Introduction: Metalworking 101
It’s often necessary to do basic metalwork when building and repairing objects around the house or while repairing appliances. Basic metalwork involves marking, cutting, drilling, cutting internal and external threads, filing and joining. It’s not difficult to work with metal, but, like working with wood, it requires specific skills and specialized tools. Fortunately, most of this work can be done with the kind of inexpensive hand tools that you can buy in a hardware store.
Other processes, such as brazing, welding, machining and grinding, require more advanced skills and equipment than those we show here. The only power tool you really need for basic metalwork is an electric drill with a 3⁄8-in.-dia. chuck, although for large jobs, a drill press is helpful. Good information can also be considered a tool. Contact toolmaker L.S. Starrett Co., 121 Crescent St., Athol, MA 01331. Its free, 73-page booklet, Tools & Rules, covers precision measuring and marking and can be ordered from its advertising department at firstname.lastname@example.org or by writing to the address above. Another fine book available from the company is The Starrett Book For Student Machinists. It costs $14.25 postpaid (credit card orders only).
Step 1: Making Metal
Before you can accurately cut or drill any workpiece, you must mark it with layout lines. The most common layout tools are a centerpunch and a scriber (Photo 1). A combination square is also essential. The scriber can be either a short length of sharply pointed, hardened steel or a pencil-like marking tool with a carbide tip. In either case, it is used to scratch a fine line on metal. The centerpunch has a blunt point and it’s made from a steel rod. It’s tapped with a hammer to mark the center of holes that are to be drilled.
The dimple it leaves behind keeps the drill from spinning away from the point to be drilled—more about this in a moment. Scribed marks on shiny metal are hard to see, so a coating of fast-drying blue layout dye is used to provide contrast. Lines scribed on the coated surface stand out sharp and bright. In a pinch, a black felt-tip marking pen may be substituted for the dye (Photo 2). Use the kind of felt-tip pen that is designed to mark different kinds of materials. On black iron or hot-rolled steel, use a white soapstone metal marker to make coarse lines. These markers are sold in industrial-supply catalogs, and in some hardware stores and welding-supply stores. You can also use a sharp pencil to mark metal, but first, you must apply a coat of fast-drying, light gray metal primer.
Step 2: Cutting
Metal can be cut with a hacksaw, cold chisel, or in the case of sheetmetal, snips. Generally speaking, hacksaws are used with blades in three levels of coarseness: 18, 24 or 32 teeth per inch (Photo 3). Blade coarseness depends on the thickness of the stock to be cut. A coarse-tooth blade is used for heavy stock and a fine-tooth blade for thin stock. An important rule of thumb is that at least two, but ideally three, teeth should always be in contact with the edge of the stock.
There are two different kinds of hacksaws: high-tension and standard. High-tension hacksaws hold the blade with greater tension than standard types. This keeps the blade straight even during heavy cutting, helping you to cut accurately. High-tension saws are used when making cuts that could subject the blade to twisting and bending, or when the cut could be suddenly interrupted. It’s important to use a bimetal blade in a high-tension hacksaw. A bimetal blade is made from two different types of metal in such a way that it can withstand the stretching forces imposed on it by the hacksaw frame and by the cutting.
A standard blade, made from one piece of metal, will shatter when used in a high-tension hacksaw frame, especially during the demanding cutting for which such a hacksaw is used. To use a hacksaw properly, grip the frame firmly with both hands, apply pressure on the forward stroke, and very slightly lift the saw on the return stroke (Photo 4). For rough cutting, especially when the metal can’t be cut with a hacksaw, use a cold chisel (Photo 5). A cold chisel is a rugged tool designed to shear off unheated metal.
Aviation snips are useful for cutting sheetmetal. They come in three color-coded types. Those with red handles cut straight or to the left, those with green handles cut straight or to the right, and those with yellow handles make only straight cuts (Photo 6).
