Презентация "Thread cutting"

Thread cutting

Internal and external thread

Created by Severyukhin Maxim

Tapping of external thread

The thread is a screw groove formed on the rotating parts. Widely used for joining parts between (fastening) and for transferring motion (as, for example, in the screw of a lathe).      The main elements of the thread: the angle of the helix a, the thread pitch p, the profile angle y, the outer and inner diameters. Depending on the purpose of the threaded connection, different types of threads are used.     In the direction of the turns the thread is right and left. Most often, cut the right-hand thread. For cutting external fixing threads use a special tool-dies. They are round, thread-rolling and sliding. Round die is made in the form of a nut made of hardened steel. The thread of the die is crossed by through-holes. The resulting cutting edges in the form of a wedge and grooves ensure the cutting of the workpiece and the simultaneous release of chips . In order for the end face of the rod (workpiece) to fit into the die from the end faces, its thread has a lower profile height. This is the so-called fence part. Round dies in accordance with the standard are provided for cutting metric threads in diameter from 1 to 76 mm. They are laid in the nests of the plate holder and fixed there with studs with a slot for a screwdriver.

Elements of thread. Types of thread: a-right; b-left.

In the case of a thread-rolling plate, roll-adjustable rollers with thread are installed. The metal of the workpiece is not cut, but is squeezed out. Due to this, the surface of the thread is more clean, and the thread itself is better and more precise.    Sliding prismatic dies consist of two separated and retractable half-plates.    In order to cut the thread die on the rod, it is necessary first determine the outer diameter of the thread and its pitch p. These the data are indicated on the plate. Then, from the table, determine the diameter of the rod for this thread and select the workpiece.

In this case, it must be taken into account that when the thread is cut, metal, especially copper, soft steel, "stretches". As a result, the diameter of the rod slightly increases and the pressure on the threaded surface of the plate increases. It heats up, the shavings stick to the cutting edges, and the thread becomes "torn". All this reduces its quality. Therefore, the diameter of the rod should be less than the outer diameter of the thread by 0.1 ... 0.3 mm, depending on the size of the thread. If the diameter The rod will be smaller by 0.4 ... 0.5 mm external thread diameter, the thread profile is incomplete.

Kinds of dice: a-round; b-thread rolling; c-sliding. Table for determining the diameter of the rod for the thread.

Thread cutting: a - chamfering; b - installation of the workpiece along the angle piece; c - installation dies; d - tapping; e - checking the quality of the thread.

The selected workpiece must be straightened, marked, cut off by marking and, fixing it in the vice, with a file to remove the chamfer to ensure that the fence part of the plate is easier to grasp the metal. It is necessary to check the quality of the die by external inspection and screwing it onto a bolt or stud with intact thread. It is also necessary to carefully check the quality of the dowel attachment in the plate holder to exclude its possible skewing and slippage in the nest.

Before threading, the length of the rod is marked on the rod, the rod is fixed in a vice so that the end projecting over the upper plane of the jaws is larger than the cut part by 20 ... 25 mm. The rod is pivoted at a 90 ° angle to the upper planes of the jaws. Plate, fixed in the plate holder, is placed on the upper end rod and with a slight pressure, not allowing the skewing of the plate, rotate it. After cutting 1-2 threads of thread, once again check the coincidence of the axes of rotation of the plate and rod.

After this, oil the threaded part of the stem, cut the plate and rotate the plate, evenly pressing on both knob arms. Rotation should be reciprocating: One or two turns to the right and half a turn to the left. At the same time, the shavings break, go through longitudinal opening. This facilitates threading and improves its quality.

The quality of the cut thread in production conditions is checked by threaded micrometers, threaded calibers and threaded plugs. In school conditions it is allowed to check the threads with nuts.     After the end of the work, the plate is removed from the plate holder, thoroughly cleaned with a brush from the chips, wiped with rags and oiled.     Thread cutting can also be performed on a lathe machine tool.

When cutting the thread, the plate should be securely fastened to the support plate. When working, be careful not to get your hand between the handle of the plate and the support. For lubrication, use a brush or lubricator. Do not blow off the chips from the plate, but use a brush with a note. Do not allow oil to enter clothing or hands.

The enterprises use hardened screws, which screw through the punched holes in two or more connected parts of sheet metal. Screws, cutting into threaded holes, connect these parts. This type of threaded connection is economical and speeds up the assembly process. Many enterprises now use hardened self- extruding screws for steel and cast iron parts, the hardness of which is less than the hardness of the screws.

Thread on bolts and small diameter pins are made on automatic lathes while making bolts themselves. Screws and bolts are also stamped on presses.     In mass production, the rolling of the external thread is widespread. After the passage between the rollers, a thread is formed on the rod. In some thread-cutting devices, solid carbide plates are used instead of rollers.

CUTTING INNER THREAD

An internal thread (threaded hole) cut into the tap . It consists of a shank and a work piece. Shank tap is attached to the collar or Chuck of the machine. The working part of the tap is a screw with longitudinal or helical grooves for threading. As in dies, in the working part of the tap there is a fence part to facilitate the entry of the tool into the hole. Screw grooves, similar to longitudinal holes in the die, form cutting edges. On him same are getting away shavings.

Hand taps for cutting metric threads produced in a set of two of tap for thread with a diameter of 3 mm and three (No. 1 roughing No. 2 medium and No. 3—finish) for thread with a diameter of more than 3 mm. Taps included in the kit are of different diameters and threading parts, and different shape of profiles. On the tail of all taps kit knocked out circular risks (1,2,3) or affixed numbers taps, and also identifies the size of the thread—diameter and pitch.

For rotation of the tap when cutting threads by hand is used device—driver.

Before you start threading in the hole,

perform a layout of places of the hole with its mandatory nigerianism. Taking into account the sizes of the future carving on the table select diameter of a drill.

When tapping the internal thread, the metal is squeezed out, decreasing the diameter of the hole.

Thread tapping; a - tap installation; б - check by a square of tap setting; c - tapping; e - checking the quality of the thread.

Therefore, the diameter of the drill must be somewhat larger than the inner diameter and less than the outer diameter of the thread. If the diameter of the hole is less than the required, the tap will break, and if more-thread is incomplete, weakened.

The drilled hole is treated with a countersink. The use of this tool allows to improve the quality, reduce the taper, ovality of the lateral surface of the hole. Zenker work the same way as a drill. For quality threading it is important to properly fix the part in the vice and install the first tap in the hole. The part is fixed so that the surface with the hole is parallel to the planes of the jaws of the vice, and the tap is perpendicular to the plane of the part and to the jaws. Perpendicularity (angle 90 °) is checked by a square.

Thread the thread as follows. First, the tap No. 1 is installed. First, its threaded portion is lubricated with oil. Pressing the wrist button with the left hand to the trowel, the right smoothly rotate it to the right until the tap breaks into 1-2 threads. At the same time, the right angle is maintained, if necessary, by directing the tap. After the tap has taken the correct steady position and the threading began, the wrencer is taken with both hands and rotated with light pressure, intercepting every half-turn. In order for the chips to break and go into the grooves of the tap, it is rotated back and forth: torus forward and half a turn back.

Having completed the passage with the tap No. 1, it is turned out, inserting the tap No. 2, threading, installing the wrench and cutting. Finally, thread the tap No. 3 and check the thread.     Deep thread holes are drilled to a depth slightly greater than the length of the thread.