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Bending Bronze Cap Rail Tips and Techniques

Bending Bronze Cap Rail Tips and Techniques

Bending Bronze Rail Tips and TechniquesBelow are some tips for bending Bronze Cap Rail.  Again, these techniques come from a shop demonstration focusing on the specialized skill of forming cap rail. 

Alex Klahm of Alex Klahm Architectural Metals Design Inc., of St. Petersburg Florida and NOMMA (National Ornamental & Miscellaneous Metals Association) published an article in Fabricator Magazine in 1993 that remains the informal industry trade practice for cap rail.  Enjoy the read.  Send comments to ms@macmetals.com.  Additional thanks to Bluegrass Ironworks, David Ponsler and Jerry Grice.

Hot Forming Techniques

Bronze Cap Rail can be bent hot using a rosebud torch as a heat source.  Many craftsmen prefer to do this bending in the evening when they can reduce the light in their shop.  The bronze is heated to a dull red color, which is easier to perceive in the reduced light, and the material is then formed onto pre-formed bars or around forms.  An ability to determine the optimal bending temperature is an important part of the process.  Some craftsmen determine this by rubbing a piece of pine wood over the heated metal.  The optimal bending temperature is reached when the pitch in the wood leaves a brown stain on the bronze.  Other fabricators gauge the bending temperature by making felt-tip marker lines on the bronze bars just before heating them.  The amount of felt-tip marker residue is then used as a “temp-stick” to judge when the heat is right for bending.  Either method can work well in different situations, depending on your own experience and your feel for the technique.

Cold Forming Techniques

Hossfeld Bender 

Bronze Cap Rail can be bent cold in a Hossfeld bender using the flat or cap rail bending dies.  The material is generally covered with two layers of duct tape to protect the bronze from being scratched by the steel dies.  Also, a felt-tip marker is used to mark the duct tape every two inches so that each small bend will be consistent and form a graceful, flowing curve.  While this forming can be done on a Hossfeld using a hand lever, most craftsmen agree that the hydraulic cylinder attachment makes the work much easier.

Greenlee Bender 

A Greenlee bender can also be used with a hydraulic cylinder and foot-operated air pump to accomplish this same cold forming.  Many of us make our own custom dies, or adapt the Hossfeld dies to fit the Greenlee.

Strait-O-Flex

A Strait-O-Flex is a lightweight and portable bending tool that can also be used to form cap rail.  Designed for straightening railings, stair stringers, bar stock and pipe, it is available through J. Blum & Co

Rolling Machines

Many craftsmen achieve consistent curves by rolling the cap rail through a three-headed rolling machine.  A ½ round groove is machined into the rolls to fit the side profile of the material, and as many passes as required are then made to curve the cap to the pattern.

Please share this post with others who are interested in bending bronze cap rail.

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