A wide variety of ball screws can be used to transmit force and motion. The most widely used type is the ball screw drive. It provides linear movement of the actuator, which converts rotation into linear motion. Among the features of this process, one can note extremely low friction, since it leads to wear of the material and a significant decrease in efficiency and heating of the rubbing elements. Let us consider the features of this process in more detail.
Functional purpose and device
As previously noted, a ball screw is used to transmit force and convert rotation into translational motion. The device is characterized by the presence of several elements:
- Rod with helical grooves.
- Nut with suitable thread and size.
The most widely used versions are those characterized by threads with a semicircular profile. Ball screws are quite simple in design, which determines their reliability and long service life.
Principle of operation
The screw pair is characterized by a fairly simple design, which works as follows
- As the nut rotates, the balls roll along the created channels.
- The balls are capable of progressively moving the nut, pushing it out of the thread. In this case, there is a bypass channel, due to which the balls return to their original position.
- The ball moves along a closed contour, which is located inside the nut.
- The most widespread variants are ball screw gears, in which the return channel connects two adjacent turns.
There are a variety of options for the design in question. They are selected depending on operating conditions and purpose. An example is that in machine tool construction a ball screw with a three-circuit nut is used. For this purpose, a special liner is created, for which an oval-shaped window is created. To reduce friction and increase efficiency, three liners are used at once, placed at an angle of 120 degrees relative to each other.
High-speed or high-speed ball screws
Modern machines and other equipment are characterized by high productivity and versatility in use. As a rule, the force is created by a motor that makes a rotational movement. In order to convert rotation into reciprocating motion, a screw gear is used. The conventional screw and nut combination is less efficient than newer high-speed designs.
The high-speed ball screw has the following features:
- In production, a material is used that is characterized by high wear resistance. Too much wear results in loss of accuracy.
- A special ball screw drive ensures fast movement of the nut.
Most often, high-speed ball screws are installed on CNC machines. Their use ensures rapid movement of the executive bodies.
Classification
In the manufacture of ball screws, the most various technologies. Depending on their characteristics, they distinguish the following types designs:
- Rolled ones are obtained by applying the cold rolling method. As a rule, such technology is characterized by lower costs when using it. Due to this, the price-quality ratio is as high as possible, but the accuracy of the resulting products is low.
- Ground – precision products that are ground after threading and hardening. This ensures a high degree of smoothness. Most products from this group are characterized by increased accuracy. However, the process of hardening and grinding determines a significant increase in the cost of the product.
- The classification can also be carried out according to design features:
- When manufacturing standard ball screws, DIN standards are used.
- Precision ones are obtained by using grinding technology. The design may consist of one or two nuts that are pre-tensioned.
- There are versions obtained by grinding, with a separator. This design is characterized by the presence of a structure that ensures the return of the balls to their initial position.
- The ball screw drive with a rotating nut has a built-in bearing that ensures precise movement of the moving element.
- This category also includes a splined shaft with ball-type bushings. This ball screw design is compact and easy to install.
- Console type version. Used when compact transmission is required.
This classification is taken into account when choosing the required design.
When choosing a ball screw, its main characteristics are taken into account. As a rule, they are as follows:
- Length of the rod. The characteristics of ball screws for CNC equipment are characterized by a maximum length of about 2 meters. This is due to the fact that a product that is too long can become deformed when subjected to a single point impact.
- Linear speed movement is the main indicator that is worth considering.
- The diameter and pitch of the screw can also be called important indicators. They determine what kind of load can be applied.
- The accuracy of the product, which varies from C1 to C10.
You can also find tabular information that is used to determine the main characteristics.
Gear Setting
The selection of ball screws can be carried out in the process of analyzing the structure and preliminary design. Before installing the rack and pinion ball gear, the following calculations are carried out:
- Table stroke values.
- The required force that should be on the screw.
- The most suitable screw length is selected.
- Accuracy determines whether a ground or cold rolled ball screw needs to be installed.
