Radial Line Pattern Development

In Parallel Line Pattern Development, we required parallel element line or bends. Some objects are of a conical shape and parallel line will not work on them. Rather, we will look at using Radial Line Pattern Development.

In radial line, we develop patterns for shapes that have a taper, all element lines (bends) must radiate back to a common point, a radius point. We need two things for this process to work:

  • A radius point that is on centre (right cone).
  • A radius point that is within a reasonable distance.

So, when we find ourselves determining if radial line will work, we look at those two things. If the cone is a scalene or oblique cone, it will not work. If a radius point is 40 feet away, it is not worth the effort with this process, another should be chosen, but if it will fit in our bench space, then it will work.

Being one of the simplest forms of layout, it allows us to create these patterns with accuracy and speed. If we can use radial line, it is an effective and efficient choice.

Learning Objectives

  1. Understand the process of Radial Line Pattern Development and its uses.
  2. Understand the language of Radial Line.


  1. Apex – the intersection point of a cone, as seen in the elevation view.
  2. Slant Height (small or large) – the hypotenuse of a cone, outside edge. The slant height is always a true length in the elevation view.
  3. Stretch-Out Angle/Arc – the angle or arc which encompasses a radial line pattern.
  4. Frustum – a cone with the top cut parallel to the base.
  5. True length – a dimension or line that is not distorted by the view.

Basic Steps

  1. Draw a full elevation view and plan view complete with all element lines.
  2. Swing the slant height with your compass. Remember, in the elevation view, the slant height is always a true length. This arc is also called the stretch-out arc.
  3. Make the length of the stretch-out arc equal to the distance/circumference of the base. There are many ways to accomplish this, but we will focus on the most common method, using step-offs.
A step-off can come from calculating the circumference and dividing by 12 or simply set your compass to one of the profile divisions. Keep in mind that either way will have accuracy problems, it depends on how accurate the pattern must be. We will cover the most accurate method, layout by mathematics, in another unit later.


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Pattern Development: Sheet Metal Level 1 Copyright © 2021 by Brian Coey is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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