Selection: During the selection process of the ball screw, the main parameters that need to be paid attention to the ball screw itself are as follows--

1---Nominal diameter. That is, the outer diameter of the screw, common specifications are 12, 14, 16, 20, 25, 32, 40, 50, 63, 80, 100, 120, but please note that among these specifications, each manufacturer generally only prepares 16~50 goods, that is to say, most of the other diameters are futures (produced according to the order, the delivery period is about 30 to 60 days, Japanese products are about 2 to 2.5 months, European and American products are about 3 to 4 months) . The nominal diameter is basically proportional to the load. The larger the diameter, the greater the load. For specific values, please refer to the manufacturer's product sample. Only two concepts are explained here: dynamic rated load and static rated load. The former refers to the rated axial load in the moving state, and the latter refers to the rated axial load in the static state. Just refer to the former when designing. It should be noted that the rated load is not the maximum load. The smaller the ratio between the actual load and the rated load, the higher the theoretical life of the screw. Recommendation: Try to choose diameter 16~63.

2---lead. Also called pitch, it is the distance of linear movement of the nut per revolution of the screw. Common leads are 1, 2, 4, 6, 8, 10, 16, 20, 25, 32, 40. Small and medium lead spot products generally only have 5, 10. Large leads generally include 1616, 2020, 2525, 3232, and 4040 (the first two digits of the 4 digits refer to the diameter, and the last two digits refer to the lead). Most manufacturers of other specifications produce them upon request. The lead is related to the linear speed. When the input speed is constant, the larger the lead, the faster the speed. Recommendation: Try to choose 5 and 10 for the guide.

3---Length. There are two concepts of length, one is the full length and the other is the thread length. Some manufacturers only calculate the total length, but some manufacturers need to provide the thread length. There are also two parts in the thread length, one is the full length of the thread, and the other is the effective stroke. The former refers to the total length of the threaded part, and the latter refers to the theoretical maximum length of the nut's linear movement. Thread length = effective stroke + nut length + design margin (if a protective cover needs to be installed, the compressed length of the protective cover must also be considered. Generally calculated as 1/8 of the maximum length of the protective cover). When designing and drawing, the full length of the screw can be roughly accumulated according to the following parameters: full length of the screw = effective stroke + nut length + design margin + support length at both ends (bearing width + locking nut width + margin) + power Enter the connection length (roughly half the coupling length + allowance if using a coupling). What needs special attention is that if your length is too long (more than 3 meters) or the aspect ratio is large (more than 70), it is best to consult the manufacturer's sales staff in advance whether it can be produced. The overall situation is that the maximum length of conventional products from domestic manufacturers is 3 meters, 16 meters for special products, 6 meters for regular products from foreign manufacturers, and 22 meters for special products. Of course, it doesn’t mean that domestic manufacturers can’t produce longer ones, but the price of customized products is quite outrageous. Recommendation: Try to choose a length of less than 6 meters. If it is longer than 6 meters, it is more cost-effective to use a rack and pinion.

4---Nut form. Each manufacturer's product catalog will have many types of nuts. The first few letters in the general model number indicate the nut type. According to the flange form, there are round flange, single trimmed flange, double trimmed flange and flangeless flange. According to the length of the nut, there are single nuts and double nuts (note that there is no difference in load and rigidity between single nuts and double nuts. Do not listen to the manufacturer's sales staff's speech on this point. The main difference between single nuts and double nuts is that the latter can adjust the preload. The former cannot, and the price and length of the latter are roughly twice that of the former). When the installation size and performance permit, the designer should try to choose a conventional form when selecting to avoid the delivery date problem of spare parts during maintenance. Recommendation: Choose double nuts for frequent movements and high-precision maintenance, and double and single-sided nuts for other situations. Recommendation: As far as possible, the nut form should be a single nut with an internal circulation double trimming flange.