- The design features of the nut are determined: the return of the balls to their original position, whether a bearing is needed, what the nut should be like. An example is that a design with a single nut is much cheaper, but the double nut version is more wear-resistant.
- It is clarified whether the free end should be securely fixed.
- How the ball screw connects to the housing is determined.
After selecting the appropriate ball screw design, its installation is carried out. Fastening can be done using screws and rivets or by welding.
Application area
The main characteristics determine the widespread use of ball screws. An example is various components of automobiles and machine tools. More obvious applications of ball screws include the following cases:
- Manufacturing of CNC machine drives. Modern versions have several linear drives. An example is the case where the Tornos machine has 14 controlled axes.
- KAMAZ and some other automakers use a similar rack in the manufacture of the steering mechanism. This simplifies the process of changing the position of heavy wheels that are burdened with dirt.
- During the production of printers and other printing equipment, a similar rail is installed.
As previously noted, the engine is installed as the main source of force. The rotation is converted by the rack into a reciprocating motion, which is quite common.
Advantages of ball screws over other types of gears
Ball screws have quite a lot of advantages. This design is characterized by the following advantages:
- Low coefficient of friction, which is achieved through the use of balls.
- Higher efficiency value. If we compare other analogues that can transmit translational motion, they are significantly inferior. For many versions, the ball screw has an efficiency rate of 90%.
- There is no sliding due to the use of grooves with balls. This also significantly increases the service life.
- Ease of maintenance and repair. If necessary, you can quickly add oil to the propeller travel area. The lubricant is evenly distributed over the surface, thereby increasing the service life.
- High speed of movement, which can be achieved through the use of special versions of ball screws.
- Reduced power requirements for the drive. This is due to the low resistance of the propeller.
However, there are several significant disadvantages that must be taken into account when choosing a drive. An example is the high probability of reverse motion when installing a screw at a large angle or vertically. This disadvantage is due to the fact that friction is minimal.
The ball screw in question is not recommended for use when creating manual feeds. In addition, the high cost of the product can be considered a negative factor, since it consists of several precise elements. To ensure a low degree of wear, the surface is hardened, which also increases the cost of the product.
A ball screw consists of a screw and a nut and is used to convert rotational motion into linear motion. In ball screws, screw 1 and nut 2 have helical grooves (threads) of a curved profile, which serve as raceways for balls placed between the turns of the screw and nut. The most widely used threads are those with a semicircular profile. In this case, rotation of the nut secured against axial movements causes translational movement of the screw, or rotation of the screw secured against axial movements leads to translational movement of the nut.
Basic geometric parameters of the transmission: nominal diameter d 0, i.e. the diameter of the location of the centers of the rolling elements, the thread pitch P and the diameter D w of the rolling elements (usually D w = 0.6P).
Advantages of a ball screw: the ability to create large axial forces; low friction losses (transmission efficiency 0.9 and above); the ability to obtain translational movement with high accuracy; small dimensions with high load-bearing capacity; significant resource.
The disadvantages include the complexity of the nut design, the need for high manufacturing precision and good protection of the transmission from contamination. Ball screws are used in precision movement mechanisms, in servo systems and in critical power transmissions (machine tool building, robotics, aviation and space technology, nuclear energy, press-forging equipment, etc.).
DEVICE AND PRINCIPLES OF OPERATION
When the screw rotates, the balls are drawn into motion along the screw grooves, progressively moving the nut and. rolling out of the thread, they return to their original position through the bypass channel (return channel). Thus, the movement of the balls occurs along a closed circuit inside the nut. The most common design is the ball screw. in which the return channel connects two adjacent turns.
In machine tool industry, three-circuit nuts are used. The bypass channel is made in a special liner, which is inserted into the oval window of the nut. A three-circuit nut has three liners located at an angle of 120° to one another and offset along the length of the nut by one thread pitch relative to each other. Thus, the balls in the nut are divided into three (according to the number of working turns) independent groups.
When the transmission is operating, the balls, having passed along the helical groove on the screw a path equal to the length of one or several turns, roll out of the thread into the bypass channel of the liner and return back to their original position on the original turn of the nut.
