Machine Drawing: Free-hand Sketches

About this unit

Engineers often need to show a part quickly without instruments. This unit develops free-hand sketching of threads and common fasteners, drawn in good proportion rather than to exact scale. It covers the conventional representation of threads, studs, different kinds of screws and rivets. Neat proportioned sketches are an important skill for communicating ideas on the shop floor.

Key ideas

• Threads are not drawn as true helices; standard conventions using thick and thin lines are used.
• Studs: plain, square-neck and collar studs, threaded at both ends.
• Machine screws and cap screws: round head, cheese head, 90° countersunk head, hexagonal socket head and grub screws.
• Rivets are permanent fasteners; their heads include snap, flat, pan and 60° countersunk.
• Proportions based on the shank diameter D keep sketches realistic.

How to prepare

Practise sketching each fastener in two views (front and top or side) keeping proportions roughly correct. Learn the line conventions for external and internal threads thoroughly, and remember the typical use of each type of screw and rivet head. Questions may be situation-based, asking which fastener suits a given need.