Introduction to Machine Drawing

Study Notes

Machine drafting specializes in creating technical drawings of machine parts and components.
Orthographic views are used to depict size and shape accurately.
Familiarity with terminologies enhances understanding in machine drawings.

Key abbreviations include A/F (across flats), Alum (aluminum), ASTM (American Society for Testing Materials), and DWG (drawing).
Symbols represent specific attributes like CPL (cutting plane line), OD (outside diameter), and RAD (radius).

Importance of manufacturing processes in representing a part's features accurately.
Understanding the part's intended use enhances the effectiveness of the drawing.

Material selection is essential based on characteristics such as availability, cost, workability, stability, and machinability.
Key considerations include weight, wear resistance, corrosion resistance, and strength.

Ferrous Metals: Contain iron and have magnetic properties; includes pig iron, cast iron, and steel.
- Pig iron is the base for producing all types of iron and steel.
- Cast iron is preferred for casting parts; examples include engine blocks and parts requiring durability.
- Malleable iron has refined structures for improved toughness.
Non-Ferrous Metals: Do not contain iron, are typically non-magnetic, and corrosion-resistant.
- Brass: Alloy of copper and zinc; easy to machine and cast.
- Bronze: Alloy of copper and tin; used for bearing applications.
- Aluminum: Lightweight, extracted from bauxite; alloyed for strength and flexibility.

Processes that give parts their basic shapes include machining, casting, forging, stamping, and welding.
Machining: Material is cut into desired shape and size, often using lathes for cylindrical shapes.
Casting: Liquid material is poured into molds to solidify; includes sand casting and die casting.
Forging: Metal is shaped by force; includes cold and hot forming for increased strength.
Stamping: Shaping flat sheet-metal by pressing through dies.
Welding: Joining metals by melting and cooling; provides high strength and is ideal for small parts.

Secondary processes refine parts after primary shaping to meet specific dimensions outlined in drawings.
Drilling: Creates cylindrical holes for fitments; accuracy is variable.
Reaming: Finishes drilled holes to precise dimensions.
Boring: Enlarges existing holes.
Counterbore: Enlarges a hole to a required depth for a flush fitting.
Spotface: Provides a machined area over a hole, typically on rough surfaces.
Countersink: Bevels the edge of a hole for tapered shoulder accommodation.
Knurling: Creates a textured surface for improved grip; can be varied by pattern.
Chamfer: Beveled edges that eliminate sharpness on handled parts, enhancing safety.