The included point angle is the angle measured between the two cutting lips at the tip of the drill. At 118°, the two lips form a sharper, more conical tip. At 135°, the point is flatter.
Here's what that directly affects:
Chisel edge length. The chisel edge is the dead zone at the very center of the drill — the short flat segment that doesn't cut, it scrubs. It can't cut because it has no meaningful rake angle and near-zero surface velocity. At 118°, the chisel edge is longer relative to the drill diameter. At 135°, especially on a split-point geometry, the chisel edge is dramatically shorter — sometimes nearly eliminated.
Thrust force to engage. A longer chisel edge requires more axial thrust to push through the center of the hole. That thrust is wasted energy that compresses and work-hardens the material instead of cutting it. At 135° with a short chisel, the cutting lips engage immediately and most of the applied force becomes productive cutting force rather than dead-zone pressure.
Lip angle and attack geometry. As the point flattens from 118° to 135°, the rake angle at the cutting lip changes. The lips sit more tangentially to the rotation, which changes the chip formation angle and affects how aggressively the drill self-feeds.
Self-centering behavior. This is the practical difference that shows up most immediately on the floor. A 135° drill centers itself. A 118° drill skates.
On a flat, un-spotted surface, the 118° drill touches down on its chisel edge first. The chisel edge has no cutting geometry — it's a flat grind — and it slides around on the surface until enough pressure pushes it into a slight indent. Until the cutting lips engage, the drill wanders.
This is why center punching and spot drilling exist. They create a conical divot that catches the chisel edge and gives the drill a starting reference. On manual work this is standard practice. On CNC work it's an extra tool, extra operation, extra cycle time.
The 135° point — particularly the split-point variant — eliminates most of this problem. The flatter geometry brings the cutting lips to the work surface at almost the same moment the drill touches down. The lips start shearing material almost immediately, which self-centers the drill through cutting action rather than by relying on a pre-formed pocket.
In production on CNC mills and drill presses with consistent fixturing, 135° split-point drills frequently eliminate the spot drill operation entirely. The time savings per hole is small. Across thousands of holes per shift, it's significant.
If 135° self-centers better and reduces thrust, why use 118° at all?
The answer is mostly material and application. For soft to medium steels, cast iron, and general work, 118° geometry produces excellent chip formation. The slightly more aggressive attack angle works well in compliant materials. The longer chisel edge is less of a problem in mild steel where thrust loads are low and the material doesn't work-harden under the chisel.
There's also a geometry-resharpening consideration. The 118° point is more forgiving to grind. Half-angle symmetry is easier to achieve by hand, and small errors in the grind produce smaller performance degradations. For hand-sharpened drills or shops without a precision drill grinder, 118° is more consistent across the fleet.
Additionally, 118° drills are more widely available in every size range, and the geometry is well understood by anyone who's spent time near a bench grinder. There's a certain operational simplicity in standardizing on 118° and training the team to use center punches — it works reliably and requires no special knowledge.
The calculus changes based on volume. For a job shop doing one-off or small-batch work in a mix of materials, standardizing on 118° with center punching is sensible. The flexibility to drill almost anything with one geometry type simplifies tooling decisions and the knowledge required at the machine.
For production work — same part, same material, thousands of holes — the investment in optimizing drill geometry pays off. If you're drilling 304 stainless all day, you want 135° split-point with web thinning and possibly a specialized point grind. If you're drilling mild steel plate for a structural fab application, 118° is probably already working fine.
The resharpen decision also applies here. When sending drills out for reconditioning, you can specify the angle. If your material mix has shifted — if you've landed a stainless contract and your old mild-steel drills are now running in harder material — that's worth noting in the resharpen order. Coming back with 135° geometry on a drill previously ground to 118° is a real option, not just a theoretical one.
The difference between these two angles isn't dramatic in a single hole. It adds up over a production run, a quarter, a year. Getting the geometry right is free — it happens at the resharpening stage, not by buying new drills.
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