THREAD PROFILE
The main parameters of a semicircular profile thread (Fig. 1.a):
R = (0.515...0.525) Dw- radius of grooves;
α = 45°- ball contact angle;
ψ = arctan- thread lead angle (here z is the number of thread starts).
In Fig. 1. b shows the thread profile of a screw with a relief groove in a normal section, and in table. 1 shows the dimensions of the relief grooves according to OST 2 RZ1-5-89.
1. Dimensions of unloading grooves, mm
| Nominal diameter d 0 | Thread pitch P | b | r | Nominal diameter d 0 | Thread pitch P | b | r |
| 16 25 25 32 32 40 40 40 50 |
2,5 5,0 10,0 5,0 10,0 5,0 6,0 10,0 5,0 |
- 1,0 1,5 1,0 1,5 1,0 1,0 1,5 1,0 |
- 0,55 0,85 0,55 0,85 0,55 0,55 0,85 0,55 |
50 50 63 80 80 100 100 125 |
10,0 12,0 10,0 10,0 20,0 10,0 20,0 20,0 |
1,5 1,8 1,5 1,5 3,0 1,5 3,0 3,0 |
0,85 0,95 0,85 0,85 1,60 0,85 1,6 1,6 |
PRELOADED Ball Screw
In order to eliminate the axial gap in the screw-nut interface and thereby increase the axial rigidity and accuracy of movement of the driven element, the ball screw is assembled with preload.
For a transmission with a semicircular thread profile, the interference is created by installing two nuts followed by their relative axial displacement. The relative displacement of the nuts is carried out by installing spacers between them or by their relative angular rotation.
The thread profile and nut design (ball return channel, tension adjustment, etc.) are determined by the manufacturer.
Ball screws are used in a wide range of sizes.
SIZES OF BALL SCREWS
according to GOST 25329-82
| Nominal diameter d o , mm |
Nominal pitch P, mm | |||||||||
| 2,5* | 3 | 4 | 5* | 6 | 8 | 10* | 12 | 16 | 20* | |
| 6 | + | |||||||||
| 8 | + | |||||||||
| 10 | + | |||||||||
| 12 | + | + | + | + | ||||||
| 16 | + | + | + | + | + | |||||
| 20 | + | + | + | + | + | |||||
| 25 | + | + | + | + | + | |||||
| 32 | + | + | + | + | + | + | ||||
| 40 | + | + | + | + | + | |||||
| 50 | + | + | + | + | + | + | ||||
| 63 | + | + | + | + | + | + | + | |||
| 80 | + | + | + | + | + | + | ||||
| 100 | + | + | + | + | + | |||||
| 125 | + | + | + | + | ||||||
| 160 | + | + | + | + | ||||||
| 200 | + | + | + | + | ||||||
| *Preferred steps | ||||||||||
TECHNICAL CONDITIONS
Technical specifications for ball screws used in machine tool industry have been established GOST 2 RZ1-5-89. This standard applies to ball screws used to complete metal and woodworking machines, industrial robots, and press-forging equipment.
The standard establishes the main dimensions, basic parameters, completeness, marking, procedure and composition of acceptance tests, packaging, transportation and storage conditions, operating instructions and manufacturer's warranties for centrally manufactured ball screws.
The standard takes into account the requirements ISO/DP 8931, ISO/DP 8932, ISO/DP 3408, ISO/DP 9783, ISO/DP 9784.
Hull gears manufactured in 4 versions:
I - ball screw with one or two nuts without a housing;
II - ball screw with two nuts in a cylindrical body having a flange;
III - ball screw with two nuts in a prismatic body with through mounting holes;
IV - ball screw with two nuts in a prismatic body with blind threaded mounting holes.
The use of type III ball screws is not preferable.
According to their accuracy parameters, ball screws are divided into positional and transport ( OST 2 RZ1-7-88). Positional ball screws allow indirect measurement of axial displacement depending on the angle of rotation and thread stroke of the screw. In transport ball screws, displacements are measured directly using a separate measuring system that does not depend on the angle of rotation of the screw.
