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4 JOINT
4.1 TYPES OF JOINT

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.

4.2 AN REPRESENTATION AND DENOTATION OF SCREW-THREAD ON DRAWINGS

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 is a screw-thread on a cylinder surface, and conical on 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.

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