5---Accuracy. Ball screws are classified according to GB into P type and T type, that is, transmission type and positioning type. There are several accuracy grades: 1, 2, 3, 4... Foreign products are generally classified as C0 regardless of transmission or positioning. ~C10 or specific numerical representation. Generally speaking, for general machinery or ordinary CNC machinery, choose C7 (positioning error within any 300 strokes ±0.05) or below. For high-precision CNC machinery, choose C5 (±0.018) or above and below C3 (±0.008). For optical or detection machinery, choose C3 or above. What needs special attention is that accuracy and price are closely related, and the concept of accuracy is combination and maintenance. In other words, the lead error of the screw cannot explain the error of the entire set of screws, and the qualified factory accuracy cannot explain the rated service life. This accuracy is maintained. This is a reliability issue, related to the manufacturer's production process. Recommendation: Choose C7 for accuracy.

The above mentioned are the main parameters. When selecting the model, the following parameters must also be used: number of bead rolls, bead diameter, manufacturing method code, preload level, etc. The respective descriptions are as follows:

Number of bead rolls: This parameter is generally marked after the lead of the model, such as 4010-4. This "-4" is the number of bead rolls, because there is a problem with the circulation method, which is more complicated to talk about. Complex, users can simply understand it as the number of cycles of rolling elements. "-4" means 4 cycles. The larger the value, the greater the load and the longer the length of the nut.

Bead diameter: This parameter refers to the diameter of the rolling element. It will not be reflected in the model number, but will be marked in the technical parameter table of each manufacturer. It is generally related to the nominal diameter and lead, and users do not need to pay attention to it. However, some users should pay attention to this parameter when the balls fall out of the nut due to improper use and need to reinstall the balls. The size is generally accurate to 0.001. Of course, users are not recommended to install it by themselves, otherwise the manufacturer will not provide free maintenance, even if the product is still in use. Within the warranty period. If the ball accidentally falls, the supplier should be notified to assist with installation.

Manufacturing method code: There are two main manufacturing methods for ball screws: rolling and grinding. The former is also called rolling manufacturing or transformation, and is generally represented by F. The latter is also called grinding manufacturing. Generally represented by G. Due to different processes, the accuracy levels that the two can achieve are different. Currently, the highest accuracy that the rolling method can achieve is C5 level. As far as I know, only REXROTH can achieve this accuracy. Grinding can produce products with higher precision. However, please note that there is no inverse inevitability between the two manufacturing methods and accuracy and performance. That is to say, if the accuracy you choose is C7, it has nothing to do with how it is manufactured. In fact, I have met many professional salespeople from manufacturers who may not know the detailed differences between the two, so I will say a few words: rolling belongs to batch manufacturing, grinding belongs to precision manufacturing, and the production efficiency of the former is much higher than that of the latter. , but the manufacturing equipment cost of the former is also much higher than that of the latter. In other words, the entry threshold for ground screws is lower, while the entry threshold for rolling production is higher. Manufacturers that can produce rolled screws can generally also produce ground screws, while manufacturers that can produce ground screws cannot. We must be able to produce rolled screws. Therefore, if you can buy rolled products with the same precision, don’t buy ground products. The reason is simple: they are cheap. In addition, rolling and grinding only refer to screws, and nuts are all made by grinding.

Preload: also called preload. Regarding preloading, users do not need to know the specific preloading force and preloading method. They only need to select the preloading level according to the manufacturer's sample. The higher the grade, the tighter the nut and the screw fit, and the lower the grade, the looser the nut. The principles to be followed are: large diameter, double nuts, high precision, and large driving torque. If the preload level is large, the preload level can be selected higher, otherwise, the preload level can be selected lower

There are usually three fixing forms of the screw, namely : Both ends are fixed, one end is fixed with a support section, one end is fixed and the other is free. Among these three cases, the rigidity of the screw is the best when both ends are fixed. The bearings at the fixed end generally use a pair of face-to-face angular contact bearings, and the supporting end generally uses deep groove ball bearings.

For our ordinary DIYers, it is better to have one end fixed and one end supported. The z-axis can also be fixed with one end and free.