Tip #26
Drill Press (continued)
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Drill Bits

Figure 7-3. The most common types of drill bits are: (A) twist bits, (B) spade bits, and (C) power auger bits. Examples of specialized drill bits include: (D) brad-point bits, (E) Forstner bits, (F) multispur bits, (G) screw bits, and (H) plastic-drilling bits.

There are three types of drill bits commonly available to woodworkers: twist bits, used to drill both wood and metal; spade bits, used when rough splintered holes are acceptable; and power auger bits, which drill slower and leave a smoother hole than either twist or spade bits (Figure 7-3). There are also specialty bits: brad-point, Forstner, multispur, screw drills, and plastic-drilling.

Most woodworkers aren't half as concerned with the type of bit they use as they are with the quality of the hole it leaves. As mentioned, in the course of a single project you might drill dozens of different holes for many difterent functions. For almost every hole you can imag-ine, there is a bit designed to make it a little better and a little easier to drill.

General Purpose Holes--Brad-point bits (also called machine spur bits) are a vast improvement over twist bits. A small point at the bottom of the bit bites into the wood first, holding the bit on center so it will not wander. Two side spurs slice through the wood grains to make a clean entrance, leaving a clean hole. Brad-point bits are your best choice for general drilling in wood. However, they should not be used to drill other materials.

Twist bits, usually associated with metal drilling, can be used to make holes in hard or soft woods. The hole will be rougher than you might want, and there can be considerable feathering or splintering when the bit breaks through, even when the work is supported on scrap stock.

Super-Smooth Holes--Decorative holes and holes for pivoting dowels need to have extremely smooth, splinter-free sides. Forstner bits were designed for just this purpose. They will bore small, shallow holes with flat bottoms and polished sides. Multispur bits will also bore flat-bottomed, smooth-sided holes, but they are designed to drill much deeper and much larger holes than Forstner bits.

Screw Holes--Screw bits will drill a pilot hole, shaft hole, and countersink for wood screws all in one operation. They can be ad-justed for different lengths of screws.

Holes in Plastic--To avoid cracks and splinters, use plastic drilling bits to drill holes in plastic. Plastic-drilling bits will drill clean holes in many types of plastic.

If you drill mostly in wood, we suggest you start with brad-point bits. While they can be purchased individually, it's a good idea to begin with an assortment that includes the most useful sizes-1/4", 3/8", 1/2", 5/8", and 3/4". A complete set of brad-point bits start at 1/8" and increases to 1" in increments of 1/16".

The flutes in a bit are channels that guide waste material out of the hole. If the channels are clogged, waste will back up and both bit and wood will burn. That is why you should not drill deeply enough to bury the flutes. On most jobs it is good practice to retract the bit frequently so waste can be ejected. Adjust feed pressure to the job you are doing and the speed you are using. A heavy feed will clog the cutter; one that is too light is just as bad because the bit will do more burnishing than cutting.

Figure 7-4. Drill bits are secured in the chuck with a special key.

Provide good storage for your bits so they'll keep clean and can't be knocked around.

Drill bits are secured in the chuck with a key that causes the chuck's jaws to close firmly about the shank of the bit (Figure 7-4). Be sure to allow enough shank for the chuck to grip.Warning: Remove the key from the chuck immediately after securing the bit.

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