What to Look For When Purchasing a Drill Press - Part II
What to Look For When Purchasing a Drill Press - Part II
Bits and Drills
To be technically correct, you bore a hole in wood (even though twist bits are used) and drill a hole in metal. Today, however, this terminology is not followed rigidly and usually the two terms "bore and drill" are used interchangeably in discussion of power drills. However, the bits used to cut into wood and those used to cut into metals are usually different from each other.
Wood Bits. Several types of wood bits are used for boring wood with a drill press.
A machine spur bit has a brad and lip point and is one of the cleanest, fastest-cutting bits for dowel holes. The opening in the spiral of a machine spur bit is called the throat. In some styles of machine spur bit the throat is designated by the term flute. Both terms mean the same thing. These bits come in standard sizes from 1/4 to 1 in. and are generally available in thirty-seconds of an inch.
To drill larger holes in wood a spade or speed-type bit is generally recommended. A spade bit is flat and has a brad point. Bits of this style range from about 3/8 in. to as large as 1-1/2 inches. They relieve the chips easily, and binding is not much of a problem.
Spade or speed bits have a tendency to split not only the front surface of the wood, but the back surface as well. The front surface can be drilled without splintering by starting the hole slowly. (That is, do not press too hard. Also, be sure the bit goes in square to the wood.) The back surface can be drilled clean without splintering by using either of two methods: First, as soon as the pilot (the center of the bit) comes through the back, stop drilling. Complete the hole by drilling from the back. Second, place a piece of scrap behind or under the workpiece. Drill through the workpiece and into the scrap piece.
Holes larger than 1-1/2 in. can be cut with a rotary hole saw. This is literally a saw bent into a circle. It will make a clean, round hole in anything a hacksaw will cut, including metal, plastic and composition board. The pilot bit of the hole saw's mandrel, or shaft, can be centered on a punch mark to locate a large hole with great accuracy. The most popular sizes of hole saws range from 3/4 to 2-1/2 in. in diameter. Some come with fine-tooth blades that cut slowly but smoothly, while others come with several teeth for quick but rough cutting. The task of the rotary hole saw is to remove a diameter of wood. Therefore, the tool must cut completely through the wood's thickness. To accomplish this, manufacturers make these saws for various cutting depths. Thus you can buy a tool to cut 3/4 in. plastic or another to cut through a 1-1/2 in. thick floor joist.
One-size rotary hole saws are more expensive. More economical is the type with a shaft, or mandrel, on which saws of various sizes can be mounted. The cup-like saw shells range from approximately 5/8 to 2-1/2 in. in diameter and are deep enough to cut through 3/4 in. thick material. (A few are designed to cut up to 2 inches.) Be sure to tighten the chuck for maximum grip when using a hole saw, since its large diameter puts great stress on the spindle. At any angle other than 90 degrees, the hole saw will start cutting on one edge instead of all around. So take pains to start the pilot drill straight. In thick or hard wood, withdraw the saw occasionally to clear the chips and help cool the hole saw.
Fly-cutter-type circle makers are available for cutting holes from 1/2 to 8 in. in diameter. Actually, the size of the hole is controlled by loosening a set-screw and then sliding the cutter blade in or out. For best results when cutting circles in wood, cut halfway through each side of the wood, or back up the wood so the cutting blade does not tear and splinter the wood as it comes through. The cutter blade should be set back behind the center drill bit approximately 1/2 in. (where the flutes end on the drill bit), so the blade will be held firmly in place when it begins to bite into the wood. Since the circle cutter has an off-center load, it works more smoothly and with less vibration at slower speeds. When using a fly-cutter, be sure that the workpiece is securely clamped to a solid surface.
With either the rotary hole saw or fly-cutter, splintering of the far side of the work will be prevented if you bore the hole about halfway through and then finish cutting it from the other side of the work. The pilot hole, having passed through the work, centers the tool for its second cut.
What we have covered is only a sample of the many bits available to you. Most can be used on a drill press, with one exception: Never use a self-feed bit on your drill press. A self-feed bit has a screw at the end. This bit will quickly dig into the material, attempting to swing the workpiece itself. Or if the workpiece is tightly clamped, the motor will stop. This operation is dangerous to both you and your machine.
Twist Drills. While twist drills are designed for drilling metal, they can be used to make holes in most materials -- wood, plastic, ceramic or other materials. They often are rated as the most efficient of all cutting tools, based on the length of the cutting edge in proportion to the amount of metal that supports it. This is a tool that will stand a tremendous amount of abuse and still keep cutting. Nevertheless, any drill will work better and last longer if properly ground.
The lip or cutting edge of a drill is that part of the point that actually cuts away the metal when a hole is drilled. Ordinarily, it is as sharp as the edge of a knife. A point angle of 118 degrees should be maintained for general work. However, for extensive drilling in wood, a much sharper angle should be used.
The standard 118 degree angle drill is easily checked with a drill-point gauge. Gauges in a variety of styles can be purchased at a nominal cost, or can be made from sheet metal. The markings on the edge need not be exact, since they are used only to check the length of one lip against the other. In use, the drill body is held against the edge of the gauge, and in such a position that the angular edge is over the cutting lip of the drill. The gauge will then show whether one edge of the point is at the correct angle. Besides being ground to the correct angle, both lips must be exactly the same length. If not, the resulting hole will be out of round and larger than the drill.
The shank is the part of the drill that fits into the spindle or chuck of the drill press. Drills used on the drill press commonly have straight shanks to fit the adjustable chuck on the machine. It is also possible to mount taper-shank drills by using a taper-shank spindle.
Twist drills are made of either carbon-steel or high-speed steel. High-speed steel drills, made of an alloy that usually contains tungsten, chromium and vanadium, are designed expressly for work on metal and can take considerable heat without weakening or becoming dull. Usually, high-speed drills can do their work without the use of a coolant. The carbon-steel drills are softer, and are used solely on wood and soft metals or plastics. They cost much less than the harder high-speed steel drills but will wear quickly and become distorted if overworked. When drilling soft metals, they require a flow of cooling liquid on the tip to prevent burning. Carbide-tipped drills are also available. These are primarily used for drilling masonry, ceramics and extra-hard materials.
