*note: Special thanks to Kevin Roselli (Metal Solutions LLC) for the photographs of the copper bell tower project in this post

“Whatever good things we build, end up building us…”

There is something fascinating about architectural copper work. The green patina of copper helps tell the story of the structure it surrounds. In particular, projects with radius work are meticulous and often subbed out or avoided by the average roofer.  However, it may pay dividends to learn to bid architectural radius jobs.  With some patience and some practice, you can master the ancient techniques that wow the viewer below.  Lets take a look at some of the tools and techniques needed to complete these projects.

Shrinkers & Stretchers – Getting the radius right

Getting a panel to curve to the proper radius can be tricky. Too often, people think that you need a large expensive machine to get those kind of panels produced.  If you are a small crew that is running into projects like sweep seams for bay windows, or convex barrel dormers, you can affordably get the proper tools to create the radius needed and produce double lock panels.

Shrinker and stretcher units are a good addition to any metal workers shop. These portable units use jaws that are designed to grip the metal and either squeeze or pull the flange in order to bend a curve into the panel.  Notice that a 90° flange must already be turned onto the panel and the flange is what is being “fed” through the shrinker.

Tweaking the Radius for the Perfect Fit

To fine tune your panel to get a perfect radius fit flat against your decking, you can use a Portable Shrinker / Stretcher tool. The portable version has interchangeable jaws for shrinking or stretching and only weighs 6lbs.  This means you can install the panel and complete some final tweaks while the panel is already in place to make sure the fit is snug. It is worth noting that the portable version will move the metal at a fraction of the speed that a bench mounted version will.

Four Steps for Creating a Double Lock on a Radius

  1. Create a metal panel with two 90° flanges on opposite sides. The flange heights should vary from one another by a 1/4″.
  2. Using either the shrinker (inside radius) or the stretcher (outer radius), feed the metal through the jaws and crimp the panel to form the radius needed. It is recommended to start slow and progress toward the radius needed one pass at a time.
  3. Once the radius has been achieved, the panels should be cleated into place and should butte up against one another exposing the 1/4″ difference in heights
  4. Now follow a traditional double lock standing seam method for hammering closed the double lock.  You will need a seaming anvil and a soft faced PVC hammer to work the seam.  Often the 4″ blade seaming anvil is recommended for working with curves

Note: Check out this 9 step how to guide for pictures of this process on a flat sheet

A Bigger, Better, (More Expensive) Method Exists

For larger projects that may require long substantial panel lengths to be curved to specified radii, there is a particular machine that is used.  This machine is called an RBM machine and is manufactured by Schlebach in the EU.