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Metalsmithing 101: Dapping

Learn more about this process of forming metal sheet by hammering. The process is easy to do with just a few basic implements. 
 
Dapping Everything you need
One of the simplest ways to transform metal sheet into a volumetric shape is to dome it. Goldsmiths call this process dapping. Silversmiths call it sinking. In either case, it refers to forming metal sheet by hammering, and the process is easy to do with just a few basic implements.

Dapping usually involves sinking flat metal into a depression in a wood or metal block to create a dish shape. In large-scale work, the metal is often formed into a depression with a rounded face of a hammer or mallet. For jewelry-scale work, forming is usually done with a dapping block, a hammer, and punches.
BasicDappingSet
THE TOOLS

The standard shape for blocks used for dapping small to medium objects is a cube, with various sizes of round, concave depressions on all six sides. For medium and large objects, dapping blocks are usually flat, with graduated round, concave depressions. 

The most common and least expensive dapping tools are wood blocks and punches. You can buy these ready-made and nicely finished, but you can also make your own punches from hardwood dowels. You can also fashion a tree stump or scrap lumber into a basic dapping block by gouging a depression in the surface and smoothing it into a concave shape. 

Steel dapping blocks and punches are widely used. Steel blocks are most often used with corresponding round punches. Sets of graduated, highly polished metal punches range from professional-quality to less expensive options. If you’re buying an inexpensive set, check each punch closely; the shape and finish of an economy punch may be less than perfect. The shape and depth of the hemispheres in metal blocks vary; older versions often have deeper depressions than modern blocks. The more expensive blocks generally have deeper depressions.

You can use many types of hammers or mallets to strike punches. I favor a weighty chasing hammer for its solid impact — after all, this is what chasing hammers are designed for! If you’re using wood blocks and punches, you can use a mallet instead of a chasing hammer. A weighted, deadblow mallet has the edge over a rawhide or plastic mallet; using a striking tool that’s too light will cause you to swing the tool with a heavier hand, which doesn’t improve aim or accuracy. I prefer to use a chasing hammer regardless of which dapping tools I’m using.
 
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THE PROCESS

To dap metal sheet, you’ll use punches to hammer the sheet into a succession of depressions in your dapping block, forcing the sheet into smaller and smaller depressions until it becomes a domed hemisphere that’s the desired final size. You can complete this process using as few as three to four depressions. The dome’s surface will be smooth and even. 

The efficacy and result of the dapping process is affected by which tools you use: metal, wood, or a combination of both. Using a steel block and steel punch together is the most efficient forming method. If you need precise, perfectly domed hemispheres (say, if you’re making hollow beads), this is a reliable approach to forming halves of a sphere. 

The steel-on-steel combination has a downside: It will also thin and stretch the metal. As the metal is forced into a contour between the steel tools, it also work-hardens. Depending on the type and thickness of metal, you may have to anneal your dome occasionally. 

You can use wood punches with either a steel or wood block to form a smooth dome without thinning the metal or marring its surface. The wood-on-wood combination takes more time and a slightly different approach. Wood punches aren’t generally available in the same variety of evenly graduated shapes as steel punches. Also, wood punches are usually less domed than steel punches, and the depressions in wood blocks are generally shallower than those in metal blocks.

To dome a disk, first determine the appropriate size of your disk blank. Start with prebought disks, or cut them yourself using a jeweler’s saw or disk cutter. 

Tip!
CALCULATING DISK DIMENSIONS FOR DAPPED HEMISPHERES

To make a dome that’s a specific diameter, you’ll need to start with a metal disk in the appropriate size. What’s the appropriate size? Use this formula, taken from the book Professional Goldsmithing, by Alan Revere, to find out. The formula accounts for the stretching that results from dapping with a steel block and punch. First, determine the desired diameter of the dome (measuring from the outside of the rim) and the thickness of the metal sheet. 

(Dome diameter – Metal thickness) x 3.14 x 0.9 ÷ 2 = Disk diameter 

Example: For a 15 mm dome in 0.7 mm metal sheet: (15 – 0.7) x 3.14 x 0.9 ÷ 2 = 20.21 mm

To make a closed form of two hemispheres, the calculation is slightly different.

(Dome diameter – Metal thickness) x 3.14 x 0.9 ÷ 2 – (2 x Metal thickness) = Disk diameter

Example: For a 15 mm dome in 0.7 mm sheet metal: (15 – 0.7) x 3.14 x 0.9 ÷ 2 – 1.4 = 18.81 mm
 
Place the disk over the dapping block depression it most closely matches in size. Choose a punch that is slightly smaller than the depression. Set the punch on the disk, and strike the punch with the hammer until the metal sinks into the depression. Your first blow will make a shallow indentation; each successive blow will carry that indentation inward toward the center of the disk. 

When the metal conforms completely to the contour of the depression, move it to the next smaller depression in the block and switch to a smaller punch. Form the dome in stages until you have achieved the desired size and shape. A wood dapping block can also be used with steel punches to smooth and refine a dome’s contour to the desired shape. 
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ALTERNATE METHODS

If you don’t have a dapping block, you can dome metal using a wood punch with common materials. A sandbag or a cushion of leather, fabric, rubber, or cardboard are suitable substitutes for a dapping block. You can use steel punches with these materials, but a small steel punch will likely leave dents on the back of the disk that may appear as dimples on the exterior of the dome. You can smooth these out in the final shaping and refining process. 

When shaping over a cushion, it’s often necessary to hold the metal upright, at a steep angle to the dapping surface. This allows the punch to bend the edge of the metal downward at an angle, creating a dish or depression. Rotating the disk slightly after each blow of the punch and keeping the strikes of the tool evenly spaced will form the metal into a symmetrical dome. You may need to work through several sizes of punches with overlapping blows to smooth and refine the shape into a nice contour. 

You can dap shapes other than a hemisphere in the same fashion by using alternative shaped blocks, or by dapping them over a cushion or sandbag. You can make any shape of punches and depressions in wood to use as dapping tools. Just follow the same principles and apply the same approach as for a dome.
 
Doming with a nylon mallet
FINISHING UP

Forming a dome is a process of dapping, adjusting, and refining. Thicker and harder metals will likely require annealing during the doming process. If so, anneal the metal before you dap it into the final depression. During the final stage of forming a dome, you may need to straighten the dome’s edge; you don’t want to be working with freshly annealed metal when you straighten the edge, or you may collapse the form. This last course of dapping ensures that the dome is at least partially work-hardened before you straighten the edge.

Doming often leaves the edge of a hemisphere slightly uneven. To correct this, place the hemisphere concave-side down on a steel block or anvil so the hemisphere’s edge slightly overhangs the edge of the block. Rotate the hemisphere to see where the gaps are between its edge and the block. Gently tap these spots with a nylon mallet to bring the metal down onto the block, correcting and straightening the edge of the dome. Make final adjustments with a file to achieve a perfect edge. 
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