Tips for making thin metal designs safe and strong
By Charles Lewton-Brain
When precious metal prices are high, it’s natural for jewelers to turn to thinner metals to keep their costs down. However, there are two issues to consider when working with thin metal: designing for maximum strength with minimal material, and dealing with the edges to make it safe and strong.
To learn how to best work with thinner metals, it is helpful to look outside our industry to plastics manufacturing, as there is a great deal of overlap between the fields. Both industries use casting and experience similar problems with flow and shrinkage. And the materials are similar as well in that both plastics and precious metals are terrible materials for building anything strong. They are soft, floppy, and weak. Therefore, whether you’re working in plastic or 18k gold, structural design is very important.
This is best illustrated by plastic cutlery manufacturing. If a plastic fork designer can shave a tenth of a gram off of a design, then the company can save $50,000 that year. Because this is the same problem a goldsmith has in designing a thin piece while retaining its strength, I tell my students to study the ribs and supports of disposable plastic forks and spoons. By studying the plastic cutlery, they will better understand the principles of constructing with thin materials. Just as with a plastic fork, if you can have supporting ribs, I-beams, and struts in the right places, then you can replace thickness strength with structural strength, allowing you to use less metal and saving you money.
The second problem when working with thin metal sheet is making the edges thicker for safety. Thin metal edges on jewelry can be dangerous. When evaluating her own work, a friend of mine asks herself, “Would I want to be wearing this in a car accident?” In this age of litigation, this is a serious question that all jewelers should ask themselves.
If you do create a piece with thin, sharp edges that could cause harm to the wearer, there are a number of ways to make the edges thicker and safer.
1. The easiest way is to fold the edge over. This can be done by hammering the metal end over a sharp 90° edge, such as a bench block. You can do either a simple one fold or a double fold for additional strength.
2. You can also wire the edge. To create, bend the metal edge over a sharp 90° corner to make an L shape. Then tap it until it forms a U-cross section. Lay the wire into the U and tap the sheet tight around the wire. This will create a very strong edge.
3. A standard solution for thickening the edge of a plate in silversmithing is to solder a wire to the end or the edge of a sheet. It can be tricky to get the fit right and you need to make sure the seam is tight all the way around the edge.
4. You can also solder modified tubing to the edge. To do this, create a tube but leave the seam unsoldered. Then slip the tubing over the edge of the sheet and solder it in place. This technique has the advantage of accommodating any curves along the edge.
5. My favorite method is to thicken the edge by “upsetting” it. This entails hammering against the edge until it thickens. The fastest tool to use for this is a margin roller. While it’s used primarily for eliminating porosity in castings, if used against a metal edge, it will thicken it quickly and dramatically. You can use your flex-shaft to roll it over using multiple passes to make the edge thick, smooth, and rounded. The key is that it has roller bearings that spin so it won’t chew up your metal.