Engineering Drawing - Part 2

Terminology & representations of standard components

Here are some examples of commonly used engineering components and features of components.

General:

Housing: A component into which a 'male' mating part fits, sits or is 'housed'.
Bush/bearing: A removable sleeve or liner. Known also as a simple or plane bearing.
Boss: A cylindrical projection on surface of component.
Curved slot: Elongated hole, whose centerline lies on an arc. Used usually on components requiring adjustment.
Rib: A reinforcement, positioned to stiffen surfaces.
Fillet: A radius or rounded portion suppressing a sharp internal corner.
Key: A small block or wedge inserted between a shaft and a mating part (a hub). Used to prevent relative rotation of the two parts.
Key way: A parallel sided slot or groove cut into a bore or a shaft, to 'house' a mating key.
Tee Groove (slot): Machined to 'house' mating fixing bolts and prevent them from turning.
Flat: A surface machined parallel to the shaft axis.

Fasteners:

Bolts, screws & studs:
Threaded fasteners. Bolts have a shank partially threaded, whereas screws are threaded along the entire length.

For guidance on dimensioning, see second next image. 

The last three examples here are called set screws and are used to position or lock components. 

This diagram gives approximate dimensioning methods for drawing hexagon headed metric bolts, nuts and plane washers.

(Manufacturers data sheets may give more accurate measurements.)

Circlip:

Internal & external.

Pins:

Split Cotter Pin: Used to lock components, prevent fasteners from coming 'un-fastened'. e.g. lock-nuts on suspension systems.
Cotter Pin: Used to retain components, usually where loads are transmitted.
Dowel Pin & Taper Pin: Provides location, alignment.

Features usually relating to components turned on a lathe:

Holes:

Drilled: Loose tolerance, for pilot holes or clearance holes for fasteners.
Reamed: Accurate finishing process after drilling or boring.
Counterbore: Usually used to recess the head of a square shouldered fastener.
Countersunk: Usually used to recess the head of a countersink screw.
Spotface: Used to clean up and level the surrounding area, usually for a fastener or something such as a hydraulic fitting using a seal.

Screw threads:

Female thread, through: Usually drilled and tapped.
Female thread, blind: Usually drilled and tapped.
Male thread: Usually cut with a die, turned or rolled. Note use of undercut or groove and appearance of thread in sectioned view.
Male & Female: e.g. a fastener in a tapped hole. Note here that the tapped hole is sectioned, the fastener is not.

Compression Springs:

Tension Springs:

Diamond & Straight Knurling:

Bearings:

Some examples of rolling element bearings. Arrows indicate directions of load bearing.

Deep groove Ball Bearing

Angular contact Ball Bearing

Roller Bearing

Taper roller Bearing

Thrust Bearing

Standard drawing representation of a bearing

Long components:

Rectangular bar: Round bar: Round tube:

Gears:

Bevel:
Spur:
Worm & wheel:

Shaft ends:

Square: Frequently used for hand driven adjustments with removable handles, such as those found on machine tools, etc.
Serrations: Often used for push fit components such as plastic fans or pulleys, or levers such as motorcycle gear shifters.
Splines: Usually used for transmitting rotational torque and allowing an axial 'sliding' movement. Examples can be found on automotive drive shafts. The figures opposite show splined shafts and housings in sectioned and non-sectioned views.

Belt drives:

V belt drives: Used for transmission of rotary power, good for space restricted applications. Vbelts grip on the sides of the V. Often found on automotive engines to drive alternators and water pumps, or on pillar drills, and other industrial drives.
Timing or synchronous drives: Used for transmission of rotary power, as are v-belts, and, because of the toothed design (no slip) they are used for timed (synchronized) drives, where relative rotational positions have to be controlled. Some type of tensioning system is usually required. These drives are often found on camshaft drives on modern automotive engines, replacing chains.