Foundation of Drill Geometry and Heat Control for Hudson Valley Mechanics

Introduction

This technical reference examines the 118° jobber drill bit—one of the most widely used geometries in machining. It focuses on the fundamentals: point geometry, material composition, coatings, and maintenance principles that define cutting accuracy and tool life. Together, these aspects provide a complete, field-grounded understanding for machinists and maintenance professionals working to improve precision and consistency in daily shop operations.

The 118-degree jobber drill bit is widely recognized as a general-purpose global standard in machining. Its defining feature is the 118-degree point angle, measured across the full conical tip. This geometry offers an excellent balance between cutting speed, self-centering ability, and overall durability of the cutting edges.

Technically, the 118-degree geometry results in a relatively sharp cutting action when compared to the flatter 135-degree point. This sharpness concentrates cutting forces over a smaller area, which translates into more efficient penetration and typically requires lower thrust forces from the machine.

The bit itself conforms to the Jobber Length standard, meaning the flute length is generally between three and four times the drill diameter. For example, a 1/2-inch drill bit will have a flute length of approximately 4-1/2 inches.

A key consideration for the standard 118-degree point is its centering ability. Because the main chisel edge of this geometry is wider than a 135-degree split point, it has a greater tendency to “walk” or deflect upon initial contact with the workpiece. Therefore, a center punch, spot drill, or pilot hole is often required before initiating the full hole drilling process.

It is important to note that many modern 118-degree bits feature a split point or web thinning, which substantially reduces the required thrust force and greatly improves self-centering capability.

Materials, Coatings, and Standards

The most common material substrate for these general-purpose tools is High-Speed Steel (HSS), valued for its cost-effectiveness and inherent resistance to heat generated during cutting. For applications involving harder materials or requiring superior heat resilience, HSS-Cobalt (HSS-Co), typically containing 5% to 8% cobalt, is utilized.

In terms of surface treatments, the drill bit may be Bright/Uncoated for general use, especially in softer materials like aluminum. Alternatively, the bit may feature a Black/Steam Oxide finish, which enhances abrasion resistance, helps prevent chips from welding to the cutting edge, and improves lubrication and chip flow, making it common for drilling steels. High-performance 118° bits are often coated with Titanium Nitride (TiN). This hard, wear-resistant coating can increase surface hardness to approximately 2300 HV and tolerate temperatures up to 1100 °F, significantly extending tool life.

The standard geometry and tolerances for these tools are defined by international specifications, including ANSI/ASME B94.11M in the United States and DIN 338 in Europe. The flutes typically employ a regular spiral with a helix angle between 24° and 32°, providing an optimal balance between the structural strength of the tool and efficient chip evacuation.

Performance and Application Data

The 118-degree point geometry is generally favored for softer and more common engineering materials because of its efficient chip formation and lower overall power requirement. It is categorized as having priority use for materials like low to medium carbon steel (below 180 HB), soft gray cast iron, and all non-ferrous materials such as aluminum, brass, and bronze. The sharpness of the 118° edge is particularly ideal for softer, gummier materials like aluminum.

When operating an HSS 118° drill in mild steel, recommended starting parameters for Surface Feet per Minute (SFM) typically range from 80 to 110. For softer materials like aluminum, speeds can be increased significantly, often ranging from 200 to 300 SFM. Conversely, drilling tougher materials like stainless steel or high-nickel alloys requires lower speeds, generally 30 to 50 SFM. 

The accompanying feed rate, expressed in Inches per Revolution (IPR), is highly dependent on diameter: very small drills (under 1/8 inch) start at 0.001 to 0.003 IPR, while larger drills (1/2 to 1 inch) can use heavier feeds of 0.007 to 0.015 IPR.

While the 118-degree point is sharper, requires higher thrust (unless split-point ground), and is prone to walking, its versatility makes it the default choice for general applications. By contrast, the 135° split point excels specifically in hardened steels, stainless steel, and high-tensile alloys due to its self-centering feature and lower thrust requirement.

Field Experience — Middletown, N.Y.

“I once serviced a large OEM in Middletown, NY that made duct tape. Purchasing was pushing maintenance to cut costs, and drill bits came under the knife. I sold them the cheapest imports I could find—but warned them they wouldn’t last.