Step 3: Drillling
Although there are many kinds of twist-drill bits, there are two basic types used in everyday metal drilling: high-speed steel (HSS) and carbon steel. HSS bits are preferable because they last longer than carbon steel types. A split-point cobalt steel bit is used for drilling stainless steel and other extremely tough metals (Photo 7). The bit’s split point reduces the tendency of a spinning bit to rotate away from the point at which you want to drill—a phenomenon known as walking.
The split point also causes the bit to penetrate the metal more quickly and with less force than is needed with other bits. In many cases, using a split point eliminates the need to mark the hole with a centerpunch.
Regardless of the type of metal you are drilling or the type of bit you are using, reduce pressure on the bit as it exits the work. This prevents the bit from grabbing the surrounding metal and violently twisting the drill and perhaps your wrist.
Step 4: Thread Cutting
Cutting internal threads is a process known as tapping. To do this, first choose a tap to match the pitch and number of threads per inch on the fastener you plan to use. Although metal threading kits (also called tap and die kits) can be large and quite extensive, a small kit suitable for the home workshop will have taps sized for the most common fasteners, so the process of matching taps to common bolts is easy.
Cutting internal threads is a two-step process. First, you drill a hole, then you cut threads on its wall. The drill bit used to make the hole must be of a specific size to work with a given tap, and the tap will have the drill-bit information stamped on its side (Photo 8). Also stamped on the tap’s side is the kind of thread it will cut—you use this information to match a tap to a bolt. It’s helpful to first countersink the tap hole—that is, drill a slightly larger diameter hole at its top—then turn the tap into the hole.
Keep the tap perpendicular to the workpiece surface, and turn it backward slightly after each half-turn forward (Photo 9). Use ordinary machine oil to lubricate the tap when cutting threads in steel and kerosene for tapping in brass and aluminum. Don’t use any lubricant when tapping holes in cast iron. A die is used to cut external threads, and the process is known as threading. To thread a rod, first bevel its end and clamp it in a vise. Place the die on the rod, and lock the die guides in place. Keep the die perpendicular to the rod, and turn it backward slightly after each half-turn forward (Photo 10). Use the same kinds of lubricants as in tapping. Like a tap, a die will have the necessary thread information stamped on it.
Step 5: Filling
Files are used for shaving, smoothing and fitting metal parts, and for basic sharpening, such as with axes and lawnmower blades. For most basic metalwork, a double-cut machine file and a single-cut mill file will work well (Photo 11). They are available in four levels of coarseness: coarse, bastard, second and smooth cut. Mill files leave a smoother finish than machine files but cut more slowly.
Files may also be abrasive devices (Photo 12). A diamond file uses abrasive diamond particles to do the cutting. The beauty of this tool is that it’s very long-wearing and can be used in a back-and-forth or even a circular motion. You also can make a file by gluing emery paper to a piece of metal. You can make such a file in any size or shape you like and dispose of it after it becomes worn or dirty.
For typical crossfiling, grip the file with one hand on the handle and the other hand on the point. Stroke the file forward across the workpiece at a shallow angle. Apply pressure on the forward stroke and lift the file clear of the work on the return stroke (Photo 13). Drawfiling is done when a smooth, polished finish is desired. Use a single-cut file gripped as shown (Photo 14). Push and pull the file at a right angle to the workpiece.
Step 6: Joining
A simple means of joining two pieces of metal is to use a blind rivet. This is especially useful for joining thin pieces of aluminum or steel when the back or blind side of the workpiece is not accessible. The rivet has a single flange, and it is held on a pin with a ball-shaped end. The ball does two things: It prevents the rivet from sliding off the pin, and it presses a second flange into the rivet’s blind side. The plain end of the pin is inserted into the rivet tool, and the ball-shaped end is placed into the hole—the existing flange is placed firmly against the metal’s surface.
When you squeeze the rivet tool’s handles together, you pull the pin through the rivet. The two pieces of metal are forced together because the existing flange is bearing down on one side of the joint, while the ball is drawing through the rivet, forming a flange on the opposite side. As the handles reach the bottom of their travel, the pin is stretched to the point at which it snaps off, and the two pieces of metal are clamped tightly between the existing flange and the one newly formed (Photo 15).