Every angle on a drill bit exists for a reason. Change one and you change the cutting behavior — sometimes for better, sometimes catastrophically. This guide covers all the major geometry parameters: what each angle is, what range is normal, and what happens when it's wrong. Keep it handy when you're evaluating drill performance or deciding what to specify on a regrind.
Point Angle
The point angle is the included angle at the drill tip, measured across both cutting lips. On a standard jobber drill for general-purpose use in steel, this is 118 degrees. Higher-end tooling and drills intended for harder materials are often ground to 135 degrees.
A 118-degree point is more aggressive — it cuts faster and requires less thrust in softer materials, but it's more prone to walking on entry into hard surfaces. A 135-degree point is flatter and more self-centering; it starts more accurately and handles hard materials better because the flatter geometry distributes cutting force across a wider area. Some specialty drills go to 90 degrees or even flatter for specific applications like plastics or composites, where a steeper point would cause breakout on exit.
If your drill is wandering off layout on entry, the point angle may be too shallow for the workpiece hardness. If you're getting breakthrough burrs or exit-side delamination in stacked material, a flatter point (higher angle) will help.
Helix Angle
The helix angle is the angle the flutes make with the drill's axis — essentially how steeply the flutes spiral. It determines how aggressively chips are evacuated and how much axial force the cutting action generates.
| Helix Type | Typical Angle | Best For |
|---|---|---|
| Slow helix | 12–18° | Brass, bronze, deep holes where packing is a concern |
| Standard (jobber) | 28–32° | General purpose steel, aluminum, most ferrous |
| High helix | 35–45° | Soft aluminum, copper, plastics — fast chip ejection |
A high-helix drill in steel will grab and chatter; a slow-helix drill in aluminum will pack chips and friction-weld them to the flutes. Match the helix to the material. If you're running standard jobber drills in everything and having chip trouble, this is the first geometry parameter to examine.
Lip Relief Angle
Also called the clearance angle — this is the relief ground behind each cutting lip that allows the edge to bite into the material rather than rub against the just-cut surface. Without it, the bit would spin without cutting, generating heat instead of chips.
Standard relief for HSS in most steels is 8–12 degrees. Softer materials tolerate more relief (up to 15–18 degrees) because the cutting forces are lower and there's less risk of edge rollover. Harder materials need less relief — around 6–8 degrees — because more material behind the edge provides support against the higher cutting forces.
Insufficient relief is one of the most common results of a poor regrind. The bit looks sharp because the cutting edge exists, but it rubs rather than cuts. Symptoms: squealing, rapid heat, blue chips in steel, hole diameter that grows as the bit warms up. A competent regrind restores correct relief angle — this is exactly why sending drills to a precision service shop beats freehand grinding on a bench grinder.
Chisel Edge Angle
The chisel edge is the short cutting section at the very center of the tip. The chisel edge angle describes how this section is oriented relative to the cutting lips — typically 120–135 degrees on a standard grind.
The chisel edge doesn't cut the way the lips do. It scrapes and extrudes material, which is why it's the primary contributor to drilling thrust. A properly ground chisel edge is short and narrow relative to the drill diameter (roughly 10–20% of diameter on a standard bit). As the bit wears and is shortened through multiple regrinds, the web thickens and the chisel edge widens, increasing thrust dramatically.
Web thinning — grinding a relief into the web to reduce chisel edge width — is the solution. Split-point geometry eliminates the chisel edge entirely by creating secondary cutting edges in its place, which is why split-point bits start so easily and require so much less thrust than conventional ground bits of equivalent diameter.
Web Thickness
Web thickness isn't an angle, but it belongs in this guide because it governs chisel edge width and determines how much of the bit's center section cuts versus scrapes. Standard web thickness tapers from tip to shank — typically around 15–20% of diameter at the tip on a new jobber drill.
As noted above, repeated regrinds that shorten the bit move the working tip to a section where the web is thicker. A 1/2" drill with a web that's grown to 30% of diameter needs about twice the axial thrust of the same drill with a proper web. This is the physics behind why reconditioning is sometimes the right answer instead of a standard regrind.
Margin Width and Land
The margins are the narrow cylindrical bands on the outside of the flutes that ride against the hole wall. They control the drill's diameter accuracy, guide the bit axially, and finish the bore surface. On a new drill, they're ground to a precise width and smooth surface finish.
Margin wear typically shows up as diameter loss (the drill starts cutting undersize), chatter from reduced guidance, and surface finish degradation in the bore. In abrasive materials — cast iron, hardened steel, composites — margins wear faster than the cutting edges, and the bit becomes effectively undersize before the tip is dull.
Understanding these parameters gives you a vocabulary for describing drill performance problems and makes the difference between guessing at a fix and specifying the correct one. When you send drills for service with notes on what you've observed — excessive thrust, oversized holes, chatter — a good shop will connect those symptoms to the geometry and address the actual cause.