Carving is a universal element for connecting any structural units in engineering, construction, in all areas of business and in everyday life. It reliably fixes parts, but allows them to be disconnected if necessary, without violating the structural integrity of individual parts. In addition to the function of fasteners, a threaded connection is one of the types of hinges. Completely different mechanisms, from simple to complex, often contain threads as a way of transmitting movement.
Threading - General Information
What is a thread? This is a line twisted by a screw, which looks like a protrusion having a vertex of various shapes on the cylindrical surface of the body. She has a step, it can be different and is defined as the gap between neighboring peaks. The protrusions are divided by a hollow. Threads for various purposes have their own protrusion shape.
To get a thread, it needs to be cut, that is, using a tool, select a groove in the metal along the path of the screw. To do this, there is a special tool - both manual and one that is fixed in an electric (lathe) machine. The common thing between them is that the cutters are made of special strong steel, which makes it easy to remove chips from steel billets.
To obtain different quality of thread, various grades of metal are used. Hence the division into fixing, fixing, running, special. Parts at the factory are cut by qualified turners. A high-quality helical surface should not have chips, scoring and roughness.
Types of thread
Threads perform many functions, hence their wide classification. Screw surfaces have differences in:
- The shape of the repetition of the surface where it is cut is of a cylindrical form, a conical type.
- The location 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 is with a small step, with a large step.
- The number of entries - single-thread rifling, multi-thread rifling.
- The direction in which the line of the screw goes around the surface of the part is left-handed, right-handed.
- Appointment - fastening type, sealing fasteners, running use, special applications.
Threads made on tool steel blanks serve as a tool for cutting all other screw surfaces.
Production Methods
Threading can be done manually, using special kits for threading.
The same work can be carried out on machines - by machine. In the case of work, parts are made manually either in small batches or singly. 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 by 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 small step.
- Screw-cutting machines.
- Aggregates for sampling internal threads in blanks for nuts.
- Machines for vortex heads, where not one but several edges for threading are installed.
Vortex cutting of a screw differs from the traditional method in that not one cutter but four comes into contact with the workpiece. Alternating their cutting does not allow the tool to overheat and, as a result, the processing speed of the material increases. The head is driven by an independent drive. The helical surface obtained in this way is characterized by high quality indicators.
What tool
The main tool for threading, which receive screw surfaces in the workplace and in the household, is a die, tap, and various cutters. The first two cutting ones are universal, and can be installed both in the machine tool and in the manual fixture. Cutters are exclusively fixed in turning and similar machines.
The tap tool looks like a screw, where grooves are located along it (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, gauge section and the end shank. For the last element, the tap is fixed in a special wrench. Cutters are divided into manual, machine and nut. When carrying out the whole complex of work on threading, one type of tap is not enough, there are usually three of them: for roughing, semi-finishing and fine-tuning of the screw.
Cutters-dies make the outer screws on the parts - screw hardware, bolts and studs. The shape of the die is somewhat similar to a flat cylinder. In the middle of this cylinder, a hole was drilled in which there is a thread, but not ordinary, but with sharp edges. There are also channels for removing metal shavings around this thread. The die has a conical conical part on both sides, between them there is a calibration zone. The gate for the die is equipped with fixing bolts.
Specialized tool for machine tools
On threading machines, special cutters are used, combined in the following groups:
- Rod tool;
- Equipment of a prismatic form;
- Round incisors.
How to chop
To get the screw manually using a tapping tap, perform the following sequence of actions:
- The workpiece is fixed with a clamping clamp for the part that does not interfere with cutting. If the workpiece is hollow inside (pipe), its fastening must be very neat in order to avoid flattening of the surface.
- Take a draft tap and its shank is fixed in the winch.
- 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 face of the workpiece, simultaneously turn the tap from left to right (right-hand thread). Finishing a complete revolution with an instrument, they rotate it back, about one third of a revolution. So the channel is released from the resulting chips.
- After cutting the full length of the thread, the rough tap is laid aside, and work begins to be finished or semi-finished according to the same principle.
- The finished surface is cleaned of the remains of steel chips and checked for quality visually. Then they take a bolt and tighten it into the nut obtained - 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 of the diameter of the workpiece and the cutting tool.
How to cut a die
When working with a die for threading, it is also important to observe some rules:
- The diameter of the workpiece should not be too thin - the thread will turn out to be “liquid,” and too large - the cutting edges of the die can break off.
- To make the cut clear, and easier for the tool to pass, it is necessary to apply lubricant to it before work.
- For a normal approach, the dies on the part at the last facet are chamfered with an emery, file or grinder.
- A mandatory requirement is that at the time of rotation of the die its surface is perpendicular to the cylinder of the workpiece. Otherwise, the wobble of the thread is possible, which will subsequently affect the poor tightness of the nut to the thread and the breakdown of the nut under load.
- It is necessary to go through the workpiece 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 with a brush from the surface of the thread.
- When threading a pipe, it is not necessary to fix it in a vise, where it can be flattened and poorly fixed, but in a special device for fixing the pipes.
Pipe Threading
The pipe handle is selected in strict proportion to the diameter of the workpiece. So, pipes are:
- For half an inch - correspond to a diameter of 15 millimeters.
- Three-quarter - 20 millimeters in diameter.
- Per inch diameter is 25 millimeters.
- Inch plus a quarter - 32 pipe.
These indicators correspond to the diameter of the pipes on the inside, therefore, in order to accurately select the tool, you need to add double wall thickness.
For the convenience of choosing a cutting tool on the handle for threading (die) there is a corresponding marking, where:
- 1, ¾, ½ - pipe diameter for which the lerka is suitable;
- K, G, R - type of keys, respectively, conical, cylindrical shape, pipe conical tool.
The tool holding the cutter, with which the rotation of the handle is carried out, has two handles that fix the bolts. The guide on the one hand prevents distortion during operation and violates the clarity of the resulting helical surface.
Conclusion
When performing threading work, you must adhere to safety regulations. It is very important to work in protective gloves and goggles to avoid damage to the skin tissue with sharp metal shavings.