How to thread a lathe


Do not use a drill or other mechanical tools for tapping. An exception is the universal drilling machine, whose rotation is adjustable up to 0.3 per second, and which also has a reversing function (reverse rotation). A simple drill can be damaged, and so can the tap itself.

Do not deviate from the vertical and perpendicular position when drilling, otherwise the drill bit will break. If the same is done to the tap, it could be bent and the alignment given to it in the factory would be upset. A tap can only be straightened by using a lathe or a drill as a guide. However, a non-ideal, slightly crooked tap immediately leads to poor-quality internal threads in the workpiece. bolts and studs turn hard or refuse to screw in properly at all.

Threading on a lathe classification, deciphering and diagrams

Automatic thread rolling machines are used for mass production of hardware. Individual parts are produced by threading on lathe machines. The pitch is maintained by a specially installed lead screw. Setting is performed according to tables. Threads of up to 40 mm in diameter are made with taps and dies, regardless of the type of protrusion. On large parts, weighing over 500 kg, with a diameter exceeding the length of the part, threading can be performed on lathe-turning machines with a guitar in their design.

Threading on a lathe

When moving with feed (constant) along the workpiece being machined on the lathe, the tip of the pick on the workpiece traces a helical line. The inclination of the latter to the plane oriented perpendicular to the axis of movement of the specified part, in the environment of specialists is called the angle of increase of the helical mowing line. The inclination we have described depends on two factors:

By the pitch of the mowing line we are interested in, we understand the distance between adjacent lines. The pitch is measured along the axis of the product to be machined.

When the cutting tool deepens into the part, a helical surface is formed along the helical mowing line, which is just called a thread. Its task is to ensure the planned movement, sealing or articulation of the elements of various mechanical devices.

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All existing threads are referred to as either tapered or cylindrical. The first of the voiced are formed on conical surfaces, the second, as you yourself understand. on cylindrical. The function of a threaded joint depends on the thread profile. By this we mean the diameter of the threaded contour in the plane. There are most often threads in three profile variants:

They are made in multiple or single thread. The former are formed by two threads (sometimes by a greater number of threads), which are positioned at an equal distance (equidistant) from each other on the workpiece; the latter are formed by a continuous single thread. The exact number of threads in multiple threads is calculated at the point where the thread starts. It is important to know that the nature of these threads is conditioned by two indicators. pitch and travel. The stroke is understood as the distance between the points (of the same name) of one thread (of course, we are talking about one thread). This parameter is equal to the number of starts multiplied by the thread pitch.

Threading on a lathe: technology

Types of threads

Blanks for threading are used in the form of cylinders and cone (tapered) components. Threads may be cut as male threads (spiral grooves) or as female threads. The structure of the threaded joint is determined by its profile. In practice, several profile types are used:

In turn, thread grooves are made in one or more strokes. In the first case, the spiral groove is presented in a single version: only its turns are adjacent to each other, the others (accompanying) are not used. Thread pitch is the distance between the central edges (recesses) of neighboring turns in relation to each other. The thread groove stroke is determined by multiplying the thread pitch by the number of thread windings or steps of several thread grooves (if more than one thread groove is used).

After defining the thread type, the appropriate cutters are selected. Such a tool is a combination of a shank and a working part. The quality level of the helical groove is determined by the execution of these components. The shank has basically a square or regular multifaceted cross-section, which ensures its alignment. It is difficult to attach the torch to the chuck without a shank. The working part cuts a helical groove. It includes cutting planes and sharp edges. Cutter angle is determined by the alloy the workpiece is made of. They are mainly used to cut steel and nonferrous parts. After selecting the type of cutter, proceed to the technological process.

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Threading tool

Tap. Threads are cut with dies on the outside surface. They are made in the form of a nut. Holes are drilled into the workpiece to receive cutting elements and to remove swarf. The die has cutting elements on each side that form a fence cone (angle 20⁰-30⁰). In the middle part there is a calibrating zone.

Slotted tap is fixed in the collar with screws. After each revolution of the die, turn it one-third of the way back. This is needed to clean the holes of chips and obtain a high-quality threaded surface.

Tap. A tap is used for tapping internal threads. It has cutting edges that are produced by making longitudinal or helical grooves. Grooves form the front surfaces on the teeth. The working area of a tap forms the fence and gauge areas. The tapping part is also called the cutting part. It is tapered and plunges progressively.

A distinction is made between hand, machine and wrench taps. Hand taps are made as single taps and as a set: for roughing and finishing threads. A set consists of 3 taps. Tapping is indicated by the number of round notches on the shank (1 for roughing, 2 for semi-roughing and 3 for finishing).

A roughing tap has the largest tapping hole. Taps have a square shank in order to transmit the working force with a screwdriver. Taps are subdivided for threading through holes and blind holes. Taps are made with a straight or curved shank.

Cutter. The threads are cut by the tip of the tool fixed in the slide as it moves relative to the rotating workpiece. In doing so, the thread pitch of the pick is equal to the distance between the vertices of the consecutive projections in the workpiece axis.

Threading cutters are structurally sound:

  • Solid (made of high-speed steel or tungsten carbide);
  • with soldered tungsten carbide plates (GOST 18885-73);
  • Assembled with mechanical fastening of SMF (changeable multifaceted plates).

A tapped or indexable multi-faceted plate (SMF) cutter must have cutting angles that ensure the production of the appropriate thread profile. These picks are used for tapping metric and trapezoidal threads.

NC cutters are used on CNC turning milling machines, which can provide the required cutting conditions and obtain a finished part in one cycle (machining centers).

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Always use coolant (emulsion, sulfofresol, etc.) when threading to ensure thread quality.

How to cut a thread on a manual lathe (Intermediate method ideal for home workshop & hobby engineer)

High-speed steel grades for cutters: P6M5K5, P6M5, P9M4K8, P9K5, P12F3, P9M4K8.

Threading with a die

Tapping of external threads is an operation without which it is difficult to imagine any production of machines, mechanisms or supporting structures. Riveting and spot (or plane) welding are not always appropriate here, which means that screw or bolt connections are still the solution.

Tapping with a chisel

The basic thread-cutting tool are picks. Typology of cutters by design features:

  • Mono-stranded, with a carbide plate, high-speed steel, brazed and prefabricated;
  • Prismatic single- and multi-piece prefabricated, soldered;
  • Disk single- and multi-piece prefabricated.

Turning picks are mounted on a slide, in mandrels, counter-rotation heads (vortex threading with 4 elements).

The quick mounting of the prefabricated cutter holds the exchangeable multifaceted plate with the finished shaped profile. Primarily used for tapping metric and trapezoidal threads.

The apex configuration of the finishing tool is sharpened according to the profile geometry of the screw groove. The front angle is set in inverse proportion to the hardness and thermal resistance of the material. When machining ductile metals the angular value increases.

The template setting of the thread cutter along the central scythe of the machine determines the surface finish. Side faces that are not involved in threading, have no contact with the ingot, are sharpened in excess of the thread lift’s angularity.

Equipment errors during threading are taken into account when setting the degrees of the working face. A 30′ reduction is common practice. The recess is rounded off by the radius of the tool.

Drilling or boring for the cutting of internal threads is performed with an increase in diameter to 0.2 mm for fragile metals, up to 0.4 mm. for ductile materials, taking into account the thickness of the wall. The end groove for non-cutting threads is 0.3 mm smaller in cross-section than the pitch.