The kinematic and geometric accuracy classes of ball screws must comply with OST 2 RZ 1-4-88. According to this standard, accuracy classes are established for positional (P) and transport (T) ball screws, respectively: P1, P3, P5, P7 and T1, TZ, T5, T7, T9, T10.
In-plant acceptance standards for kinematic accuracy must comply GOST 2 R31-5-89.
According to OST 2 RZ1-5-89 the quality of materials, processing and assembly of the ball screw must comply GOST 7599-82, and for export supplies - OST 2 N06-1-86.
LOADING CAPACITY
When designing, in accordance with the main criteria for the performance of ball screws, calculations are carried out using dynamic load capacity to prevent fatigue failure (chipping of working surfaces) and static load capacity to prevent plastic deformation of bodies and rolling surfaces.
When choosing the values of dynamic C a and static C oa load capacities, as well as the minimum and maximum values of the ball screw idle torque T xx, you can rely on the data in Table 2.
Basic static axial load capacity C oa is the static axial force (N) that causes a total permanent plastic deformation of the ball, screw grooves and nut equal to 0.0001 of the ball diameter.
2. Basic lifting characteristics of ball screws
| Standard size d 0 x P, mm | Load capacity, N | Idle torque T xx , Nm |
||
| static C oa | dynamic S a | min | max | |
| 16x2.5 25x5 25x10 32x5 32x10 40x5 40x6 40x10 50x5 50x10 50x12 63x10 80x10 80x20 100x10 100x20 125x20 |
9600 28100 48800 37500 65000 49400 56400 85900 62800 112500 119900 149700 197700 297600 251100 386400 729000 | 5000 16580 46400 17710 49800 19170 23700 54700 20640 57750 65400 62030 66880 143400 71840 151800 278000 |
0,05 0,08 0,11 0,18 0,22 0,30 0,32 0,45 0,50 0,48 0,49 0,75 1,23 2,30 2,04 2,75 2,80 |
0,20 0,32 0,35 0,56 0,60 0,84 0,83 0,95 1,35 1,23 1,09 2,03 3,25 3,88 5,20 5,23 5,50 |
Note. The given values for case ball screws correspond to versions II, III and IV.
Basic dynamic axial load capacity C a is the axial force that the ball screw can support with a basic life of 1,000,000 screw revolutions.
Basic load capacities correspond to gears made of commonly used steels (see Table 3). If the properties of the material differ from the usual ones, and also depending on the accuracy class, hardness of the working surfaces, etc., the value of the adjusted static and adjusted dynamic load capacity is calculated.
TECHNICAL REQUIREMENTS
Technical requirements on the main parts of ball screws used in machine tools are installed OST 2 RZ1-5-89(Table 3). Screw accuracy standards are according to OST 2 RZ1-4-88.
3. Technical requirements for the main parts of the ball screw
Notes:
1. Heat treatment according to RTM2 MT11-1-31.
2. For balls, accuracy level 20 according to GOST 3722-81.
3. The difference in size of the balls in one gear is no more than 0.001 mm.
4. Deviation of the average diameter of the balls at D u
Screws are also made from steel grades HVG And 7G2VM with volumetric hardening, steel grade 8ХВ with hardening by induction heating, steel grade 20Х3МВФ with nitriding.
For nuts, steel grade is used HVG with volumetric hardening and case-hardened steel grades 18ХГТ, 12ХН3А, 12Х2Н4А.
The balls are made from chromium steel grade SHH20SG.
The materials of the screw, nut and rolling elements must ensure a hardness of the working surfaces of at least 61 HRC e.
During assembly, the nut cavity is filled with grease grade lubricant CIATIM-201 or CIATIM-203.
Transmissions require good protection against contamination. The most commonly used are harmonica-shaped bellows, telescopic casings and dirt removers - plastic sealing nuts with two or three convex turns along the profile of the grooves. Contaminant removers are attached to each end of the main nut.
