Hammer forming is one of the oldest methods of shaping metal — and one of the easiest for DIYers to employ. Often used for automotive body work, this technique has many applications for other metalworking projects. Using only basic shop tools and a little practice, you can fabricate one-of-a-kind parts for just about any project.
Virtually any type of sheet metal can be hammer formed, although the thickness and type of material will determine the amount of effort needed to form it. Simply put, steel will be harder to form than brass, aluminum or copper.
A hammer form can be made from a variety of materials; the best choice depends on the metal being formed as well as the number of times the form will be used. Wood, plywood and medium-density fiberboard (MDF) are excellent choices for single parts being formed out of aluminum and light-gauge steel. If you intend to make several parts or form heavier-gauge metals, you’ll need stronger form materials, such as metal.
To learn more about this process, we visited WyoTech, an automotive-based technical college in Wyoming. Instructor Eric Griffith demonstrated some of the techniques he uses to create truly one-of-a-kind parts that look factory-made. Follow the photo sequence to see how you can fabricate an engine air cleaner; then you can apply the techniques shown to your own projects.
Use an 11-in.-dia. air filter as a template to trace an oblong shape on a 3/4-in. piece of MDF. Then squeeze the filter to the desired shape before tracing a rough outline around it.
A final size of 8-3/4 x 12-3/4 in. was established with this filter. Clean up the rough pencil outlines using a compass and straightedge.
Use a jigsaw to cut a 5-1/8-in.-dia. hole in the MDF to accommodate the combined size of the carburetor and the thickness of the metal to be used for the air cleaner.
Use a router and roundover bit to ease the edges of the carburetor opening. This detail will improve airflow to the carburetor and helps to maintain strength in this critical area.
The clamp (left) is cut 1/4 in. smaller on all sides than the form (right), and the clamp’s center hole is 3/4 in. larger.
Rough-cut a piece of 14-gauge aluminum sheet 2 in. larger than the form; then cut a 4-in.-dia. hole in the center using a fly cutter mounted in a drill press.
Sandwich the metal between the clamp and the form, and begin the forming process by making overlapping strikes with a soft-face hammer.
To completely shape the aluminum inside the form, you’ll need to make several “corking tools” out of 1-1/2-in. wood dowels.
Use the corking tools slowly and steadily to achieve a smooth result. Trying to work the metal too quickly will create a crude product.
Use a relatively flat corking tool and overlapping hammer strikes to shape the aluminum smoothly against the bottom of the form.
Before removing the sheet from the form, use a 1/2-in. transfer punch to scribe a line 1/4 in. from the outside edge of the form.
A throatless shear was used to trim the formed sheet to the scribed line. Tin snips or a similar tool can also be used.
After inverting the aluminum in the form, use several clamps to secure it for the hammer-forming process.
Use a soft-face hammer to make repeated overlapping strikes at a 45-degree angle to define the metal edge.
After removing the piece from the form, use a hammer and dolly to lightly planish (smooth) the outside edge and smooth out imperfections.
The process of stretching the aluminum over the form may leave the edge a little wavy. You can quickly clean this up using a metal file.
With the base of the air cleaner complete, repeat the process to form the top cover, but without the carburetor center hole.
After forming the top, drill a 1/4-in. hole for the carburetor stud. (Eric recommends using a Unibit to prevent tearing the aluminum.)
To give the top a little more strength and a more finished look around the stud hole, fabricate a simple “press form” using 1/4-in. steel plate and a rod.
Use a large C-clamp to force the press form into the top cover. Don’t overtighten the clamp or you could stretch the metal too far.
Work with care and the finished product will have a professional appearance. Although this project is relatively basic, you can use the same techniques for any project, whether you’re building parts for a hot rod or a custom aluminum table for your patio.
This project is part of HANDY's Top 5 Collection: Metalworking Ideas & Tips.
Click here to check out the other four metalworking articles in this collection.