The 118 and 135 degrees drill bit angles are two of the most common cutting angles in drills. What is the difference? When would you use a 118° drill bit, and when should you opt for a 135° point angle? Let’s find out.
But first, let me briefly explain what is a drill bit point angle, and why does it matter.
What Is the Point Angle of Drill?
Twist drill bits have a conical tip to ease the drilling process and allow the drill bit to bite into the workpiece. This also reduces the thrust needed for the drill bit to sink into the material. This drill point tip has chisel edges that are ground at an angle to perform the cutting action efficiently.
The drill bit point angle refers to the included angle between the two faces of the cutting edges. Since both edges are sharpened equally relative to the drill shaft, the drill point angle technically refers to the sum of the angles of both faces.
Over the years, the angles at which these conical tips are manufactured, standardized into one of two angles: 118° and 135°.
The 118° drill bit is more pointed, with a steeper angle and smaller chisel than its 135° counterpart. When you purchase specialty drills, you can find ones at angles other than the standard 118° and 135°, although this is rare.
Standard Drill Point Angle
The standard drill point angle used in most applications is 118° since it is suited to most materials. It is commonly used for general-purpose, high-speed drilling. Here, you would typically drill into softer metals, mild steel, and aluminum. The 118° angle is usually found on drill bits of jobber length (standard size). as opposed to stub drill bits.
In contrast, the 135° drill point angle is usually paired with a stub length drill bit and used for hard steels and other hard materials. As the name suggests, stub length drill bits are shorter than their jobber counterparts.
118° vs. 135° Drill Bit Angles
The 118° and 135° drill bits can be used interchangeably in some applications. Still, if you want to prolong to tool’s lifespan, it’s best to use the right tool for each application.
Which Drill Bit is Better?
“Better” is a subjective term, and the “best” drill bit angle depends on the job at hand.
118° Drill Bit
The 118° drill bit cuts far more aggressively than its 135° counterpart, but the steeper point makes it weaker. For this reason, the 118° drill bit will dull far quicker than the 135° when used on hard materials, such as steel. So, it’s best to use the 118° drill bit on softer materials.
The more aggressive cutting action on the 118° drill angle reduces the axial thrust required compared to the 135° drill point angle. In short: the smaller the angle, the lower the required axial thrust. This is good news when using a hand-held drill.
118° point drill bits aren’t suited to drilling on curved or slippery surfaces. They slip right off, damaging the surface and potentially causing injuries to the operator.
When you buy a 118° twist drill bit, it tends to be longer than the 135° stub drill bit, so it tends to be less stable than the 135°. This is another reason why the 118° drill point angle isn’t suited to drilling into hard materials. (Of course, you can grind it to the required angle using a drill sharpener.) When applying the amount of thrust required to drill into hard materials, the longer drill bit could deflect slightly, affecting the accuracy and neatness of the hole. Deflecting drill bits tend to splinter and chip hole edges, making for a rougher, more sloppy finish.
135° Drill Bit
The 135° drill bit has a less aggressive cutting action than the 118° due to the lower pitch, making it better suited to cutting hard materials, such as tool steel. This drill will remain sharp for longer, even when drilling through tough materials. It requires a more significant axial thrust than the 118° drill point angle, though.
135° split point drill bits are ideal for drilling into curved or slippery surfaces. These drill bits grip the surface well and make for neat, clean holes, especially when you’re using a high-quality drill bit.
135° drill bits are generally shorter than their sharper counterpart. For this reason, they are better suited to drilling into harder materials that require accurate hole spacing and crisp finishes. These shorter drill bits aren’t as likely to deflect under the thrust required for them to bite into harder materials. Thus they will get the job done more efficiently.
Standard vs. Split Point Drill Bit
Standard drill bits require a starter spot drilling or pilot hole to be drilled before drilling the actual hole, whereas split point drill bits are self-centering and self-starting. They don’t require pilot holes.
What Is a Standard Point?
A standard point drill bit has two cutting edges on the chisel point with a web in the center. When used to cut directly material, this drill bit tends to wobble and “walk,” compromising the hole position accuracy.
When using this drill bit, it’s best to spot drill with a center drill or drill a pilot hole first, using a split point drill bit. Once this is complete, the standard point drill bit is used to complete the hole.
What Is a Split Point Drill Bit?
As the name suggests, a split point drill has a split drill point. This drill bit has two extra cutting edges at the chisel edge. Here, it creates a self-centering drill bit and is found on nearly all carbide drills and many cobalt drills. Using this drill point eliminated the need for a starting drill and increased drilling accuracy.
High-speed twist drills usually aren’t self-centering. Non-self-centering drills tend to walk or wobble when drilling into a flat surface. That’s why these need a started hole.
Note that the split point drill bit usually has a 135° drill point angle, making it suitable for cutting hard materials.
Pros and Cons of Split Point
Split point drill bits don’t require a starter spot drilling or pilot hole. The machining time that you save by eliminating the spot drilling operation can improve productivity. They are thus typically more efficient on jobs that require many repetitive holes on CNC drills or mills. They’re also well-suited to drilling hard materials with bits that have a 135° drill point angle.
Due to the improved grip and stability, the split point offers, these drills bits are better suited to drilling on slippery surfaces. Examples include metal pipes and other curves working surfaces.
That said, the split point drill bit is more prone to damage than the standard drill bit, so you need to look after it more carefully than its standard counterpart.
Unlike the standard drill bit, the split point drill bit can’t be sharpened easily. The edges are likely to break if you attempt to sharpen the split point by hand on a bench grinder. So, if your split point drill bit becomes dull, unfortunately, you have to replace it, or need a professional drill grinder.
Flute and Helix Angle
The flute of a drill bit refers to the spiral grooves cut into the drill’s shaft. These allow drilling chips to be removed from the hole and is an important feature of the drill bit. The flute’s configuration determines how effective the drill bit is at removing chips from the hole, which affects heat build-up and the potential to damage the workpiece.
An important factor to bear in mind here is the helix angle, which is the angle at which the flute is cut around the drill bit. The helix angle determines how the chips are formed – a function that differs depending on the material being drilled.
Soft materials require large helix angles, while hard materials require small helix angles. For more information on this, refer to our full article on drill flutes and helix angles.