Nomenclature of quality indicators used in assessing the quality level of ball screws used in metal and woodworking machines, sections, lines, complexes, industrial robots and press-forging equipment, installed OST 2 RZ1-6-87.
Related documents:
GOST 3722-81 - Rolling bearings. Balloons. Technical specifications;
calculation of lead screws;
calculation of cargo propellers;
example of a lead screw drawing
Since many questions arose after the first publication, I will post step-by-step information for assembling a CNC router yourself
To start basic elements- bearing supports for ball screws type BK12 and BF12
They are necessary to install the ball screw lead screw for each axis of the machine.
Appearance, characteristics, drawings under the cut
So, I am gradually receiving the ordered components for assembling a CNC milling machine myself.
Just recently I received a parcel with mechanics and chassis.
The chassis for the planned design of the router is. To attach it, you will need special bearing units - these are supports BK12 and BF12
Strictly speaking, the screw is installed at both ends in the supports, on one end the support rigidly fixes the screw (longitudinal and radially) and provides connection to the engine through the coupling, and on the other side the support is “floating”, which fixes the screw only radially and allows it to be “tensioned” .
The photo shows a pair of such supports necessary for installing one ball screw 
I’ll say right away: the block support with fixed end and installation on the engine side is BK12
Second block support with " floating"the end is BF12
Typically sold in sets.
Additional information - types of chassis and types of supports
As for the SFU1605 ball screw, there are different kinds supports: in the form of a support block, flange, etc. 
That is, for flange installation, FF12 (floating end) and FK12 (fixed end) supports are used
So, the BK12 type support is designed for rigid fixation of the 1605 (and 1610) ball screw. The support is equipped with two 6001ZZ radial bearings. The kit includes a special lock nut for preloading the screw with M12x1.0 thread.
The support type BF 12 is designed to support the second end of the ball screw; fixation is ensured only by a locking ring.
That is, the BF12 bearing block is a “floating” support block. The floating bearing is equipped with a 6000ZZ radial bearing.
Appearance of a pair of supports 
Received everything in one big package 
Inside there were several different sets of BF12/BK12/FK12/FF12 - I took a lot of things for several axes 
Here's what the packaging looks like for one of the support kits: 
There are a couple of supports inside, in bags, in oil. Plus accessories - a locking ring, a nut. My kit also included an elastic coupling for connecting the motor shaft. Coupling size 6.35x10mm 
The kit includes:
1 x support type VK12
1 x support type BF12
1 x muff 6x10
1 x nut
1 x retaining ring
So, I took everything out and unpacked it. 
Weighing and checking dimensions
Weight of kit parts, for rough estimate 
Coupling for connecting the motor. On the motor side the diameter is 6mm (for NEMA23), on the ball screw side the diameter is 10mm. Naturally, after installation, the coupling is tightened with hexagon screws 
The coupling length is 3 cm, keep this in mind when designing the axle stroke. 
Support BK12 (fixing). Screw diameter 12mm, nut thread M12x1.0mm. The distance between the mounting holes is 46mm, that is, I need to drill holes in the 30th series profile 
Support BF12 (floating). The diameter is already 10 mm. The screw is secured with the included locking ring. 
Now some photos of the supports.
Support BK12 (fixing). You can remove two bushings (of different sizes), they fit freely into the bearings on both sides, plus a separate M12 fixing nut. 
WITH reverse side there is an oil seal with a mounting plate 
Inside there is a pair of 6001 radial bearings (28 mm x 12 mm x 8 mm) 
The photo shows the marking 6001RS 
Here is a photo of the support with the seal and plate removed 
Support BF12 (floating).
There is one 6000zz radial bearing inside (26mm x 10mm x 8mm) 
Mounting hole distance is the same as 46mm 
The end of the screw is secured with a locking ring. 
Now a little about the assembly.
For starters, the “floating” BF12. Initially, it was assumed that there would be seals, but the Chinese are smarter than any GOST standards 
The BF12 support is installed on the machine frame and secured. then the end of the screw is threaded into it (where the diameter is 10 mm). 
