The crafting or constructing of some metal projects requires the need to join two or more pieces of metal. There are several techniques in doing this through the use of seams. Seams are used to join two pieces of metals to meet the requirements of a project. Among the common metal seams used are:
1. Butt seam. This is the simplest form of seam made by butting together the edges of metals. The metal should be cut carefully so that the edges will join accurately with a tight-fitting seam edge. If the piece is rectangular or cylindrical in shape, file the two edges at the same time by moving the piece back and forth across the face of a file that has been locked in a vise. Since most butt seams are fastened permanently by soldering, it is a good idea to file a slight V-joint to enable the solder to run freely along the seam.
2. Locked or dovetail joint. This is used in metalcraft work because it gives unusual strength and looks inconspicuous. To do this, on one edge of the joint, divide the length into equal sections about 1/8 to 1/4 inch wide. Mark back from the edge a distance equal to the width of the section. Layout squares alternately and cut one square after the other.
On the other edge, mark the laps in the same manner in order that the edges will lock together. The seam is improved by laying out the laps in dovetail fashion.
With a tin snip, cut out the laps of the seam on either side that are to be removed. Use a file to finish the joint so that it will fit perfectly. The seam is usually soldered on the side to make it permanent.
3. Lap seam. This is made by lapping one edge of metal over the other and riveting or soldering it. The most common kind is the plain lap. If the two metal surfaces is to be made smooth, a countersunk or offset lap is made. An inside or outside corner lap may be used on the corner of sheet metal projects.
4. The double seam. This is used to join the bottom of the sides of rectangular or circular containers. The double seam can also be used in making corner joints on a rectangular container.
5. Folded or grooved seam. This consists of two folded edges that are hooked together. In a grooved seam, the folded edges are locked together. Note that there are three thicknesses of metal above the joined sheets.
Hand Groover
Hand groovers and a hammmer are used to lock a grooved seam. Hand groovers vary in size from Number 0 to 8. The common sizes are Number 0 with a 3/8 inch groove, Number 2 with a 5/16 inch groove, and Number 4 with a 7/32 inch groove. The groover should be wider than the width of the finished seam. Number 2, for example, is made to lock at a 1/4 inch seam.
In making this seam, it is necessary to allow extra material by adding an amount equal to three times the width of the seam. Usually half the amount of stock needed is allowed on either side of the seam during layout. For example if a 1/8 inch folded or groove seam is to be made, 3/8 inch of extra stock must be allowed with 3/16 inch added as an allowance of the two pieces to be joined.
The fold on either edge of the seam is made in the same manner as in making a hem. However, do not close the fold completely. In making a seam on a continuous piece such as a cylinder, the edge must be folded in the opposite way on each end. Join the two edges together by placing the seam over a solid backing. Close the joint by striking it with a wooden mallet.
If the grooved seam is to be made, select a hand seamer that is a groove equal to the width of the seam. Place the groovebed directly over the seam and strike it with a hammer until the two edges are flushed. Move the hand groover along the seams to make it water-tight.
The following are the steps in making a folded or grooved seam:
- Determine the width of the seam and allow extra material equal to three times the seam width. For example, if it is a 1/8 inch seam, allow 3/8 inch extra. Sometimes additional material allowed for the rise in the seam, specially if the metal is heavier than 22 gauge. This amount should be about one and a half times the thickness of the metal.
- Fold the edges by hand or in a bar folder. The metal should be bent as in making an open hem. When using a bar folder, adjust the machine to the seam to be made on one continuous piece, such as a cylinder. Remember to fold the ends in opposite directions.
- If the project is to be of some particular shape like cylindrical or rectangular, form it at this point.
- Place the metal over a solid backing, such as a stake if it is circular, or over a flat metal table if the pieces is flat. Hook the folded edges together. To make a folded seam, strike the seams along its length to close it, using a wooden mallet.
- To make a grooved seam, select a hand groover that is 1/16 inch wider than the seam. Hold the groover over the seam, with one edge of the groover over one edge of the seam. Strike the groover solidly with a metal hammer to close one end of the seam. Slide the groover along as you strike it, to complete the seam. You can further lock the seam with prick punch marks about 1/2 inch from either end of the seam.
- Check the seam after it is locked. Make sure the joined sheets of metal are level in height, the seam well formed, smooth, and without a neck.
