it is important to pay attention to the fact that it is operational and allows the machine to realize all its functionality. Such software must contain drivers for the controllers that will be installed on your mini-milling machine.
In a homemade CNC machine, an LPT port is required, through which the electronic control system is connected to the machine. It is very important that such connection is made through installed stepper motors.
When choosing electronic components for your homemade machine, it is important to pay attention to their quality, since the accuracy of the technological operations that will be performed on it will depend on this. After installing and connecting all electronic components of the CNC system, you need to download the necessary software and drivers. Only after this is a test run of the machine, checking the correctness of its operation under the control of loaded programs, identifying deficiencies and promptly eliminating them.
In preparation for the design of a technological process, a detailed analysis of the drawing is carried out to identify missing dimensions and design and technological data. Missing dimensions and other data can be obtained from the designer, from assembly drawings, or by geometric construction of the contour of the part.
In order to facilitate the preparation of the NC, the dimensions in the part drawing must satisfy the programming requirements.
Since processing on CNC machines is carried out using commands that determine the coordinates of trajectory points in a rectangular coordinate system, the dimensions in the drawings must also be specified in a rectangular coordinate system from the unified design bases of the part. To do this, you need to select the origin and direction of the axes. It is desirable that the direction of the axes of the relative coordinate system of the part coincide after its installation on the machine with the direction of the coordinate axes of the machine.
When drawing dimensions on drawings, in some cases, holes, groups of holes or parts elements can be specified in a local coordinate system, as shown for hole B (Fig. 11.8a). The transition from such a system with the beginning at point A to the main system does not cause difficulties.
Fastening holes located at one or another radius from the center of the main hole are usually specified by the central angle of the arc between their axes and radii. For CNC machines, such information should be replaced by the coordinates of the axes of each hole (Fig. 11.8, b). In the example under consideration, it is advisable to assign the axis of the large hole as the origin of coordinates, because it ensures a minimum length of idle (positioning) strokes during processing.
Rice. 11.8. Dimensions on drawings of parts for CNC machines:
a) in the local coordinate system; b) in the coordinate system of the main hole
Often parts have a large number of small mounting holes. It is impractical to indicate the coordinates of the axis of each of them, because this makes the drawing difficult to read. In such cases, it is rational to use a tabular method to indicate dimensions, which is also convenient for programming (Fig. 11.9a).
Rice. 11.9. Dimensions on drawings of parts using the tabular method:
a) axes of mounting holes; b) curved contours
According to the general rule for drawing dimensions in the drawings of parts processed on lathes, areas with tight tolerances (dimensions a 1, a 2, and 3 in Fig. 11.10a) and intermediate sections with wide tolerances (dimensions a 1, a 2 , in 3, in 4). This is quite justified for manually controlled machines, because... the worker only needs to maintain exactly these dimensions. For a CNC machine, this does not matter, because the accuracy of the displacement count is the same, and the reference point, as a rule, does not coincide with the design base and is located outside the part. Therefore, dimensions for such parts should be applied in a chain (Fig. 11.10, b).
Rice. 11.10. Dimensions on drawings of parts for turning:
a) on manually operated machines; b) on CNC machines
In general, the application of dimensions on the drawings of parts processed on CNC machines should be such that when preparing the control program there is no need to recalculate them.