The screw is secured with a locking ring 
Next is the assembly of BK12 
Assembly with oil seals is also assumed. In fact, we only have one oil seal. 
Don’t forget to screw the nut onto the screw, right with the housing. Next, we put on the support and screw on the lock nut. We install the support on the machine frame. We fasten and fix the nut. This nut can be used to pre-tension the screw. 
Don’t forget to attach the coupling, which will then drive the propeller from the engine 
So, here is my ball screw assembled with supports 
Now about the application.
The BK12/BF12 support sets are used to assemble axes for moving the work table, portal and tools of a CNC milling machine.
As a matter of fact, here is a drawing of the placement of axes for a small router 
X axis close-up. I removed the excess from the drawing. The SFU1605 screw and two supports BK12 and BF12 are clearly visible 
Appearance of the future router. Three ball screws are used, profile type 6060. 
I’ll finalize the drawings and post them to the public.
Review of a specific product: a set of ball screws type SFU1605-1000 as elements of CNC machine gears.
The review will provide brief information about what a ball screw is and how to use it
As a matter of fact, when trying to calculate and build an amateur CNC machine (milling machine) on my own, I was faced with the fact that we either have expensive components for the machines, or are not quite what we need. Specifically, there was a problem with purchasing a lead screw or ball screw as transmission elements along the axes of the machine. 
There are the following types of gears for CNC:
- belt used together with gears mainly for lasers, since the laser has a light “head”
- gear. These are spur or helical racks and gears for moving along them
- lead screws There are T8 type (mainly used in 3D printers and other small-sized machines), TRR type, for example TRR12-3 with a POM nut (plastic).
- ball screws- this is a screw and a nut for it. The nut has special bearings that move along a channel inside the nut.
As a rule, they are chosen taking into account the load (weight of the moving portal/axle) and the influence of backlash. In ball screws, there is less play due to bearings; they are considered more accurate and preferable, but at the same time they are quite expensive for homemade products.
Quote from
A helical gear is a mechanical transmission that converts rotational motion into linear motion, or vice versa. In general, it consists of a screw and a nut....one of the main types: ball screw (ballscrew).
Ball screw(hereinafter referred to as a ball screw) is a more reliable analogue of a lead screw, but instead of a brass nut (or a plastic one as for TRR-12-3 type screws, as I had on my old project) there is a special nut with balls that engage with the ball screw, select all the play and at the same time reduce friction. To independently assemble a CNC machine or 3D printer on a ball screw, you will need a ball screw, a nut for it, a coupling for attaching it to the motor and hanging bearings.
Here is a small render from the Internet. You can clearly see how the balls are distributed along the screw. Similar to T8, the ball screw has multi-start threads. 
For the CNC machine, two sets of 1000 mm ball screws were needed for the Y axis, and 600 mm for the X axis.
I received the ball screw by courier mail. This is not an expensive option, considering the weight of the package (about 8 kg). 
The packaging is a long narrow box, inside cardboard packaging There is packaging like a synthetic bag, a very durable material. Carefully unpack. Inside is the familiar bubble-wrap, that is, a bubble film that protects the product from mechanical influences. 
We remove the film. The parcel contained three sets of ball screws: a screw + a nut, of different sizes. Two sets are designed to move the machine portal along the Y axis, the third short set is for the X axis. 
All kits are wrapped in inhibitory green film, which prevents moisture from entering. Plus there is a fair amount of lubricant on the surface of the product. 
In this kit, I paid extra for ending one kit at 600 mm (it turned out cheaper this way). I ordered the ending (machined) separately from the same seller (he has such a service in the catalogue), it cost 1 buck for each end of the screw. A good option for those who take screws in a specific size. 
That's what the "ending" is. This is grinding a 16.05mm screw to 12mm diameter to fit into the outboard bearing, then the threaded part to secure the screw, then grinding down to 10mm to clamp the end into the elastic coupling of the engine 
The parcel arrived safe and sound, Express delivery This is not Russian Post. I applied a ruler in different places to find the curvature. I couldn’t find it, the ball screws are straight. Installation and use will show the rest. 