A week later, the call came in: “These bits couldn’t cut through butter.” They’d learned what I already knew—cheap tools cost more in the long run. I told purchasing, “Top quality is the lowest price when it lasts.” They agreed. It’s never about price; that’s the easy way out. And when it’s too easy, bad things usually follow. Never apologize for selling or buying quality—it always pays off in the end.”

🔬 Technical Procedures for Resharpening the 118-Degree Jobber Drill Bit

The effective resharpening of a 118-degree drill bit hinges on accurately restoring three critical geometrical features: the point angle, the lip clearance (or relief) angle, and the symmetry of the two cutting lips. Failure to precisely restore these features results in rapid tool wear, poor hole quality, and excessive operational loads.

Restoration of Point and Lip Angles

The target point angle must be an included angle of 118°. This means each individual cutting edge, or lip, must form an angle of 59° relative to the central axis of the drill. This geometry is fundamental to the tool’s general-purpose performance, balancing penetration force and edge durability. Maintaining this 118° angle ensures the cutting edges remain straight; angles less than 118° produce a convex edge, while angles greater than 118° result in a concave edge—both reducing cutting efficiency.

The second critical angle is the lip clearance angle, also referred to as the relief angle. This is the angle at which the material directly behind the cutting lip is ground away, ensuring that only the cutting edge itself makes contact with the workpiece and preventing excessive friction and heat generation. For general-purpose drilling in materials like mild steel, the clearance angle should be maintained between 12° and 15°. 

For smaller diameter drills, this angle can be increased up to 18° to account for reduced material strength and inherent deflection. The relief must be ground with a slightly curved profile, starting with the highest clearance near the chisel point and gradually diminishing toward the perimeter of the drill.

Symmetry and the Chisel Edge

Symmetry is paramount for producing a round, accurate hole. The two cutting lips must be ground to exactly the same length, and the clearance angles must be identical. If one lip is longer than the other, the drill’s rotation center will shift, causing only the longer lip to perform most of the cutting work. This results in an off-center chisel point, an oversized and non-straight hole, and unbalanced cutting forces that overload both the machine and the drill bit.

The chisel edge, formed by the intersection of the two ground relief surfaces at the drill’s center, is a non-cutting element that merely smears material into the path of the cutting lips. For effective drilling—especially with the 118-degree geometry—the length of this chisel edge should be minimized during the sharpening process to reduce the required thrust force.

The Sharpening Process and Equipment

Resharpening is typically performed either by hand using a bench grinder or with a specialized drill bit sharpener.

When sharpening by hand, a corundum grinding wheel of medium grit is recommended for standard High-Speed Steel (HSS) bits. For HSS-Cobalt or TiN-coated tools, a specialized Cubic Boron Nitride (CBN) wheel is advised due to its high heat resistance. The procedure requires the operator to simultaneously present the drill tip at the correct 59° angle to the wheel’s face and rotate the drill bit in a sweeping motion. 

This combination of movement establishes the correct 118° point angle and generates the necessary 12° to 15° curved relief behind the cutting lip. Consistent cooling of the bit in water is mandatory to prevent overheating, which can compromise the temper and hardness of the cutting edges, leading to immediate failure. Drill point gauges are essential for periodically checking the 59° lip angle and ensuring equal lip lengths.

Professional and high-volume environments utilize dedicated drill sharpeners. These machines use precision chucks and mechanical cams to control the grinding motion, ensuring perfect pitch and relief angles and achieving superior consistency and accuracy compared to manual methods. Many advanced models also feature a port for an optional secondary operation of splitting the point, which removes a portion of the chisel edge to improve self-centering and lower thrust force.

The technical goal of the entire maintenance process is to restore the cutting edges to a condition where they can produce two equal, helical shavings, thus distributing the cutting load evenly and maximizing tool life.

Conclusion

Understanding the 118° jobber drill bit begins with its geometry, materials, and the precision needed to keep it sharp. These fundamentals set the stage for every accurate hole and long tool life in the shop—reminding every mechanic that true precision starts at the point.