The lead screw is an important detail thatUsed as a motion converter. It changes the rotational motion into a forward-rectilinear motion. To do this, it is supplied with a special nut. In addition, it provides movement with a specified accuracy.
Screw, as a very important detail, shouldmeet a variety of requirements. In order to be able to use it, for example, in a desktop vice, it should be suitable for such parameters as: diametral size, accuracy of the profile and accuracy of the thread pitch, the ratio of the screw thread to its supporting necks, wear resistance, thread thread thickness. It is also important to note that, depending on the degree of accuracy of the movement provided by the screws, they can be divided into several accuracy classes from 0 to 4. For example, the lead screws of metal cutting machines must correspond to the accuracy class from 0 to 3. 4 accuracy class is not suitable for use in such equipment.
As a workpiece for screw productionuse a conventional rod, which is cut from the sort metal. However, it is important to note that some requirements are imposed on the material that serves as a preparation. The metal should have good resistance to wear, good machinability, and also have a stable equilibrium state under conditions of internal stress that occurs after treatment. This is very important, since this property helps to avoid deformation of the lead screw during its further use.
For the production of this component with the middle classaccuracy (2 nd or 3 rd), which will not require increased resistance to temperature, use A40G steel, which is medium carbon, with additions of sulfur and steel 45 with the addition of lead. This alloy improves the possibility of processing the screw, and also reduces the roughness of the surface of the material.
There are three screw profiles thatare used in the manufacture of the screw of the lathe or any other. The profile can be trapezoidal, rectangular or triangular. The most common type is a trapezoidal thread. Its advantages include the fact that it is higher in accuracy than rectangular. In addition, using a split nut, it is possible to adjust the axial clearances with a trapezoidal screw, which arise due to wear of the equipment.
It is also important here to note that cutting, as well asgrinding the trapezoidal thread on the screw is much easier than rectangular. But it should be understood that the accuracy characteristics of rectangular threads are higher than those of trapezoidal threads. This means that if the task is to create a screw with the best adjustment in accuracy, then you still have to cut a rectangular thread. Trapezoidal screws are not suitable for very precise operations.
The basic details on which the screw is based inthe machine tool, steel support cervical and beads. The screw's external surface is considered to be its thread. The greatest accuracy in the desktop vise and any other machines that have such a screw must be provided between the workpiece surface of the workpiece and the main basing surface. The technological base in the manufacture of the lead screw is its center hole. For this reason, in order to avoid deformation, the processing of all these surfaces is carried out using a mobile lunette. The use of this part determines the specificity of the processing of the lead screw.
It is also important here to note that the screw with differentaccuracy class, is processed to different values. Details that will belong to the 0,1 and 2 accuracy classes are processed up to the 5th qualitet. Screws belonging to the 3rd accuracy class are processed to the 6th qualitet. Screws belonging to the 4th category are also processed up to the 6th grade, but they also have an admittance margin with respect to the outer diameter.
In order to obtain an acceptable qualityscrew, it is necessary to carry out several more operations. One of them was the centering of the part, which takes place on a lathe. The lead screw, or more precisely, the workpiece for this part is centered on the specified equipment and here the ends are cut to it. In addition, an operation is carried out to polish the workpiece. For this, centerless grinding or cylindrical grinding machines are used. It is important to add here that grinding in the centers is carried out only for screws of 0,1 and 2 classes of accuracy.
Further, before proceeding to thread cutting,the workpiece must be corrected. Here it should be noted that only screws with the 3rd and 4th accuracy class are subjected to this operation. After that, their surface is additionally polished. As the equipment for threading on the screw, a screw-cutting lathe is used.
The nut of the spindle screw is intended for,to ensure accurate installation movements. In some rare cases, they can be made from a material such as antifriction cast iron. This element must ensure a permanent engagement with the turns of the screw, and also act as a compensating part. Compensate for the gap, which will inevitably arise when the screw is worn. For example, nuts for threaded spindles used in lathes are made in pairs. This is necessary in order to remove the gap that can arise either as a result of the production and assembly of the machine, or as a result of the wear of its parts.
The peculiarity of the screw with a double-type nut is,that it has a fixed and moving part. The movable part, which is the right one, can move along the axis of the fixed part. It is this movement that will compensate for the gap. Manufacture of a nut is carried out only for screws of zero, 1st and 2nd class of accuracy. For their manufacture use tin bronze.
The most common materials forThe production of this type of steel parts is made of aluminum-ferruginous bronze, according to the norms of the machine tool MT 31-2. In addition to this material, antifriction cast iron can also be used as a substitute for non-compliant screw gears.
It is important to add here that the nut wears out much faster than the directional screw itself. There are several reasons for this:
For these reasons, screws with a nut should be checked more often, as the wear of the nut comes fairly quickly.