The Fundamentals of Drills

Drills are used in a variety of operations, from maintenance and repair to high volume precision holemaking. When selecting a drill it is important to keep the following steps in mind: Choose the right drill style, grade and length for the job, match the tool material to the workpiece material and select the best drill point for your application. For improved tool performance and tool life, add a coating or surface treatment.

With all the choices in the market, choosing the right drill can be difficult. If you know the diameter and depth of the hole, amount of holes you need to make and the type of job, you are already halfway there. 

Styles:
Straight shank drills are the most common style in the world. Shank size always matches the cutting diameter.
• Twist drills are the most widely used style in the world. For use in the widest application in ferrous and nonferrous materials
• Parabolic drills are for deep-hole drilling, reducing the need to peck
• Slow spiral drills are used for long chipping materials, such as aluminium and copper
• Fast spiral drills are used for small chipping materials like stainless steel
• Straight flute drills are designed to drill the hardest steels

Reduced shank drills are a popular choice for maintenance and repair. Because the shank size is smaller than the drill diameter, they can drill holes larger than the typical drill chuck capacity.
• 3/8" reduced shank drills holes up to 1/2" with a standard 3/8" chuck
• Silver and deming (1/2" reduced shank) drills holes up to 1-1/2" with a 1/2" drill chuck
• 3/4" reduced shank drills holes up to 2" with a 3/4" drill chuck

Taper shank drills are long-length drills that are fitted with a special shank called a Morse Taper. These drills are made specifically for spindles that can hold Morse Taper shank drills.
• Taper shank drills come in many styles: Stub length, extra long, core drills, hi-helix, slow-helix and coolant-fed

Grades:
• General purpose is a perfect choice for maintenance and repair or short production runs in soft ferrous and non-ferrous materials
• Heavy-duty drills typically combine a split point to prevent walking, and stronger flutes for better rigidity. They
are an excellent choice when drilling harder materials
• High-performance drills are typically designed for application-specific operations where productivity and cost per hole is a concern. Maximising speeds/feeds is essential, so always review published manufacturer's recommendations

Lengths:
• Stub - short length
• Jobber - standard length
• Long series - long length
• Extra length - extra long length

In today’s competitive environment, getting the most out of your tooling is vital. Selecting the right tools and material is a big step towards maximising productivity and reducing cost per hole.

High Speed Steel (HSS: M1, M2, M7, M50):
• Combines good tool life and productivity with minimal cost
• Works well in free cutting and carbon steels, as well as soft, non-ferrous materials like aluminium, brass, bronze and copper
• Able to handle less-than-ideal set-ups

Cobalt (M-35, M-42):
• Provides better wear resistance, higher hardness and toughness than HSS
• Very little chipping or micro-chipping under severe cutting conditions, allowing the tool to run 10% faster than HSS
• With the right point angle and helix, cobalt is the most cost-effective for machining cast iron, heat-treated
steels and titanium alloys
• Able to handle less-than-ideal set-ups

Powdered Metal (PM) Cobalt (ASP-30, ASP-60):
• A cost-effective alternative to solid carbide, powdered metal is tougher and less prone to breakage
• Tools perform well in materials <30HRC, as well as highly abrasive materials like high-silicon aluminium

Solid Carbide:
• For high-performance applications; carbide can run faster and withstand higher temperatures while providing good wear resistance
• Provides better rigidity than HSS, yielding a higher degree of dimensional accuracy, often eliminating the need to ream
• Carbide is brittle, and tends to chip when conditions are not ideal; heavy feed rates are more suitable for HSS and cobalt tools
• Carbide is used in abrasive and tough-to-machine materials: cast iron, non-ferrous alloys, glass, plastics and composites
• Carbide-tipped tooling offers many of the advantages of solid carbide tooling at a reduced cost, especially
larger diameter tools

The drill point you use has an impact on performance. Flat points provide better-cutting action, while more aggressive point angles create torque.

Styles:
• 118° Point is designed to be an all-purpose point for soft metal, wood and plastics. Common on general-purpose tools

• 135° Split Points is designed to cut metal. Self-centring, it will not walk or slide when starting a hole. Common on heavy-duty tools

• 130° Point is common on high-performance HSS parabolic drills. Disperses heat well and helps drill straight in deeper holes

• 140° Point is common on high-performance carbide drills, and helps get the cutting edge into tough materials quickly

One of the best methods to improve the productivity or tool life of a drill is to add a coating or surface treatment. Coatings and surface treatments build a barrier between the drill and the workpiece. Different coatings provide different results, so select carefully.

Black Oxide (Surface Treated):
• Retains lubricants to aid in wear resistance and chip flow
• Not to be used in non-ferrous materials
FIREX®
• Exclusive by Guhring, alternating ultra-thin coating layers combines the performance benefits of single layer
coatings: universal application of TiN, hardness and heat-resistant of TiAlN and shock resistance of TiCN
Bright Finish (Polished)
• Polished drills do not have a coating, which helps increase chip flow in soft materials
TiN (Titanium Nitride - Gold Colour):
• Multi-purpose coating which increases tool life and performance
• Hardness and heat resistance allows tools to run at higher speeds and feeds (approximately 25% to 30% higher than uncoated tools)
TiAlN (Titanium Aluminium Nitride - Violet Black Colour):
• For high temperature and/or abrasive conditions
• Use in stainless steel, high alloy carbon steels, nickel-based high-temp alloys and titanium alloys. Not to be used in aluminium
• Requires an increase of 75% to 100% in machining speeds