Photo of the threaded part of the screws 
Appearance of the kits 
And further. The nuts arrived already screwed onto the screw... The balls are filled inside, there is lubricant. When ordering, ask for spare balls, at least a few. 
Next, we begin to check the sizes of the screws. Short by 600 mm. That is, these 600 include a threaded part on both sides. The actual travel along the machine axes will be less.
note, that in the lot the size is indicated for a ball screw along with threads and turned ends, that is, the working stroke of the ball screw will be less than its length! Specifically, 65 mm less. 
Second and third ball screws 1000 mm 
The diameters of the threaded part are respectively 1605 
seats for bearings 10 and 12 mm, respectively. 
And on the other side under the bearing. The diameter of the SFU1605 nut itself is 28 mm. 
If you remove the plastic plug from the nut, you can service the ball screw, lubricate or change the balls. I check that everything is in stock)))) 
In fact, you can remove the nut, wipe it, re-lubricate it, and put the balls back in. The plastic cover is secured with a countersunk screw for a 2.5 hexagon (you can see it at the top). 
To install the ball screw in the machine, you will need suspension bearings of type BK12+BF12 (straight) or FK12+FF12 (flange), an elastic coupling 6.35*10mm for connection to a NEMA23 type motor on one side (6.35mm) and to the end of the ball screw on the other (10mm ).
External view of the assembled axle kit: bearings BK12, BF12, retaining ring, nut for fixing the screw, nut holder SFU1605, coupling for the motor and the screw itself with the nut. 
Ball screw dimensions for those who are planning to purchase or are designing machine mechanics 
And separately for SFU1605 
Appearance of nut SFU1605 
External view of bearings (left) and bearings with flange (right). They differ in the way they are installed on the frame. 
The ball screw nut is attached through a special adapter housing. , aluminum 
For installation on one axis (I have two per axis for Y) you will need:
- 1 x screw SFU1605-1000mm;
- 1 x bearing BK12;
- 1 x BF12 bearing;
- 1 x motor coupling 6.35x10mm
- 1 x retaining ring
- 1 x nut.
We attach it to the profile/frame of the machine through the holes in the bearing. For FK12/FF12 bearings everything is similar, only they must be attached with a flange to the hole for the ball screw. The meaning doesn't change.
Now a little video explaining the principle of operation of a ball screw. Pay attention to the movement of the balls (through the built-in channel inside the nut).
And this is how threads are rolled onto ball screws
Machining the ends of the ball screw (what I called “machined”). For such an operation they ask us for 600....1000 rubles, in China $1.
The following photographs give a general idea of the use of ball screws in CNC machine design. 
Here is a photo of a homemade machine in which the ball screw is fixed motionless, and the nut rotates using a belt drive and gear 
As a result, ball screws are a more expensive and reliable transmission option for machine tools and are suitable for moving heavy portals with high precision. Depending on the weight and design of the machine, you can use SFU1205, SFU1605/1610, SFU2005/2010 or the even more massive SFU2505/2510.
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To create machines with computer numerical control, it is necessary to use ball screws. They differ not only appearance, but also by design. To select a specific model, you should familiarize yourself in advance with the structure and components of the ball screw.
Purpose of ball screws
All types of ball screws for CNC machines are designed to convert rotational motion into linear motion. Structurally they consist of a housing and a lead screw. They differ from each other in size and technical characteristics.
The main requirement is to minimize friction during operation. To achieve this, the surface of the components undergoes a thorough grinding process. As a result, during the movement of the lead screw there are no sharp jumps in its position relative to the housing with bearings.
Additionally, to achieve a smooth ride, not sliding friction relative to the pin and body is used, but rolling. To achieve this effect, the principle of ball bearings is used. Such a scheme increases the overload characteristics of ball screws for CNC machines and significantly increases efficiency.
Main components of ball screw:
- lead screw Designed to convert rotational motion into translational motion. A thread is formed on its surface, the main characteristic is its pitch;
- frame. As the lead screw moves, displacement occurs. Various machine components can be installed on the body: cutters, drills, etc.;
- balls and liners. Necessary for smooth movement of the housing relative to the axis of the lead screw.
