Most drilling problems get blamed on the wrong variable: feed rate may get adjusted, the coolant pressure may be increased, the fixture will be checked twice, but nothing happens. In all of this, the drill point angle stays unchanged and unquestioned, usually whatever came default on the tool order. That is where the problem often begins.
In CNC machining, engineers track more than diameter. They review hole straightness, entry condition, burr formation, surface finish, and tool life across a production run. Drill point geometry contributes directly to each of these outcomes.
Introduction: What Is a Drill Bit Angle?
A drill bit isn’t a single geometry; rather, it is a system of angles that work together to determine how the tool enters material, how chips evacuate, and where exactly the heat goes during the cut.
The most referenced of these is the point angle. It is the included angle formed at the tip of the bit between the two cutting lips. A standard general-purpose twist drill ships with a 118° point angle. The second critical angle is called the lip relief angle, also called the clearance angle. It is ground behind each cutting edge. This determines how aggressively the cutting lip engages the workpiece. Then there’s the chisel edge, the dead zone at the center of the tip where no cutting happens, but only pressing and scraping. The geometry of the chisel edge directly affects how much thrust force is required to feed the drill.
Understanding these three elements will help you make drill bit decisions that will actually improve your machining results.
The Significance of Drill Bit Angles
The angle geometry of a drill bit controls four major variables that all affect the outcome of production. Each of these doesn’t work independently; rather, they all interact, and this interaction is decided by the workpiece.
Cutting Force and Thrust
Point angle sets how much push the drill needs to feed forward. A wider angle spreads the cutting load over a longer edge, but it takes more thrust to drive the tip in. A sharper angle puts that same force on a smaller area, so it needs less push. That’s why 90° and 118° drills bog down in hard materials, while 135° or 140° split-point drills bite cleaner under load in stainless or titanium.
Heat and Built-up Edge
Lip relief angle controls how much the drill’s flank rubs against the bore wall after the cutting edge cuts through. Too little relief, and heat builds fast. In aluminum, that heat softens the chip and smears it right back into the hole, forming a built-up edge. In stainless steel, it’s worse: not enough relief hardens the layer just below the cut, so the next pass has to dig through tougher material than the one before it.
Chip Evacuation
Point angle shapes the chip, decides its thickness, and determines how it curls. Steeper angles cut thicker and shorter chips that snap and clear easily.
However, shallower angles cut longer and thinner chips that like to pack instead. Past 3 times its diameter, that packing turns fails. The drills seize, bores get scored, and tools snap in material that should cut properly otherwise. Lastly, helix angle helps move chips out once they form, but the tip is what decides their shape in the first place.
Hole Quality
A split-point drill self-centers without needing a pilot hole. It shears from the center out instead of just pressing down, so entry comes out much cleaner. A standard 118° bit, however, cannot do that. On curved or angled surfaces, it needs a center punch or pilot just to hold its position.
Practical Applications and Common Drill Bit Angles
118° Standard Point
This is the default. It can be set up by most of the general and common drills. It also covers wood, soft plastics, mild steel, and general aluminum work. The 118° geometry balances the lip engagement and point stability reasonably. However, it tends to require a center punch for curved and hard surfaces.
135° Split-Point
The 135° split point is the practical upgrade from the 118° standard for anyone working with medium to hard materials. Since it is a wider angle, it reduces the length of cutting lip contact per revolution, which then lowers the cutting force per edge.
At Premium Parts, we generally recommend a 135° split point as the default specification for customers who order precision drilling operations in ferrous materials.
90° Flat-Point
Spade drills operate on wide and flat materials. They allow a shallow 90° geometry, which creates high radial cutting forces. This is manageable in wood, soft aluminum, and plastic, but it is very aggressive in steel, hence avoidable there. In production, spade drills are preferred for large bores, typically 25mm and above.
60° Countersink/Brad Point
Brad point drills, having a 60° center spur and flat outer cutting lips, normally work well in certain composite and fiberglass applications. The center spur scores the material surface before the outer lips cut, which prevents delamination in woven carbon fiber and fiberglass panels.
In aerospace and automotive composite work, brad point geometry is used to control interlaminar shear during drilling.
How to Choose the Right Drill Bit Angle for Your Material
Material selection for drill bit geometry is important to understand what failure mode you are trying to prevent.
Aluminum and Aluminum Alloys
For aluminum, the geometry priority is chip evacuation and relief angle, not point angle. A high helix drill (40° or greater helix angle) with 118° or 135° point and generous lip relief (12-15°) will outperform a stiffer geometry every time. Carbide or carbide-coated drills with polished flutes reduce chip adhesion.
Stainless Steel (304, 316, 17- 4)
Stainless is the material that exposes poor drill geometry the fastest. For the geometry recommendations, 135° split point with cobalt or TiAlN-coated carbide is considered preferable. The split point eliminates chisel edge rubbing at center, the wider angle reduces per-tooth cutting force, and the coating resists the heat spike that stainless generates.
Conclusion
Drill bit angle isn’t a specification to be left at default. Every material pair, wall thickness, tolerance requirement, and exit condition has a geometry that produces acceptable results and several that produce failures. For teams working with precision components, the right geometry must be decided before programming, not after the first batch is produced.
The engineering team at Premium Parts makes sure tooling geometry is confirmed against your material, tolerance, and hole quality requirements before a single cut is programmed
Talk to a Premium Parts engineer about your next project, before you make the tooling decision.
FAQs
Why does my drill bit wander on entry?
It primarily happens due to a chisel edge problem. It can be avoided by using a pilot hole to mark the location, or a switch to split-point geometry.
What drill angle works best for stainless steel?
135° split-point in cobalt HSS or TiAlN-coated carbide. Also keep the feed rates up to prevent dwell and work hardening.
Can I use the same drill bit angle for aluminum and steel?
You can use a 118° or 135° bit in both, but the geometry optimized for each material differs. Even in a mixed material shop, 135° split-point cobalt is the best single compromise across both.
Reach out to us at Premium Parts, and our engineers will help you make the right decisions.
When should I use a pilot hole?
Whenever the drill diameter is large enough that the chisel edge contact area becomes a significant portion of the tip, which means roughly above 12mm on standard geometry drills.
