This is a project I've run at MakerFaire for several years now. It incorporates the basic techniques of metalsmithing in a five minute lesson that is accessible to a very wide range of abilities. It is also an introduction to Fold Forming, a novel method of metal working that can rapidly produce unique 3D forms from sheet metal. Once you've accumulated the tools and materials, it is possible to take these techniques in many different directions. Some suggestions are offered in the final section.
Step 1: Tools and Materials
Thin Copper Sheet: 24 gauge (0.5mm or .020") thick in 1" x 3" or 4" pieces. These are sizes which are the most amenable to achieving good results with a wide range of people. Fold forming can be practiced on most types of sheet metal in scales ranging from jewelry to large sculpture.
Cross Peen Hammer: The most important characteristic of this hammer is the shape on the narrow end. It should be a rounded wedge shape without any sharp edges. My favorite hammer for fold forming is a 300 gram "Locksmith" hammer from Peddinghaus. It is possible for a handy person to make this by modifying an existing hammer with a grinder and sander. A brand new Locksmith hammer will still need to be prepared by sanding away any edges and corners. This process is referred to as "dressing" the hammer.
Something to hammer on: Traditionally, this would be an anvil. Minimally, what is required is a flat piece of steel. This can be a small piece of at least 1/2" thick steel, 3" x 3" or larger. Cold rolled steel from scrapyard, cleaned with a flap wheel on an angle grinder will work. Alternately, a "Bench Block" can be purchased from any place that sells jewelry tools.
Opening Tool: A bowl scraper from Bed, Bath & Beyond. It should be a stiff plastic like polyethylene or polypropylene. Silicone will be too soft. Many people just use a blunt stubby blade like a pen knife or oyster knife to open.
Metal Shears: Smooth jaws will require less cleanup than serrated jaws
Cleanup Tools: Files, Burnishers. A burnisher is primarily a polished piece of steel. Any smooth steel will do the job, like the shaft of a screwdriver or the back of a butter knife.
Torch: We need to heat the small rectangles of copper to about 1000 degrees F. A hardware store propane torch is sufficient to do this. Additionally, you'll need a fire safe surface to place the copper on. A pair of firebricks will work.
Step 2: Folding and Cutting
We start by folding the rectangle of copper in half the long way. To precisely fold metal in half, use the same technique you would if it were a piece of paper. Start with a gentle bend in the middle, line up the edges in a teardrop cross section, then hammer backward from the edges, creasing the metal.
Since leaves come to points, trim the folded metal. If there are overhangs because the copper is not exactly folded in half, this is an opportunity to remove them. Ideally, the cut line is a gentle curve. This requires some practice to get right. Cutting through 2 layers of metal simultaneously can be a challenge for some people. A simpler method is to cut a straight line, then file the curve in later.
After cutting, burs on edge may need to be cleaned up. They are usually found where the shears had to stop and start again. The shape of the curve can also be refined at this point with a file.
Cutting can also be done with a jeweler's saw. It will be slower but much more complicated shapes can be achieved.
Step 3: Hammer Time
When a cross peen strikes the metal, it stretches it in a direction at right angles to the peen. This is in contrast to a ball peen which stretches the metal in a circle all around the strike.
Conceptually, we divide the trimmed and folded copper in half lengthwise. We will hammer on only one side of the division. The side we hammer will get longer and longer with each hammer blow. As the hammered side lengthens and the other side does not, the entire form will begin to curve. The amount of curvature is a function of the density of hammer blows. If you want more curvature after hammering on one side, flip the copper over and continue to hammer on the same half (open or fold) you were hammering on before.
The two sides of the form are the side with the fold and the open side. Hammering on the open side will, after opening, produce leaf like forms. Hammering on the fold side will produce pod like forms.
Step 4: Forging Tips
Some suggestions on how to avoid whacking your holding hand follow. Keep the holding hand off the anvil. You can hold one side of the form on the edge of the anvil. Start hammering in the middle and work away from the holding hand. When you reach the end, grab the other end, and again, start from the middle working away from the holding hand. When I'm working with small children, I'll put the anvil on the ground and masking tape the ends of the form to the anvil.
When you drive a car, you look at where you are going. Forging is the opposite. It is important to look at where you've been. In particular, pay attention to the last hammer mark. It should be a straight line dent (1). If it is a dot or wedge shape, away from the edge(2), that tells you the hammer is slightly twisted from the correct orientation. Before the next strike, twist the hammer in your grip to compensate. Dots and wedges on the edge(3) indicate the opposite twist.
Let the hammer do the work. You shouldn't be pushing the hammer into the metal. The experience should be more like letting the hammer drop. If you need more force, get a bigger hammer.
Take your time. It is easier to get it right and then speed up rather than trying to get it right while going fast.
Step 5: Opening
The hammering has made the metal stiff. This is known as "work hardening". Continued hammering would eventually crack the metal. Before we can open the fold, we need to make the metal soft again. As a baseline, try bending the metal at this point.
Optionally, now is the best time to place holes for stringing on one end of the form. For speed, I usually use a Roper-Whitney hand punch but the holes could just as easily be made by drilling a 1/8" hole through both layers.
To anneal (soften) the metal, it must be heated to 800-1000 degrees. The temperature will be visible as a dull red glow when the torch is removed. Quenching the hot metal in water allows us to continue immediately.
Bend the form in half and then bring it back to straight. You should find it a lot easier to bend now that the metal has been annealed. This will open up a small pucker which will allow you to get the tip of your opening tool into the fold. Use a small twisting motion to open the fold and a rocking motion to move further down the closed fold. The goal is to separate the 2 sides to the point where you can get your thumbs on each side.
Opening with the thumbs together will make a symmetric leaf (or pod). Opening with the thumbs offset, will put a twist in the form.
Step 6: Finishing
If a stray hammer blow has caught an edge and as a consequence, there is a small bulge away from the edge, it will be sharp. It should be filed back to the edge. To smooth out the edges, you can rub a burnisher along it in different orientations. In addition to removing any sharpness, the burnisher will leave a shiny polished rim.
Step 7: Further Study
If you made a leaf, try making a pod and vice versa. If you've done both, try hammering on the open side partway before switching to the fold side for the rest of the way. The first picture of the pendant was hammered 2/3 on the open side and the bottom 1/3 on the fold side.
After hammering and annealing, instead of opening, you can do another round of hammering. This cycle can be repeated, with the curvature increasing with each round of hammering.
Try different starting shapes, such as a long (1" x 12") strip. With repeated rounds of hammering, a long strip can be made into a spiral or a helix.