Trapezoidal thread - properties and methods of cutting

The most widely used are trapezoidal threads and rectangular threads, they are used in the manufacture of a variety of screws, for example, screw screws of metal cutting machines, screws of presses and various lifting devices, as well as worm gears.

If the rectangular thread has a profile in the form of a rectangle, then the trapezoidal thread has the appearance of an equilateral trapezoid. This thread can have a profile angle that is 15.24.30 and 40 degrees. During the work of the screw, natural frictional forces arise which are caused by the presence of lubricant, surface roughness, materials from which the parts are made, and also the values of the profile angle. If a rectangular thread with a profile angle of zero will have a smaller coefficient of friction, the trapezoidal thread wins in that its radial clearances can be determined by fitting to the average diameter, whereas in a rectangular thread, they are determined by the outer or inner diameter.

If you compare these threads in terms of complexity, then the trapezoidal thread is easier to make, and therefore is used much more often. Most often it is made with a profile angle of 30 °.

The trapezoidal thread has a cutting process similar to that of a rectangular process. There are some features of cutting, which depend on the size of the surface cleanliness and its accuracy.

There are several methods of cutting the specified type of thread.

Thread cutting with one cutter:

• The workpiece is measured and the groove groove is used to exit the tool;
• In accordance with the existing template, the sharpening tool is sharpened;
• Exact fixing of the tool and its fixing is carried out, while it must be on the center line and parallel to the axis of the thread to be cut;
• Setting up the machine and feeding the cutter for cutting the thread profile;
• Check the obtained profile using a template, as well as the average thread diameter.

Thread cutting with three incisors:

• Preparation of preparation is conducted;
• Sharpened three cutters - a slotted straight, narrow and profile cut;
• Installation of slotted incisors and their reliable fastening is carried out. Depending on the angle of elevation, they are located 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 center line.

In some industries, the following method has become widespread, with the help of which screws with trapezoidal threads are made:

• The equipment for this operation is adjusted;
• The groove is cut through to a half of the required depth using a slotted tool;
• Using a narrow slotted cutter, further grooves are cut to the size of the inner diameter;
• Using a profile cutter, the final cutting of the trapezoidal thread is carried out;
• The work performed is checked, for which the thread gauge and the template are used.

Thus, we have considered the basic ways of performing this type of thread. Now let's take a closer look at how the cutting of trapezoidal threads is practically done:

1. It is necessary to prepare a blank for carrying out this type of work.
2. Following the treatment scheme, it is necessary to sharpen the profile roughing, grooving and finishing cutters.
3. Carry out all necessary equipment adjustments for this type of work.
4. Using the first profile tool, cut the trapezoidal groove 85% of the depth.
5. Carry out groove bottom processing with a groove cutter.
6. Carry out the final cutting and scraping the sides of the resulting profile.
7. Check the quality of the work done with the template and the caliber.

As you can see, everything is quite understandable and easy to implement.