interpenetration

Intersection of Solids

This is a common exam question and can be quite satisfying to do. It has appeared as both a short and long question.

A question is generally broken up into 4 main parts:

1. Reproduce the given plan and elevation (18-20 marks). Standard orthographic drawing, sometimes needs a true shape.
2. Interpenetration of the easy side (4-6 marks). Usually just project between plan and elevation.
3. Interpenetration of the hard side (10-15 marks). Project across surfaces, often needs an auxiliary view.
4. Connecting all the dots (5-12 marks). Is the edge hidden or visible? Label your points to help see what connects to what.

This means that with some decent orthographic skills and a half decent ability to visualise the object, you can about 2/3 of the marks available. The final 1/3 takes a bit more effort and here are the skills you'll need.

Terminology

Apex - the pointy tip of a pyramid or cone

Bend Points - when a line of interpenetration meets the edge of one of the shapes, it turns. The point on the edge where this happens is bend point.

Intersection - one solid going through another

Line of Interpenetration - the edge where the solids meet, this is what we're trying to find

Orthographic Views - Elevation, Plan or End View

Typical Exam Question

Always label your points - it makes things much easier!

The example below is a worked example from Graphics in Design & Communication, p186

1 - Draw Plan and Elevation

• Let the question guide you rather than worry about where to start, do part (a) first etc.
• Make sure you're clear about how to go from a true shape in elevation to the plan.
• Label your points