How to Safely Drill Metal
Rotating drill bits can be hazardous if your metalworking rig is not set up correctly. To safely drill metal, use a vise to secure the metal piece to a stable work surface before drilling.
You can drill metal in a variety of ways using a portable drill or a drill press.
Using A Drill-Press
Because of the force of its rotating bit, a drill press can be hazardous. Work clamped too loosely can be caught by the spinning bit and sent flying, or clothing can get tangled in the bit.
- To prevent mishaps, never use your hands to hold the work you are drilling. Use at least two C clamps to fasten the work to the machine's table. Special drill-press vises are good for holding small or odd-shaped objects.
- Roll up your sleeves and tuck in your shirt for safety's sake. And never wear work gloves when you use a drill press. The loose fabric of the glove could be caught in the bit.
- Always wear safety goggles when operating a drill press — or using a hand-held drill.
Choosing the Right Drill Speed for the Job
Choose the most effective drill speed, expressed in revolutions per minute (rpm), by finding the hole diameter in the left-hand column and the metal you are drilling in one of the three right-hand columns. These figures are approximate and may not correspond exactly to the speeds that are recommended by the manufacturer of your drill press. In general, the smaller the metal bit and the softer the metal, the faster the speed you will need.
Drilling High-Precision Holes in Metal with Power Tools
You may frequently need to make holes in sheet metal to accommodate fasteners and other mechanical parts that require an opening of an exact size. Although an ordinary electric hand drill bores a hole that is precise enough for some of these needs, use a drill press for more professional work. This machine combines a powerful, variable-speed drill with a secure, adjustable work surface. You change the drill's speed by moving a motor-driven belt from one pulley-step to another. In this way, you can vary the torque, or turning force, of the drill to suit the hardness of the metal.
With any type of drill you determine the size and shape of the hole you'll make by the drill bit you choose. A common twist bit a pointed metal cylinder with a helical channel that spirals down its length — makes a straight (but sometimes inexact) hole. A twist bit bores into the metal and carries the cut chips up the channel and out of the hole. In soft sheet metals such as aluminum or copper, such a bit often cuts a ragged hole; for these metals you should choose a sheet-metal bit, which has a point flanked by two cutting flanges.
Always use high-speed drill bits for making holes in metal. Fashioned of the hardest steel, these bits range in diameter from less than 1/64 inch up to 1 inch. Sizes are designated in different ways: by letters from A to Z, by wire-gauge sizes, in millimeters, in inches, or by numbers. To make holes larger than 1 inch, you can fit the drill with a hole saw — a toothed cylinder that cuts holes up to 6 inches in diameter and up to two thirds the depth of the hole saw itself..
For perfectly precise holes up to 1-½ inches in diameter, you will need to ream the hole after you drill it, either by hand or machine. Hand reamers are straight bits with four or more lengthwise cutting edges. They gradually pare away the inside of the hole as you rotate the reamer. Adjustable hand reamers are available, but they are less exact than fixed-size reamers. Machine reamers fit in a drill press.
Anytime you drill a hole, you will need to use a special metal-cutting fluid that reduces friction and cools the bit as it turns. You will also need clamps and vises to hold the work exactly where you want it and to prevent it from being wrenched from your grip. To mark the place where you will drill, use a center punch to make a small dimple for the drill point. You can find all of these metalworking supplies at most hardware stores.
If you don't need the precision of a drill press you can use a heavy-duty electric hand drill, which has the advantage of being easily transported to the job site. But unless it is a variable-speed drill, you can only slow it for metalwork by a technique known as feathering — pressing the trigger in repeated short bursts.
Drill Press and Bits for Working with Metal
A drill press consists of an adjustable table beneath a motor-driven spindle and bit-holding chuck that lower the spinning drill into the metal. Inside the machine's head, a pair of four-step pulleys and a vee-belt connect the electric motor to the spindle.
The chuck grips the drill bit. You lock the bit in place by tightening the chuck with a cogged key. Pulling on the feed handle lowers the bit. The operator controls the hole's depth either by setting the depth stop or by raising or lowering the drill-press table. The spindle, rotating inside a sleeve called the quill, retracts into the head when not in use.
You'll use two kinds of drill bits for metal. For drilling metal thicker than ¼ inch, the high-speed twist bit (inset, left) has a shank, a helical channel called a flute that carries drilled debris out of the hole, and a land — the untooled section of the shank, rimmed with a cutting edge beside the flute. The flat cutting tip is called the web. A sheet-metal bit (inset, right) cuts a clean edge around a hole in thin metal, thus preventing any tearing of the metal.
Marking the Hole on Metal
To locate the hole on the metal workpiece, use a ruler and a scriber to draw two short lines intersecting at right angles at the center of the hole. To align the bit and help keep it from wandering, make a tiny dent at the center point, using a center punch and a ball-peen hammer.
Adjusting the Drill Speed on the Drill Press
Determine the necessary drill speed, then set the drill to operate at that speed. Open the drill press belt guard and release the tension on the pulleys by unscrewing the motor-housing knob. To change speeds, push the motor frame forward and slip the belt from one pulley level to another, according to the speed ratings printed on the nameplate of the drill press or listed in the owner's manual. You'll obtain the slowest speeds and the highest torque at the lowest tier of pulleys, with the belt looped between the smallest motor pulley and the largest spindle pulley. Conversely, you'll obtain the fastest speed when the belt is looped around the highest pulleys.
Make sure the belt runs horizontal between the pulleys. Then push the motor back to its original position and tighten the motor-housing knob.
Drilling the Hole
Put the drill bit into the chuck and tighten the chuck. Adjust the drill press for the depth of the hole by lowering the bit alongside the work and turning the depth stop to the desired point on the calibrated stop rod. Then raise the bit just enough to slide the work under it, using the quill lock to hold the bit so that you can position the punched hole exactly under the point. Clamp the work well with C clamps. Do not hand-hold the work, clamp it in a vise or to the machine table.
Loosen the quill lock and turn on the power to the drill press. Place a drop of cutting fluid on the hole you punched previously, pull on the feed lever and begin drilling. Apply even pressure. Use a brush to remove chips and shavings as they collect, adding more cutting fluid as you work. If smoke begins to drift out of the bored hole, ease up on the feed handle and check the color of the metal chips. They should be silver or straw yellow. If they are bluish the metal is overheating, and you should add more cutting fluid and reduce the speed of the drill press. When you finish the hole release the feed handle slowly to retract the bit, then turn off the power.