Despite all the advantages of this design, CNC ball screws are used only for medium and small machines. This is due to the possibility of screw deflection when the housing is located in its middle part. In on standing time the maximum permissible length is 1.5 m.
The screw-nut transmission has similar properties. However, this scheme is characterized by rapid wear of components due to their constant friction with each other.
Application areas of ball screws
The relative simplicity of the design and the possibility of manufacturing a ball screw with different characteristics expands the scope of its application. Nowadays, ball screws are integral components of homemade milling machines with numerical control. Well, the scope of application is not limited to this.
Due to their versatility, ball screws can be installed not only in CNC machines. Smooth running and virtually zero friction make them indispensable components in precision measuring instruments, medical installations, and mechanical engineering. Often for bundling homemade equipment they take spare parts from these devices.
This was made possible thanks to the following properties:
- minimizing friction losses;
- high load capacity factor with small design dimensions;
- low inertia. The movement of the body occurs simultaneously with the rotation of the screw;
- no noise and smooth running.
However, the disadvantages of ball screws for CNC equipment should also be taken into account. First of all, these include the complex design of the housing. Even if one of the components is slightly damaged, the ball screw will not be able to perform its function. There are also restrictions on the speed of rotation of the propeller. Exceeding this parameter may result in vibration.
To reduce the axial clearance, the assembly is performed with interference. To do this, balls of increased diameter or two nuts with axial displacement can be installed.
Characteristics of ball screws for CNC equipment
To select the optimal ball screw model for numerically controlled machines, you should familiarize yourself with the technical specifications. In the future, they will affect the performance of the equipment and the time of its maintenance-free operation.
The main parameter of ball screws for CNC machines is the accuracy class. It determines the degree of position error of the moving system according to the calculated characteristics. The accuracy class can be from C0 to C10. The movement error must be given by the manufacturer and indicated in the technical data sheet of the product.
| Accuracy class | C0 | C1 | C2 | C3 | C5 | C7 | C10 |
| Error at 300 µm | 3,5 | 5 | 7 | 8 | 18 | 50 | 120 |
| Error per screw revolution | 2,5 | 4 | 5 | 6 | 8 |
In addition, when choosing, you need to consider the following parameters:
- the ratio of the maximum and required motor speed;
- total thread length of the lead screw;
- average load on the entire structure;
- axial load value - preload;
- geometric dimensions - diameter of the screw and nut;
- electric motor parameters - torque, power and other characteristics.
These data must be previously calculated. It should be remembered that the actual characteristics of ball screws for CNC equipment cannot differ from the calculated ones. Otherwise, it will cause the machine to malfunction.
The number of revolutions of the balls in one circle will determine the degree of transmission of torque from the shaft to the housing. This parameter depends on the diameter of the balls, their number and the cross-section of the shaft.
Installing a ball screw on a CNC machine
After choosing the optimal model, it is necessary to think over the installation scheme of the ball screw on the CNC machine. To do this, a design drawing is first drawn up, and other components are purchased or manufactured.
When performing work, you should take into account not only specifications ball screw drive. Its main purpose is the movement of machine elements along a certain axis. Therefore, you should think in advance about attaching the processing unit to the ball screw housing for CNC machines. It is necessary to check the dimensions of the mounting holes and their location on the body. It should be remembered that any mechanical treatment of the ball screw may lead to negative changes in its characteristics.
Installation procedure in the body of a CNC machine.
- Determination of optimal technical characteristics.
- Shaft length measurement.
- Creation of a diagram for coupling the mounting part of the shaft with the motor rotor.
- Installing the gear on the machine body.
- Checking the functionality of the node.
- Connecting all main components.
After this, you can perform the first test run of the equipment. There should be no vibrations or vibrations during operation. If they appear, perform additional component calibration.
If the ball screw breaks down during operation of a CNC machine, you can repair the transmission yourself. You can order a special kit for this. You can see the specifics of the restoration work in the video:
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