Thread is a universal element for connecting any structural units in engineering, construction, in all areas of management and in everyday life. It securely fixes the parts, but allows them to be separated if necessary, without violating the structural integrity of individual parts. In addition to the fastener function, a threaded connection is one of the types of hinges. Completely different mechanisms, from simple to complex, often contain carvings as a way to convey movement.
Threading - general information
What is carving? This is a line twisted by a screw, which looks like a protrusion with a vertex of a different shape on the cylindrical surface of the body. She has a step, it can be different and is defined as the gap between adjacent vertices. The protrusions are separated by a depression. Threads for different purposes have their own protrusion shape.
To get a thread, you need to cut it, that is, use a tool to select a groove in the metal along the path of the screw. For this, there is a special tool - both manual and one that is fixed in an electric (lathe) machine. What they have in common is that the incisorsmade of special strong steel, which makes it easy to remove chips from a steel workpiece.
To obtain different thread quality, different grades of metal are used. Hence the division into fixing, fixing, running, special. Parts are cut in production by qualified turners. A high-quality helical surface should not have chips, scuffs and roughness.
Thread Types
Threads perform many functions, hence their broad classification. Helical surfaces are differentiated by:
- The shape of the repetition of the surface where it is cut - cylindrical, conical.
- The position of the surface on the part on which it was received - outside, inside.
- The shape of the profile section of the protrusion is trapezoidal, round, with a rectangular profile and triangular.
- The size of the segment between adjacent vertices of the helix - with a small step, with a large step.
- Number of runs - single-start cut, multi-start cut.
- The direction in which the screw line goes around the surface of the part - left-handed, right-handed.
- Purpose - fastening type, sealing fastener, running use, special application.
Threads made on workpieces of tool steel serve as a tool for cutting all other helical surfaces.
Getting Methods
Carving can be done by hand using special threading kits.
The same work can be carried out on machines - by machine. In the case of manual work, parts are made either in small batches or individually. To cut a lot of blanks, you need to use the appropriate equipment:
- Screw-cutting turning units.
- Rolling threaded machines, where there are rollers, and the cut itself is carried out with a flat die.
- Milling machines that allow you to get large-sized steps on workpieces.
- Grinding devices where wheels with a thread profile are used. They receive high-precision screws, as well as a fine pitch.
- Screw-cutting machines.
- Assemblies for cutting internal threads in blanks for obtaining nuts.
- Machines for vortex heads, where not one, but several threading edges are installed.
Cutting a screw with a vortex head differs from the traditional method in that not one cutter, but four, comes into contact with the workpiece. Their alternate insertion prevents the tool from overheating and, as a result, the speed of material processing increases. The head is driven by an independent drive. The helical surface obtained in this way is of high quality.
What tool
The main tool for threading, which is used for screw surfaces in production and at home, is a die, a tap and a variety of cutters. The first two cutting blades are universal, and can be installed both in the machine and in a manual fixture. incisorsexclusively fixed in turning and similar machines.
The tap tool looks like a screw, where grooves are located along it (the space for chip removal), and with the help of which internal threads are cut in the workpieces, in their holes. The body of the cutter is divided into three parts - this is the intake, calibrating section and the end shank. For the last element, the tap is fixed in a special collar. Cutters are divided into manual, machine and wrench. When carrying out the whole complex of work on threading, one type of tap is not enough, there are usually three of them: for a rough pass, semi-finishing and finishing of the screw.
Cutters-dies make external screws on the parts - screw hardware, bolts and studs. The shape of the plate is somewhat similar to a flat cylinder. A hole is drilled in the middle of this cylinder, in which there is a thread, but not ordinary, but with sharp edges. Around this thread there are also channels for removing metal chips. The intake conical part of the die is on both sides, between them there is a calibration zone. The collars for the die are equipped with fixing bolts.
Dedicated tool for machine tools
On threading machines, special cutters are used, combined into the following groups:
- Rod tool;
- Prismatic rig;
- Round cutters.
How to cut with a tap
To obtain a screw by hand using a tap for threading, perform the following sequence of actions:
- Tisochnya clamp fixes the workpiece for that part that does not interfere with cutting. If the workpiece is hollow inside (pipe), fixing it must be very careful in order to avoid flattening the surface.
- They take a rough tap and fix its shank in the collar.
- The cutting part of the tap is applied to the workpiece, observing the coincidence of the axes between the part and the tool.
- Directing the force to the end of the workpiece, simultaneously turn the tap from left to right (right thread). Completing a full revolution with the tool, they rotate it back, about one third of a revolution. So the channel is released from the formed chips.
- After cutting the full length of the thread, the rough tap is put aside, and work begins with a finishing or semi-finishing according to the same principle.
- The finished surface is cleaned from the remnants of steel chips and checked for quality visually. Then they take the bolt and twist it into the resulting nut - it should go in without effort and using keys. At the same time, significant play between the hardware is unacceptable, which indicates an unsuccessful ratio between the diameter of the workpiece and the cutting tool.
How to cut into slices
When working with a threading die, it is also important to follow some rules:
- The diameter of the workpiece should not be too thin - the thread will turn out "liquid," and too large - the cutting edges of the die may break off.
- To make the cut clear and the tool easier to pass, it is necessary to apply lubricant to it before work.
- For the normal entry of the die onto the part, the latter is chamfered at the end with emery, a file or a grinder.
- Mandatory requirement - that at the moment of rotation of the die its surface is perpendicular to the cylinder of the workpiece. Otherwise, the thread may wobble, which will further affect the poor fit of the nut to the thread and the breakdown of the latter under loads.
- The workpiece must be passed at least twice - with a rough die for the entire length, then with a finishing die.
- After each pass, it is advisable to remove the remaining chips from the thread surface with a brush.
- When threading a pipe, fix it not in a vise, where it can be flattened and poorly fixed, but in a special device for fixing pipes.
Organization of pipe threads
Lerku for pipes is selected in strict proportion to the diameter of the workpiece. So, pipes are:
- Half an inch - corresponds to a diameter of 15 millimeters.
- Three-quarters - 20 millimeters in diameter.
- On an inch diameter - 25 millimeters.
- Inch plus a quarter - 32 trumpet.
These figures correspond to the diameter of the pipes from the inside, therefore, in order to accurately select the tool, you need to add twice the wall thickness.
For the convenience of choosing cutting equipment, there is a corresponding marking on the threading lerk (die), where:
- 1, ¾, ½ - the diameter of the pipe for which the lerka is suitable;
- K, G, R – typeLerok, respectively, conical, cylindrical shape, pipe conical tool.
The device that holds the cutter, with which the lehrka is rotated, has two handles that fix the bolts. The guide on one side prevents distortion during operation and disrupts the clarity of the resulting helical surface.
Conclusion
Carrying out threading work, you must adhere to safety regulations. At the same time, it is very important to work in protective gloves and goggles in order to avoid damaging the skin tissues with sharp metal shavings.
