The Shop Work Horse - Twist Drill bits

If you don't know anything about drill bits this will be a short tutorial, if you are already familiar with them, it can be a brief review. Most of the drill bits will be talking about are commonly available from the hardware store or big box/home center. If you have a hard time finding them locally, you can also get any of the bits mentioned in this article at Rockler woodworking, hartville tools or lee valley tool

Twist bits are made mostly from 3 common types of material.

• Carbon Steel - the cheapest and lowest grade, doesn't stay sharp for long.
• 
  High Speed Steel or HSS - better quality, stays sharper longer.
• 
  Alloy Steels - Most common is cobalt, used to drill stainless steel.

Twist Bit Coatings

Coatings are applied to give bits better performance. The two most common coatings, identified by their colors are.

Black Oxide Coated - Heat significantly reduces the life of a bit, black oxide is applied to the bit to reduce heat build up. Less heat buildup means better drilling performance and longer bit life.

Titanium - Nitride Coated - Titanium - nitride coated bits are easily identified by their bright gold color. This coating increases the surface hardness of the bit and serves as a lubricant as well. Titanium coated surfaces are highly resistant to corrosion.

Drill Bit Length

The length of twist drills are usually expressed as Mechanics, Jobber and Installer. The first two refer too a ratio of the length x the diameter, jobber being 10 times in length as the diameter. These first two are the most common. Installer bits are commonly used in the trades by, Electricians, Telephone & Electronics installers and are 18" in length.


Drill Bit Diameter

Drill bits come in different sizes. Most people are familiar with the fractional drills 1/16" thru 1/2" variety, there are also letter drills A-Z, these are most commonly used when you want to get a specific percentage of threads cut into metal when tapping, number drills 1 - 60, these are the really small bits you'll need for making holes for scroll saw blades, and there are metric drill bits available as well.


Point Type & Angle

General purpose bits are generally ground at 118 deg. Bits can be ground at 60 - 118 deg. for soft materials like wood and plastic. For harder materials like steel, a flatter angle of 138 - 143 deg. is required.

We'll separate these into two categories, woodworking and general purpose & metalworking.

Woodworking - Brad point bits make the cleanest holes for woodworking and are the first bits a woodworker should buy. They come in three styles, utility, radius and lipped. The lipped type makes the cleanest holes as it scores the circumference of the hole before it chips out the center, but cost more and are usually purchased on-line. The utility type is the most common and cost less, it still makes a clean hole, but not as well as the lipped type.

The pilot type is also commonly available, most people will recognize this as the style DeWalt sells, these work well for both wood and soft metals like aluminum and brass.

General Purpose & Metalworking -

• Regular or Plain Point -The most common, also the cheapest, is difficult to center and wanders easily. Best to use a center or prick punch before drilling.
• Split point -The tip is split at the center. this makes starting a hole easier and keeps the bit from wandering as you begin drilling.
• Pilot Tip Design -The pointed tip starts drilling on contact without wandering. it also doesn't lock-up when the bit breaks through the back side of the material being drilled.