AN REPRESENTATION AND DENOTATION OF SCREW-THREAD ON DRAWINGS

TYPES OF JOINT

JOINT

QuestionS for SELFcheck

1. Where are Axonometric projections used?

2. What types of axonometric projections do you know?

3. What are difference between dimetry and isometry?

 

 

Machines and mechanisms can be generally divided into component parts which form the unique functional system of the united elements and details.

Joints of details can be split-face and fixed.

Split-face joints allow to connect and disconnect details without a damage or plastic deformation of the both details.

Fixed joints are impossible to disconnect without a damage or plastic deformation of details of this connection (joints by welding, soldering, agglutination, press joints by riveting, etc.).

Split-face joints are divided into mobile in which the relative moving of connecting details (the key, splining but other) is possible, and immobile in which the connected details do not move in relation to each other (screw-thread joints by fixings, etc.). Let’s consider sectional screw-thread joints. Examining this question it is necessary to find out basic determinations and classification of screw-threads. Basic determinations of screw-threads are resulted in State Standard 11708-66.

A screw-thread is a surface formed at the spiral moving arbitrary plane a contour on the cylinder, conical or other surface of rotation.

All screw-threads are drawn conventionally on drawings, in accordance with the requirements of State Standard 2.311-68:

on a bolt (external thread): major diameter – by a mainline, minor – by a continuous thin in the distance not less than 0,8mm and no more to the size thread pitch from a thick mainline, on the left side view the minor diameter of screw-thread is shown by an arc, broken in an arbitrary place out of axial lines, length of arcs is ¾ circles;

in an opening (internal thread): minor diameter – by a continuous thick line, major – by a continuous thin line, on a left side view the major diameter of screw-thread is drawn by an arc on ¾ circles, the distance between is the same as for a screw-thread on a bolt .

The limits of screw-thread on the length of a bolt or an opening are drawn by a continuous thick line.

For all screw-threads (except of a pipe and one conical inch) conventional denotations are marked above the size line of major diameter. Pipe screw-threads, cylinder and conical are marked by the lines of foot-notes with pointers and shelves above which the conventional denotation of screw-thread is written. For a conical one inch screw-thread above a shelf the conventional denotation and standards on its basic parameters are written.

A cylinder screw-thread isa screw-thread on a cylinder surface, and conicalon a conical surface. For implementation of screw-thread joints it is necessary to have two parts on one of which a screw-thread is on an external surface (external thread), and on the second – on internal surface (internal thread). A thread formed clockwise and moves along the ax of rotation from an observer is called a right-hand thread. A plane contour that moves anticlockwise along an ax from an observer forms a left-hand thread (LH).

A thread can be formed by spirally moving of one or a few identical plane contours which are located densely near each other along the ax of rotation. In the first case it is a single-start thread, in the second – a multiple-start thread (double-start thread or triple-start thread).

The thread profile is determined by the shape of the cutting tool. They are triangular, square, acme, round and others.

According to their purposes screw-threads can be fastener, motion (translating) (transformation of rotation of motion of one detail on straight line motion) and special.

Let’s consider the basic parameters of screw-thread on the example of metric thread, shown in figure 4.1.

Figure 4.1 - Basic parameters of screw-thread

Parameters of a metric thread: d, d1 - according to major and minor diameters of external and internal -threads, d2 is a middle diameter of a screw-thread, a - a thread angle, Р- a thread pitch, Н- a height. The thread pitch Р is a distance between two neighboring points of thread profile. A lead of thread t– is a distance on which one turn of a screw-thread surface will move along the ax of a screw-thread.