Due to their widespread use, it is necessary to constantly meet with threaded connections. This article discusses the main types of carving and tools for its implementation. As a practical part, an example of cutting pipe threads is given.
Threaded connections are the most common way of mounting various structures and parts of mechanisms. They are characterized by such advantages as reliability, versatility, the ability to withstand heavy loads, multiple use, ease of manufacture..
The thread is a spiral made on a cylindrical surface. The main elements of metric threads are shown in the picture below..
When dividing threads into different types, the following parameters are taken into account:
- Location: indoor and outdoor.
- Direction of rotation: right and left.
- Profile shape: rectangular, triangular, round, trapezoidal.
- Surface character: conical and cylindrical.
- Purpose: fixing, running, special and others.
- Number of passes: single or multiple.
Metric thread has an equilateral triangle profile, respectively, its profile angle is 60 °. This type is the most used when making fasteners. It can be with large and small steps with diameters of 1–68 mm, and over 68 mm – only with small steps. For its symbol, millimeters are used:
- М12х1 – metric thread with a nominal (external) diameter of 12 mm and a pitch of 1 mm.
- М16LHх0.5 – metric thread with a diameter of 16 mm, left, pitch – 0.5 mm.
- М8 – thread with a large pitch with a diameter of 8 mm.
In units requiring fixation and tightness without additional elements, a tapered metric thread (MK) is used.
Inch threads also have a triangular profile, but with a top of 55 °. The numerical value (2 “) indicates the conditional clearance in the pipe, and not the actual diameter of the pipe. Under the pitch of an inch thread, it is customary to consider the number of turns located on one inch. Widespread in foreign countries, in Russia it is used to repair equipment, in new developments it is not used by.
The inch profile also has a cylindrical pipe thread, which is used to connect fittings, couplings, pipes and other elements of water pipes up to 6 inches in size. Example of a symbol:
- G? -B – cylindrical pipe thread, nominal bore (inner pipe diameter)? inch, B – accuracy class.
For trapezoidal threads (Tr), the profile has the shape of a trapezoid cut from a triangle with a vertex of 30 °. There are multi-threaded varieties, it is used in the design of reciprocating mechanisms and screws that are exposed to heavy loads.
Thrust thread – a profile in the form of a trapezoid with different sides, used in presses, jacks and other devices experiencing one-sided loading. Designation:
- S70х8 – single-thread, diameter 70 mm, pitch 8 mm.
Square (in other words – rectangular) thread is not standardized, it is made according to the dimensions required in a particular case, it is found on lead screws.
Round thread – withstands loads well, has a significant service life even in dirty conditions. Therefore, it is used in valves or spindles – denoted by Rd, as well as in various sanitary devices – Kr12x2.54.
The internal thread is made with a tap – a screw with longitudinal cutting edges. Consists of a shank for fastening in a wrench and a working part for threading. They are conventionally divided into two types: manual (locksmith) and machine.
A locksmith set for making metric threads is completed depending on the size of the thread:
- one tap (8-18 mm);
- two (6–24 mm) – roughing and finishing;
- three taps (2-52 mm) – roughing, medium, finishing.
Product marking is applied on the shank, where the thread size (M10) is displayed and one risk if it is a rough tap, two for deepening the thread, three or without them – a finishing tap. Sometimes there is a designation with numbers 1, 2, 3.
Combination taps are designed with two sections with different cutting edge sizes, which saves time. The cutting part of the tap can be made in the form of a cone for through holes or in the form of a cylinder for blind holes.
Before cutting an internal thread, a hole of a smaller diameter is drilled, the value of which is in special tables. In the process of work, the tap is kept strictly perpendicular, lubricant is added to the working area. Every 4-5 turns, unscrew the tap and remove the chips, which is convenient to do with a special brush.
The external thread is carried out on an industrial scale on lathes with cutters or thread rolling devices; for one-time needs, dies are used:
- Solid round – ensure high quality, for operation they are fixed in the holder and fixed with set screws.
- Split – they consist of two halves, therefore they have less rigidity, are used for undemanding connections.
- Sliding – used in dies that allow the production of pipe threads of various sizes.
Externally, the die resembles a nut with inside cutting edges and holes for the removal of chips. There are dies for the manufacture of threaded connections of different measurement systems: inch or metric, incompatible with each other. The diameter of the rod to be processed must be the same as the outer dimension of the die. For greater accuracy, paired tools are used, the thread sizes they perform differ by half a millimeter.
For the execution of pipe threads, die plates of various designs are produced. In the body of these devices there are movable cutting dies, which are installed by turning the planes to the required thread diameter. The tools are completed with two sets of dies for pipes with a diameter of 15, 20 mm and 25, 32, 38, 50 mm. In confined spaces, a ratchet die with a ratchet mechanism is used.
Practical example of cutting pipe threads
The work used:
- Die? inch.
- Pipe vise.
- Die holder.
- Machine oil.
- Stainless steel pipe.
1. The end of the pipe being processed is clamped in a vice, the cut is trimmed with a grinder – it must be even. The file runs in (chamfer is removed).
2. A threading tool is put on the pipe, which, thanks to its guide sleeve, immediately rises perpendicular to the pipe. We begin, while pressing, rotate it clockwise – the die should “catch”. We make about two turns, unscrew a little back so that the chips break and add oil. We cut another 2-3 turns – we put it back again.
3. We carry out the thread of the required length, in this case, about 18 mm is enough to screw on the coupling.
4. Next, we twist the die holder and clean the threaded surface from sawdust, that’s it – the work is finished within half an hour.
Having figured out what threads are and how they are performed, it will be possible without much difficulty to independently replace a hairpin or bolt, repair furniture, cut pipes for a summer residence, and much more.