Machine Drawing: Machine Parts

About this unit

Machine drawing is the language used to make and assemble machine parts. This unit introduces the most common threaded fasteners: screw threads, bolts, nuts and washers. They are drawn full size with instruments, using standard proportions expressed in terms of the nominal (major) diameter D of the thread. Knowing these proportions lets you draw a bolt or nut of any size quickly and correctly.

Key ideas

• Screw thread terms: major diameter, minor diameter, pitch, lead, crest, root, flank and thread angle.
• Thread profiles: square, knuckle, BSW (55°) and ISO metric (60°).
• Right-hand and left-hand threads; single-start and multi-start threads.
• Hexagonal and square nuts and bolt heads drawn with proportions based on D.
• Chamfering of nuts and bolt heads, which produces curved arcs on the side faces.
• Plain washers and the assembly of two parts with a nut and bolt.

How to prepare

Memorise the standard proportions used in your drawing book (for example width across flats, nut thickness and washer size in terms of D) and practise drawing a hexagonal nut in two views. Learn the thread angles and profile shapes, and be ready to calculate lead for multi-start threads.