Technical drawing is an essential skill for biomedical engineers in Kenya, enabling precise communication of complex designs and components. In biomedical engineering, accurate plane geometry drawings support the development and maintenance of medical devices, prosthetics, and diagnostic equipment. Mastery of drawing techniques ensures compliance with industry standards and facilitates collaboration across multidisciplinary teams within hospitals, research institutions, and manufacturing firms. This chapter focuses on fundamental drawing tools and line types that form the foundation of technical drawings in biomedical engineering.

2.1 Types of Lines in Drawings

Technical drawings in biomedical engineering rely heavily on standardized line types to convey detailed information clearly and unambiguously. Line types differentiate object boundaries, hidden features, centerlines, and other essential elements in plane geometry drawings. Adhering to BS EN ISO 128 standards and Kenya Bureau of Standards (KEBS) guidelines ensures that drawings produced for medical device design, hospital equipment layout, and maintenance manuals meet professional and regulatory requirements.

Principal Line Types and Their Characteristics

• Visible or Object Lines: These are continuous thick lines used to represent the edges and contours of visible parts in a drawing. They define the shape of biomedical components such as prosthetic limbs or diagnostic instrument casings.
• Hidden Lines: Depicted as short dashed lines, they indicate edges or boundaries not visible from the current viewing angle, such as internal cavities in a medical pump housing.
• Center Lines: Thin alternating long and short dashes mark axes of symmetry or center points, essential in aligning circular biomedical parts like syringes or tubing connectors.
• Dimension Lines: Thin continuous lines with arrowheads at the ends, used to indicate the length or size of features on a drawing, for example, the length of a catheter segment.
• Extension Lines: Thin lines extending from the object outline to the dimension line, helping to position dimensions clearly without cluttering the drawing.

Standards and Conventions for Line Thickness and Style

• According to BS EN ISO 128, line thickness varies depending on line type: visible lines are thick (0.5 to 0.7 mm), while hidden and center lines are thin (0.25 to 0.35 mm).
• Biomedical engineering drawings typically use a scale where line thickness must remain consistent to maintain clarity when resized.
• Dotted or dashed lines representing hidden features must have uniform dash lengths and spacing to avoid misinterpretation.
• Color coding is generally discouraged in formal technical drawings but may be used in digital presentations to highlight specific features.
• Title blocks and legends should specify the line conventions used to ensure all stakeholders interpret drawings correctly.

Procedures for Drawing and Interpreting Lines in Biomedical Plane Geometry Drawings

1. Begin by sketching the visible outline of the biomedical device component using a thick continuous line.
2. Add hidden lines where internal features such as channels or mounting holes exist, using short dashed lines.
3. Draw center lines for symmetrical parts to indicate axes, ensuring they extend beyond the object outline for clarity.
4. Insert dimension and extension lines carefully, avoiding overlap with object or hidden lines.
5. Label all dimension lines with precise measurements in millimeters, consistent with Kenyan engineering practice.
6. Review the drawing for compliance with BS EN ISO 128 and KEBS standards before finalizing.

Common Errors and Quality Checks in Line Usage

• Using inconsistent line thicknesses can cause confusion about the importance or visibility of features.
• Omitting hidden lines may result in incomplete understanding of internal biomedical device parts.
• Overcrowding dimension lines can clutter the drawing, reducing legibility during manufacturing or inspection.
• Incorrect placement of center lines may mislead assembly or alignment processes in clinical equipment.
• Quality checks should include verifying line types, thickness, and completeness against standard templates before submission.

Chapter Summary

This chapter introduces essential elements of technical drawing, beginning with the use of paper clips and other tools to organize drawing sheets efficiently. It covers the various types of lines used in technical drawings, emphasizing their purposes and standard representations. Students learn the technique of freehand printing of letters to ensure clear and consistent annotation on drawings. The chapter also details the importance of borderlines and title blocks in framing the drawing and providing key project information. Procedures for constructing different angles are explained, followed by methods for accurate bisection of angles and lines to support precise geometric constructions. Fundamental geometric forms such as circles, triangles, rectangles, parallelograms, polygons, and loci are developed through step-by-step construction techniques. The development of patterns for three-dimensional shapes including cones, pyramids, prisms, and cylinders is also covered, highlighting their practical applications. Finally, the chapter concludes with a discussion of different types of tangents to circles, both exterior and interior, and reinforces standard drawing conventions based on recognized standards to ensure clarity and uniformity in technical drawings.