The most widely used trapezoidal thread and rectangular thread, they are used in the manufacture of a variety of screws, such as running screws of machine tools, press screws and various lifting devices, as well as worm gears.
If a rectangular thread has a profile in the form of a rectangle, then the trapezoidal thread has the form of an isosceles trapezoid. This thread may have a profile angle that is 15.24.30 and 40 degrees. During the operation of the screw, natural frictional forces arise , which are caused by the presence of lubricant, surface roughness, materials from which the parts are made, as well as the profile angle. If a rectangular thread, for which the profile angle is equal to zero, has a lower coefficient of friction, then the trapezoidal thread wins in that its radial clearances can be determined by fit according to the average diameter, while in a rectangular one they are determined by the outer or inner diameter.
If we compare these threads in terms of complexity, then the trapezoidal thread is easier to manufacture, and therefore it is used much more often. Most often it is made with a profile angle of 30 °.
The trapezoidal thread has a cutting process that is almost similar to making a rectangular one. Some cutting features arise that depend on the size of the surface cleanliness and its accuracy.
There are several methods for cutting a specified type of thread.
Thread cutting with one cutter:
- the workpiece is measured and the groove groove is made to exit the cutter;
- in accordance with the existing template, the sharpening of the final cutter is carried out;
- Precise installation of the cutter and its fixing are carried out, while it should be on the line of centers and be parallel to the axis of the cut thread;
- adjustment of the machine and the feed of the tool for cutting the thread profile;
- verification of the obtained profile using the template, as well as the average diameter of the thread.
Thread cutting with three cutters:
- preparation of the workpiece is carried out;
- three cutters are sharpened - slotted straight, slotted narrow and profile;
- the installation of slotted incisors and their reliable fixing. Depending on the angle of elevation, they are either perpendicular to the sides of the helical groove, or parallel to the axis of the thread and should be at the height of the line of centers.
In some industries, the following method has become widespread, with which trapezoidal screws are made:
- equipment is being adjusted to perform this operation;
- grooves are cut to half the required depth with a slotted cutter;
- using a narrow slotted cutter, further grooving is carried out to the size of the inner diameter;
- using a profile cutter, final cutting of a trapezoidal thread is carried out;
- verification of the work performed is carried out, for which a threaded gauge and gauge are used.
Thus, we examined the main ways to perform this type of thread. Now let us consider in detail how the work on cutting trapezoidal threads is practically carried out:
- It is necessary to prepare a blank for the specified type of work.
- Following the processing scheme, it is necessary to sharpen the profile roughing, grooving and finishing cutters.
- Carry out all necessary equipment setup to perform this type of work.
- Using the first profile cutter, cut a trapezoidal groove at 85% depth.
- Cut the bottom of the groove with a groove cutter.
- Carry out the final cutting and cleaning of the sides of the obtained profile.
- Use a gauge and gauge to check the quality of the work performed.
As you can see, everything is quite clear and easy to implement.